Nitrogen Fertilizer Recovery Research Articles

Fertilizer Nitrogen Recovery Efficiency of Furrow‐Irrigated Corn

Corn (Zea mays L.) yield under irrigated production systems is influenced by N rate and timing of application. This study was conducted to determine how current N application strategies (two‐way vs. three‐way split application) and N rate (optimal vs. suboptimal) influence fertilizer‐nitrogen recovery efficiency (FNRE) for furrow‐irrigated corn production in the mid‐South. The effects of N rate and application timing on corn FNRE were investigated in Rohwer, AR, on a Herbert silt loam (fine‐silty, mixed, active, thermic Aeric Epiaqualf). Corn grain yield and total‐N uptake were both influenced by the interaction of N treatment and year (p < 0.0001). Corn grain yields were maximized when an optimal‐N rate of 235 kg N ha−1 was applied in a two‐way split application with 50 kg N ha−1 pre‐plant and 185 kg N ha−1 sidedressed at the V6 stage. The ANOVA for FNRE indicated that N treatment was the only significant factor (p < 0.0001) and varied based on N rate and time of application. The lowest FNRE was 61% and occurred when 50 kg N ha−1 was applied pre‐plant. The highest overall FNRE was 91% when 50 kg N ha−1 was applied pre‐tassel in the suboptimal‐N rate treatment. The FNRE of N sidedressed at V6 ranged from 81 to 91% and was influenced by N rate with the suboptimal‐N rate treatments tending to have significantly higher FNRE values. The results presented in this paper highlight the high FNRE that can be achieved in furrow‐irrigated corn production.Core Ideas Fertilizer N recovery efficiency ranged from 61 to 91%. Fertilizer N recovery efficiency influenced by rate and application timing. High fertilizer N recovery efficiency can be achieved in irrgated corn production systems.

Residual recovery and yield performance of nitrogen fertilizer applied at sugarcane planting

The low effectiveness of nitrogen fertilizer (N) is a substantial concern that threatens global sugarcane production. The aim of the research reported in this paper was to assess the residual effect of N-fertilizer applied at sugarcane planting over four crop seasons in relation to sugarcane crop yield. Toward this end three field experiments were established in the state of Sao Paulo, Brazil, during February of 2005 and July of 2009, in a randomized block design with four treatments: 0, 40, 80 and 120 kg ha−1 of N applied as urea during sugarcane planting. Within each plot, a microplot was established to which 15N-labeled urea was applied. The application of N at planting increased plant cane yield in two of the three sites and sucrose content at the other, whereas the only residual effect was higher sucrose content in one of the following ratoons. The combined effect was an increase in sugar yield for three of the 11 crop seasons evaluated. Over the crop cycle of a plant cane and three ratoon crops, only 35 % of the applied N was recovered, split 75, 13, 7 and 5 % in the plant cane, first, second and third ratoons, respectively. These findings document the low efficiency of N recovery by sugarcane, which increases the risk that excessive N fertilization will reduce profitability and have an adverse effect on the environment.

The fate of urea nitrogen applied to a vegetable crop rotation system

To investigate the fate of urea nitrogen (N) applied to vegetable fields, three N rates, N0 (0 kg N/ha), N1(225 or 240 kg N/ha) and N2 (450 or 480 kg N/ha) were applied to a rotation system. Nitrogen fertilizer recovery (NFR), N residue in soil, and N losses were measured in situ. Higher N application rates resulted in lower NFR, and increased N residues in soil and losses. The NFR, Chinese cabbage, and eggplant were different in the N1 and N2 groups (P < 0.01). The ratios of N fertilizer residue at 0–60 cm deep ranged from 30.2 to 41.1 % (N1), and 33.1 to 57.7 % (N2). The N loss ratios were only 6.6 % (N1) and 11.9 % (N2), because of the lower precipitation rates and temperatures characteristic of its growing season; meanwhile, N losses were 31.1 and 37.4 % in cayenne pepper, and 24.1 and 29.2 % in eggplants in the N1 and N2 treatments, respectively. The main pathways of N loss were leaching, followed by gaseous losses; these were major pathways of N loss in seasons with lower precipitation rates. NH3 volatilization was correlated with soil temperature (P < 0.01), and N2O emissions were correlated with soil moisture in the N1 treatment and with soil NH4 +-N concentration in the N2 treatment (P < 0.01). Denitrification rates were correlated with soil moisture in the N0 and N1 treatments, and with NO3 −-N content in the N2 treatment (P < 0.01). Finally, loss due to runoff was correlated with precipitation (P < 0.01).

The Influenec of Azolla pinnata on Floodwater Chemistry, Grain Yield and Nitrogen Uptake of Rice in Dano, Southwestern Burkina Faso

Nitrogen fertilizer recovery by lowland rice can be as low as 10% and rarely exceeds 60%. Azolla contributes to the nitrogen (N) nutrition of rice plant through biological N fixation (BNF). This study aimed at assessing the influence of Azolla pinatta on floodwater chemistry, rice yield, total dry matter and N uptake of rice. The study was carried out at the Dreyer Research Station in South Western Burkina Faso in 2005 using a split urea application method called Experiment 1 (E1) which was compared with what the farmer’s practice (E2), which is basal application of NPK (16 16 16) and one top-dress of urea. Four levels of nitrogen was used in the experiments (0, 40, 80, 120 kg N ha -1 ). The full Azolla cover on the floodwater surface by the time of urea application prevented rapid increase in floodwater pH in the range of 0.52 to 0.68. The presence of Azolla lowered floodwater temperature by 1.9 to 2.0 o C. There was a significant increased (p 0.05) between Azolla and nitrogen. It is concluded that Azolla brought about an additive effect and could be an efficient fertilizer alternative or supplement in flooded rice cropping system in Dano.

Nitrogen uptake and nitrogen fertilizer recovery in old and modern wheat genotypes grown in the presence or absence of interspecific competition.

Choosing genotypes with a high capacity for taking up nitrogen (N) from the soil and the ability to efficiently compete with weeds for this nutrient is essential to increasing the sustainability of cropping systems that are less dependent on auxiliary inputs. This research aimed to verify whether differences exist in N uptake and N fertilizer recovery capacity among wheat genotypes and, if so, whether these differences are related to a different competitive ability against weeds of wheat genotypes. To this end, 12 genotypes, varying widely in morphological traits and year of release, were grown in the presence or absence of interspecific competition (using Avena sativa L. as a surrogate weed). Isotopic tracer 15N was used to measure the fertilizer N uptake efficiencies of the wheat genotypes and weed. A field experiment, a split-plot design with four replications, was conducted during two consecutive growing seasons in a typical Mediterranean environment. In the absence of interspecific competition, few differences in either total N uptake (range: 98–112 kg N ha−1) or the 15N fertilizer recovery fraction (range: 30.0–36.7%) were observed among the wheat genotypes. The presence of competition, compared to competitor-free conditions, resulted in reductions in grain yield (49%), total N uptake (29%), and an 15N fertilizer recovery fraction (32%) that were on average markedly higher in modern varieties than in old ones. Both biomass and grain reductions were strongly related to the biomass of the competitor (correlation coefficients > 0.95), which ranged from 135 to 573 g m−2. Variations in both grain and biomass yield due to interspecific competition were significantly correlated with percentage of soil cover and leaf area at tillering, plant height at heading, and total N uptake, thus highlighting that the ability to take up N from the soil played a certain role in determining the different competitive abilities against weed of the genotypes.

Optimal Nitrogen Management Enhanced External Chemical Nitrogen Fertilizer Recovery and Minimized Losses in Soil-Tomato System

Excess chemical nitrogen (N) fertilization is widespread in intensive greenhouse vegetable production in China and has resulted in low recovery efficiency and high losses of chemical N fertilizer. Understanding the fate of chemical N fertilizer is crucial for best management of chemical N fertilizer. Using the technique of stable isotope 15N-labeled urea, a micro-plot experiment was conducted to estimate the recovery of 15N-labeled urea in tomato, residues in soil and losses in soil-tomato system. The treatments included the conventional N management with chemical N rate (1000 kg N/ha), named FP and optimal N management with chemical N rate (500 kg N/ha), combined with maize straw and drip irrigation, named OPT. Compared with the FP, total dry matter yield increased by 6.5%–9.3% for the OPT in the autumn-winter season (AW) and winter-spring seasons (WS), respectively. There was a significantly higher recovery efficiency (20.7%) of 15N-labeled urea in the OPT compared to the FP (11.3%; P < 0.05). The amount of residual NO3--N derived from 15N-labeled urea was significantly higher in the FP than in the OPT (P < 0.05). More inorganic N derived from 15N-labeled urea was incorporated into the stable fraction of organic matter in the OPT and had a positive effect on reducing the N leaching with increased time during the season. The loss rate of N derived from 15N-labeled urea was 46.8% in the FP, 25.8% greater than in the OPT. Optimal N management improved tomato yields, enhanced chemical N recovery efficiency, while minimizing losses in the soil-tomato system. It will be practical for maintaining the sustainability of greenhouse-based intensive vegetable systems.

Fertilizer nitrogen recovery efficiencies in crop production systems of China with and without consideration of the residual effect of nitrogen

China is the world’s largest consumer of synthetic nitrogen (N), where very low rates of fertilizer N recovery in crops have been reported, raising discussion around whether fertilizer N use can be significantly reduced without yield penalties. However, using recovery rates as indicator ignores a possible residual effect of fertilizer N—a factor often unknown at large scales. Such residual effect might store N in the soil increasing N availability for subsequent crops. The objectives of the present study were therefore to quantify the residual effect of fertilizer N in China and to obtain more realistic rates of the accumulative fertilizer N recovery efficiency (RE) in crop production systems of China. Long-term spatially-extensive data on crop production, fertilizer N and other N inputs to croplands in China were used to analyze the relationship between crop N uptake and fertilizer N input (or total N input), and to estimate the amount of residual fertilizer N. Measurement results of cropland soil N content in two time periods were obtained to compare the change in the soil N pool. At the provincial scale, it was found that there is a linear relationship between crop N uptake and fertilizer N input or total N input. With the increase in fertilizer N input, annual direct fertilizer N RE decreased and was indeed low (below 30% in recent years), while its residual effect increased continuously, to the point that 40–68% of applied fertilizer was used for crop production sooner or later. The residual effect was evidenced by a buildup of soil N and a large difference between nitrogen use efficiencies of long-term and short-term experiments.

Development and evaluation of a full-scale spray scrubber for ammonia recovery and production of nitrogen fertilizer at poultry facilities

Significant ammonia emissions from animal facilities need to be controlled due to its negative impacts on human health and the environment. The use of acid spray scrubber is promising, as it simultaneously mitigates and recovers ammonia emission for fertilizer. Its low pressure drop contribution on axial fans makes it applicable on US farms. This study develops a full-scale acid spray scrubber to recover ammonia emissions from commercial poultry facilities and produce nitrogen fertilizer. The scrubber performance and economic feasibility were evaluated at a commercial poultry manure composting facility that released ammonia from exhaust fans with concentrations of 66–278 ppmv and total emission rate of 96,143 kg yr−1. The scrubber consisted of 15 spray scrubber modules, each equipped with three full-cone nozzles that used dilute sulphuric acid as the medium. Each nozzle was operated at 0.59 MPa with a droplet size of 113 μm and liquid flow rate of 1.8 L min−1. The scrubber was installed with a 1.3-m exhaust fan and field tested in four seasons. Results showed that the scrubber achieved high NH3 removal efficiencies (71–81%) and low pressure drop (<25 Pa). Estimated water and acid losses are 0.9 and 0.04 ml m−3 air treated, respectively. Power consumption rate was between 89.48 and 107.48 kWh d−1. The scrubber effluents containing 22–36% (m/v) ammonium sulphate are comparable to the commercial-grade nitrogen fertilizer. Preliminary economic analysis indicated that the break-even time is one year. This study demonstrates that acid spray scrubbers can economically and effectively recover NH3 from animal facilities for fertilizer.

Nitrogen Management and Methane Emissions in Direct‐Seeded Rice Systems

Rice (Oryza sativa L.) establishment systems based on resource‐conserving production practices are gaining popularity globally. To investigate the potential for improved N management and mitigation of methane (CH4) emissions, field experiments were conducted in California on three crop establishment systems: water‐seeded (WS) conventional, WS stale seedbed, and drill‐seeded (DS) stale seedbed. Fertilizer nitrogen recovery efficiency (NRE) and rice yield as affected by N rate, source, and application timing were evaluated for 2 yr in each system. Methane emissions were monitored over a full annual rice production cycle (growing season plus fallow period). Results indicated that neither split N applications nor ammonium sulfate increased yields or NRE compared with a single application of urea, regardless of system. However, the economic optimum N rate increased by approximately 30 kg N ha−1 in WS stale seedbed compared with the conventional system. Since NRE generally remained similar across N treatments that maximized yields, applying the appropriate N rate as a single dose before the permanent flood would satisfy both agronomic and environmental goals of N management within each system. Both WS systems resulted in similar growing season CH4 emissions. However, the DS system reduced CH4 emissions by 47% compared with the conventional WS system, possibly due to a decreased period of anaerobic soil conditions. This study highlights the importance of assessing benefits as well as tradeoffs when evaluating opportunities for increasing the sustainability of direct‐seeded establishment systems with respect to N management and CH4 emissions.

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Rapid increases in atmospheric carbon dioxide concentration ([CO2]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO2] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO2] on the growth, grain yield and the recovery of 15N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions. Residue for ambient and elevated [CO2] treatments, obtained from wheat grown previously under ambient and elevated [CO2], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage 15N-labeled granular urea (10.22 atom%) was applied at 50 kg N ha−1 and the wheat grown to maturity. When residue was not incorporated into the soil, elevated [CO2] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO2] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO2] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO2] decreased fertilizer N recovery. A higher fertilizer application rate will be required under future elevated [CO2] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO2] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.

Does elevated atmospheric carbon dioxide concentration increase wheat nitrogen demand and recovery of nitrogen applied at stem elongation?

The effect of elevated carbon dioxide concentration ([CO2]) on fertilizer nitrogen (N) recovery in wheat grown under open-air conditions in the North China Plain has not been reported. Winter wheat (Triticum aestivum L. cv. Zhongmai 175) was grown to maturity under ambient (415±16μmolmol−1) and elevated (550±17μmolmol−1) [CO2] at the free-air carbon dioxide enrichment (FACE) facility in a semi-arid region in northern China. We applied 15N-enriched (10.22at.%) granular urea to microplots at either 25 or 95kgNha−1 at the stem elongation stage of wheat. Elevated [CO2] increased wheat biomass (29%) and grain yield (23%), but had no significant effect on grain protein concentration. The [CO2]-induced N demand (19%) was satisfied mostly by increased uptake of indigenous N (19%). Elevated [CO2] had no significant effect on the recovery of fertilizer 15N (applied at stem elongation) by the plant or on the amount that remained in the soil. Of the fertilizer 15N assimilated by the whole plant, the allocation to grain increased from 62% under ambient [CO2] to 72% under elevated [CO2]. High N application did not increase wheat biomass, grain protein concentration, or fertilizer N recovery in the plant, irrespective of [CO2]. The results suggest that current fertilizer practice in a wheat cropping system such as in the North China Plain will have to be adjusted in a CO2-rich world.

Yield, water productivity and nutrient balances under the System of Rice Intensification and Recommended Management Practices in the Sahel

Consumer demand for rice in sub-Saharan Africa (SSA) is increasing faster than for any other cereal. Governments in the Sahel are responding by promoting double-cropping of irrigated rice in the region's river basins, although rising fertilizer and water costs cast doubt on the future profitability of such systems. Despite controversy, the System of Rice Intensification (SRI) is widely promoted as a potential solution to this dilemma. SRI includes transplanting young, single seedlings at wide spacing, compost application, mechanical weed control, and alternate wetting and drying irrigation. However, independent evaluation of the system in comparison to an appropriate control is lacking in SSA, and the Sahel in particular. Responding to this need, we compared SRI to flooded rice production following regionally Recommended Management Practices (RMP), in a five-season experiment in the Senegal River Valley. Our objectives were to evaluate yield, water productivity, fertilizer nitrogen recovery efficiency, partial macronutrient balances and soil quality under both management systems. But because compost production in the Sahel is constrained by low labor and biomass availability, we replaced these materials with waste rice straw, and compared the impact of sole mineral fertilizer application to rice straw residue incorporation with fertilizer addition, under both SRI and RMP. In seasons 1–3, fertilizer alone significantly increased yield, with no differences found between management systems. In season 4, beneficial effects of straw incorporation and fertilizer addition were observed, as significant additive increases in yield, straw and fertilizer nitrogen recovery were found for each management system. In season 5, additive benefits were found only for SRI, although SRI yields never exceeded any fertility management treatment under RMP. Across seasons, water savings from 16% to 48% were obtained with SRI, resulting in significant (11%–45%) increases in water productivity. Combined straw incorporation and fertilizer application helped stabilize partial nitrogen and potassium balances across management systems. Compared to controls, straw incorporation also increased total soil nitrogen and carbon. In contrast to the literature on SRI in the Sahel, our findings indicate that when nutrient additions are held constant, significant yield increases should not be expected over conventionally recommended rice crop management systems. However, should farmers choose to experiment with SRI to reduce water use, they would be most likely to benefit from combining rice straw incorporation with mineral fertilizer, although several seasons may be required for additive yield effects to occur.

Recovery of Fertilizer Nitrogen by Maize Grown with Nutriseed Pack and Soil Nitrogen Retention Using 15N Tracer

In a cropped land plant and soil utilizes nitrogen (N) mainly from fertilizer. Deep placement of fertilizer N enhances added N use efficiency. Nutriseed Pack technique is a way of deep placing fertilizer in the root zone simultaneously when sowing the seed. A Green house experiment with 15 N tracer technique was conducted during 2009 at open premises of green house in the Department of Soil Science and Agricultural Chemistry, TNAU, Coimbatore to evaluate the effect of application of fertilizers in maize by surface broadcast and Nutriseed Pack. Each Nutriseed Pack was assembled by stacking of seed, manure and fertilizer pellets and then wound in newspaper as a roll. On placement in soil, supply of nutrients is expected from Nutriseed pack throughout the crop period. Column study on 15 N recovery of added fertilizer by maize resulted in high recovery (NUE) for horizontal placement of Nutriseed Pack (36.17%) followed by placement of vertical Nutriseed Pack with Furadan (33.62%), and moderate recovery for surface broadcast (30.45%). The applied labelled N retained in surface layer was high in horizontal placement of Nutriseed Pack which ranged from 8.0 to 18.1 per cent in surface layer (0-15 cm), 4.9 to 10.8 per cent in sub-surface layer (15-30 cm), and 2.8 to 6.0 per cent the lower layer (30-45cm) respectively. In case of surface application of fertilizers, N retained was 5.5 per cent in surface layer (0-15 cm), 3.2 per cent in sub-surface layer (15-30 cm), and 11.1 per cent in lower layer (30-45 cm) respectively.

Effect of Slow Release Fertilizer on Nitrogen Absorption and Fertilizer Nitrogen Recovery Rate in Chinese High-Yielding Rice Cultivars

中国における水稲の多収穫多施肥栽培において施肥窒素（N）吸収率の向上を目的とし，多収性水稲品種のN吸収に及ぼす緩効性肥料の施用効果を調査した．緩効性肥料の施用は，中国産多収性品種の揚稲4号（YD）および武育粳3号（WY）において幼穂形成期までの肥料由来N吸収量を有意に増加させた．この結果，施肥N吸収率が有意に増加し，YDでは成熟期N含有量の有意な増加も認められた．YDは幼穂形成期から出穂期にかけてのN吸収量が高かったが，WYはより早い時期のN吸収量が高く，YDに対してはWYより肥効の長い緩効性肥料の施用が有効であると推察される．YDの施肥N吸収率は，シグモイド型緩効性肥料（S区）＞リニア型緩効性肥料（L区）＞塩安の分施（C区）の傾向があり，施肥N量の増加に伴いC区では有意に増加したが，S区およびL区では有意な変化は認められなかった．以上のことから，YDへの緩効性肥料，特にシグモイド型肥料の施用は施肥N吸収率が高いこと，それにより施用量の削減が可能であることから，環境負荷の軽減に有効であると考えられた．

Nitrogen Release from Environmentally Smart Nitrogen Fertilizer as Influenced by Soil Series, Temperature, Moisture, and Incubation Method

Environmentally Smart Nitrogen (ESN) is a polymer-coated urea fertilizer with potential to increase crop recovery of fertilizer nitrogen (N). Our research objectives were to characterize ESN N retention across time as affected by soil series, temperature, moisture, and incubation method. A rumen bag containing 38 to 44 mg ESN N was placed in 400 g soil, and the amount of ESN N remaining in prills was measured every 5 d for 40 d. Soil was incubated at 25 °C and 250 g H2O kg−1 soil, except in experiments where soil temperature or moisture was varied. Nitrogen retention in ESN was linear for three silt and sandy loams and curvilinear in two clayey soils with retention declining more rapidly in clayey soils. Soil temperature had the greatest effect on N retention with the rate of ESN N release increasing as soil temperature increased. Near complete release of ESN N was achieved by 40 d with temperatures ≥ 20 °C.

Nitrogen Use Efficiency and Nitrogen Fertilizer Recovery of Durum Wheat Genotypes as Affected by Interspecific Competition

A better understanding of the genotype response to N fertilization under weed competition is necessary to identify varieties that exhibit high N use efficiency even when weeds compete for available N. Such varieties may be more suitable for low input or organic systems. This study assessed the variations in nitrogen use efficiency (NUE) (and its components) and the recovery of 15N‐labeled fertilizer in three durum wheat (Triticum durum Desf.) genotypes (one landrace and two varieties that differ in terms of plant growth, grain yield potential, and adaptability to stressful environments) grown in the presence or absence of interspecific competition and varying soil N availability (0 or 80 kg N ha−1 fertilization). The results showed that wheat genotypes had different grain yield potentials and the yields were similar when plants were grown in conditions of low N availability and in presence of interspecific competition. Differences among genotypes in N uptake efficiency were very small, and the low NUE value observed for the landrace seemed to be due to its reduced ability to use absorbed N for increasing grain yield compared with the two varieties. Furthermore, the genotypes showed different competitive abilities against competitor, and seemed to depend on the genotypes' ability to reduce resource availability (N) for their competitors rather than on their ability to tolerate a reduction in contested resources due to competitors.

Recovery of nitrogen fertilizer by traditional and improved rice cultivars in the Bhutan Highlands

The recovery of soil derived nitrogen (NDFS) and fertilizer N (NDFF) was investigated in highland rice (Oryza sativa L.) fields in Bhutan, characterized by high inputs of farmyard manure (FYM). The effect of 60 kg N ha−1 (60 N) applied in two splits to a traditional and an improved cultivar, popular among the farmers, was investigated using the 15N isotope dilution technique. No differences were found between cultivars with respect to the uptake of NDFS and NDFF, but the improved cultivar yielded 27% more (P ≤ 0.05) grain compared with the traditional cultivar. This was largely due to its greater harvest index (HI). The mean percentage recovery of fertilizer N (REN) applied at 45 days after transplanting (DAT) was 34% compared to 22% at 7 DAT, resulting in 56% greater uptake of NDFF at 45 DAT. The overall REN for both the improved and the traditional cultivars were 25.7% and 30% respectively, with no difference between cultivars, but REN decreased with increasing FYM inputs. Fertilizer N recommendations that allow for previous FYM inputs combined with applications timed to coincide with maximum crop demand (45 DAT), and the use of improved cultivars, could enhance N fertilizer recoveries (REN) and increase rice yields in the Bhutan Highlands.

Will Variable‐Rate Nitrogen Fertilization Using Corn Canopy Reflectance Sensing Deliver Environmental Benefits?

Within‐field variability of corn (Zea mays L.) N need calls for development of precision fertilizer application strategies. One approach many are investigating is in‐season canopy reflectance sensing. Justification for this strategy partly rests with the premise it will improve N use and reduce N loss from fields. The objective of this study was to determine the potential environmental benefits using corn canopy reflectance sensing for N fertilization. On 16 field‐scale sites, multiple blocks of randomized N rate plots (0–235 kg N ha−1) traversing fields were side‐dressed between the V7 and V11 growth stages. Sensor measurements were obtained from these and adjacent N‐rich reference strips at side‐dressing. Environmental indicators were examined at the determined optimal nitrogen rate (Noptimal) and the nitrogen rate the producer used (Nproducer). A partial nitrogen mass balance (PNB) on response blocks within fields highlighted how variable Noptimal likely resulted in multiple and different N loss pathways. For many fields, Noptimal was less than Nproducer, and the observed trends were as expected: higher yield efficiency (YE), higher nitrogen fertilizer recovery efficiency (NFRE), lower unaccounted for N, and less postharvest inorganic N. For a measurement examining canopy sensor‐based N applications, N savings of 10 to 50 kg N ha−1 would be expected, but savings varied by reflectance readings, soil type, and fertilizer and grain prices. In some situations sensor‐based N would be greater than Nproducer. Given that sensor information can be processed into an N rate that approximates Noptimal, the results support sensor‐based N applications have potential for environmental benefits.

Triangular Transplanting Pattern and Split Nitrogen Fertilizer Application Increase Rice Yield and Nitrogen Fertilizer Recovery

Field experiments were conducted to evaluate the effects of improved crop management (OPT) for irrigated rice (Oryza sativa L.) on grain yield and N recovery efficiency in southwestern China. In the OPT treatment, rice seedlings were transplanted in a triangular spatial pattern and the N fertilizer was split, based on the difference between the estimated total N requirement and the soil and environmental N supply. Fine‐tuning of application rates was achieved using leaf greenness measurements. The performance of OPT was tested in two adjacent fields in which the crops preceding rice were wheat (Triticum aestivum L.; Rw) and rapeseed (Brassica napus var. napus; Ro). The OPT and traditional farming practice (TRA) treatments both gave higher average grain yields than zero‐N controls (CK). Rice yields were considerably smaller in Rw than Ro under CK. Compared with TRA, OPT led to significantly higher aboveground N uptake, biomass accumulation, and grain yield in Rw Over the 2 yr of the study, average rice grain yields under OPT increased by 19 and 22% compared with TRA and 30 farmers' fields, respectively. The OPT treatment performed better than TRA in 15N recovery efficiency. Compared with TRA, OPT led to increased 15N fertilizer recovery efficiency from 19% in TRA to 42% in OPT, and decreased loss from 68% in TRA to 39% in OPT. In conclusion, OPT practice is a feasible means to attain increased yield with efficient N use. This study provides guidance for farmers using rice‐based cropping systems, especially in southwestern China.

Quantitative difference method for estimation of fertilizer nitrogen balance and uptake by zea mays on an orthic oxisol of North Central Nigeria

The percentic recovery and balance of fertilizer nitrogen can be determined by different methods. In this study, quantitative difference method in recovery of Nitrogen of above-ground dry matter was applied to investigate the uptake of field applied nitrogen by maize cultivated in an orthic oxisol soil. It was found that the maximum uptake of fertilizer N is about 75 % decreasing at the end of the growing period to about 65%. About 25% of the N remains in the upper part of the profile, while about 10% can not be localized and presumably lost by denitrification.