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Conventional farming has led to extensive use of chemicals and, in turn, to negative environmental impacts such as soil erosion, groundwater pollution and atmosphere contamination. Farming systems should be more sustainable to reach economical and social profitability as well as environmental preservation. A possible solution is to adopt precision agriculture, a win–win option for sustaining food production without degrading the environment. Precision technologies are used for gathering information about spatial and temporal differences within the field in order to match inputs to site-specific field conditions. Here we review reports on the precision N management of wheat crop. The aims are to perform an investigation both on approaches and results of site-specific N management of wheat and to analyse performance and sustainability of this agricultural practice. In this context, we analysed literature of the last 10–15 years. The major conclusions are: (a) before making N management decisions, both the measurement and understanding of soil spatial variability and the wheat N status are needed. Complementary use of different sensors has improved soil properties assessment at relatively low cost; (b) results show the usefulness of airborne images, remote and proximal sensing for predicting crop N status by responsive in-season management approaches; (c) red edge and near-infrared bands can penetrate into higher vegetation fraction of the canopy. These narrowbands better estimated grain yield, crop N and water status, with R ² higher than 0.70. In addition, different hyperspectral vegetation indices accounted for a high variability of 40–75 % of wheat N status; (d) various diagnostic tools and procedures have been developed in order to help wheat farmers for planning variable N rates. In-season adjustments in N fertilizer management can account for the specific climatic conditions and yield potential since less than 30 % of spatial variance could show temporal stability; (e) field studies in which sensor-based N management systems were compared with common farmer practices showed high increases in the N use efficiency of up to 368 %. These systems saved N fertilizers, from 10 % to about 80 % less N, and reduced residual N in the soil by 30–50 %, without either reducing yields or influencing grain quality; (f) precision N management based on real-time sensing and fertilization had the highest profitability of about $5–60 ha⁻¹ compared to undifferentiated applications.

The irrational use of nitrogen (N) fertilizer has become a major threat to soil quality and food security, resulting in serious ecological and environmental problems. Holistic approaches to N fertilizer application are required to maintain a high N utilization efficiency (NUE) and sustainable agriculture development. Biochar is an efficient carbon-rich material for amending soil quality and promoting crop N uptake, but knowledge pertaining to the promoting effects of biochar application on N fertilizers is still limited. In this study, a field plot experiment was designed to detect the combined effects of biochar (0, 15 and 30 t ha−1) and N fertilizer (204, 240 and 276 kg N ha−1) on the soil nutrient levels, NUE, plant growth performance and crop production of maize. The results demonstrated that the combined application of N fertilizer and biochar can significantly decrease the soil pH and increase the contents of soil organic carbon, mineral N, available phosphorus and potassium. The crop N uptake and N content were largely promoted by the addition of N fertilizer and biochar, resulting in higher leaf photosynthetic efficiency, dry matter accumulation and grain yields. The highest yields (14,928 kg ha−1) were achieved using 276 kg N ha−1 N fertilizer in combination with 15 t ha−1 biochar, and the highest NUE value (46.3%) was reached with 204 kg N ha−1 N of fertilizer blended with 30 t ha−1 of biochar. According to structural equation modeling, the beneficial effects of N fertilizer and biochar on the plant biomass of maize were attributed to the direct effects related to soil chemical properties and plant growth parameters. In conclusion, N fertilizer combined with biochar application is an effective strategy to enhance the utilization of N fertilizer and crop production for maize by increasing soil fertility, improving plant crop uptake and promoting plant growth.

A 15N labeling and lysimeter experiment was conducted with mesocosms of a semi-arid Leymus chinensis grassland. The aim of the study was to evaluate the effects of N fertilization timing (fertilization in fall or spring) and rate (0, 56, and 112 kg-N ha−1 year−1) on ecosystem services (seed yield and forage yield), ecosystem disservices (N leaching surveyed during 1 year and emissions of NH3 and N2O integrated over 76 days after fertilization), and recovery of added fertilizer N in plants and soil. Seed and forage yields increased more under fall than spring N fertilization. Further, N fertilization was linked to higher soil NH3 and N2O emissions, particularly under high N rate for both NH3 (2.0 and 1.6 kg-N ha−1 under fall and spring N fertilization, respectively) and N2O (0.24 and 0.21 kg-N ha−1, respectively). N leaching was never observed. A significant N fertilization timing × rate interaction effect was observed on plant recovery efficiency of added fertilizer N (Plant-NRE). Plant-NRE was higher for high than moderate N rate, with + 13.2% (from 22.8 to 36%) and + 16.4% (from 28.2 to 44.7%) for fall and spring fertilization, respectively. Fertilizer N recovered in soil was highest for moderate N rate in fall (68% of total N fertilizer) and lowest for high N rate in spring (46%). Our results show synergies among the ecosystem services (seed and forage yields) and among the disservices (NH3 and N2O emissions), and trade-offs between the services and disservices, some of these synergies and trade-offs being modulated by N fertilization timing and rate. Our study is the first one analyzing the possibly interactive effects of the N fertilization timing and rate on this range of ecosystem services and disservices in semi-arid perennial grasslands, which can be useful for N risk: benefit analysis when evaluating N fertilization strategies.

The continuous increase of nitrous oxide (N ₂O) abundance in the atmosphere is a global concern. Multiple pathways of N ₂O production occur in soil, but their significance and dependence on oxygen (O ₂) availability and nitrogen (N) fertilizer source are poorly understood. We examined N ₂O and nitric oxide (NO) production under 21%, 3%, 1%, 0.5%, and 0% (vol/vol) O ₂ concentrations following urea or ammonium sulfate [(NH ₄) ₂SO ₄] additions in loam, clay loam, and sandy loam soils that also contained ample nitrate. The contribution of the ammonia (NH ₃) oxidation pathways (nitrifier nitrification, nitrifier denitrification, and nitrification-coupled denitrification) and heterotrophic denitrification (HD) to N ₂O production was determined in 36-h incubations in microcosms by ¹⁵N- ¹⁸O isotope and NH ₃ oxidation inhibition (by 0.01% acetylene) methods. Nitrous oxide and NO production via NH ₃ oxidation pathways increased as O ₂ concentrations decreased from 21% to 0.5%. At low (0.5% and 3%) O ₂ concentrations, nitrifier denitrification contributed between 34% and 66%, and HD between 34% and 50% of total N ₂O production. Heterotrophic denitrification was responsible for all N ₂O production at 0% O ₂. Nitrifier denitrification was the main source of N ₂O production from ammonical fertilizer under low O ₂ concentrations with urea producing more N ₂O than (NH ₄) ₂SO ₄ additions. These findings challenge established thought attributing N ₂O emissions from soils with high water content to HD due to presumably low O ₂ availability. Our results imply that management practices that increase soil aeration, e.g., reducing compaction and enhancing soil structure, together with careful selection of fertilizer sources and/or nitrification inhibitors, could decrease N ₂O production in agricultural soils.

Although N fertilizers are not acidic, their inputs to soil are acid forming. As a result of the long-term use of N fertilizers, soils in the Great Plains are becoming more acidic and this acidity may become a yield-limiting factor. In 1970, long-term plots were initiated to compare sources (anhydrous NH3, NH4NO3, urea, and S-coated urea), application rates (34, 68, 136, and 272 kg N ha−1), and an untreated check (0 N) on wheat (Triticum aestivum L.) grain yield, soil pH, exchangeable base cations, and Al saturation. For the soil properties evaluated, significant differences among the different N sources did not exist after 30 annual applications of N fertilizer. The long-term N fertilization significantly reduced soil pH in the surface soil layer (0–15 cm), especially at the higher application levels. Soil pH decreased with time and was significantly related to the amount of total N applied for each N source. Nitrogen fertilization with each N source significantly increased exchangeable Al and Al saturation (Alsat) but decreased exchangeable base cations (Ca2+ and Mg2+). Both exchangeable Al and Alsat increased with increasing N rate and were inversely related to soil pH. Despite decreased soil pH levels to <5.0 as early as 1980 in the experiment, significant reductions of wheat yield did not occur until 1995. Reductions in yield occurring between 1995 and 2002 coincided with the greatest change in soil pH occurring during the same time period.

Some wheat cultivars show a linear relationship between grain protein concentration (GPC) and baking volume, but others display a saturation curve. Such a saturation curve could be general, but in some cultivars it might only appear at GPC > 17%. However, such GPC is mostly not achieved in the field. Pot experiments with high nitrogen application reliably result in GPC > 17%. In a pot experiment with a high (N1) and an excessive N level (N2) and four cultivars (Akteur, Arnold, Discus and Hystar), the change in grain protein composition and the relationship between different protein fractions and baking volume at GPC > 17% was investigated. GPC ranged from 17 to 24% and mean nitrogen content per grain from 1.2 to 1.8 mg. The N2 treatment increased GPC and mean nitrogen content per grain in the Akteur and Discus cultivar, but not in Arnold and Hystar. N2 increased concentration of gliadin by 10 to 34% and glutenin macropolymer (GMP) in all cultivars by 12 to 73%. Glutenin concentration was increased by N2 in Akteur and Discus (19 to 36%), but was decreased by N2 in the Arnold and Hystar cultivar. Baking volume was moderately increased by N2 in all cultivars by 6 to 9% and correlated significantly with most glutenin fractions in the Akteur and Discus cultivar, with GMP in Arnold and with HMW-GS to LMW-GS ratio in Hystar. Thus, specific effects on grain protein by N2 were responsible for the increased baking volume in each cultivar. However, as gliadin and its sub-fractions hardly correlated with baking volume, a positive effect of increasing gliadin proteins on baking quality was not obvious.

Excessive nitrogen (N) application to rice (Oryza sativa L.) crop in China causes environmental pollution, increases the cost of rice farming, reduces grain yield and contributes to global warming. Scientists from the International Rice Research Institute have collaborated with partners in China to improve rice N fertilization through site-specific N management (SSNM) in China since 1997. Field experiments and demonstration trials were conducted initially in Zhejiang province and gradually expanded to Guangdong, Hunan, Jiangsu, Hubei and Heilongjiang provinces. On average, SSNM reduced N fertilizer by 32% and increased grain yield by 5% compared with farmers' N practices. The yield increase was associated with the reduction in insect and disease damage and improved lodging resistance of rice crop under the optimal N inputs. The main reason for poor fertilizer N use efficiency of rice crop in China is that most rice farmers apply too much N fertilizer, especially at the early vegetative stage. We observed about 50% higher indigenous N supply capacity in irrigated rice fields in China than in other major rice-growing countries. Furthermore, yield response of rice crop to N fertilizer application is low in China, around 1.5 t ha super(− 1) on average. However, these factors were not considered by rice researchers and extension technicians in determining the N fertilizer rate for recommendation to rice farmers in China. After a decade of research on SSNM in China and other Asian rice-growing countries, we believe SSNM is a matured technology for improving both fertilizer N use efficiency and grain yield of rice crop. Our challenges are to further simplify the procedure of SSNM and to convince policy-makers of the effectiveness of this technology in order to facilitate a wider adoption of SSNM among rice farmers in China.

The combined application of organic resources (ORs) and mineral fertilizers is increasingly gaining recognition as a viable approach to address soil fertility decline in sub-Saharan Africa (SSA). We conducted a meta-analysis to provide a comprehensive and quantitative synthesis of conditions under which ORs, N fertilizers, and combined ORs with N fertilizers positively or negatively influence Zea mays (maize) yields, agronomic N use efficiency and soil organic C (SOC) in SSA. Four OR quality classes were assessed; classes I (high quality) and II (intermediate quality) had >2.5% N while classes III (intermediate quality) and IV (low quality) had <2.5% N and classes I and III had <4% polyphenol and <15% lignin. On the average, yield responses over the control were 60%, 84% and 114% following the addition of ORs, N fertilizers and ORs + N fertilizers, respectively. There was a general increase in yield responses with increasing OR quality and ORN quantity, both when ORs were added alone or with N fertilizers. Surprisingly, greater OR residual effects were observed with high quality ORs and declined with decreasing OR quality. The greater yield responses with ORs + N fertilizers than either resource alone were mostly due to extra N added and not improved N utilization efficiency because negative interactive effects were, most often, observed when combining ORs with N fertilizers. Additionally, their agronomic N use efficiency was not different from sole added ORs but lower than N fertilizers added alone. Nevertheless, positive interactive effects were observed in sandy soils with low quality ORs whereas agronomic use efficiency was greater when smaller quantities of N were added in all soils. Compared to sole added ORs, yield responses for the combined treatment increased with decreasing OR quality and greater yield increases were observed in sandy (68%) than clayey soils (25%). While ORs and ORs + N fertilizer additions increased SOC by at least 12% compared to the control, N fertilizer additions were not different from control suggesting that ORs are needed to increase SOC. Thus, the addition of ORs will likely improve nutrient storage while crop yields are increased and more so for high quality ORs. Furthermore, interactive effects are seldom occurring, but agronomic N use efficiency of ORs + N fertilizers were greater with low quantities of N added, offering potential for increasing crop productivity.

Background and aims Nitrogen (N) nutrition is a critical factor in zinc (Zn) acquisition and its allocation into grain of wheat (Triticum aestivum L.). Most of the information collected about this topic is, however, derived from the pot experiments. It is also not known whether optimal N management by decreasing N input could affect the Zn status in grain and plant in the field. The aim of this research is to investigate the impact of N management on grain and shoot Zn status of winter wheat. Methods Field experiments were conducted in two cropping seasons. Results Results showed applying N at optimal rate (198 kgN ha−1 in 2007–2008 and 195 kgN ha−1 in 2008–2009) maintained or resulted in significantly higher grain Zn concentration and especially grain content of Zn compared to no or lower N treatments. For example, grain Zn concentration increased from 21.5 mgkg−1 in the control to 30.9 mgkg−1 with optimized N supply in 2007–2008 and from 24.7 mg kg−1 in the control to 29.1 mgkg−1 with optimized N supply in 2008–2009. Further increasing N supply from optimal to excessive N supply resulted in non-significant increases in grain Zn concentration and content. Generally, similar trends were also found in shoot Zn. Moreover, 72 % to 100 % of the shoot Zn requirement had been accumulated at anthesis, and accordingly 67 % to 100 % of grain Zn content was provided by Zn remobilization from pre-anthesis Zn uptake with N supply. Grain Zn accumulation mainly originates from Zn remobilization and the optimal N management would ensure better shoot Zn nutrition to contribute to increasing Zn remobilization from vegetative tissues and to maintain relatively higher grain Zn for better human nutrition.

BACKGROUND: Although plant growth in alpine steppes on the Tibetan Plateau has been suggested to be sensitive to nitrogen (N) addition, the N limitation conditions of alpine steppes remain uncertain. METHODS: After 2 years of fertilization with NH₄NO₃ at six rates (0, 10, 20, 40, 80 and 160 kg N ha⁻¹ yr⁻¹), the responses of plant and soil parameters as well as N₂O fluxes were measured. RESULTS: At the vegetation level, N addition resulted in an increase in the aboveground N pool from 0.5 ± 0.1 g m⁻² in the control plots to 1.9 ± 0.2 g m⁻² in the plots at the highest N input rate. The aboveground C pool, biomass N concentration, foliar δ¹⁵N, soil NO₃ ⁻-N and N₂O flux were also increased by N addition. However, as the N fertilization rate increased from 10 kg N ha⁻¹ yr⁻¹ to 160 kg N ha⁻¹ yr⁻¹, the N-use efficiency decreased from 12.3 ± 4.6 kg C kg N⁻¹ to 1.6 ± 0.2 kg C kg N⁻¹, and the N-uptake efficiency decreased from 43.2 ± 9.7 % to 9.1 ± 1.1 %. Biomass N:P ratios increased from 14.4 ± 2.6 in the control plots to 20.5 ± 0.8 in the plots with the highest N input rate. Biomass N:P ratios, N-uptake efficiency and N-use efficiency flattened out at 40 kg N ha⁻¹ yr⁻¹. Above this level, soil NO₃ ⁻-N began to accumulate. The seasonal average N₂O flux of growing season nonlinearly increased with increased N fertilization rate and linearly increased with the weighted average foliar δ¹⁵N. At the species level, N uptake responses to relative N availability were species-specific. Biomass N concentration of seven out of the eight non-legume species increased significantly with N fertilization rates, while Kobresia macrantha and the one legume species (Oxytropics glacialis) remained stable. Both the non-legume and the legume species showed significant ¹⁵N enrichment with increasing N fertilization rate. All non-legume species showed significant increased N:P ratios with increased N fertilization rate, but not the legume species. CONCLUSIONS: Our findings suggest that the Tibetan alpine steppes might be N-saturated above a critical N load of 40 kg N ha⁻¹ yr⁻¹. For the entire Tibetan Plateau (ca. 2.57 million km²), a low N deposition rate (10 kg N ha⁻¹ yr⁻¹) could enhance plant growth, and stimulate aboveground N and C storage by at least 1.1 ± 0.3 Tg N yr⁻¹ and 31.5 ± 11.8 Tg C yr⁻¹, respectively. The non-legume species was N-limited, but the legume species was not limited by N.