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Dividing fields into a few relatively homogeneous management zones (MZs) is a practical and cost-effective approach to precision agriculture. There are three basic approaches to MZ delineation using soil and/or landscape properties, yield information, and both sources of information. The objective of this study is to propose an integrated approach to delineating site-specific MZ using relative elevation, organic matter, slope, electrical conductivity, yield spatial trend map, and yield temporal stability map (ROSE-YSTTS) and evaluate it against two other approaches using only soil and landscape information (ROSE) or clustering multiple year yield maps (CMYYM). The study was carried out on two no-till corn-soybean rotation fields in eastern Illinois, USA. Two years of nitrogen (N) rate experiments were conducted in Field B to evaluate the delineated MZs for site-specific N management. It was found that in general the ROSE approach was least effective in accounting for crop yield variability (8.0%–9.8%), while the CMYYM approach was least effective in accounting for soil and landscape (8.9%–38.1%), and soil nutrient and pH variability (9.4%–14.5%). The integrated ROSE-YSTTS approach was reasonably effective in accounting for the three sources of variability (38.6%–48.9%, 16.1%–17.3% and 13.2%–18.7% for soil and landscape, nutrient and pH, and yield variability, respectively), being either the best or second best approach. It was also found that the ROSE-YSTTS approach was effective in defining zones with high, medium and low economically optimum N rates. It is concluded that the integrated ROSE-YSTTS approach combining soil, landscape and yield spatial-temporal variability information can overcome the weaknesses of approaches using only soil, landscape or yield information, and is more robust for MZ delineation. It also has the potential for site-specific N management for improved economic returns. More studies are needed to further evaluate their appropriateness for precision N and crop management.

Aims Grain yields of summer maize are significantly affected by different nitrogen (N) rates and depths through regulating root growth and distribution in soil. Understanding of effects of the deep placement of N on the root and shoot growth, grain yield and N use efficiency in summer maize are limited. Methods In this study, four N rates: 225, 191.25, 157.5 and 0 kg ha −1 applied at four depths: 5, 10, 15, and 20 cm were studied. Soil N content, root dry weight, root length density, biomass, grain yield and N use efficiency of maize were measured. Results Compared to 225 kg N ha −1 applied at a depth of 5 cm, a 15% reduction in the N application rate at a depth of 15 cm induced a larger root length density in the subsoil, as well as a larger rooting depth. It also facilitated maintaining a higher level of biomass and N accumulation during the later growth period, which increased the N assimilation of grain and enhanced grain yield by 3.9%, N recovery efficiency by 66.7%, N agronomic efficiency by 38.5%, and partial factor productivity of N by 22.1%. Conclusions Overall, this study demonstrates that reducing the recommended N application rate of 225 kg ha −1 by 15% but applying it at a depth of 15 cm might be considered an efficient fertilization method that increases agricultural productivity and N use efficiency.

Background Effective nitrogen (N) fertilizer management can improve photosynthetic performance of maize and enhance the grain yield. However, the effects of the deep placement of N on post-silking photosynthetic performance in maize and its relationship with grain filling are limited. The study was a split-plot design with N application rates as the main plots and N placement depths as sub-plots. The N application rates consisted of 225, 191.25, and 157.5 kg ha − 1 and N placement depths consisted of 5 and 15 cm, respectively. The growth parameters, photosynthetic capacity, subcellular ultrastructure, antioxidant system in maize leaves, and grain filling characteristics were measured. Results Increasing the N placement depth counteracted the adverse effects of reduced N availability on the leaf area index, leaf area duration, and photosynthetic performance of plants. Compared to 225 kg N ha − 1 applied underground at 5 cm, a 15% reduction in the N application rate at 15 cm reduced oxidative stress through the activation of antioxidative enzymes, which enabled plants to maintain their chloroplast ultrastructure, achieving 20.7% higher chlorophyll content, 7.8% higher photosynthetic rate per unit of leaf area, and 5.6% higher leaf area index during the later growth period. It also facilitated enhancing the growth rate during maximum filling and extending the active filling duration of grains. Conclusions Overall, reducing the recommended N application rate of 225 kg ha − 1 by 15% but applying it at a depth of 15 cm might delay plant senescence and extend grain filling active time, improved photosynthetic performance in late growth period, and finally increased grain weight and grain yield of maize.

The great challenges of ensuring global food security and reducing environmental risk caused by excessive fertilizer inputs require optimizing fertilizer rates to maintain crop production and environmental sustainability. Previous results regarding optimizing N-fertilizer rate for potato were mainly based on case studies and lacked regional-scale information on N-fertilizer management. We hypothesized that regional optimum N rates would increase N use efficiency without sacrificing potato yield compared with low and high N rates. We determined the optimal N-fertilization rates for Chinese potato production at a regional scale based on a dataset of 706 observations from 142 peer-reviewed publications. The linear-plus-plateau model was used to estimate regional optimum N rates, which were 115, 150, 120, and 126 kg N ha −1 for the northern, central, southwestern, and southern regions of China, respectively. The target yield could be obtained by applying less N fertilizer when the indigenous N supply was higher across the main potato production region in China. Compared with high N rates, recommended N rates increased N use efficiency and agronomic efficiency by 48.60–81.67% and 17.12–72.90%, respectively, without any yield losses. Recommended N rates also achieved 5.95–14.70% greater yield than low N rates. Here, we show for the first time that, based on a comprehensive literature review, regional optimum N-fertilizer rates result in increased yield and N use efficiency, and reduced negative environmental impacts, all of which play a vital role in maintaining sustainable potato production. The present study highlights the importance of research for achieving a reasonable trade-off between food security and N-fertilizer management for sustainable agriculture.

Nitrogen (N) leaching to surface waters from grain farms in the Mississippi River Basin (MRB), USA, is the primary cause of hypoxia in the Gulf of Mexico. Regional-scale N mass balances indicate that a small, intensively cropped area of the upper MRB contributes disproportionately to nitrate loading. These aggregate balances miss small-scale variability, especially that caused by differences in farm management. We constructed N mass balances for a gradient of farm types, from corn-soybean monocultures to diversified grain farms that rely on biological N fixation (BNF) as a primary N source, to compare the relative efficiency of diverse farming systems in the MRB. Five-year N balances were calculated for a most and least productive field on each farm using data collected from interviews with 95 grain farmers in Iowa, Ohio, Minnesota, and Wisconsin; from legume biomass and corn grain samples collected from a subset of farms; and published values from the literature. Nitrogen balances ranged from high average annual surpluses (149 kg N·ha −1 ·yr −1 ) to large deficits (80 kg N·ha −1 ·yr −1 ), and differed based on N source and crop rotation. Fields with >50% of total N additions from legume N sources and fields with complex crop rotations that included both annual and perennial species were approximately in balance (3.7 kg N·ha −1 ·yr −1 and 5.7 kg N·ha −1 ·yr −1 , respectively) compared to fertilizer-based practices in corn-soybean rotations with average annual surpluses near 35 kg N·ha −1 ·yr −1 . Surplus N was also inversely related to the proportion of total N inputs from BNF for medium (80-160 kg N·ha −1 ·yr −1 ) to high (>160 kg N·ha −1 ·yr −1 ) N rates. Diversified farmers were more likely to adjust their management practices in response to environmental variability compared to fertilizer-based farmers. Taken together, results from this study suggest that significantly reducing surplus N in agroecosystems will require reducing N inputs and increasing C availability to support the internal biological mechanisms for storing N in farm fields.

This data paper provides some biogeochemical nitrogen (N) properties and related chemical properties of forest soils from 39 sites throughout the Japanese archipelago. The data set was collected and analyzed under the GRENE (Green Network of Excellence) environmental information project and the ReSIN (Regional and comparative Soil Incubation study on Nitrogen dynamics in forest ecosystems) project. The sites cover 44°20′N to 26°50′N and the climate ranges from cool-temperate zone to subtropical zone. At each site, litter on forest floor and soil samples (three or four layers to 50 cm depth) were collected between August and November in 2010–2013 from five soil profiles. From the litter layer samples, the stocks and concentrations of total carbon (C) and N were measured. From the mineral soil samples, bulk density, pH (H 2 O), total C and N concentrations, net and gross rates of N mineralization, nitrification and concentrations of water-soluble substances were measured. The measurements are relevant for other biogeochemical N studies in forest ecosystems and the data set provides basic information on the N pool and fluxes with related chemical properties of forest soils across the Japanese archipelago. The average rates of net and gross N transformation at 20 °C across the sites were 0.26 ± 0.47 mgN kg −1 soil d −1 for net N mineralization, 0.25 ± 0.45 mgN kg −1 soil d −1 for net nitrification, 4.06 ± 0.47 mgN kg −1 soil d −1 for gross N mineralization, and 1.03 ± 1.29 mgN kg −1 soil d −1 for gross nitrification (average ± SD).

The application of nitrogen (N) fertilizer both underpins high productivity of agricultural systems and contributes to multiple environmental harms. The search for ways that farmers can optimize the N fertilizer applications to their crops is of global significance. A common concept in developing recommendations for N fertilizer applications is the “mass balance paradigm” – that is, bigger crops need more N, and smaller less – despite several studies showing that the crop yield at the optimum N rate (N opt ) is poorly related to N opt . In this study we simulated two contrasting field experiments where crops were grown for 5 and 16 consecutive years under uniform management, but in which yield at N opt was poorly correlated to N opt . We found that N lost to the environment relative to yields (i.e., kg N t -1 ) varied +/- 124 and 164 % of the mean in the simulations of the experiments. Conversely, N exported in harvested produce (kg N t -1 ) was +/- 11 and 48 % of the mean. Given the experiments were uniformly managed across time, the variations result from crop-to-crop climatic differences. These results provide, for the first time, a quantitative example of the importance of climatic causes of the poor correlation between yield at N opt and N opt . An implication of this result is that, even if yield of the coming crop could be accurately predicted it would be of little use in determining the amount of N fertilizer farmers need to apply because of the variability in environmental N losses and/or crop N uptake. These results, in addition to previous empirical evidence that yield at N opt and N opt are poorly correlated, may help industry and farmers move to more credible systems of N fertilizer management.

Knowing the influence of long-term N fertilization is a key aspect in improving the yield of most crops, including sugarcane ( Saccharum spp.). We aimed to assess the effect of N-fertilizer sources and rates on sugarcane yield, biomass partitioning, juice quality, nutrient accumulation, and N efficiency in acid soils. Two field experiments were carried out in southeastern Brazil for consecutive five years. Six N-fertilizer managements [ammonium nitrate and urea at a rate of 100 kg N ha − 1 (AN100 and UR100, respectively), calcium ammonium nitrate at a rate of 50, 100, 150, and 200 kg N ha − 1 (CAN50, CAN100, CAN150, and CAN200, respectively)] were applied to acidic soils. Nitrogen fertilization did not affect sugarcane and sugar yields at the site with previous rotation with peanut ( Arachis hypogea ) before crop replanting. Conversely, at the site under continuous monoculture, AN100, CAN100, and CAN150 showed increases of 7–25% in sugarcane and sugar yields, and 3–7% in Brix and recoverable total sugar content. We conclude that in responsive sites, fertilizer N additions improve crop yield and juice quality, although high N inputs in the long term (> 100 kg N ha − 1 ) can reduce sugarcane sustainability. Similarly, non-responsive sites can exhibit substantial economic losses and environmental pollution. Identifying responsive and non-responsive sites to fertilizer N is required for improving N use efficiency and reducing environmental risks and economic losses.

Improving nitrogen use efficiency (NUE) without compromising yield remains a crucial agroecological challenge in theory and practice. Some meta-analyses conducted in recent years investigated the impact of nitrogen (N) fertilizer on crop yield and gaseous emissions, but most are region-specific and focused on N sources and application methods. However, various factors affecting yield and N fertilizer efficiency in wheat crops on a global scale are not extensively studied, thus highlighting the need for a comprehensive meta-analysis. Using 109 peer-reviewed research studies (published between 2000 and 2022) from 156 experimental sites (covering 36.8, 38.6 and 24.6% of coarse, medium, and fine texture soils, respectively), we conducted a global meta-analysis to elucidate suitable N management practices and the key factors influencing N fertilization efficiency in wheat as a function of yield and recovery efficiency and also explained future perspectives for efficient N management in wheat crop. Overall, N fertilization had a significant impact on wheat yield. A curvilinear relationship was found between N rates and grain yield, whereas maximum yield improvement was illustrated at 150-300 kg N ha -1 . In addition, N increased yield by 92.18% under direct soil incorporation, 87.55% under combined chemical and organic fertilizers application, and 72.86% under split application. Site-specific covariates (climatic conditions and soil properties) had a pronounced impact on N fertilization efficiency. A significantly higher yield response was observed in regions with MAP > 800 mm, and where MAT remained < 15 °C. Additionally, the highest yield response was observed with initial AN, AP and AK concentrations at < 20, < 10 and 100-150 mg kg -1 , respectively, and yield response considerably declined with increasing these threshold values. Nevertheless, regression analysis revealed a declining trend in N recovery efficiency (REN) and the addition of N in already fertile soils may affect plant uptake and RE. Global REN in wheat remained at 49.78% and followed a negative trend with the further increase of N supply and improvement in soil properties. Finally, an advanced N management approach such as “ root zone targeted fertilization ” is suggested to reduce fertilizer application rate and save time and labor costs while achieving high yield and NUE.

This study was carried out to estimate the genetic parameters, heritability in broad sense, Phenotypic coefficient (PCV), Genotypic coefficient (GCV) and phenotypic and genotypic correlation among characteristics of sunflower genotypes. Eight sunflower genotypes were evaluated in the randomized complete block design (RBCD) with three replications under three nitrogen rates (50, 100 and 200) Nkha -1 at spring and fall season. The results indicated that the sunflower genotypes were significantly for all characteristics. The phenotypic coefficient (PCV) was largest than the genotypic coefficient (GCV). The seed yield showed the highest PCV under 200 Nkha -1 (15.73) and the highest GCV (12.48) under 50 Nkha -1 . Higher value of heritability in the broad sense was obtained (92.66, 94.13) % for seed weight and seed yield under (200) Nkha -1 . while the lowest value of heritability was scored (44.56)% for seed yield in the fall season under 200 Nkha -1 . However, characteristics having high stability, like disc diameter and seed weight under all nitrogen fertilizer rates, therefore can be used a selection criteria to improve some sunflower genotypes under nitrogen fertilizers.