N uptake

Soil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH 4 + -N and NO 3 --N, with one N form labelled with 15 N at a time, and in the case of glycine, also labelled with 13 C, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH 4 + -and NO 3 --15 N, respectively, recovered in the plant-soil system, and the major part of 15 N in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover transferred about half of the immobilized 15 N to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention in both tundra types. The ECM mycelial communities at the two tundras differed in Nform preferences, with a higher contribution of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated against NO 3 -. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well as for soil microorganisms.

† Background and Aims French wheat grains may be of little value on world markets because they have low and highly variable grain protein concentrations (GPC). This nitrogen-yield to yield ratio depends on crop nitrogen (N) fertilization as well as on crop capacity to use N, which is known to vary with climate and disease severity. Here an examination is made of the respective roles that N remobilization and post-anthesis N uptake play in N yield variations; in particular, when wheat crops (Triticum aestivum) are affected by leaf rust (Puccinia triticina) and Septoria tritici blotch (teleomorph Mycosphaerella graminicola). † Methods Data from a 4-year field experiment was used to analyse N yield variations in wheat crops grown either with a third or no late N fertilization. Natural aerial epidemics ensured a range of disease severity, and fungicide ensured disease-free control plots. The data set of Gooding et al. (2005, Journal of Agricultural Science 143: 503-518) was incorporated in order to enlarge the range of conditions. † Key Results Post-anthesis N uptake accounted for a third of N yield whilst N remobilization accounted for twothirds in all crops whether affected by diseases or not. However, variations in N yield were highly correlated with post-anthesis N uptake, more than with N remobilization, in diseased and also healthy crops. Furthermore, N remobilization did not significantly correlate with N yield in healthy crops. These findings matched data from studies using various wheat genotypes under various management and climatic conditions. Leaf area duration (LAD) accurately predicted N remobilization whether or not crops were diseased; in diseased crops, LAD also accurately predicted N uptake. † Conclusions Under the experimental conditions, N yield variations were closely associated with post-anthesis N uptake in diseased but also in healthy crops. Understanding the respective roles of N uptake and N remobilization in the case of diseased and healthy crops holds the promise of better modelling of variations in N yield, and thus in GPC.

Greater species diversity in natural ecosystems increases plant biomass production and stability. Intercropping is an agricultural practice that aims to accrue the benefits of species diversity by growing two or more species simultaneously in the same space. Functional group diversity is considered important for enhancing the beneficial effects of species diversity, but most previous intercropping studies used combinations of only two functional groups. Thus, we used three green manure species from different functional groups: sorghum (Sorghum bicolor (L.) Moench.), a C4 grass; crotalaria (Crotalaria juncea L.), a legume; and sunflower (Helianthus annuus L.), a forb. We examined the effects of intercropping on biomass, nutrient uptake, and their stability using a proportional replacement series in a field experiment for three years with four trials. The aboveground biomass was higher with dual and triple-component intercrops compared with sole crops; however, there were no superior effects of triple-component intercropping over dual-component intercropping. There were also no clear advantages of intercropping in terms of the nutrient uptake amount and stability.

Particulate organic matter nitrogen (POM-N) was evaluated as an indicator of crop residue source (pulse versus cereal) and residue management (no-tillage [NT], stubble burned [SB] or stubble mulched [SM]) on soil quality and subsequent crop productivity in a continuous cropping experiment in northern New South Wales (NSW), Australia. The relative contributions to POM of pulse versus cereal, and shoots versus roots, were studied using in situ 15 N shoot labelling. Under NT, a greater proportion of organic N was found in POM-N > 250 µm (5.5% versus 3.5% [SM] and 2.7% [SB]) and POM-N > 53 µm (10.3% versus 9.7% [SM] and 8.7% [SB]). Pulse residues (particularly roots) contributed 2-7 times more N to POM and 2-4 times more N to non-POM-N than barley ( N data), but this increased contribution was not detectable with non-isotopic analysis. POM-N was sensitive to residue management, but was not a reliable measure of N inputs from pulse versus cereal residues, nor a useful tool for predicting subsequent crop N uptake. pulse / cereal / crop residue / particulate organic matter / soil nitrogen Résumé -Relation entre la matière organique azotée particulaire et non particulaire et les résidus de culture de légumineuses, leur gestion et le prélèvement d'azote par les céréales. La matière organique particulaire POM-N a été évaluée comme indicateur des sources des résidus de cultures (légumineuses ou céréales) et de la gestion des résidus (non-labour [NT], brûlage des pailles [SB], mulch de paille [SM]) sur la qualité du sol et la productivité induite des cultures dans une expérience continue de culture sans le Nord des New South Wales en Australie. Les contributions relatives des POM des légumineuses par rapport à celles des céréales et des tiges par rapport aux racines ont été étudiées en utilisant des tiges marquées à l'azote 15 N in-situ. Sous NT, une plus grande proportion de l'azote organique a été trouvé dans la fraction POM-N > 250 µm (5,5 % par rapport à 3,5 % pour [SM] et 2,7 % pour [SB]) et POM-N > 53 µm (10,3 % par rapport à 9,7 % pour [SM] et 8,7 % [SB]). Les résidus de légumineuses (particulièrement les racines) ont apporté 2 à 7 fois plus d'azote sous forme POM et 2 à 4 fois plus d'azote sous forme non particulaire que l'orge (données de 15 N) mais cette contribution accrue n'était pas détectable avec une analyse non isotopique. POM-N était sensible à la gestion des résidus mais n'était pas une mesure fiable pour les apports d'azote à partir des légumineuses comparativement aux résidus de céréales ni un outil utile pour prédire le prélèvement induit d'azote par la culture.

Decentralized or onsite wastewater treatment (OWT) systems have long been implicated in being a major source of N inputs to surface and ground waters and numerous regulatory bodies have promulgated strict total N (TN) effluent standards in N-sensitive areas. These standards, however, most of which have effluent limitations of <10 mg/L TN, were generally developed without data on treatment performance and attainable compliance levels of operating OWTs designed to remove N. This paper reviews OWT technologies that rely on preanoxic or postanoxic denitrification, or simultaneous nitrification-denitrification, and frequently include compact, mechanized components. TN effluent data from 20 OWTs in 3 long-term N removal demonstration projects in Florida, Oregon, and New Zealand are analyzed and compared with the performance of 15 centralized N removal treatment plants from the US and Canada. A reliability and stability analysis shows that only one of the 20 OWTs approaches the reliability and stability of centralized plants, and can comply with a <10 mg/L TN effluent standard with a 99% probability; all of the remaining 19 OWTs have a <50% probability of compliance. The lower reliability of OWTs, many of which are energy-intensive, scaled-down models of centralized plants, is due to the inherent variability of decentralized wastewater characteristics and the challenges of operationally controlling N removal processes at the level of residences. However, the small footprint (required land area) of these compact designs offers important opportunities for retrofitting OWTs on small lots, in shoreline developments where land is at a premium and where communities wish to foster and sustain compact, village developments that reflect "smart growth" strategies. Other approaches to decentralized N management emphasizing passive, robust, ecologically engineered designs are reviewed and include natural wastewater treatment systems such as single pass sand filters with denitrifying bioreactors, which performed better than any other OWT technology; shallow trenches and drip irrigation for denitrification or plant N uptake in the carbon-rich root zone; denitrification beds/layers installed down gradient from effluent plumes; and the consideration of watershed N sinks in estimating the risks of N loading to receiving waters. These alternative approaches require further research and development, but can offer alternatives or additional treatment to mechanized OWTs. More comparative studies of long-term operation of OWTs under field conditions in other parts of the world are needed to further quantify performance capabilities.

 The highest copper release was observed from copper materials at pH 5. After about one day of exposure, the copper concentration was more than 6 mg/L (970 mg/m 2 ).  Copper release was also found for the other materials, but at much lower concentrations.

Improvements of nitrogen use efficiency (NUE) may be achieved through the use of sensing tools for N status determination. Leaf and canopy chlorophyll, as well as leaf polyphenolics concentrations, are characteristics strongly affected by N availability that are often used as a surrogate to direct plant N status estimation. Approaches with near‐term operational sensors, handheld and tractor‐mounted, for proximal remote measurements are considered in this review. However, the information provided by these tools is unfortunately biased by factors other than N. To overcome this obstacle, normalization procedures such as the well‐fertilized reference plot, the no‐N reference plot, and relative yield are often used. Methods to establish useful relationships between sensor readings and optimal N rates, such as critical NSI (nitrogen sufficiency index), INSEY (in‐season estimated yield), and the relationship between chlorophyll meter readings, grain yield, and sensor‐determined CI (chlorop...

The aim of the paper is to enter into a discussion concerning the title question. In our opinion it is N uptake efficiency that affects N uptake, but not vice versa, mainly because the former is a genotypic characteristic, and as such is not influenced by N uptake. To support the conclusions we also show a similarity between the model used for the problem in question and a yield component model. Nitrogen Á Yield component model Abbreviations N Nitrogen Nupt Plant nitrogen uptake Nsup Total crop nitrogen supply RE N Nitrogen recovery efficiency Communicated by A. Kononowicz.

Las bacterias productoras de auxinas participan en el crecimiento de las plantas en el suelo, ante ello, se determinó el potencial del crecimiento del pasto Panicum maximun cv.-Tanzania a partir del uso de biofertilizante provenientes de las bacterias diazótrofas y productora de auxina Azospirrillum sp y Azotobacter sp. Se aislaron las bacterias de la rizosfera de cultivos ubicados en el municipio de La Paz, Cesar que fueron sometidas a pruebas bioquímicas, observaciones macroscópica y microscópica. Posteriormente se evaluó la capacidad fijadora de nitrógeno y productora de auxina, evidenciándose que la bacteria Azotobacter obtuvo una mayor producción con respecto a la Azospirillum. Se ejecutaron pruebas piloto de las bacterias en diferentes concentraciones con el pasto en un modelo experimental de 10 tratamientos 3 repeticiones; tomándose como variables: número de hojas, área foliar, longitud de la planta y raíz, %nitrógeno. Al finalizar, se concluyó que la bacteria Azospirrillum estimuló el crecimiento del pasto Panicum maximun cv. Tanzania.

Nitrogen deficiency causes significant reduction in yield in maize. The objectives of present study was to evaluate the performance of various shoot traits in selected maize genotypes for tolerance to low nitrogen stress and to understand the morphological changes that take place in the plants under nitrogen stress condition. The intermated B73-Mo17 (IBM) recombinant inbred lines were used, because the parents differ in response to nitrogen stress while the recombinant inbred lines have been thoroughly genotyped. Ten IBM genotypes from the published Maize Genome Database database were evaluated in this study along with their parents B73 and Mo17. Plants were grown in Guterman Green House of Cornell University, USA. Two nitrogen treatments (solution with high N contained 65.79 g Ca (NO3)2 4H2O in 100L of 1X solution making 5.0mM NO3 and solution with low N contained 2.63 g Ca (NO3)2 4H2O in 100L of 1X solution making 0.2 mM NO3) were given to understand the effect of different nitrog...

Recycling/composting of organic wastes is one of the major solutions for reducing the huge piles of organic wastes and converting it into a value added product. The fruit and vegetable wastes composted in a locally fabricated unit were enriched with urea fertilizer @ 100 and 200 g N kg-1 compost (25 and 50% of full dose of N i.e. 120 kg ha-1). Pot and field experiments were conducted on sandy clay loam soil to evaluate the integrated effect of N-enriched compost and inorganic N fertilizer on wheat crop. Phosphorus and potassium fertilizers as basal dose were kept constant in all treatments. Treatments receiving enriched (with 25% N) compost (300 kg ha-1) were supplied with additional 25 (30 kg ha-1) and 50% (60 kg ha-1) of the total N fertilizer. Wheat cv. Wattan-93 was planted and canal water was used for irrigation. Results of pot and field experiments revealed that integrated application of enriched compost and 60 kg ha-1 N (50% N fertilizer) significantly improved plant height, ...

The interactions between phytoplankton nutrition and the response of carbon (C) and nitrogen (N) uptake to irradiance relationships were examined during September 1993 in Monterey Bay, California, an eastern boundary current upwelling regime. Measurements of N uptake and C assimilation rates versus irradiance (V:I and P:I) experiments were performed using trace-level additions of l5 N-labeled NO 3 " and NH 4 + , and l4 C-labeled bicarbonate to water collected from a depth of -30% of surface photosynthetic photon flux density (PPFD). An upwelled water mass was sampled consecutively, with hydrographic stations located at the upwelling site, 48 h later down the horizontal axis of the upwelling plume, and a final time (24 h later) with waters consisting of a mixture of 5-6 day aged upwelled water and warmer surface water from outside the plume. As the water aged, a progressive shift in the rates of C and N utilization occurred, with C assimilation increasing while N uptake rates decreased. At the same time, NH 4 + dominated the nitrogenous nutrition in older upwelled water, even in the presence of high concentrations of ambient NO 3 ". Dark-uptake rates for all substrates were uniformly low at all stations; NH 4 + uptake demonstrated the least dependence on PPFD. The results of this study demonstrate dramatic changes in the light-mediated response of C and N uptake, resulting in assimilation ratios considerably different from predicted values assuming phytoplankton C:N uptake rates will be proportional to Redfield C:N composition. These data provide clear evidence of physiological changes in the natural planktonic assemblage of this evolving upwelling ecosystem.

The growth promotant gibberellic acid variant 3 (GA3) is widely used to increase ryegrassdominant pasture production in late autumn and during winter, often in conjunction with fertiliser N. However, there is relatively little information available regarding its effectiveness in warmer months, especially in temperatures close to those that induce heat stress in ryegrass (&gt;30 o C). Reduced pasture production at these temperatures have serious effects on farm profitability. To specifically examine the potential of GA3 in these conditions, field trials were conducted on five irrigated dairy farms that were using ONEsystem® (wetted, nbpt-treated prilled urea) as their standard input of fertiliser N year-round. This form of fertiliser N had been demonstrated to be twice as efficient in earlier trials than granular urea throughout the year, but N efficiencies were markedly lower with both forms in the warmest months than in the remainder of the year. The application of GA3 increased th...

The influence of crop density on the remobilization of dry matter and nitrogen from vegetative plant parts to the developing grain, was investigated in the durum wheat (Triticum durum Desf.) varieties Creso, Simeto and Svevo cultivated in the field at three seeding rates, 200, 250 and 400 seeds m -2 . Variety × seeding rate interaction was unsignificant for all recorded characters. Grain yield declined in the order Svevo > Simeto > Creso. Yield differences mainly depended on the different number of kernels per unit land and, secondly, on mean kernel weight. Spike components differed among varieties: Svevo and Simeto showed more kernels per spikelet and Creso more spikelets per spike. Grain yield was highest with 400 seeds m -2 primarily due to the higher number of spikes per unit area, and secondly, to the higher mean kernel weight. Post-heading dry matter accumulation was highest in Svevo and lowest in Creso, but varieties showed a reverse order for dry matter remobilization and contribution of dry matter remobilization to grain yield. The increase of seeding rate increased both the post-heading dry matter accumulation and the dry matter remobilization from vegetative plant parts to grain. Nitrogen uptake of the whole crop and N content of grain was higher in Simeto and Svevo than in Creso. The N concentration of grain did not vary among varieties, but Svevo showed a markedly lower N concentration and N content of culms at maturity, which may be consequence of the high N remobilization efficiency performed by this variety. The N uptake by the crop was highest with 400 seeds m -2 , but the N concentration of culms, leaves and even grain was slightly lower than with the lower seed rates. The post-heading N accumulation was by far higher in Simeto and Svevo than in Creso, whereas remobilization was highest in Svevo and lowest in Simeto. The percentage contribution of N remobilization to grain N was by far higher in Creso than in the other two varieties. Post-heading N accumulation and N remobilization were highest with the highest plant density, but the contribution of N remobilization to N grain content did not differ between seeding rates.

Sorghum is a species sensitive to chilling temperatures. In the cultivation areas at higher latitudes chilling sensitivity may significantly influence plants growth in early spring, resulting in significant yield reductions. The effects of chilling stress were investigated in a controlled environment experiment on sorghum plants fertilised with 0 and 44 mg per pot of N. Plants were grown at 27 • C until eighth leaf development stage, exposed to 2, 5, and 8 • C for time period varying from 1 to 8 days, and then returned to 27 • C. Dry weight of plants, leaf area and N and P concentration and content were determined before and after each period of cold treatment and after a 10-day recovery period. Plant relative growth rate (RGR), leaf relative growth rate (RLGR) and N and P uptake rates were calculated during the chilling and the recovery period. Chilling treatments greatly inhibited sorghum growth and N uptake during chilling exposure. The nature and severity of chilling damage was a function of the severity and duration of the exposure: plants suffered short chilling injury at all temperatures, when the duration of chilling was prolonged plants were able to react to chilling, but the ability of the plant to adapt decreased with the decrease of temperature. Plant shoot growth was found to be more sensitive to chilling than leaf area growth and non-fertilised plants were more tolerant to chilling than N-fertilised plants. Also the ability of the plant to recover was a function of the severity and duration of the exposure and of N availability. The recovery of growth rate decreased as temperature was lower and as exposure was longer. Non-fertilised plants were able to recover higher growth rates following chilling stress than N-fertilised plants, while for N uptake the reverse was true, with N-fertilised plants having higher N uptake rates than non-fertilised ones.

Plants of miscanthus were grown in a Cd-free solution up to 1 month before heading and then were exposed to 0, 0.75, 1.5, 2.25 and 3 mg l -1 cadmium for 36 days. All cadmium levels were toxic to miscanthus. Growth response was not dose-dependent and two toxicity thresholds were identified: one between 0 and 0.75 mg l -1 Cd, the other between 2.25 and 3 mg l -1 Cd. The former caused a biomass decrease by about 50%, whereas the latter completely inhibited growth and disrupted the mechanisms that restricted Cd translocation to the shoot. Growth of the aerial part was affected by cadmium more than that of the hypogeal one. Cadmium did not change the N concentration of different plant parts, but markedly reduced the N uptake of the plant, the N net uptake rate (NUR) and the N net translocation rate (NTR) from the rhizome to the aerial part. These two indexes equalled zero when plants ceased to grow. Otherwise, the Cd-NUR increased with Cd supply and the Cd-NTR from rhizome to aerial part showed the highest increment when plants did not grow at all. This suggests different uptake pathways for the two elements, active for nitrogen and passive for cadmium. The Cd concentration and the Cd content markedly increased with all Cd levels, following the order roots rhizome > culms > leaves. The Cd concentration and the Cd content of aerial organs increased with Cd supply, but increments were highest between 2.25 and 3 mg l -1 Cd. The highest Cd concentrations were recorded in plants grown with 3 mg l -1 Cd and were 41 and 122 mg kg -1 , respectively, for the aerial and the hypogeal plant parts. The hypogeal plant part retained most of the cadmium taken up from solution, accounting for approximately 87% of total plant cadmium with the three lower Cd levels, and for 73% with the highest one. The maximum Cd content of the entire plant was achieved with the two higher Cd levels and was approximately 4.7 mg, while the Cd content of the aerial part was highest with 3 mg l -1 Cd (1.2 mg Cd per plant) and that of the hypogeal one with 2.25 mg l -1 Cd (4 mg Cd per plant). The highest aerial content achieved in this experiment was 10-fold that obtained in a previous research when small-sized plants were exposed to the same Cd level.

The effects of local climate and silvicultural treatment on the inorganic N availability, net N uptake capacity of mycorrhizal beech roots and microbial N conversion were assessed in order to characterise changes in the partitioning of inorganic N between adult beech and soil microorganisms. Fine root dynamics, inorganic N in the soil solution and in soil extracts, nitrate and ammonium uptake kinetics of beech as well as gross ammonification, nitrification and denitrification rates were determined in a beech stand consisting of paired sites that mainly differed in aspect (SW vs. NE) and stand density (controls and thinning treatments). Nitrate was the only inorganic N form detectable in the soil water. Its concentration was high in control plots of the NE aspect, but only in canopy gaps and not influenced by thinning. Neither thinning nor aspect affected the abundance of root tips in the soil. Maximum nitrate net uptake by mycorrhizal fine roots of beech, however, differed with aspect, showing significantly lower values at the SW aspect with warm-dry local climate. There were no clearcut significant effects of local climate or thinning on microbial N conversion, but a tendency towards higher ammonification and nitrification and lower denitrification rates on the untreated controls of the SW as compared to the NE aspect. Apparently, the observed sensitivity of beech towards reduced soil water availability is at least partially due to impaired N acquisition. This seems to be mainly a consequence of reduced N uptake capacity rather than of limited microbial re-supply of inorganic N or of changed patterns of inorganic N partitioning between soil bacteria and roots.

Leaching of nitrate (NO3-) below the root zone and gaseous losses of nitrogen (N) such as ammonia (NH3) volatilization, are major mechanisms of N loss from agricultural soils. New techniques to minimize such losses are needed to maximize N uptake efficiency and minimize production costs and the risk of potential N contamination of ground and surface waters. The effects of

The integration of multipurpose legumes into low-input tropical agricultural systems is needed because they are a nitrogen (N) input through symbiotic fixation. The drought-tolerant cover legume canavalia (Canavalia brasiliensis) has been introduced for use either as forage or as a green manure into the crop-livestock system of the Nicaraguan hillsides. To evaluate its impact on the subsequent maize crop, an in-depth study on N dynamics in the soil-plant system was conducted. Microplots were installed in a 6-year old field experiment with maizecanavalia rotation. Direct and indirect 15 N-labelling techniques were used to determine N uptake by maize from canavalia residues and canavalia-fed cows' manure compared to mineral fertilizer. Litter bags were used to determine the N release from canavalia residues. The incorporation of N from the amendment into different soil N pools (total N, mineral N, microbial biomass) was followed during the maize cropping season. Maize took up an average of 13.3 g Nm -2 , within which 1.0 gNm -2 was from canavalia residues and 2.6 gNm -2 was from mineral fertilizer, corresponding to an amendment N recovery of 12% and 32%, respectively. Recoveries in maize would probably be higher at a site with lower soil available N content. Most of the amendment N remained in the soil. Mineral N and microbial N were composed mainly of N derived from the soil. Combined total 15 N recovery in maize and soil at harvest was highest for the canavalia residue treatment with 98% recovery, followed by the mineral fertilizer treatment with 83% recovery. Despite similar initial enrichment of soil microbial and mineral N pools, the indirect labelling technique failed to assess the N fertilizer value of mineral and organic amendments due to a high N mineralization from the soil organic matter. Keywords Canavalia brasiliensis . 15 N . Indirect and direct labelling techniques . Microplot study . Organic amendments Abbreviations DAA days after amendment DLT direct labelling technique

The nutrient uptake and distribution patterns for N, P, K, Ca, and Mg were determined in mature (23 to 24 year old), field-grown, rainfed grapevines (Vitis vinifera L. `Pinot noir&#39;) growing in a red hill soil in Oregon in 2001 and 2002. Biomass, nutrient concentrations, and nutrient contents of all plant organs, including roots, were determined on 14 sampling dates over 2 years. There was no seasonal change in the standing biomass of primary roots (fine feeder roots), small woody (&lt;4 mm diameter) or large woody (&gt;4 mm diameter) roots. Trunk biomass also did not change during the 2 years, but all other vine organs showed significant seasonal changes in biomass. The rate of N uptake was greatest at bloom, when remobilization from reserves was also high. Nitrogen was also taken up after leaf fall in 2001, but not in 2002, when an early frost occurred before soil moisture recovery by fall rains. Uptake of N, K, and Ca from soil was similar between years, even though canopy dem...

The number of organic farmers has increased from 0.2 million in 1999 to 2.4 million in 2015, and organic crop field covers 3.71 MHA. The increasing food requirement
from the growing population pressure has forced many countries to use chemical fertilizers to reduce the gap between farm production and demand for a crop with a detrimental socio-economic-ecological impact. The review paper highlights the need for the utilization of digested biogas slurry (DBGS) with an average nutrient
composition of 1.36% N, 1.6% P, and 1.1 % K. Apparently, the production from the utilization of DBGS is higher to the production from utilization of FYM. A 2 m3 biogas plant produces about 0.16 to 1.05 kilogram of Nitrogen (bioslurry) equivalent to 0.35 to2.5 kilograms of Urea, thus reducing the use of chemical fertilizer about 15 to 20%. Thus this review study brings forth the concept of utilization of biogas slurry
for sustainable agriculture.

The grain N uptake response of an opportunity cropping regime comprising summer and winter cereal and legume crops to fertiliser nitrogen (N) and phosphorus (P) applications was studied in 2 long-term experiments with contrasting durations of cultivation. At the longer cultivation duration Colonsay site (&gt;44 years at commencement), grain N uptake increased with fertiliser N application in 15 of 17 harvested crops from 1985 to 2003. Grain sorghum on short-fallow consistently responded to applied fertiliser N at higher rates (≥80 kg N/ha) than crops grown on long-fallow where either fertiliser at nil or 40 kg N/ha maximised grain N uptake. Winter cereal response to applied N was influenced by fallow length, generally smaller responses in long fallow years, although in-crop rainfall affected this. Short-fallow crops responded up to 40 or 80 kg applied N/ha, while seasonal growing-season rainfall affected the responses of the double-crop winter cereals the most. Responses to applied ...

Biochar and the use of legumes in cropping systems are considered sustainable approaches to boost crop yield and preserve soil fertility. In the current study, the effects of leftover biochar and previously planted legumes on wheat yield and soil N status were examined at various nitrogen (N) levels. The experiment included testing two levels of previously applied biochar (0 and 50 tons ha-1), three legumes under four levels of N (0, 60, 90, and 120 kg ha-1), cowpea (Vigna unguiculata) for fodder, Sesbenia (Sesbenia grandaflora) for green manuring, and mung bean (Vigna radiata) for grain. Results showed that biochar application enhanced wheat tiller m-2 , spikes m-2 , grains per spike, thousand grain weight, grain yield, biological yield, and soil total N status by 3%, 6.5%, 3.7%, 1.8%, 7.8%, 9.5%, and 11%, respectively. Moreover, applying nitrogen at a rate of 90 kg ha-1 increased the amount of wheat spike m-2 by 20%, grain spike-1 by 10%, grain yield by 70%, biological yield by 48%, harvest index by 27%, and the N content of the grain, straw, and soil by 13%, 14%, and 36% respectively. Meanwhile, 1000 grain weight resulted higher by 6.17%. Legumes that had been previously seeded outperformed fallow and increased spikes m-2 , grain yield, biological yield, grain N content, and soil total N content by 8.2%, 11%, 6.78%, 25%, and 42%, respectively. It is determined that applying biochar to the summer gap left by legumes can increase soil fertility and wheat output.

The contribution of nitrogen reserves to regrowth following defoliation was studied in white clover plants (Trifolium repens cv. Huia). This was found to be closely linked to the morphological pattern of development of the aerial parts during the same period. Low temperature (6 °C) and short day exposure (8 h photoperiod) were used to induce dwarf development, i.e. to increase branching rate and to enhance new sites of leaf production during a period of regrowth. Treated plants exhibited a large reduction in leaf area and a large increase in leaf pool size for the ®rst 10 d of a subsequent regrowth under standard culture conditions (16 h daylight; 22/18 °C day/ night). The contribution of nitrogen from storage compounds in organs remaining after defoliation (sources) to regrowing tissues (sinks) was assessed by 15 N pulse±chase labelling during regrowth following shoot removal. The mobilization of nitrogen reserves from storage tissues of regrowing clover was closely linked to the pattern of differentiation of the newly developed organs. It appeared that regrowth was supported less by endogenous N for the ®rst 10 d after defoliation in treated plants, compared with control plants grown continuously in standard conditions. It is assumed that dwarf plants exhibit a lower dependence upon the mobilization of soluble proteins previously accumulated in roots and uncut stolons. The relationship between leaf development rate and N-uptake recovery following defoliation is discussed.

Granular urea is known to be an agronomically inefficient source of N when surface-applied, with Nitrogen Utilisation Efficiencies (NUEs) of 20-40%. Two of the main reasons for this include volatilisation losses of ammonia, and poor distribution efficiency to individual plants (coverage). However, its relatively low cost, high N content (46%) and ease of spreading makes it popular with farmers. Recently, granular urea treated with the urease inhibitor nbpt (SustaiN®, N-Protect® and Green Urea®) has taken an increasing share of the NZ and to a lesser extent in Australia. My minimising ammonia volatilisation, nitrogen utilisation efficiency (NUE) is improved 20-25% on average compared to granular urea. Much greater efficiencies again have been achieved since 2005 by fluidising urea (either onboard the spreading truck or separately). Increases in efficiency of up to a factor of 2 (200%) have been recorded, provided nbpt is added. However, the high costs of specialised equipment, mainte...

Isotopically labeled nitrate ( 15 NO ) was added continuously to the Rowley estuary, Massachusetts, for 22 d to Ϫ 3 assess the transport, uptake, and cycling of terrestrially derived nitrogen during a period of high river discharge and low phytoplankton activity. Isotopic enrichment of the 3.5-km tidal prism (150,000 m 3 ) was achieved for the 3 weeks and allowed us to construct a nitrogen mass balance model for the upper estuary. Mean ␦ 15 NO in the Ϫ 3 estuary ranged from 300‰ to 600‰, and approximately 75%-80% of the 15 N was exported conservatively as 15 NO to the coastal ocean. Essentially all of the 20%-25% of the 15 N processed in the estuary occurred in the Ϫ 3 benthos and was evenly split between direct denitrification and autotrophic assimilation. The lack of water-column 15 N uptake was attributed to low phytoplankton stocks and short water residence times (1.2-1.4 d). Uptake of watercolumn NO by benthic autotrophs (enriched in excess of 100‰) was a function of NO concentration and satisfied up to 15% and 25% of the total nitrogen demand for benthic microalgae and macroalgae, respectively. Approximately 10% of tracer assimilated by benthic autotrophs was mineralized and released back to the water column as 15 NH . By the end of the study, 15 N storage in sediments and marsh macrophytes accounted for 50%-70% of the ϩ 4 15

Andisols are very important land resources supporting high human population density. Maize (Zea mays L.) production on Andisols located in the Purhepecha Region of central Mexico is representative of the highlands conditions of Mexico and Latin America. Farmers struggle with low crop yield and low soil nutrient availability. A 2-year field study was conducted to evaluate the effects of green manures either tilled into the soil (CT) or cut and left on the surface as a mulch (ZT), on maize yield and soil quality. Green manure treatments were: vetch (Vicia sativa L.), oat (Avena sativa L.) and none. No extra N was added to maize. Green manure and tillage had a significant effect on maize grain yield, N uptake and P uptake with CT vetch performing better than ZT oat. Soil organic C and total N were significantly higher under ZT than under CT management. Soils with vetch had higher P concentration. Soil under ZT oat had the highest infiltration rate and penetration resistance compared with other treatments. There appears to be a trade off between soil productivity and intrinsic soil physical properties among soil treatments.

The role of S in legume growth, N uptake, and N 2 fixation was investigated using white clover (Trifolium repens L.) as a model species. We examined whether the effect of sulphate addition on N fixation resulted from a stimulation of host plant growth, a specific effect of S on nodulation, or a specific effect of S on nodule metabolism. Clones of white clover, inoculated with Rhizobium leguminosarum, were grown for 140 d in a hydroponic system with three levels of sulphate concentration (0 mM, 0.095 mM, and 0.380 mM). Nodule morphological and biochemical traits, such as root length, nodule biomass and volume, nodule protein contents (nitrogenase and leghaemoglobin obtained by an immunological approach), and root amino acid concentrations, were used to analyse the effect of sulphate availability on N 2 fixation. The application of sulphate increased whole plant dry mass, root length, and nodule biomass, expressed on a root-length basis. N uptake proved less sensitive than N 2 fixation to the effects of S-deficiency, and decreased as a consequence of the lower root length observed in S-deficient plants. N 2 fixation was drastically reduced in S-deficient plants as a consequence of a low nodule development, but also due to low nitrogenase and leghaemoglobin production. This effect is likely to be due to down-regulation by a N-feedback mechanism, as, under severe S-deficiency, the high concentration of whole plant N and the accumulation of N-rich amino acids (such as asparagine) indicated that the assimilation of N exceeded the amount required for plant growth.

Recycling/composting of organic wastes is one of the major solutions for reducing the huge piles of organic wastes and converting it into a value added product. The fruit and vegetable wastes composted in a locally fabricated unit were enriched with urea fertilizer @ 100 and 200 g N kg-1 compost (25 and 50% of full dose of N i.e. 120 kg ha-1). Pot and field experiments were conducted on sandy clay loam soil to evaluate the integrated effect of N-enriched compost and inorganic N fertilizer on wheat crop. Phosphorus and potassium fertilizers as basal dose were kept constant in all treatments. Treatments receiving enriched (with 25% N) compost (300 kg ha-1) were supplied with additional 25 (30 kg ha-1) and 50% (60 kg ha-1) of the total N fertilizer. Wheat cv. Wattan-93 was planted and canal water was used for irrigation. Results of pot and field experiments revealed that integrated application of enriched compost and 60 kg ha-1 N (50% N fertilizer) significantly improved plant height, ...

The disposal of industrial wastewater in Queensland is subjected to the strict environmental guidelines enforced by the Environmental Protection Authority. The most common method of treating industrial wastewater in Queensland is by land irrigation, which is presently based on tropical and subtropical pasture plants. However with limited land area available for irrigation, these plants are not efficient enough to sustainably dispose of all the effluent produced by the industries. Therefore to comply with the new standards, most industries are now under strong pressure to upgrade their treatment processes. Over the past two years a series of research projects conducted at GELITA Australia gelatine factory in Beaudesert, Queensland and at Teys Bros. abattoir in Beenleigh to determine a viable means to achieve these goals. The Vetiver System has been identified as having the potential to meet all the criteria: • Vetiver has the potential of producing up to 132 t/ha/year of dry matter yield as compared to 23 and 20 t/ha/year for Kikuyu and Rhodes grass respectively. • With this production vetiver planting has the potential of exporting up to 1920 kg/ha/year of N and 198 kg/ha/year of P as compared to 687 of N and 77 kg/ha/year of P for Kikuyu and 399 of N and 26 of P for Rhodes grass respectively. • Vetiver growth can respond positively to N supply up to 6000 kg/ha/year and to ensure this extraordinary growth and N uptake, P supply level should be at 250/ha/year. Based on the above results the two companies have developed long term implementation plans for effluent and other solid waste product disposal.

Nitrogen release patterns from decomposing shoot residues of Tephrosia candida, Crotalaria grahamiana, Mucuna pruriens, Macrotyloma axillare, Macroptillium atropurpureum and Desmodium intortum were studied in the laboratory for a period of 22 weeks in a sandy clay soil and 10 weeks in a clay soil using a leaching tube technique. The residual effect of soil incorporated shoot residues of T. candida, T. vogelii, C. grahamiana, M. pruriens and C. juncea on maize yield was evaluated at four sites each in the high rainfall zone (mean precipitation 2100 mm year )1 ) and low rainfall zone (mean precipitation 800 mm year )1 ) of Bukoba District, Tanzania. N mineralised from the legume residues ranged from 24 to 61% of the initial N after 22 weeks in a sandy clay soil and )1 to 34% after 10 weeks in a clay soil. The N mineralisation rates of the residues decreased in both soils in the order M. atropurpureum>M. axillare>C. grahamiana>D. intortum>T. candida>M. pruriens and were mostly strongly related to (polyphenols+lignin)-to-N ratio, lignin-to-N ratio and lignin. Relative to the control, legume residues resulted in two and threefold increase in maize grain yield i.e. from 1.1 to 3.2 Mg ha )1 and from 1.4 to 3.8 Mg ha )1 in a high and low rainfall zone respectively. However, maize yield response to legume residues was limited when compared with application of 50 kg N ha )1 of mineral fertiliser. The % fertiliser equivalency (%FE) of legumes ranged between 25 and 59% with higher values recorded with C. grahamiana. At harvest, apparent N recoveries in maize ranged between 23 and 73% of the N applied in the legume residues. Highest recovery was found with application of C. grahamiana and least recovery from T. candida residues. These results suggested that application of legume residues alone might not be sufficient to meet N requirements and to achieve the yield potential of maize crop in Bukoba soils unless supplemented with small doses of mineral fertilisers.

The disposal of industrial wastewater in Queensland is subjected to the strict environmental guidelines enforced by the Environmental Protection Authority. The most common method of treating industrial wastewater in Queensland is by land irrigation, which is presently based on tropical and subtropical pasture plants. However with limited land area available for irrigation, these plants are not efficient enough to sustainably dispose of all the effluent produced by the industries. Therefore to comply with the new standards, most industries are now under strong pressure to upgrade their treatment processes. Over the past two years a series of research projects conducted at GELITA Australia gelatine factory in Beaudesert, Queensland and at Teys Bros. abattoir in Beenleigh to determine a viable means to achieve these goals. The Vetiver System has been identified as having the potential to meet all the criteria: • Vetiver has the potential of producing up to 132 t/ha/year of dry matter yield as compared to 23 and 20 t/ha/year for Kikuyu and Rhodes grass respectively. • With this production vetiver planting has the potential of exporting up to 1920 kg/ha/year of N and 198 kg/ha/year of P as compared to 687 of N and 77 kg/ha/year of P for Kikuyu and 399 of N and 26 of P for Rhodes grass respectively. • Vetiver growth can respond positively to N supply up to 6000 kg/ha/year and to ensure this extraordinary growth and N uptake, P supply level should be at 250/ha/year. Based on the above results the two companies have developed long term implementation plans for effluent and other solid waste product disposal.

Net soil N mineralization is a driver for N uptake and N losses at an annual scale, but is itself dependent on longterm N surplus and C-N storage in agricultural systems. The accurate modelling of N mineralization remains challenging. Thus, the STICS research version V1610 that includes modified soil organic nitrogen (SON) mineralization and root biomass turnover modules was assessed in this study regarding its predictions of net N mineralization and long-term N fate in a 34-year experiment comparing crop rotations with or without catch crops (CC) and bare soil. The in situ gross balance method was used as a reference to estimate net N mineralization based on measured N variables (i.e. N uptake, exported N and N leaching). The Index of Agreement (IA) of STICS predictions concerning crop biomass, crop yield, N uptake and exported N ranged between 0.61 and 0.76, 0.79-0.89, 0.49-0.64 and 0.47-0.58, respectively, depending on the crop rotations. STICS also enabled a good simulation of annual drainage and N leaching with IA ranges of 0.92-0.96 and 0.78-0.93, but high leaching values were not captured by the model. The STICS research version simulates the decay of deep roots (below a depth of 25 cm) but it neglects their decomposition. This simplification could cause an underestimation of N leaching. The observed N surplus ranged from 27 to 51 kg N ha -1 yr -1 in the cropped rotations depending on the crop rotations, and the N surplus was accurately simulated with an IA of 0.75-0.84. STICS produced a good prediction of changes in SON stocks under cropped rotations and bare soil, with both the rRMSE and rMBE being lower than 10%. Estimated mean annual N mineralization was 115 kg N ha -1 under cropped rotations and 42 kg N ha -1 under the bare soil treatment. STICS relatively well predicted net N mineralization regarding both differences between crop rotations and over time. Moreover, STICS correctly simulated the long-term effects of CC on drainage, N leaching, SON accumulation and net N mineralization. To conclude, STICS is a useful model to predict net N mineralization and N fate in long-term crop rotations. Moreover, this work raised new questions concerning the long-term fate of N stored in deep dead roots. Further improvements to describe the fate of these residues should enhance the prediction of N leaching by the STICS model and enable the optimization of N management in cropping systems.

The N uptake by crops, soil distribution and recovery of 15N labelled urea-N (100 kg N ha-1) were investigated in a sorghum-wheat rotation in two silty clay soils (Foggia and Rieti Casabianca) and one silt loam soil (Rieti Piedifiume) under different mediterranean conditions. Non-exchangeable labelled NH4-N represented an important pool at both Rieti sites with higher values (p&lt;0.05) under sorghum

The use of kinetic equations of NO 3 Ϫ transport systems in oilseed rape (Brassica napus), determined by 15 NO 3 Ϫ labeling under controlled conditions, combined with experimental field data from the INRA-Cha ˆlons rape database were used to model NO 3 Ϫ uptake during the plant growth cycle. The quantitative effects of different factors such as day/night cycle, ontogenetic stages, root temperature, photosynthetically active radiation, and soil nitrate availability on different components of the constitutive high-affinity transport systems, constitutive low-affinity transport systems, inducible low-affinity transport systems, and inducible high-affinity transport systems of nitrate were then determined to improve the model's predictions. Simulated uptake correlated well with measured values of nitrogen (N) uptake under field conditions for all N fertilization rates tested. Model outputs showed that the high-affinity transport system accounted for about 89% of total NO 3 Ϫ uptake (18% and 71% for constitutive high-affinity transport systems and inducible high-affinity transport systems, respectively) when no fertilizer was applied. The low-affinity transport system accounted for a minor proportion of total N uptake, and its activity was restricted to the early phase of the growth cycle. However, N fertilization in spring increased the duration of its contribution to total N uptake. Overall, data show that this mechanistic and environmentally regulated approach is a powerful means to simulate total N uptake in the field with the advantage of taking both physiologically regulated processes at the overall plant level and specific nitrate transport system characteristics into account.

The top-down analysis of nitrate influx isotherms through the Enzyme-Substrate interpretation has not withstood recent molecular and histochemical analyses of nitrate transporters. Indeed, at least four families of nitrate transporters operating at both high and/or low external nitrate concentrations, and which are located in series and/or parallel in the different cellular layers of the mature root, are involved in nitrate uptake. Accordingly, the top-down analysis of the root catalytic structure for ion transport from the Enzyme-Substrate interpretation of nitrate influx isotherms is inadequate. Moreover, the use of the Enzyme-Substrate velocity equation as a single reference in agronomic models is not suitable in its formalism to account for variations in N uptake under fluctuating environmental conditions. Therefore, a conceptual paradigm shift is required to improve the mechanistic modelling of N uptake in agronomic models. An alternative formalism, the Flow-Force theory, was p...

The use of kinetic equations of NO 3 Ϫ transport systems in oilseed rape (Brassica napus), determined by 15 NO 3 Ϫ labeling under controlled conditions, combined with experimental field data from the INRA-Cha ˆlons rape database were used to model NO 3 Ϫ uptake during the plant growth cycle. The quantitative effects of different factors such as day/night cycle, ontogenetic stages, root temperature, photosynthetically active radiation, and soil nitrate availability on different components of the constitutive high-affinity transport systems, constitutive low-affinity transport systems, inducible low-affinity transport systems, and inducible high-affinity transport systems of nitrate were then determined to improve the model's predictions. Simulated uptake correlated well with measured values of nitrogen (N) uptake under field conditions for all N fertilization rates tested. Model outputs showed that the high-affinity transport system accounted for about 89% of total NO 3 Ϫ uptake (18% and 71% for constitutive high-affinity transport systems and inducible high-affinity transport systems, respectively) when no fertilizer was applied. The low-affinity transport system accounted for a minor proportion of total N uptake, and its activity was restricted to the early phase of the growth cycle. However, N fertilization in spring increased the duration of its contribution to total N uptake. Overall, data show that this mechanistic and environmentally regulated approach is a powerful means to simulate total N uptake in the field with the advantage of taking both physiologically regulated processes at the overall plant level and specific nitrate transport system characteristics into account.

The top-down analysis of nitrate influx isotherms through the Enzyme-Substrate interpretation has not withstood recent molecular and histochemical analyses of nitrate transporters. Indeed, at least four families of nitrate transporters operating at both high and/or low external nitrate concentrations, and which are located in series and/or parallel in the different cellular layers of the mature root, are involved in nitrate uptake. Accordingly, the top-down analysis of the root catalytic structure for ion transport from the Enzyme-Substrate interpretation of nitrate influx isotherms is inadequate. Moreover, the use of the Enzyme-Substrate velocity equation as a single reference in agronomic models is not suitable in its formalism to account for variations in N uptake under fluctuating environmental conditions. Therefore, a conceptual paradigm shift is required to improve the mechanistic modelling of N uptake in agronomic models. An alternative formalism, the Flow-Force theory, was p...

Field screening trials were conducted in two dry seasons to assess variability in grain yield, N uptake and N utilization for 180 rice genotypes, mostly lowland indica improved varieties or elite breeding lines of different growth durations [60 each of early (100-110 days), medium (111-119 days) and late (120-135 days)], without the addition of N fertilizer and to identify genotypes with the potential to produce high yields at suboptimal N levels through efficient uptake and/or utilization of N. Available soil N was lower in year 2 (20 kg ha 1) than in year 1 (64 kg ha-i). In both years significant differences in grain yield, N uptake and N-utilization efficiency (NUE) were observed among genotypes within each growth-duration group. Genotypes varied in their response to change in available soil N. The average increase in grain yield for each kilogram increase in N uptake was 61.9 kg in year 1 and 82.7 kg in year 2. However, some genotypes absorbed similar amounts of N but produced different grain yields and/or total dry matter. Some genotypes with similar harvest index exhibited significantly different NUEs -e.g., IR50363-61-1-2-2 (NUE=64.4 in year 1 and 71.9 in year 2) and IR51009-155-2-3-3 (55.3 and 60.8) in the early-duration group; BG380-2 (70 and 78.8) and IR50391-100-2-3-3-2 (56.3 and 58.9) in the medium; and IR27325-63-2-2 (69.7 and 69.8) and BR51-46-1-C1 (57.9 and 60.5) in the late. Those with higher NUE had lower percentage straw N at maturity. Grain N concentration also affected NUE, but the coefficient of variation in percentage grain N among genotypes was less than that of percentage straw N. The relative performance of genotypes in terms of NUE was more consistent than plant N uptake, based on rank correlations between the two trials. High N uptake and NUE were observed in IR13429-150-3-2-1-2 (NUE 65.4, N uptake 9.1 g m -z) in the early-duration group, IR44 (NUE 67.2, N uptake 8.3 g m -z) in the medium-duration group and IR39323-182-2-3-3-2 (NUE 64.8, N uptake 9.3 g m -2) in the late-duration group. The study identified genotypes which may possess promising traits for improved N uptake and utilization efficiency. Further studies are needed to elucidate the mechanisms involved in high N uptake and N-use efficiency.

A ®eld experiment was conducted in the dry season at Los Ban Äos, Philippines, to assess the differences in grain yield and N utilization of 10 medium-duration (119AE4 days after seeding [DAS]) genotypes and 10 long-duration (130AE4 DAS) ones with varying acquisition and usage of soil and fertilizer N.

Comparam-se as eficiências de soluções de aquamônia e de carbonato/bicarbonato de amônio contendo sais de K e de P quanto à produção de material seco da parte aérea e ao aproveitamento do N aplicado como fertilizante por cana-de-açúcar. Soqueiras de cana-de-açúcar da variedade &quot;RB72454&quot; foram transplantadas para vasos de 100 dm³ de terra e cultivadas por noventa dias. O delineamento experimental utilizado foi em esquema fatorial 2 x 3 inteiramente casualizado, com 4 repetições. Os tratamentos consistiram no fornecimento de fontes de N em combinações ou não com KCl e NH4H2PO4. Os nutrientes P e K não incluídos em cada tratamento foram aplicados em outro ponto, à mesma distância e profundidade das soqueiras que as soluções de tratamento, para assegurar a igualdade das quantidades de N, P e K aplicadas a todas as parcelas. Avaliaram-se a produção de material seco da parte aérea, a extração total de N e a recuperação do N do fertilizante. Considerou-se, para este último parâme...

There is a need for an improved understanding of nitrogen (N) dynamics in depleted sandy soils in southern Africa. A field experiment was conducted to evaluate the performance of different soil fertility improvement practices on a degraded granitic sandy soil in Zimbabwe. Legumes capable of accumulating large amounts of N through biological N 2 fixation and subsoil N capture were tested against soybean/maize rotation, cattle manure fertilization and continuous maize (Zea mays L) with or without fertilizer. Soybean (Glycine max) accumulated 82 kg ha -1 N (seed + stover), while mucuna (Mucuna pruriens) produced 87 kg ha -1 N in its biomass. Soybean fixed 76% of its N, while mucuna fixed 96% of the accumulated N as estimated by the 15 N natural abundance method. Although the following maize crop in the second season suffered from drought stress, maize N uptake was 14.8 kg ha -1 following soybean and 16.4 kg ha -1 following mucuna, compared with 5.2 kg ha -1 for the unfertilized maize and 25.6 kg ha -1 for the maize fertilized with N at 90 kg ha -1 . Cajanus cajan and Crotalaria paulina added barely 10 kg ha -1 of N through their biomass and had no effect on N uptake by maize. Apparent recovery of the added N by maize was 47% for the fertilized maize, 36% for soybean, 12% for mucuna and 9% for cattle manure. There was very little partitioning of N into grain and uptake was mostly before the onset of the drought. Despite the large differences in added residue N, differences in soil mineral N were only evident up to 4 weeks after the beginning of the rains, after which mineral N concentrations became very small in all treatments due to leaching, rather than crop uptake. By the eighth week after crop emergence, maize root length density had increased to about 0.1 cm cm -3 at the 60-80 cm depth, the rapid increase apparently stimulated by the drought. It was concluded that mineral N available to maize from the residues tested falls short of what is required to sustain high maize yields. In these environments where biomass accumulation in many legumes is restricted by soil biophysical factors (poor nutrient concentrations, acidity, coarse texture), combinations of legume rotations and mineral N fertilization will remain the most viable option for sustainable agriculture.

ÐLaboratory scale experiments were performed in a non-continuous batch reactor system with 0.8±41.2 l domestic sewage exposed to constant light intensity, temperature and humidity. The treatment performance of duckweed (L. gibba)-covered sewage lagoons (DSL) was studied within a COD total range of 200±500 mg/l (113±294 mg COD ®lt /l), in 10, 30, 70 and 95 cm deep reactors, and liquid mixing intensity (power dissipation) of 0, 0.3, 1.0, 2.3 and 34.1 W/m 3. The duration of each experiment was 20 days with biomass harvesting every 5 days. COD removal at extreme depths and extreme mixing intensities was compared with that in covered control reactors without duckweed. Removal of COD ®lt did not dier in duckweed-covered and control reactors. The role of duckweed cover was marginal in changing the redox potential or the DO. COD removal l r (kg COD ®lt /ha 20 days) correlated strongly with initial surface load l s (kg COD ®lt /ha). Concentration removal (as mg COD ®lt /l) was also proportional to initial COD ®lt concentration. For a given COD ®lt mass input, increasing depth up to 1 m aected DSL performance only by increasing surface load, and not by hampering oxygen transfer. Mixing (up to 2.3 W/m 3) raised COD ®lt removal. Therefore, at depths beyond 70 cm, moderate mixing is recommended. The ®rst-order kinetic removal rate coecient for COD ®lt was 0.04±0.06 d À1 .

Although intermittent irrigation is widely regarded as a saving irrigation water technology in paddy fields, it can cause water and air pollution by changing the nitrogen cycle. A two-year lysimeter experiment was conducted to investigate the effect of intermittent irrigation on the nitrogen cycle. For applying intermittent irrigation, soil drying began about 30 days after transplanting and the alternate wetting and drying was considered weekly. To investigate the nitrogen cycle in the lysimeter, nitrate and ammonium concentrations and acidity were measured periodically at depths of 18, 30, and 70 cm. Results showed that water saving was 23-24%, which varied over two years depending on the weather conditions. The most nitrate and ammonium concentration changes occurred at a depth of 30 cm in 2018 and a depth of 70 cm in 2019. Nitrate concentration after two dried periods at a depth of 30 cm indicated the producing and leaching of nitrate in the soil, which upraised the risk of groundwater contamination. Nitrate concentration in the dried period increased compared to the previously flooded period, although the rate of increase was variable in each alternation. The reduction of ammonium concentration was about 13% in the first alternation at a depth of 30 cm, which was much lower in the following periods. Nitrogen balance in the surface layer showed that 39 and 51% ammonium volatilization and rice uptake occurred, respectively. Denitrification was obtained 0.5 kg N ha-1 which could be as an index for the emission of N2O. Total nitrogen loss based on applied nitrogen fertilizer was 52%, of which 47% is caused by ammonium volatilization. Results showed the importance of the number of alternations in nitrogen changes in paddy fields.