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Nitrogen (N) is an essential plant nutrient, therefore, N-deficient soils affect plant growth and development. The excessive and unwise application of N fertilizers result in nutrient losses and lower nutrient use efficiency that leads to the low crop productivity. Ammonia volatilization causes a major loss after N fertilization that causes environmental pollution. This experiment was conducted to evaluate the effectiveness of coating and uncoating N fertilizer in enhancing yield and nutrient-use efficiency with reduced ammonia emissions. The recommended rate of nitrogen and phosphorus, urea and di-ammonium phosphate (DAP) fertilizers were coated manually with 1% polymer solution. DAP (coated/uncoated) and potassium were applied at the time of sowing as subsurface application. While urea (coated/uncoated) was applied as surface and subsurface application. Results showed that nutrient use efficiencies of wheat were found to be maximum with the subsurface application of coated N fertilizer which increased nutrient-use efficiency by 44.57 (N), 44.56 (P) and 44.53% (K) higher than the surface application of uncoated N fertilizer. Ammonia emissions were found the lowest with subsurface-applied coated N fertilizer. Thus, coated fertilizer applied via subsurface was found the best technique to overcome the ammonia volatilization with an improvement in the yield and nutrient-use efficiency of wheat.

To assess the synergistic effects of nitrogen (N) application rates on soil properties, maize yield, and water-N use efficiency under aerated irrigation in red loamy soils of Guangdong, a 3-year field experiment (2021-2023) was conducted with three N levels [150 (N1), 300 (N2), and 450 kg·hm (N3)] and a control (CK). Results showed that N2 (300 kg·hm ) and N3(450 kg·hm ) treatments significantly reduced soil bulk density by 3.87% and 5.23% (  < 0.05), and increased total porosity by 5.40% and 6.27%, respectively, compared to CK. Soil water storage and respiration were highest under N2 (300 kg·hm ) during key growth stages (V6-VT, VT-R2). N application enhanced organic carbon (up to 59.6% in 300 kg·hm ) and total nitrogen (up to 96.2% in 450 kg·hm ), while decreasing C/N ratio and increasing microbial biomass (up to 78.9% higher in 300 kg·hm vs. CK). N2 (300 kg·hm ) significantly improved maize yield by 63.7%, WUE by 70.9%, and N use efficiency (agronomic efficiency: 25.1 kg·kg ; recovery rate: 41.9%). A quadratic yield model indicated 250-300 kg·hm N as optimal. These findings suggest that moderate N application 300 kg·hm under aerated irrigation enhances soil structure, nutrient availability, and crop productivity, offering a sustainable approach for nitrogen-efficient maize production and red soil management in subtropical regions.

Excessive or improper nitrogen (N) application rates negatively affect crop production and thereby environmental quality, particularly for winter wheat production in the North China Plain. Therefore, it is very important to optimize N fertilizer input to balance grain yield, environmental risk, and benefits under irrigated conditions. Three long-term stationary field experiments including five N levels, from 0 to 300 kg ha [0 (N0), 90 (N90), 180 (N180), 240 (N240), and 300 (N300) kg ha ] were carried out to investigate the effects of N regime on wheat yield, photosynthesis, and N balance at different sites. The grain yield and protein content increased quadratically with N rate, and the maximum values were 8087 kg ha and 13.9% at N application rates of 250 and 337 kg N ha , respectively. N application increased the photosynthetic fluorescence parameters (Pn, Gs, and Tr) and N metabolism enzyme activities (NR and GS) which then increased grain yield. The leaching of soil nitrate into the deeper soil layers ( > 100 cm) increased with higher N fertilization and experimental years. The partial factor productivity (PFPN) was decreased by N because the apparent N loss increased with N application rate. In order to balance grain yield, N use efficiency (NUE), and N loss, the recommended N rate should be 120-171 kg N ha , and the corresponding yields and apparent N loss were 7278-7787 ka ha and 22-37 kg ha , respectively.

Variable rate technology offers a sustainable, efficient, and cost-effective solution for fertilizer application. A study was conducted to design and develop a variable rate fertilizer applicator to detect real-time deficiency of N within the field and apply it per requirement of the crop. The microcontroller system was designed to receive a signal from the N sensor and send a signal to the pulse-width-modulation valve to vary the rotational speed of the hydraulic motor resulting in variation in the rotation of the metering mechanism drive shaft based on the recommended amount of fertilizer. During the field study, three replications were conducted, each of which was divided into four plots. The response time between the N sensing and fertilizer discharging fell within the range of 3.49 to 4.90 s. Fertilizer applied using the developed variable rate applicator indicated that when the fertilizer rate is increased from N1 to N4 (kg ha−1), NDVI increased from 0.56 to 0.78 and drive shaft rotational speed decreased from 20 to 0 rpm in order to apply the fertilizer at a rate of 0.00 instead of 78.36 kg ha−1. Using the developed applicator demonstrates that this technology could reduce environmental impact, making farming more sustainable.

Chemical fertilizer overuse is a major environmental threat, critically polluting soil and water resources. An optimization of nitrogen (N) fertilizer application in winter wheat ( Triticum aestivum L.) in association with various irrigation scheduling is a potential approach in this regard. A 2-year field experiment was carried out to assess the growth, yield and photosynthetic capacity of drip-irrigated winter wheat subjected to various split applications of urea (240 kg ha −1 , 46% N). The eight treatments were, two irrigation scheduling and six N application modes in which, one slow-release fertilizer (SRF). Irrigation scheduling was based on the difference between actual crop evapotranspiration and precipitation (ETa-P). The two irrigation scheduling were I 45 (Irrigation scheduling when ETa-P reaches 45 mm) and I 30 (Irrigation scheduling when ETa-P reaches 30 mm). The six N levels were N 0-100 (100% from jointing to booting), N 25-75 (25% during sowing and 75% from jointing to booting), N 50-50 (50% during sowing and 50% from jointing to booting), N 75-25 (75% during sowing and 25% from jointing to booting), N 100-0 (100% during sowing), and SRF 100 (240  kg ha −1 , 43% N during sowing). N top-dressing application significantly ( P< 0.05) influenced wheat growth, aboveground biomass (ABM), grain yield (GY) and its components, photosynthetic and chlorophyll parameters, and plant nutrient content. According to the averages of the two winter wheat-growing seasons, the I 45 N 50-50 and I 45 SRF 100 treatments, respectively had the highest GY (9.83 and 9.5 t ha −1 ), ABM (19.91 and 19.79 t ha −1 ), net photosynthetic rate (35.92 and 34.59 µmol m −2 s −1 ), stomatal conductance (1.387 and 1.223 mol m −2 s −1 ), SPAD (69.33 and 64.03), and chlorophyll fluorescence F V /F M (8.901 and 8.922). The present study provided convincing confirmation that N applied equally in splits at basal-top-dressing rates could be a desirable N application mode under drip irrigation system and could economically compete with the costly SRF for winter wheat fertilization. The I 45 N 50-50 treatment offers to farmers an option to sustain wheat production in the NCP.

Aims Replenishment of soils with carbon (C) produced during photosynthesis plays an important role in global C cycling. Nitrogen (N) fertilization is critical for rice production, but its effects on the deposition of photosynthesis-derived C into soil C pools is poorly understood. To address this, we used continuous 14C-labeling to quantify the deposition of photosynthesis-derived C into various soil organic pools in a rice-soil system. Methods Rice (Oryza sativa L.) was continuously supplied with 14C-labeled CO2 (14C-CO2) for 36 days, with increasing N fertilizer rates (0 [N0], 10 [N10], 20 [N20], or 40 mg N kg−1 soil [N40], respectively). Results Rice shoot and root biomass significantly increased following N fertilization. The amount of photosynthesis-derived C converted into soil organic carbon (14C-SOC) was proportional to the soil N concentration, and accounted for 8.0–19.3 % of rice biomass C. The 14C-SOC content was positively correlated with the rice root biomass, suggesting that N increased root exudation of photosynthesis-derived C. The amounts of 14C-labeled C in the dissolved organic carbon (14C-DOC) and in the microbial biomass carbon (14C-MBC), as proportions of 14C-SOC, were 3.9–7.8 and 6.6–24.0 %, respectively. The 14C-DOC, 14C-MBC, and 14C-SOC as proportions of total DOC, MBC, and SOC were 9.7–11.6, 6.9–10.6, and 0.37–1.71 %, respectively. Conclusions Nitrogen fertilization promotes deposition of photosynthesis-derived C into SOC pools in a rate-dependent manner. However, the 14C-MBC as a proportion of both 14C-SOC (14C-MBC/14C-SOC) and MBC (14C-MBC/MBC) increase during rice growth at lower N concentrations.

Low temperature and overcast rain are harmful to directly seeding early rice, it can hinder rice growth and lower rice biomass during the seedling stage, which in turn lowers rice yield. Farmers usually use N to help rice recuperate after stress and minimize losses. However, the effect of N application on the growth recovery for rice seedlings after such low temperature stress and its associated physiological changes remain unclearly. Two temperature settings and four post-stress N application levels were used in a bucket experiment to compare B116 (strong growth recovery after stress) with B144 (weak growth recovery). The results showed that the stress (average daily temperature at 12°C for 4 days) inhibited the growth of rice seedlings. Compared to the zero N group, the N application group’s seedling height, fresh weight and dry weight significantly increased after 12 days. In particular, the increases in all three growth indicators were relatively higher than that of N application at normal temperature, indicating the importance of N application to rice seedlings after low temperature stress. The antioxidant enzyme activity of rice seedlings increased significantly after N application, which reduced the damaging effect of ROS (reactive oxygen species) to rice seedlings. At the same time, the soluble protein content of seedlings showed a slow decrease, while the H 2 O 2 and MDA (malondialdehyde) content decreased significantly. Nitrogen could also promote nitrogen uptake and utilization by increasing the expression of genes related to NH 4 + and NO 3 − uptake and transport, as well as improving the activity of NR (nitrate reductase) and GS (glutamine synthetase) in rice. N could affect GA 3 (gibberellin A3) and ABA (abscisic acid) levels by regulating the anabolism of GA 3 and ABA. The N application group maintained high ABA levels as well as low GA 3 levels from day 0 to day 6, and high GA 3 levels as well as low ABA levels from day 6 to day 12. The two rice varieties showed obvious characteristics of accelerated growth recovery and positive physiological changes by nitrogen application after stress, while B116 generally showed more obvious growth recovery and stronger growth-related physiological reaction than that of B144. The N application of 40 kg hm -2 was more conducive to the rapid recovery of rice growth after stress. The above results indicated that appropriate N application promoted rice seedling growth recovery after low temperature stress mainly by increasing the activities of antioxidant enzymes and nitrogen metabolizing enzymes as well as regulating the levels of GA 3 and ABA. The results of this study will provide a reference for the regulation of N on the recovery of rice seedling growth after low temperature and weak light stress.

Background Lodging in rice production often limits grain yield and quality by breaking or bending stems. Excessive nitrogen (N) fertilizer rates are the cause of poor lodging resistance in rice, but little is known about the effect of top-dressing N application rates on the mechanical strength of japonica rice plants, especially how the anatomical structure in culms is affected by N. In this study, field experiments on two japonica rice varieties with three top-dressing N application rates, 0 kg N ha −1 (LN), 135 kg N ha −1 (MN), and 270 kg N ha −1 (HN) as urea, were conducted. Wuyunjing23, a lodging-resistant japonica rice cultivar and W3668, a lodging-susceptible japonica rice cultivar were used. The lodging index, breaking strength, morphological and anatomical traits in culms were measured in this study. Results The visual lodging rate in japonica rice differed remarkably between genotypes and top-dressing N treatments. The higher lodging index of rice plants was primarily attributed to the weak breaking strength of the lower internodes. The longer elongated basal internodes were responsible for higher plant height and a higher lodging index. Correlation analysis showed that breaking strength was significantly and positively correlated with the thickness of the mechanical tissue but was significantly and negatively correlated with the inner diameter of the major axis (b 2 ). With increasing top-dressing N rates, the sclerenchyma cells of the mechanical tissues and the vascular bundles of the Wuyunjing23 cultivar varied little. The plant height, inner diameter of the minor axis (a 2 ) and b 2 increased significantly, but the area of the large vascular bundle (ALVB) and the area of the small vascular bundle (ASVB) decreased significantly and resulted in lower stem strength and a higher lodging index under higher top-dressing N conditions. The culm diameter of the W3668 cultivar increased slightly with no significant difference, and the sclerenchyma cells in the mechanical tissues and vascular bundles showed deficient lignifications under high top-dressing N conditions. Moreover, the ALVB and the ASVB decreased significantly, while the area of air chambers (AAC) increased rapidly. Conclusions An improvement in the lodging resistance of japonica rice plants could be achieved by reducing the length of the lower internodes, decreasing the inner culm diameter and developing a thicker mechanical tissue. Top-dressing N application increased the plant height and inner culm diameter and decreased the ALVB and the ASVB of the Wuyunjing23 cultivar and caused deficient lignified sclerenchyma cells, lowered the ALVB and the ASVB, and increased the AAC of the W3668 cultivar resulting in weaker stem strength and a higher lodging index.

Variable-rate technology (VRT) may reduce input costs, increase crop productivity and quality, and help to protect the environment. The present study was conducted to evaluate the performance of a variable-rate fertilizer applicator for rice (Oryza sativa L.). Three replications were conducted, each of which was divided into four plots. Field performance of the system was assessed at different nitrogen levels (N1 to N4, i.e., 75, 125, 175, 225 kg ha−1), growth stages (tillering, panicle initiation, heading), and heights (40, 60, 80, 100 cm) of the sensor from the crop canopy. Fertilizer rate was at minimum 12.59 kg ha−1 at 10 rpm of drive-shaft rotational speed and at maximum 50.41 kg ha−1 at 40 rpm. The system response time was within the range of 3.53 to 4.93 s, with overall error ranging between 0.83% to 4.92%. Across different growth stages, when fertilizer rate was increased from N1 to N4, NDVI increased from 0.49 to 0.69. Hence, drive-shaft rotational speed is decreased from 25 to 7 rpm to shift the application rate from 30.83 to 9.15 kg ha−1. There was a 45% reduction in total fertilizer rate applied by the system, with respect to the recommended rate.

Over 30% of the Chinese tea plantation is supplied with excess fertilizer, especially nitrogen (N) fertilizer. Whether or not foliar N application on tea plants at the dormancy stage could improve the quality of spring tea and be a complementary strategy to reduce soil fertilization level remains unclear. In this study, the effects of foliar N application on tea plants were investigated by testing the types of fertilizers and their application times, and by applying foliar N under a reduced soil fertilization level using field and 15 N-labeling pot experiments. Results showed that the foliar N application of amino acid liquid fertilizer two times at the winter dormancy stage was enough to significantly increase the N concentration of the mature leaves and improved the quality of spring tea. The foliar application of 2% urea or liquid amino acid fertilizer two times at the winter dormancy stage and two times at the spring dormancy stage showed the best performance in tea plants among the other foliar N fertilization methods, as it reduced the soil fertilization levels in tea plantations without decreasing the total N concentration of the mature leaves or deteriorating the quality of spring tea. Therefore, foliar N application on tea plants at its dormancy stage increases the N concentration of the mature leaves, improves the quality and yield of spring tea, and could be a complementary strategy to reduce soil fertilization levels.