N-use Efficiency Research Articles

Legume green manure can intensify the function of chemical nitrogen fertilizer substitution via increasing nitrogen supply and uptake of wheat

Achieving the green development of agriculture requires the reduction of chemical nitrogen (N) fertilizer input. Previous studies have confirmed that returning green manure to the field is an effective measure to improve crop yields while substituting partial chemical N fertilizer. However, it remains unclear how to further intensify the substituting function of green manure and elucidate its underlying agronomic mechanism. Therefore, In a split-plot field experiment in spring wheat, different green manures returned to the field was established in an oasis area since 2018, in order to investigate the effect of green manure and reduced N on grain yield, N uptake, N use efficiency (NUE), N nutrition, soil organic matter, and soil N of wheat in 2020–2022. Our results showed that mixed sown common vetch and hairy vetch can substitute 40 % of chemical N fertilizer without reducing grain yield or N accumulation. Noteworthily, mixed sown common vetch and hairy vetch under reduced N by 20 % showed the highest N agronomy efficiency and recovery efficiency, which were 92.0 % and 46.0 % higher than fallow after wheat harvest and conventional N application rate, respectively. The increase in NUE of wheat was mainly attributed to mixed sown common vetch and hairy vetch, which increased N transportation quantity and rate at pre-anthesis, enhanced N harvest index, optimized N nutrition index, and increased activities of nitrate reductase and glutamine synthetase, respectively. Meanwhile, mixed sown common vetch and hairy vetch under reduced N by 20 % improved soil organic matter and N contents. Therefore, mixed sown common vetch and hairy vetch can substitute 40 % of chemical N fertilizer by enhancing N supply and uptake.

Effects of Irrigation Amount and Nitrogen Rate on Cotton Yield, Nitrogen Use Efficiency, and Soil Nitrogen Balance under Drip Irrigation

Water and nitrogen (N) are major constraints for cotton growth and yield formation in arid regions. Irrigation and N application have been widely investigated to improve crop yield and water and N use efficiency (NUE). However, further optimization of water and N management is needed because the effects of N application on soil N balance and N loss under different irrigation levels remain unclear. In this study, a field experiment was conducted in 2020 and 2021 to investigate the effects of different irrigation amounts (full irrigation (100% ETc), moderate irrigation (80% ETc), low irrigation (60% ETc)) and N application rates (control (without N application, N0), low N (150 kg ha−1, N150), medium N (225 kg ha−1 and 300 kg ha−1, N225 and N300), and high N (375 kg ha−1, N375)) on cotton yield, NUE, and soil N balance. The 2-year results showed that under the 60% ETc treatment, cotton dry matter accumulation, N uptake, and yield were significantly enhanced by increasing N application. Under the 80% and 100% ETc treatments, these parameters peaked with the N300 treatment; the N375 treatment showed no significant difference or decrease compared to the N300 treatment. The 80% ETc N300 treatment had the highest cotton yield and NUE, which increased by 17.49–106.57% and 12.28–88.78% compared with other treatments, respectively. Residual soil N accumulation (RSNmin), apparent N loss (ANL), and apparent N surplus (ANS) increased as the N application rate increased under the 60% and 100% ETc treatments. While under the 80% ETc treatment, the ANS did not significantly differ between the N225 and N300 treatments, ANL significantly decreased by 43.51–88.56% when the N application rate increased from 150 to 225 and 300 kg ha−1. The ANL of the 80% ETc N300 treatment was the lowest, but ANS did not significantly increase. The regression analysis and spatial analysis results showed that under irrigation of 336–348 mm and N application of 254–327 kg ha−1, cotton yield, NUE, and WPI reached more than 80% of the maximum value, with less apparent N loss, thus maintaining the soil N balance in drip-irrigated cotton fields. This study helps to improve the utilization of water and N resources in cotton production. Future research on optimizing water and N management needs to more fully consider environmental pollution to achieve sustainable development of agricultural ecosystems.

Reproductive resilience of growth and nitrogen uptake underpins yield improvement in winter wheat with forced delay of sowing

Winter wheat production is influenced by climate extremes worldwide. Heavy precipitation induced delay of sowing generates limited photothermal resources for wheat early growth. However, how wheat build resilience from stunted seedling growth has not been fully explored. Here, a twelve-year farmers' survey of wheat yield was recorded and four-year field experiments of wheat grown in normal and late-sowing were performed under zero nitrogen (N0) and optimum nitrogen (Opt.N) supply. Wheat growth and N uptake were measured at both vegetative and reproductive stages alongside photothermal resource-use efficiency. Farmers' survey showed 10.4 % yield losses due to delayed sowing compared to the normal. However, four-year field trials revealed that the combination of increasing seeding rates and Opt.N application recovered grain yield of sowing-delayed wheat and even increased by 13.2 % compared to plants in the normal seasons. Although delayed sowing substantially suppressed seedling growth and tillering before winter dormancy, the Opt.N application increased spring tillers by 2.4-fold which were productive at maturity. Further, plant growth and N uptake from jointing to anthesis of sowing-delayed wheat were accelerated by Opt.N, but not by N0 treatment. Delayed sowing significantly shortened the duration of lag phase of grain filling by 3.5 days and by 183 growing degree days compared with the normal, which initiated the linear and fast filling earlier. Increased leaf photosynthesis by 27.4 % during grain filling further supported the fast recovery of grain filling in the sowing-delayed wheat. Concomitantly, the physiological N-use efficiency increased by 46.7 % during grain filling and by 41.5 % at maturity by enhancing N availability and seeding rates, and photothermal resource-use efficiency increased by 1.3- to 1.7-fold for wheat with delayed vs. normal sowing. Overall, these findings highlight the integrated management of nutrient and cultivation to mitigate the impacts of climate extremes on crop productivity through building plant reproductive resilience.

Nitrogen deficiency tolerance conferred by introgression of a QTL derived from wild emmer into bread wheat

Key messageGenetic dissection of a QTL from wild emmer wheat, QGpc.huj.uh-5B.2, introgressed into bread wheat, identified candidate genes associated with tolerance to nitrogen deficiency, and potentially useful for improving nitrogen-use efficiency.Nitrogen (N) is an important macronutrient critical to wheat growth and development; its deficiency is one of the main factors causing reductions in grain yield and quality. N availability is significantly affected by drought or flooding, that are dependent on additional factors including soil type or duration and severity of stress. In a previous study, we identified a high grain protein content QTL (QGpc.huj.uh-5B.2) derived from the 5B chromosome of wild emmer wheat, that showed a higher proportion of explained variation under water-stress conditions. We hypothesized that this QTL is associated with tolerance to N deficiency as a possible mechanism underlying the higher effect under stress. To validate this hypothesis, we introgressed the QTL into the elite bread wheat var. Ruta, and showed that under N-deficient field conditions the introgression IL99 had a 33% increase in GPC (p < 0.05) compared to the recipient parent. Furthermore, evaluation of IL99 response to severe N deficiency (10% N) for 14 days, applied using a semi-hydroponic system under controlled conditions, confirmed its tolerance to N deficiency. Fine-mapping of the QTL resulted in 26 homozygous near-isogenic lines (BC4F5) segregating to N-deficiency tolerance. The QTL was delimited from − 28.28 to − 1.29 Mb and included 13 candidate genes, most associated with N-stress response, N transport, and abiotic stress responses. These genes may improve N-use efficiency under severely N-deficient environments. Our study demonstrates the importance of WEW as a source of novel candidate genes for sustainable improvement in tolerance to N deficiency in wheat.

Multi-Omics Analysis Reveals the Transcriptional Regulatory Network of Maize Roots in Response to Nitrogen Availability

Nitrogen (N) availability determines higher plant productivity and yield. However, the molecular mechanisms governing N acquisition and utilization remain largely unknown in maize. In this study, ATAC-seq, RNA-seq, and Ribo-seq analyses were conducted in maize roots under different N supply conditions. A set of differentially expressed genes enriched in N and phenylpropanoid metabolisms at both the transcription and translation levels were highlighted. Interestingly, less than half of low-N responsive genes were shared between transcription and translation. The alteration of translational efficiency (TE) is also an important mechanism by which maize responds to LN. In addition, we identified low-N-induced open chromatin regions (OCRs) and observed an enrichment of transcription factor (TF) binding motifs. Furthermore, we constructed a transcriptional regulatory network for maize roots subjected to low-N. These findings extend our understanding of N availability response and provide new insights for improving N use efficiency (NUE).

Spring wheat nitrogen-use indicators responses to cropping sequence and nitrogen fertilization

ABSTRACT Spring wheat (Triticum aestivum L.) nitrogen-use efficiency (NUE) and recovery with nitrogen (N) fertilization rates in crop rotations need further exploration. The effect of cropping sequence and N fertilization rate were evaluated on spring wheat N concentration and uptake, N harvest index (NHI), N-use efficiency (NUE), and N recovery index (NRI) from 2012 to 2019 in the northern Great Plains, USA. Cropping sequences were conventional till spring wheat-fallow (CTWF), no-till spring wheat-fallow (NTWF), no-till spring wheat-pea (Pisum sativum L.) (NTWP), and no-till continuous spring wheat (NTCW), and N fertilization rates to spring wheat were 0, 50, 100, and 150 kg N ha−1. Straw N concentration and N uptake were greater for CTWF than NTWP and NTCW in 4 out of 8 years and increased with increased N fertilization rate. Grain N concentration and NHI varied with treatments and years. Grain N uptake was greater for CTWF and NTWF than NTWP and NTCW at most N fertilization rates and years. In contrast, NUE was greater for NTCW than CTWF and NTWF at all N fertilization rates in most years. The NRI was greater for NTWP or NTCW than CTWF or NTWF in most years. Increasing N fertilization rate increased grain N uptake for most cropping sequences in all years but had a variable effect on NUE and NRI. Although spring wheat N concentration and N uptake were superior for CTWF and NTWF, and NUE for NTCW, NTWP with 50 to 100 kg N ha−1 can be used to sustain grain yield, N uptake, NUE, and NRI.

NITIRSOIL: A model that balances complexity with prediction uncertainty for improving nitrogen fertilization in agriculture

Mismanagement of the nitrogen (N) fertilization in agriculture leads to low N use efficiency (NUE) and therefore pollution of waters and atmosphere due to NO3− leaching, and N2O and NH3 emissions. The use of N simulation models of the soil-plant system can help improve the N fertilizer management increasing NUE and decreasing N pollution issues. However, many N simulation models lack balance between complexity and uncertainty with the result that they are not applied in actual practice. The NITIRSOIL is a one-dimensional transient-state model with a monthly time step that aims at addressing this lack in the estimation of, mainly, dry matter yield (DMY), crop N uptake (Nupt), soil mineral N (Nmin), and NO3− leaching in agricultural fields. According to its global sensitivity analysis for horticulture, the NITIRSOIL simulations of the aforementioned outputs mostly depend on the critical N dilution curve, harvest index, dry matter fraction, potential fresh yield and nitrification coefficients. According to its validation for 35 nitrogen fertilization trials with 11 vegetables under semi-arid Mediterranean climate in Eastern Spain, the NITIRSOIL presents indices of agreement between 0.87 and 0.97 for the prediction of total dry matter, DMY, Nupt, NO3− leaching and soil Nmin at crop season end. Therefore, the NITIRSOIL model can be used in actual practice to improve the sustainability of the N management in, particularly horticulture, due to the balance it features between complexity and prediction uncertainty. For this aim, the NITRISOIL can be used either on its own, or in combination with “Nmin” on-site N fertilization recommendation methods, or even could be implemented as the calculation core of decision support systems.

Exploring genotypic variations in cotton associated with growth and nitrogen use efficiency

Low nitrogen (N) is a major limitation of cotton sustainability and productivity. N-efficient genotype cultivation can enhance productivity under the economical N usage. This study was conducted to characterize 15 cotton genotypes for N use efficiency (NUE) under differential N (0.0125 and 0.125 g kg−1 of sand) supply. All studied traits significantly responded to genotypes and N treatments. Under low N conditions, plants experienced reduced seedling height, root weight, shoot weight and total biomass (TDM) production, chlorophyll content, photosynthetic efficiency, NPK content, and N uptake efficiency (NUpE). Thus, intercellular CO2 concentration, photosynthetic N use efficiency (PNUE), and NUtE enhanced in low N supply, although these changes varied in magnitude. Based on variations in TDM production (14.6–33.1%) and NUtE (3.3–20.4%), GH-Uhad, FH-Anmol, FH-Super, GH-Haadi, and SLH-Chandani were categorized as efficient and responsive (ER), while J-7, CIM-343, FH-155, FH-492, FH-444 found as inefficient and non-responsive. The efficient and non-responsive group contained FH-142, GH-Baghdadi, and FH-490 whereas FH-152 and Cyto-179 were classified as inefficient and responsive. The scoring method provided further insight into genotypic NUE related to biomass distribution, photosynthetic rate (Pn), NUpE, and NUtE under low N. The highest cumulative score (15-18) of ER genotypes for these attributes indicated selected traits orchestrated to determine the NUE. Moreover, agronomical and NUE-related traits were positively associated with Pn, suggesting that photosynthesis is a primary manipulator of plant growth which coordinates biomass production and NUE. Overall, cultivars exhibited greater genotypic variation for NUE, providing a scientific basis to evaluate the existing germplasm and proposing that cultivation of N-efficient genotypes can decrease N application and help cotton breeding for sustainable production.

Optimizing application of dairy effluent with synthetic N fertilizer reduced nitrogen leaching in clay loam soil

High application rates of dairy effluent and manure are often associated with nitrogen (N) leaching, which can affect groundwater quality. Here, we used a lysimeter to examine N leaching losses and biomass yield following application of dairy effluent and manure under wheat-maize cropping. The field experiment included seven treatments: no N fertilizer (Control); 200/300 kg N ha−1 synthetic N fertilizer only (wheat/maize) (CN); 100/150 kg N ha−1 synthetic N fertilizer plus 100/150 (DE1), 150/200 (DE2) and 250/350 (DE3) kg N ha−1 dairy effluent; 100/150 kg N ha−1 synthetic fertilizer plus 100/150 kg N ha−1 dairy manure (SM1); and 150/225 kg N ha−1 synthetic fertilizer plus 50/75 kg N ha−1 dairy manure (SM2). Compared with CN, DE1 treatment increased maize yield by 10.0 %, wheat N use efficiency (NUE) by 26.5 %, and wheat and maize N uptake by 7.7–16.3 %, while reduced N leaching by 22.4 % in wheat season and by 40.4 % in the maize season. In contrast, DE2 and DE3 treatment increased N leaching by 27.2–241 % and reduced NUE by 26.2–55.2 %. SM2 treatment increased yield and NUE by 8.8 % and 7.8 %, respectively, and reduced N leaching by 42.9 % during the wheat but not the maize season. Annual N leaching losses were 37.6 kg N ha−1 under CN treatment, but decreased to 27.4 kg N ha−1 under DE1. In contrast, N leaching increased to 52.8 and 84.1 kg N ha−1 under DE2 and DE3 treatment, respectively (P < 0.05). Meanwhile, under SM1 and SM2 treatment, N leaching decreased by 71.2 % and 32.0 %, respectively, compared with CN. These results suggest that replacing 50 % and 25 % synthetic N fertilizer with dairy farm effluent and manure could reduce N leaching losses but had varied effects on crop productivity under wheat-maize cropping.

Integrated nitrogen fertilizer management for improving wheat yield and the efficiency of water and nitrogen fertilizer use

Improving resource use efficiency through optimized nitrogen (N) management is the key to increasing crop productivity, but it remains unclear whether integrated N management practices could better improve wheat yield and the use of N and water. Here we investigated the effects of individual and integrated N management practices on wheat production in different soil-climatic conditions, and constructed the relationship between the soil-climate factors and N application rate on wheat yield. Results showed that individual N management practice (optimized N application rate only) reduced wheat yield by 2.4 %, increased N use efficiency (NUE) by 45 %, and decreased water use efficiency (WUE) by 2.2 %; however, integrated N management practice (integrating optimized N rate with irrigation, tillage, manure, or straw return) increased yield and NUE on average by 5.4 % and 55 % respectively, without reducing WUE. In different soil-climate conditions, individual N management practice decreased wheat yield from 1.1 % to 5.0 %; however, integrated N management practice increased yield by 8.5 %, 6.4 %, and 5.8 % in soil organic carbon (SOC) ≥ 10 g kg−1, mean annual precipitation ≤ 400 mm, and 10 °C < mean annual temperature ≤ 15 °C, respectively. Mixed-effects model showed that the integrated N management practice had a higher yield by better exploiting the yield-enhancing benefits of SOC. Facing the complex production environment of the future, applying integrated N management practice will be a key alternative for improving grain production and resource use efficiency.

Establishment of a Comprehensive Evaluation System for Low Nitrogen and Screening of Nitrogen-Efficient Germplasm in Peanut

Screening for nitrogen (N)-efficient germplasm to achieve high yield and high N efficiency is an important strategy to enhance the sustainability of modern agriculture. In this study, 127 peanut (Arachis hypogaea L.) germplasm resources were comprehensively evaluated by seedling hydroponics and field. At the seedling stage, with the range of low-nitrogen screening concentrations gradually narrowed through a comprehensive membership function analysis, standard normal distribution test, and variance analysis, we found that 0.15 mM N for 24 days could be the optimal condition for evaluating the N efficiency of peanuts. Through principal component analysis and correlation analysis, dry matter weight, root/shoot ratio, N content, N accumulation, N-use efficiency, and N use index were considered to be the N efficiency parameters, and a regression mathematical model was established accordingly. In the field, peanut genotypes that differ in resistance to low-nitrogen stress were evaluated by a yield nitrogen efficiency index under normal nitrogen and no nitrogen applications to verify the results at the seedling stage. Based on the multiple phenotypic analysis, N-efficient and N-inefficient peanut genotypes among germplasm were screened, and a comprehensive evaluation system was established to provide the theoretical basis for peanut breeding and cultivation techniques.

Effects of Nitrogen Application at Different Levels by a Sprinkler Fertigation System on Crop Growth and Nitrogen-Use Efficiency of Winter Wheat in the North China Plain.

Nitrogen (N) is an essential macronutrient for crop growth; therefore, N deficit can greatly limit crop growth and production. In the North China Plain (NCP), winter wheat (Triticum aestivum L.) is one of the main food crops, and its yield has increased from approximately 4000 kg ha-1 to 6000 kg ha-1 in the last two decades. Determining the proper N application rates at different growth stages and in all seasons is very important for the sustainable and high production of wheat in the NCP. A field experiment with five N application rates (250, 200, 150, 100, and 40 kgN·ha-1, designated as N250, N200, N150, N100, and N40, respectively) was conducted during the 2017-2018 and 2018-2019 winter wheat seasons to investigate the effects of the N application rate on water- and fertilizer-utilization efficiency and on the crop growth and yield of winter wheat under sprinkler fertigation conditions. The results showed that in the N application range of 40-200 kg ha-1, crop yield and water- and fertilizer-use efficiencies increased as the N application rate increased; however, further increases in the N application rate (from N200 to N250) did not have additional benefits. The N uptake after regreening of winter wheat linearly increased with crop growth. Considering the wheat yield and N-use efficiency, the recommended optimal N application rate was 200 kg ha-1, and the best topdressing strategy was equal amounts of N applied at the regreening, jointing, and grain-filling stages. The results of this study will be useful for optimizing field N management to achieve high wheat yield production in the NCP and in regions with similar climatic and soil environment conditions.

Influence of soil organic matter, fertiliser formulation and season on fertiliser nitrogen use efficiency in temperate pastures

Intensively grazed dairy systems use high inputs of fertiliser nitrogen (N), and often supplementary irrigation, to ensure adequate pasture production to support milk output and meet the growing food demand. However, the efficiency of N use in these systems can be low and potential environmental impacts high. This study aimed to test the hypothesis that (1) use of two inhibitors, the urease inhibitor N-(n-butyl) thiophosphorictriamide (NBTPT) and the nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) reduced N loss and improved pasture production compared to conventional N fertiliser (urea) in irrigated temperate perennial ryegrass (Lolium perenne L.) dairy pasture, and (2) their efficiency was affected by soil and environmental parameters. The effect of repeated applications of urea, at different rates, and the inhibitors were studied on pasture production and agronomic apparent fertiliser N use efficiency (NUE) over 2.5 years. The fate of a single application of N was determined through recovery of 15N-labeled fertiliser applied at 20 and 40 kg N ha−1 was studied in the field for one year. The highest yield and NUE occurred in spring–summer (from August to February) reflecting optimal growing conditions. The highest NUE occurred at low rates of urea application (20 and 40 kg N ha−1). Mineralisation played a key role in supplying N to pasture with 64–82% of total plant N derived from soil organic matter (SOM). Less than 50% of the applied N was recovered in the pasture (37–43%) with a large component retained in the soil (26–43% after one year, 0–40 cm), and slowly released in small amounts (< 2%) to the pasture over time, highlighting the abundant capacity of the native soil N pool to supply pasture N. Loss of N fertiliser (14–31%) was attributed to primarily ammonia (NH3) volatilisation and nitrate (NO3−) leaching. Use of the inhibitors NBTPT and DMPP did not significantly affect pasture yield or NUE, most likely because fertiliser N saved with the inhibitors only played a minor role in plant nutrition with the majority of the plant nutrition provided by the soil organic matter pool.

Reducing fertilization with high planting density increases maize yield stability and nitrogen use efficiency in semi-arid areas

High-density planting is a vital cultivation measure to improve crop yield. In the semi-arid region, insufficient precipitation and high variability are the primary factors that restrict agricultural development. Matching planting density and fertilizer application with precipitation is a promising technical strategy to ensure yield stability and enhance nitrogen (N) use efficiency (NUE). To achieve this objective, we conducted a continuous field experiment in the Loess Plateau region of Northwest China between 2015 and 2020. Under conventional (CF) and reduced fertilization (RF, 20 % CF) conditions, we investigated the response characteristics of dry matter accumulation, yield, yield components, NUE, N surplus, and net income of maize as the density increased from 5.25 (D1) to 6.75 (D2), 8.25 (D3), and 9.75 (D4) × 104 plants ha−1. The results indicated that reduced fertilizer application led to a decrease in grain yield by 6.2–8.7 %, whereas increasing the density by at least 1.50 × 104 plants ha−1 (D2) could compensate for the yield reduction caused by reduced fertilization (N 55 + P2O5 27 kg ha−1) in normal and wet years. The compensatory effect initially increased and then decreased as the density increased, with the highest yield observed at planting density D3. By increasing the rapid growth rate of maize (6.3–17.1 %) and extending the rapid growth duration (0.9–2.5 days) through high planting density, reduced fertilization combined with high-density planting (RF·D3) significantly increased the cumulative yield, yield stability, net income, and NUE was by 9.4 %, 18.9 %, 10.6 %, and 37.0 %, respectively, over six years, compared with CF·D1 treatment. Additionally, the N surplus was reduced by 44.6 %. In conclusion, using reduced fertilization with high planting density measures can achieve yield stability and sustainable maize production in semi-arid areas.

A Review on Nitrogen Flows and Obstacles to Sustainable Nitrogen Management within the Lake Victoria Basin, East Africa

The Lake Victoria Basin (LVB) is located in the upper reaches of the Nile River Basin and is shared by five East-African countries. The population in the catchment is growing rapidly and the lake is facing several environmental problems. During the past few decades, numerous efforts have been made across the five countries, with the coordination of the Lake Victoria Basin Commission (LVBC) to reduce the loading of reactive nitrogen (Nr) into the lake and Lake Watershed. However, most of the measures envisaged to ensure long-term sustainable N management are not as easily adopted as planned. This paper reports on a review study on N flows and obstacles in achieving sustainable N management in the LVB, with the objectives of improving the understanding of the N cycle and examining the N management practices and policies that can help reduce the loss of Nr in the region. The scientific literature related to a range of N flows, N management obstacles, and options to overcome obstacles has been analyzed using N prospects developed at the global level for their potential applicability across the LVB. The study showed that an unbalanced use of N input is a serious threat to agricultural productivity leading to extreme soil N mining and degradation, with the majority of LVB farms operating within negative N balances and above the safe operating boundary for N in production systems. From the projections in N input as recommended by various stakeholders, there would likely be changes in both current yield and N use efficiency (NUE) values; however, most small-scale farmers will continue to experience low yields, which remains a challenge for food security in the area. These results suggest that scientists as well as those involved in decision-making and policymaking processes should formulate new targets for fertilizer increment to reduce the yield gap for sustainability, focusing on more integrated soil fertility as a package for nutrient management in cropping systems.

Postfire Phosphorus Enrichment Mitigates Nitrogen Loss in Boreal Forests.

Net nitrogen mineralization (Nmin) and nitrification regulate soil N availability and loss after severe wildfires in boreal forests experiencing slow vegetation recovery. Yet, how microorganisms respond to postfire phosphorus (P) enrichment to alter soil N transformations remains unclear in N-limited boreal forests. Here, we investigated postfire N-P interactions using an intensive regional-scale sampling of 17 boreal forests in the Greater Khingan Mountains (Inner Mongolia-China), a laboratory P-addition incubation, and a continental-scale meta-analysis. We found that postfire soils had an increased risk of N loss by accelerated Nmin and nitrification along with low plant N demand, especially during the early vegetation recovery period. The postfire N/P imbalance created by P enrichment acts as a "N retention" strategy by inhibiting Nmin but not nitrification in boreal forests. This strategy is attributed to enhanced microbial N-use efficiency and N immobilization. Importantly, our meta-analysis found that there was a greater risk of N loss in boreal forest soils after fires than in other climatic zones, which was consistent with our results from the 17 soils in the Greater Khingan Mountains. These findings demonstrate that postfire N-P interactions play an essential role in mitigating N limitation and maintaining nutrient balance in boreal forests.

Comparing combined application of biochar and nitrogen fertilizer in paddy and upland soils: Processes, enhancement strategies, and agricultural implications

Recently, biochar and N fertilizers have been used to tackle low N use efficiency (NUE) in crops across diverse environmental conditions. The coupling of biochar and N fertilizer may impact crop N utilization through different pathways in various soil types. However, there is currently a lack of comprehensive assessment of how coupling effects specifically influence N utilization in paddy and upland crops. We conducted a meta-analysis of 175 peer-reviewed studies to assess the responses of soil properties and crop traits in paddy and upland fields under coupling effects. The results indicate that NUE (+26.1 %) and N uptake (+15.0 %) in paddy fields increase more than in upland fields (+23.7 % and +8.0 %, respectively), with the coupling effect providing NH4+ predominantly for rice and NO3− for upland crops. NH4+ increases in paddy fields (+6.9 %) but decreases in upland fields (−0.7 %), while microbial biomass carbon (MBC) decreases in paddy fields (−2.9 %) and increases in upland fields (+36.0 %). These findings suggest that coupling effects supply soil inorganic nutrients in paddies and affect microbes in uplands, thereby positively affecting crop N utilization. Specifically, the greatest increase in paddy crop yield and N use efficiency occurs when the ratio of N fertilizer to biochar exceeds 1.5 %, and in uplands, it manifests when applying 10–20 t·ha−1 of biochar and <150 kg·ha−1 N fertilizer. In conclusion, this meta-analysis explores the differential effects of biochar and N fertilizer coupling in different arable land types, offering novel insights into the utilization strategies of biochar in agricultural fields.

Nitrogen and molybdenum fertilization influence on enzymatic activity and productivity enhancement of forage sorghum under water deficit in the Brazilian semi-arid region

Water scarcity, combined with low soil fertility, constitutes one of the main limiting factors in crop productivity in semi-arid regions. However, nutritional supplementation techniques with nitrogen (N) and molybdenum (Mo) can lead to positive enhancements in the production of these crops. The objective was to evaluate the effect of increasing doses of N in the presence and/or absence of Mo on the activity of antioxidant enzymes and the productive increase of forage sorghum subjected to water deficit in the semi-arid region. The experiment was conducted in the field using a randomized block design, with four replications, in a 5 × 2 × 3 factorial scheme, comprising five doses of N (urea): 0, 50, 100, 150, and 300 kg ha−1, two doses of Mo (sodium molybdate): 0 and 160 g ha−1, and three production cycles. The highest yields of green mass (GM) (47.98 Mg ha−1), dry mass (DM) (19.66 Mg ha−1), water use efficiency (WUE) (5.57 kg/m³), and N use efficiency (NUE) (0.26 kg2/g) occurred at the highest N dosage (300 kg ha−1 N). The highest contents and extraction of total N, Mo, chloride (Cl), and potassium (K) were found in regrowth 2 and at the highest N dose (300 kg ha−1). The interaction of N and Mo resulted in higher catalase (CAT) enzyme activity. The meteorological conditions during the cycles strongly influenced the nutrient contents and extraction. The results of the study provide support for producers to use N and Mo fertilization strategies to improve crop productivity, even under water deficit conditions.

Effects of urea topdressing time on yield, nitrogen utilization, and quality of mechanical direct-seeding hybrid indica rice under slow-mixed fertilizer base application.

The use of controlled-release nitrogen (N) fertilizers has been shown to improve yield and N-use efficiency (NUE) in mechanical transplanted rice. However, the fertilizer requirements for mechanical direct-seeding rice differ from those for mechanical transplanted rice. The effects of controlled-release fertilizers on yield, NUE, and quality in mechanical direct-seeding rice are still unknown. Hybrid indica rice varieties Yixiangyou 2115 and Fyou 498 were used as test materials, and slow-mixed N fertilizer (120kg hm-2) as a base (N1), N1+urea-N (30kg hm-2) once as a base (N2), N1+urea-N (30kg hm-2) topdressing at the tillering stage (N3), N1+urea-N (30kg hm-2) topdressing at the booting stage (N4) four N fertilizer management to study their impact on the yield, NUE and quality of mechanical direct-seeding rice. Compared with Yixiangyou 2115, Fyou 498 significantly increased photosynthetic potential, population growth rate, root vigor, and N transport rate by 3.34-23.88%. This increase further resulted in a significant improvement in the yield and NUE of urea-N topdressing by 1.73-5.95 kg kg-1. However, Fyou 498 showed a significant decrease in the head rice rate and taste value by 3.34-7.67%. All varieties were treated with N4 that significantly increase photosynthetic potential and population growth rate by 15.41-62.72%, reduce the decay rate of root vigor by 5.01-21.39%, promote the N transport amount in stem-sheaths (leaves) by 13.54-59.96%, and then significantly increase the yields by 4.45-20.98% and NUE of urea-N topdressing by 5.20-45.56 kg kg-1. Moreover, the rice processing and taste values were optimized using this model. Correlation analysis revealed to achieve synergistic enhancement of high-yield, high-quality, and high-NUE in rice, it is crucial to focus on increasing photosynthetic potential, population growth rate, and promoting leaf N transport. Specifically, increasing the contribution rate of N transport in stem-sheaths is the most important. These findings offer an effective N management strategy for 4R nutrient stewardship (right source, right method, right rate and right timing) of mechanical direct-seeding hybrid indica rice.

Changes in soil N2O emissions and nitrogen use efficiency following long-term soil carbon storage: Evidence from a mesocosm experiment

Policy and market incentives are rapidly expanding to promote soil organic carbon (SOC) sequestration in global croplands. Evidence suggests that long-term increases in SOC can influence both crop yield and nitrogen (N) fertilizer requirements, with the potential to help address two important sustainability challenges. However, increases in SOC may also trigger higher soil nitrous oxide (N2O) emissions, which would represent an important tradeoff for climate change mitigation. We tested the hypothesis that long-term increases in SOC are associated with higher crop yields and fertilizer N use efficiency (NUE), but at the cost of higher N2O emissions. Wheat was grown in two soils (SOClow and SOChigh) under three N fertilizer rates (0, 100, and 200 kg N ha−1) in a mesocosm experiment. Soils were obtained (0–25 cm) from a 22-yr field experiment on no-till and cover cropping in California. Results indicate that total biomass and grain yield were higher for SOClow than SOChigh at 100 kg N ha−1 but not the other N levels. Crop N uptake was also 28% greater for SOClow at 200 kg N ha−1, resulting in higher overall NUE. Soil N2O emissions increased for SOChigh by 25–112% compared to SOClow, likely due to long-term changes in labile C and N pools, microbial activity, and soil structure influencing porosity and gas diffusion. While there are well-documented crop and environmental benefits from enhancing SOC in agricultural soils, results from this study suggest that changes in soil N2O emissions should be considered to accurately determine net GHG emission reductions.