Increasing Nitrogen Application Rates Research Articles

Integrated organic and mineral fertilizer strategies for achieving sustainable maize yield and soil quality in dry sub-humid inceptisols

Maize is one of the important cereal crops grown in rainfed regions of northwestern Himalayas, however, persistent use of chemical fertilizers coupled with poor soil nutrients and water holding capacity due to coarse textured soils poses serious threat to sustaining maize yield and soil health. To address these bottlenecks, a long-term experiment with application of organic manures and mineral fertilizer provides insights to quantify changes in soil organic carbon (SOC), crop yield and rain water use efficiency (RWUE) in rainfed area having low water use efficiency. A twelve years field experiment was conducted under dry sub-humid Inceptisols in northern India to study the potential impacts of organic and mineral fertilization on maize (Zea mays L.) productivity, water use efficiency and soil quality. Ten treatments were assessed, involving different nitrogen levels (20, 30, and 40 kg N ha⁻¹) combined with 10 tha⁻¹ year⁻¹ of farmyard manure (FYM), in-situ green manure from sunhemp, and the incorporation of Leucaena leucocephala leaves at 5 tha⁻¹ year⁻¹, including an unfertilized control. Maize yield increased linearly with increasing nitrogen application rates. The combination of FYM @ 10t ha−1 and 40 kg N ha−1(T4) yielded the highest maize production. Manure addition improved soil organic carbon (SOC) and major soil nutrients (N, P and K) while unfertilized control showed decline in soil nutrients compared to their initial values. Compared with control, incorporation of 10 t ha−1 FYM increased SOC by 1.3, 1.41, 1.44 times at application rate of 20, 30, 40 kg N ha−1, respectively. Application of N@40 kg ha−1 + 10t FYM ha−1 showed highest rain water use efficiency (RWUE) and relative production efficiency index (RPEI) (2.74 kg ha−1 mm−1 and 82, respectively) and the lowest rank sum of 6. Highly significant positive relationship existed between RPEI and RWUE, RPEI and sustainability yield index (SYI), RWUE and SYI indicated the superiority of FYM in combination with mineral fertilizer. Regression models, correlating yield with monthly rainfall and crop growing periods, indicated that the integration of FYM (10 tha⁻¹) with 40 kg N ha⁻¹ was most effective in achieving the highest relative soil quality index (RSQI) of 76 and the greatest sustainability yield index (SYI) of 49.3%. Based on results, we recommend balanced fertilization (N@40 kg ha−1 +10t FYM ha−1) which is easily manageable by farmers as the optimal strategy for improving soil quality and achieving sustainable maize productivity in nutrient depleted Inceptisols of northern India.

Optimizing nitrogen fertilization and planting density management enhances lodging resistance and wheat yield by promoting carbohydrate accumulation and single spike development

AbstractNitrogen fertilizer application and increasing planting density have been recognized as essential measures to achieve higher wheat (Triticum aestivum L.) yields. However, inadequate management practices often lead to poor culm quality and lodging. We hypothesized that optimizing culm characteristics could be a feasible approach to improving both lodging resistance and yield. In this study, field experiments involved five nitrogen levels (0, 180, 240, 300, and 360 kg ha−1) and three planting densities (225, 375, and 525 × 104 ha−1). Two wheat cultivars with different lodging resistance were selected and their culm morphological characteristics, biochemical components, field lodging rate, and yield in different treatments were measured. We found that field lodging rate in wheat was negatively correlated with yield, and there was a contradiction between increasing spike number and lodging resistance. Culm carbohydrate accumulation affected field lodging rate by regulating culm quality rather than the center of gravity height. Compared with Xinmai 26, Xinhuamai 818 had higher culm carbohydrate accumulation, which increased the breaking strength and yield by 14.2% and 17.0%. Nitrogen application and planting density had significant effects on yield and lodging resistance. Compared with N0 treatment, increasing nitrogen application rate improved yield of 67.2%–83.2% by increasing spike number and grain number per spike, and the N2 treatment showed the largest increase. Planting density had little effect on yield. Reducing planting density can increase the culm carbohydrate accumulation and enhance lodging resistance. Compared with D3 treatment, the culm breaking strength was increased by 27.6% under the D1 treatment. This study determined that the optimal combination of nitrogen and density for improving wheat lodging resistance and yield is 240 kg ha−1 and 225 × 104 ha−1. This combination enhances culm breaking strength by increasing carbohydrate accumulation and achieves high yield by increasing grain number per spike, 1000‐grain weight, and stabilizing spike number.

Multi-objective optimization of farmland water level and nitrogen fertilization management for winter wheat cultivation under waterlogging conditions based on TOPSIS-Entropy

Aiming at the problems of reduced winter wheat yield and aggravation of nitrogen leaching pollution caused by the waterlogging in the Middle-Lower Yangtze Plain, China, a two-year field experiment with three farmland water levels (W40, W60, W80) and three nitrogen application rates (N150, N225, N300) as well as a non-waterlogged treatment (CK) was carried out, to investigate the coupling effects of farmland water level and nitrogen application rate on the plant growth, grain yield, crop water productivity (WPC) and nitrogen load with waterlogging conditions. Three man-made waterlogging events were applied at winter wheat jointing-booting stage, heading-flowering stage and grain filling stage, respectively. The results indicated that with the farmland water level decreased from −40 cm to −60 cm and the nitrogen application rate increased from 150 kg∙ha−1 to 225 kg∙ha−1, the plant height, aboveground dry matter, leaf area index, spike length, grain yield, effective panicles, grain number per ear, 1000-grain weight and WPC in the waterlogging field increased significantly. However, since the nitrogen application rate exceeded 225 kg∙ha−1 and farmland water level lowered more than −60 cm, the favorable effects of nitrogen application rate and farmland water level for winter wheat growth and production reduced. Additionally, both the nitrogen load and partial factor productivity of nitrogen (PFPN) increased with the decline of farmland water level, while the nitrogen load increased and the PFPN decreased with the increasing nitrogen application rate. The raise of nitrogen rate from 150 kg∙ha−1 to 225 kg∙ha−1 was beneficial to plant growth, however, the increase of nitrogen application resulted in the decrease of PFPN and increase of drainage nitrogen loads. Compared with the water farmland water level of −40 cm and nitrogen application rate of 150 kg∙ha−1, the increase of nitrogen application rate and the decrease of farmland water level in the range of 50%-100% resulted in yield raise by 5.78%-32.29% approximately and the increase of nitrogen load by 36.20%-178.44% approximately. The comprehensive evaluation with TOPSIS-Entropy method for plant growth, grain yield, WPC, PFPN and nitrogen loads suggested that, the appropriate nitrogen application rate for winter wheat in the waterlogging areas of Middle-Lower Yangtze Plain in China was 225 kg∙ha−1, and the proper farmland water level was lowering to −80 cm in wet year and −60 cm in dry year within 3 days after waterlogging.

Analysis of Spectral Characteristics of Cotton Leaves at Bud Stage under Different Nitrogen Application Rates

Soil salinity affects nutrient uptake by cotton. The cotton bud stage is a very important period in the process of cotton planting and directly affects the yield of cotton. The nutritional status of the bud stage directly affects the reflectance spectra of cotton canopy leaves. Therefore, it is of great significance to nondestructively monitor the nutritional status of the cotton bud stage on salinized soil via spectroscopic techniques and perform corresponding management measures to improve cotton yield. In this study, potted plants with different nitrogen application rates were set up to obtain the reflection spectral curves of cotton bud stage leaves, analyze their spectral characteristics under different nitrogen application rates, and establish spectral estimation models of chlorophyll density. The results are as follows: in the continuum removal spectrum of the cotton bud stage, the lowest point of the absorption valley near 500 nm shifted to the shortwave direction with an increasing nitrogen application rate. The mean reflectance between 765 and 880 nm was significantly different between nitrogen-stressed and nitrogen-unstressed cotton. The average reflectance of the near-infrared band, the absorption valley depths near 500 nm and 675 nm, the first derivative of the 710 nm reflectance, and the second derivatives of the 690 nm and 730 nm reflectance increased with increasing nitrogen application and chlorophyll density, and significant correlations were observed with the chlorophyll density. These parameters were modeled using support vector regression (SVR) and artificial neural network (ANN) methods, two commonly used algorithms in the field of machine learning. The determination coefficients of the three chlorophyll samples via the ANN models were 0.92, 0.77, and 0.94 for the modeling set and 0.77, 0.69, and 0.77 for the verification set. The ratio of quartile to root-mean-square error (RPIQ) of the ANN model was greater than 2.2, and the ratio of the standard error of the measured value to the standard error of the predicted (SEL/SEP) was close to 1, indicating that the chlorophyll density estimation models built based on the ANN algorithm had robust prediction ability. Our model could accurately estimate the leaf chlorophyll density in the cotton bud stage.

Effects of Different Nitrogen Application Rates on Root Growth and Distribution of Fine Root Length across Diameter Classes of Wolfberry (Lycium barbarum L.)

The optimized cultivation process of wolfberry (Lycium barbarum L.) to maintain a consistently high and stable yield relies on the prolonged use of significant amounts of nitrogen fertilizers. However, this practice leads to increased production costs and various issues, such as soil pollution and compaction. To address these concerns, a three-year field trial was conducted involving different nitrogen application rates: N1 (20% nitrogen (N) reduction, 540 kg·hm−2), N2 (medium N, 675 kg·hm−2), and N3 (20% nitrogen increase, 810 kg·hm−2). The results showed that the inter-annual growth and development of wolfberry roots had two rapid growth peaks. In comparison with the N3 treatment, the root morphological characteristics index increased significantly under the N1 and N2 treatments. Among the different diameter classes, the most significant increase in fine root length, with an average diameter between 0.4 and 0.8 mm, occurred under the N1, N2, and N3 treatments, accounting for 50.6%, 50.92%, and 47.72% of the total annual growth of root length increments, respectively. Concerning the distribution of fine roots, the active layer depth extended under the N2 treatment suggesting that medium nitrogen application favored the longitudinal extension of fine roots. Leaf nitrogen content and the chlorophyll meter values (SPAD values) in the upper part of the plant, at the tip of shoots/branches, were the most sensitive indicators to changes in nitrogen application rates. These values increased significantly with higher nitrogen application amounts. Similarly, the contents of total sugar, betaine, and β-carotene increased with increasing nitrogen application rates, while the contents of Lycium barbarum polysaccharides (LBPs) and total flavonoids decreased. Finally, based on a comprehensive principal component evaluation, the rankings for root growth and plant development under various nitrogen application treatments were as follows: N2 (1.891) > N1 (0.002) > N3 (−1.894). The results showed that both the aboveground and belowground growth and development of wolfberry plants were most optimized under the N2 treatment. These findings provide a foundational reference for constructing good root morphology of wolfberry through cultivation practices such as nitrogen fertilizer management.

Effect of nitrogen application levels on photosynthetic nitrogen distribution and use efficiency in soybean seedling leaves

BackgroundNitrogen nutrition is strongly associated with crop growth and development. Nitrogen application level affects leaf size as well as nitrogen content and distribution, and thus affects photosynthetic nitrogen-use efficiency (PNUE) and yield. In this study, soybean varieties “Jinyuan 55” and “Keshan 1” were treated with nitrogen as urea at: N0, 0 kg hm−2; N0.5, 60 kg hm−2; N1, 120 kg hm−2; and N1.5, 180 kg hm−2. We compared the effect of nitrogen level on plant morphology, biomass, photosynthetic physiology, nitrogen distribution, PNUE, and other soybean seedling leaf characteristics. ResultsMaximum carboxylation and electron transfer, net photosynthetic rates, and PNUE of both soybean varieties showed initial significant increases with increasing nitrogen application rate and subsequent stabilization. PNUE, carboxylation system components, electron transport components, and non-photosynthetic system distribution ratios in the photosynthetic system increased and subsequently decreased with increased nitrogen application rate. The nitrogen ratio between carboxylation and electron transport systems was positively correlated with PNUE in both soybean varieties. The nitrogen ratio in light-harvesting and non-photosynthetic systems showed a linear negative correlation with PNUE. ConclusionsOverall, an appropriate nitrogen level maintained a high photosynthetic nitrogen ratio, whereas low- or high-nitrogen conditions increased or decreased the nitrogen ratio in non-photosynthetic and photosynthetic systems, respectively, thus decreasing the PNUE and photosynthetic capacity. Moreover, increased nitrogen application rate led to a decreased nitrogen ratio in the light-harvesting system and an increased nitrogen ratio of electron transport and carboxylation systems. Our results provide a theoretical basis for optimizing leaf nitrogen distribution, determining optimum nitrogen levels, and promoting soybean seedling growth.

Greenhouse gas emissions and ammonia loss of maize fertigation with a centre pivot system in the North China Plain

AbstractWhether sprinkler fertigation stimulates greenhouse gas emissions and ammonia loss is an indispensable consideration for nitrogen management. To assess the effect of sprinkler fertigation on N2O, CH4, CO2 and NH3 emissions, three N recommendation methods for summer maize, including the local empirical value, mineral nitrogen method and modified mineral nitrogen method, and three topdressing methods, including no topdressing, one topdressing and two topdressings following intermittent rainfall events, were tested in the 2020 and 2021 seasons. Surface irrigation with fertilizer broadcasting was used as the control treatment. The results indicated that nitrogen topdressing and rainfall promoted soil N2O, CO2 and NH3 emissions but had no obvious effect on CH4 emissions. The increasing nitrogen application rate increased gaseous nitrogen losses of N2O and NH3. Sprinkler fertigation with the modified mineral nitrogen method and two topdressings obtained the greatest yield and nitrogen use efficiency. Compared to the control treatment, the yield and nitrogen use efficiency in the sprinkler fertigation treatments was maximally increased by 20%, and the cumulative NH3 volatilization losses and gaseous nitrogen loss rate were both reduced by 16%, while the cumulative N2O emissions increased by 4%. No significant difference in global warming potential was obtained among all treatments.

Water and Nitrogen Coupling Increased the Water-Nitrogen Use Efficiency of Oilseed Flax.

Increasing water shortages and environmental pollution from excess chemical nitrogen fertilizer use necessitate the development of irrigation-nitrogen conservation technology in oilseed flax production. Therefore, a two-year split-plot design experiment (2017-2018) was conducted with three types of irrigation (I) levels (no irrigation (I0), irrigation of 1200 m3 ha-1 (I1200), and 1800 m3 ha-1 (I1800)) as the main plot and three nitrogen (N) application rates (0 (N0), 60 (N60) and 120 (N120) kg N ha-1) as the subplot in Northwest China to determine the effects of irrigation and N rates on oilseed flax grain yield, yield components, water-use efficiency (WUE), and N partial factor productivity (NPFP). The results show that I1800 optimized the farmland water storage and water storage efficiency (WSE), which gave rise to greater above-ground biomass. Under I1800, the effective capsule (EC) number increased significantly with increasing irrigation amounts, which increased significantly with increasing nitrogen application rate (0-120 kg ha-1). Both irrigation and nitrogen indirectly affect GY by affecting EC; the highest grain yield was observed at the I1800N60 treatment, which increased by 69.04% and 22.80% in 2017 and 2018 compared with the I0N0 treatment, respectively. As a result, both irrigation and N affect grain yield by affecting soil water status, improving above-ground biomass, and finally affecting yield components. In addition, I1800N60 also obtained a higher WUE and the highest NPFP due to a higher grain yield and a lower N application rate. Hence, our study recommends that irrigation with 1800 m3 ha-1 coupled with 60 kg N ha-1 could be a promising strategy for synergistically improving oilseed flax WUE, grain yield and yield components within this semi-arid region.

Effects of irrigation and nitrogen application on NO3--N distribution in soil, nitrogen absorption, utilization and translocation by winter wheat

Irrigation and nitrogen application can not only increase wheat yield, but also cause nitrogen loss and soil nitrate accumulation. This study aimed to assess the effects of irrigation amount and nitrogen application rate on the soil NO3--N distribution and nitrogen absorption and utilization of winter wheat (Triticum aestivum L.) during the 2015–2020 growth season in the North China Plain. The experiments were designed in split plot arrangement, with irrigation amount (W0, no irrigation; W1, 60 mm irrigation at jointing; and W2, 60 mm irrigation at jointing and anthesis) as the main plots and nitrogen application rate (N0, 0; N120, 120 kg ha−1; and N240, 240 kg ha−1) as the subplots. The plants under W2N120 and W2N240 showed no significant difference in yield throughout the experimental period. With the decrease in soil total nitrogen content, the yield difference between the plants under N0 and those under N120 and N240 gradually increased throughout the experimental period. Compared with that of the plants under W2N240, the mean NO3--N content of the plants under W2N120 in the 0–1 m and 1–2 m soil layers decreased by 17.4% and 19.2%, respectively, in 2018–2020. The NO3--N concentration decreased with increasing soil depth, and the NO3--N concentration in each soil layer increased with increasing nitrogen application rate. Irrigation and nitrogen application increased nitrogen accumulation in vegetative organs at anthesis and nitrogen transport to grains. Compared with those of the plants under W2N240, the mean nitrogen uptake efficiency, nitrogen use efficiency, nitrogen fertilizer productivity, and nitrogen harvest index of the plants under W2N120 increased by 91.3%, 2.6%, 95.5%, and 1.9%, respectively. These results suggest that applying 120 kg ha−1 nitrogen and irrigating 60 mm at jointing and anthesis are the optimal measures for winter wheat in the North China Plain.

Effects of Nitrogen Application Rates and Irrigation Regimes on Root Growth and Nitrogen-Use Efficiency of Maize under Alternate Partial Root-Zone Irrigation

Root growth and its adaptation are quite important for efficient use of water and nutrients. The present study investigated the effects of alternate partial root-zone irrigation (APRI) coupled with nitrogen application on root growth and nitrogen-use efficiency (NUE) of maize (Zea mays L.). Treatments (conducted at Wuwei City, northwest China) included APRI with controlled irrigation at 45%, 65%, and 80% of field capacity (FC) (W1, W2, and W3, respectively) coupled with nitrogen application rate of 100, 200, and 300 kg N ha−1 (N1, N2, and N3, respectively). The study found a significant interaction effect of irrigation regimes and nitrogen application rates on maize root growth and NUE. Compared with N2, N3 did not increase the length, surface area, weight, and volume of roots at the filling and maturity stages under W2, while it did under W3, which suggests that increasing nitrogen application rates did not compensate for the adverse effect of drought on root growth. In addition, NUE positively correlated with these root morphological parameters but negatively with the root-to-shoot ratio at the filling and maturity stages. The W2N2 treatment with moderate soil moisture and relatively high soil nitrate-nitrogen promoted total root growth and deeper roots and optimized vertical root distribution, with a low root-to-shoot ratio, resulting in the greatest NUE. These results suggest that moderately controlled irrigation (W2) combined with a reasonable nitrogen rate (N2) improves root growth and optimizes root distribution, resulting in a high NUE in maize under alternate partial root-zone irrigation.

Simulation of the responses of spring wheat yield to the rates and depths of nitrogen application in dryland based on APSIM model

Nitrogen limitation is an important factor for the improvement of crop water production potential in rain-fed areas of the Loess Plateau. The reasonable deep application of nitrogen fertilizer is a promising method to increase yield of rain-fed crop. Based on APSIM model, this study simulated spring wheat yield under different nitrogen application rates and depths, by using meteorological observation data from 1990 to 2020 in the semiarid areas of central Gansu Province, aiming to provide theoretical reference for optimizing wheat fertilization strategy. The results showed that the determination coefficient of simulated spring wheat yield, biomass and soil water content in 0-200 cm soil profile was greater than 0.80, the normalized root mean square error was less than 0.2, and the model validity index was greater than 0.5. These results indicated that the model had good fitting and adaptability in the test area. Across all the levels within the experimental design, increasing nitrogen application rates could significantly increase the yield of spring wheat in different precipitation years, and increasing nitrogen application depth could significantly increase spring wheat yield in wet and normal years, but had no effect in dry years. The rate and depth of nitrogen application had significant interaction effects on spring wheat yield in wet and normal years, but not in dry years. According to the binary quadratic regression fitting equation, when the potential maximum yield reached 2749 kg·hm-2 in wet year, nitrogen application depth was 22.7 cm, and nitrogen application rate was 245 kg·hm-2. When the maximum potential yield reached 2596 kg·hm-2 in normal year, nitrogen application depth was 20.6 cm, and nitrogen application rate was 235 kg·hm-2. Integrating the effects of nitrogen application rate and depth on yield, biomass and agronomic efficiency of nitrogen fertilizer, and farmer's fertilizer application habits, the recommended nitrogen application depth was 20-23 cm, and nitrogen application amount was 120-150 kg·hm-2, which could further improve water productivity and nitrogen use efficiency of spring wheat in arid areas of central Gansu Province.

Response of litter decomposition and the soil environment to one-year nitrogen addition in a Schrenk spruce forest in the Tianshan Mountains, China

Human activities have increased the input of nitrogen (N) to forest ecosystems and have greatly affected litter decomposition and the soil environment. But differences in forests with different nitrogen deposition backgrounds. To better understand the response of litter decomposition and soil environment of N-limited forest to nitrogen deposition. We established an in situ experiment to simulate the effects of N deposition on soil and litter ecosystem processes in a Picea schrenkiana forest in the Tianshan Mountains, China. This study included four N treatments: control (no N addition), low N addition (LN: 5 kg N ha−1 a−1), medium N addition (MN: 10 kg N ha−1 a−1) and high N addition (HN: 20 kg N ha−1 a−1). Our results showed that N addition had a significant effect on litter decomposition and the soil environment. Litter mass loss in the LN treatment and in the MN treatment was significantly higher than that in the control treatment. In contrast, the amount of litter lost in the HN treatment was significantly lower than the other treatments. N application inhibited the degradation of lignin but promoted the breakdown of cellulose. The carbon (C), N, and phosphorus (P) contents of litter did not differ significantly among the treatments, but LN promoted the release of C and P. Our results also showed that soil pH decreased with increasing nitrogen application rates, while soil enzyme activity showed the opposite trend. In addition, the results of redundancy analysis (RDA) and correlation analyses showed that the soil environment was closely related to litter decomposition. Soil enzymes had a positive effect on litter decomposition rates, and N addition amplified these correlations. Our study confirmed that N application had effects on litter decomposition and the soil environment in a N-limited P. schrenkiana forest. LN had a strong positive effect on litter decomposition and the soil environment, while HN was significantly negative. Therefore, increased N deposition may have a negative effect on material cycling of similar forest ecosystems in the near future.

Use of Digestate as Organic Amendment and Source of Nitrogen to Vegetable Crops

Anaerobic digestion is a valuable process to use livestock effluents to produce green energy and a by-product called digestate with fertilising value. This work aimed at evaluating the fertilising value of the solid fraction (SF) of a digestate as an organic amendment and as a source of nitrogen to crops replacing mineral N. A field experiment was done with two consecutive vegetable crops. The treatments were: a control without fertilisation; Ni85 mineral fertilisation with 85 kg ha−1 of mineral N; fertiliser with digestate at an increasing nitrogen application rate (kg N ha−1): DG-N85 DG-N170, DG-N170+85, DG-N170+170; fertilisation with digestate together with Ni: DG-N85+Ni60, DG-N170+Ni60, DG-N170+Ni25. The results showed a soil organic amendment effect of the SF with a beneficial effect on SOM, soil pH and exchangeable bases. The SF was able to replace part of the mineral N fertilisation. The low mineralisation of the stable organic matter together with some immobilisation of mineral N from SF caused low N availability. The fertilisation planning should consider the SF ratio between the organic N (NO) and total N (TKN). Low NO:TKN ratios (≈0.65) needed lower Ni addition to maintaining the biomass production similar to the mineral fertilisation.

The response of potato tuber yield, nitrogen uptake, soil nitrate nitrogen to different nitrogen rates in red soil

Nutrient-deficient red soil found in the southern region of China is increasingly being used for potato crops to meet the demand for this staple food. The application of nitrogen fertilizer is necessary to support the production of higher tuber yields; however, the links between nitrate nitrogen and the nitrogen balance in red soil are unknown. A field experiment was conducted in Jiangxi Province in 2017 and 2018 to determine the effects of different nitrogen application rates, 0 kg ha−1 (N0), 60 kg ha−1 (N60), 120 kg ha−1 (N120), 150 kg ha−1 (N150), 180 kg ha−1 (N180), 210 kg ha−1 (N210), and 240 kg ha−1 (N240, the highest rate used by local farmers), on potatoes growing in red soil. Data on tuber yield, crop nitrogen uptake, and the apparent nitrogen balance from the different treatments were collected when potatoes were harvested. Additionally, the content and stock of nitrate nitrogen at different soil depths were also measured. Nitrogen fertilization increased tuber yield but not significantly at application rates higher than 150 kg ha−1. We estimated that the threshold rates of nitrogen fertilizer application were 191 kg ha−1 in 2017 and 227 kg ha−1 in 2018, where the respective tuber yields were 19.7 and 20.4 t ha−1. Nitrogen uptake in potato in all nitrogen fertilization treatments was greater than that in N0 by 61.2–237% and 76.4–284% in 2017 and 2018, respectively. The apparent nitrogen surplus (the amount of nitrogen remaining from any nitrogen input minus nitrogen uptake) increased with increasing nitrogen application rates. The nitrate nitrogen stock at a soil depth of 0–60 cm was higher in the 210 and 240 kg ha−1 nitrogen rate treatments than in the other treatments. Moreover, double linear equations indicated that greater levels of nitrogen surplus increased the nitrate nitrogen content and stock in soils at 0–60 cm depths. Therefore, we estimate that the highest tuber yields of potato can be attained when 191–227 kg ha−1 nitrogen fertilizer is applied to red soil. Thus, the risk of nitrate nitrogen leaching from red soil increases exponentially when the apparent nitrogen balance rises above 94.3–100 kg ha−1.

Benefits and limitations of straw mulching and incorporation on maize yield, water use efficiency, and nitrogen use efficiency

Straw mulching and straw incorporation are widely used for conservation tillage as the primary methods of returning straw to the field. However, few studies have investigated the effects of straw mulching and straw incorporation under various agronomic management and environmental and edaphic factors. Here, we conducted a meta-analysis incorporating 112 publications to determine whether straw incorporation and straw mulching had different effects on maize yield, water use efficiency (WUE), and nitrogen use efficiency (NUE) under contrasting soil textures, N application rates, straw returning amounts, and annual average precipitation, temperature, and evaporation. The results showed that straw mulching and straw incorporation significantly increase maize yields, WUE, and NUE. Straw mulching yield had a significant positive correlation with WUE, while straw incorporation yield had significant positive correlations with WUE and NUE. Maize yield and WUE increased and NUE decreased with increasing nitrogen application rate. Straw incorporation increased maize yield and NUE more than straw mulching at low straw returning amounts (< 6000 kg ha−1). In arid and semi-arid areas with < 400 mm average annual precipitation and > 1200 mm evaporation, straw mulching increased maize yield, WUE, and NUE more than straw incorporation. In semi-humid areas (400–600 mm), straw incorporation increased maize yield and NUE more than straw mulching. Straw mulching is more conducive to increasing maize yield and NUE with average annual temperatures < 7 °C, while straw incorporation is more conducive to increasing maize yield, WUE, and NUE with average annual temperatures > 13 °C. Of the three soil textures, the largest weighted response ratio of straw returning on yield and NUE occurred in loam soil with straw incorporation. This study identified the benefits and limitations of straw incorporation and straw mulching on maize yield, NUE, and WUE.

Effects of different nitrogen application rates on dry matter accumulation, distribution and yield of grape under alternate partial root-zone drip irrigation.

To get an optimal mode of irrigation and nitrogen supply for table grape production in North China, a pot experiment was conducted to investigate the effects of different irrigation modes and N application rates on dry matter accumulation and distribution, yield, water use efficiency, and nitrogen use efficiency of table grape. The irrigation modes included conventional drip irrigation (CDI, with sufficient irrigation), alternate partial root-zone drip irrigation (ADI, with 50% amount of the irrigation water of CDI) and fixed partial root-zone drip irrigation (FDI, with 50% amount of the irrigation water of CDI). The nitrogen application rates were set at 0.4 (N1), 0.8 (N2) and 1.2 (N3) g·kg-1 dry soil. The results showed that compared with CDI, ADI and FDI reduced new shoot pruning amount by 34.8% and 11.2%, respectively. New shoot pruning amount increased with increasing N application rates, being highest under CDIN3. Dry matter accumulation of ADI was the highest, being 5.1% and 12.8% higher than CDI and FDI. Dry matter accumulation was higher under N2 and N3 than N1. Compared with CDI and FDI, leaf to fruit ratio reduced but harvest index significantly increased in ADI, while those variables showed no significant difference among diffe-rent N application rates. The ratio of pruning amount to the biomass accumulated in the current year in ADIN2 was the lowest among the treatments. Compared with CDI and FDI, ADI increased grape fruit yield by 6.0% and 10.4%, respectively. Fruit yield was enhanced with increasing nitrogen application rates under the same irrigation condition, with the highest yield under the ADIN2 and ADIN3. Water use efficiency (WUE) increased significantly in ADI compared with CDI and FDI, with the highest value being observed in ADI coupled with N2 or N3. Nitrogen use efficiency (NUE) showed a trend of ADI＞CDI＞FDI. In addition, NUE decreased with increasing nitrogen supply level across the irrigation modes. In conclusion, ADIN2 could reduce the redundant growth of grape tree, promote the transfer of dry matter to fruit, which increased yield and use efficiency of both water and nitrogen, which is a suitable coupling water and nitrogen supply mode for grape production in northern China.

Effects of nitrogen application rate on the photosynthetic pigment, leaf fluorescence characteristics, and yield of indica hybrid rice and their interrelations

A field experiment employing the rice cultivars Qyou6 and Yixiangyou2115 as materials and different nitrogen application rates was conducted in Huangping County, Guizhou Province in 2019 to determine the effects of nitrogen application rate on photosynthetic pigments, leaf fluorescence characteristics, yield, and their interrelations in indica hybrid rice. The results showed that photosynthetic pigment contents generally increased with increasing nitrogen application rate. As the nitrogen rate increased, the maximal quantum yield of PSII (Fv/Fm), actual quantum yield of PSII (ΦPSII), and relative electron transfer rate at PSII (ETR) first decreased and then increased at the booting stage; Fv/Fm and ΦPSII decreased while ETR first increased and then decreased at the heading stage; nevertheless, Fv/Fm and ΦPSII first decreased and then increased but ETR was just the opposite at the maturity stage. Non-photochemical quenching coefficient (qN) and quantum yield of regulatory energy dissipation at PSII (Y(NPQ)) first increased and then decreased whereas quantum yield of non-regulatory energy dissipation at PSII (Y(NO)) first decreased and then increased at the booting, heading, and maturity stages with increasing nitrogen application rate. Photochemical quenching coefficient (qP) showed an increasing trend as the nitrogen rate increased in the range of 150–300 kg/ha at the heading and maturity stages. Photosynthetic pigments, leaf fluorescence characteristics, and yield and its components were significantly correlated. First, chlorophylls a and b were significantly negatively correlated with Fv/Fm while significantly positively correlated with qP at the heading stage. Secondly, Carotenoids were significantly positively correlated with the effective panicle number (EPN) at the booting stage while significantly negatively correlated with the spikelets per panicle (SPP) at the heading stage. Chlorophyll a and carotenoids were significantly positively correlated with EPN but significantly negatively correlated with spikelet filling (SF) at the maturity stage. In addition, qP was significantly negatively correlated with EPN at the booting stage. At the heading stage, Fv/Fm and Y(NO) were significantly negatively correlated with EPN and SPP, respectively, and Fv/Fm and ΦPSII were significantly positively related to SF. Moreover, qP was extremely significantly positively related to EPN whereas Fv/Fm was extremely significantly negatively correlated with grain yield at the maturity stage. Appropriate nitrogen application rates can enhance photosynthetic pigment contents, improve the photochemical efficiency and proportion of the open part of the reaction center of PSII, and promote the quantum efficiency and self-protection ability of PSII, thereby increasing photosynthetic efficiency and yield. Under the conditions adopted in this experiment, a parabolic relationship was observed between the nitrogen application rate and grain yield. The regression analysis results showed that the best nitrogen application rate of indica hybrid rice is 168.16 kg ha−1 and the highest yield is 11,804.87 kg ha−1.

Levels of Lead, Copper, and Zinc in Cabbage (Brassica oleracea sp.) and Lettuce (Lactuca sativa sp.) Grown on Soil Amended with Sewage Sludge.

The study focused on levels of selected heavy metals (Pb, Zn, and Cu) in sewage sludge, soil, and in lettuce and cabbage grown on sewage sludge amended soil. Also, the effect of sewage sludge on soil properties (pH, soil organic matter, and soil conductivity) was studied. Three treatments were used based on nitrogen application rates of the sewage sludge: 100, 150, and 200 kg N/ha for lettuce while 160, 210, and 260 kg N/ha for cabbage. A pot experiment was conducted with pots arranged in a completely randomized design and under local climatic conditions. The study revealed that soil organic matter content and conductivity increased significantly with increasing nitrogen application rates. Levels of heavy metals in the soil increased significantly with increasing application rates. The controls for both plants recorded the lowest heavy metal uptake. Cabbage had an uptake of 0.48 ± 0.13, 1.36 ± 0.23, and 2.60 ± 0.29 mg/kg for Pb, Zn, and Cu, respectively, while lettuce had 0.34 ± 0.19, 1.35 ± 0.31, and 2.30 ± 0.14 mg/kg uptake for Pb, Zn, and Cu, respectively. Highest metal uptake was recorded at the highest application rate in both plants (0.66 ± 0.17, 2.66 ± 0.09, and 4.33 ± 0.14 mg/kg for Pb, Zn, and Cu, respectively, for cabbage and 0.54 ± 0.01, 2.24 ± 0.17, and 3.88 ± 0.19 mg/kg of Pb, Zn, and Cu, respectively, for lettuce). The uptake of Zn and Cu was significant, while Pb uptake was insignificant for both plants. Yields increased significantly with increasing application rates. The study provides information on yield enhancement resulting from cultivating plants on soil amended with sewage sludge and the associated health risk implication.

Economical nitrogen application rate of winter wheat under rice-wheat rotation in the Yangtze River basin of China

To promote the rational application of nitrogen fertilizer for winter wheat under rice-wheat rotation in the Yangtze River Basin, we examined the effects of nitrogen application rates (0, 120, 210, 300 kg·hm-2, expressed as N0, N1, N2, and N3 respectively) on soil nitrate content, nitrogen balance of soil-plant system and yield. The results showed that soil nitrate content increased with increasing nitrogen application rates. Under different nitrogen application treatments, all the nitrate was significantly transfered to the 60 cm soil layer till jointing stage. After jointing stage, topdressing nitrogen significantly increased nitrate content in 0-40 cm soil layer under N1 and N2 treatments and that in the 0-60 cm soil layer under N3 treatment. Soil nitrate mainly accumulated in the 0-40 cm soil layer in the mature stage. Results from nitrogen balance analysis showed that nitrogen absorption, residue and loss varied across different growth stages of wheat, with the period from overwintering to jointing being the principal time of apparent nitrogen loss. The amount of plant nitrogen accumulation, inorganic nitrogen residue and soil nitrogen apparent loss all positively correlated with the nitrogen application rate. Based on the comprehensive analysis through Coase principle and marginal revenue of environmental economics, the optimum nitrogen application rate for production, ecology and economic benefits of winter wheat under rice-wheat rotation was 250 kg·hm-2, and the ratio of base fertilizer to jointing fertilizer was 5:5, while the corresponding grain yield was 6840 kg·hm-2.

Monitoring leaf nitrogen concentration and nitrogen accumulation of double cropping rice based on crop growth monitoring and diagnosis apparatus

To verify the accuracy and adaptability of crop growth monitoring and diagnosis apparatus (CGMD) in monitoring nitrogen nutrition index of double cropping rice, we established a monitoring model of leaf nitrogen concentration (LNC) and leaf nitrogen accumulation (LNA) for double cropping rice based on CGMD. Eight early and late rice cultivars were selected and four nitrogen application rates were set up. The differential vegetation index (DVI), normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) were collected using CGMD. Meanwhile, ASD FH2 high spectrometer was used to collect canopy spectral reflectance and calculated DVI, NDVI, and RVI. To verify the accuracy of CGMD, we compared the canopy vegetation indices change characteristics collected by CGMD and ASD FH2. The CGMD-based monitoring models of LNC and LNA were established, which was tested with independent field data. The results showed that LNC, LNA, DVI, NDVI and RVI of early and late rice increased with increasing nitrogen application rate, and increased first and then decreased with the advance of growth progress. The determination coefficient (R2) of fitting for DVI, NDVI and RVI from CGMD and ASD FH2 were 0.9350, 0.9436 and 0.9433, respectively. This result indicated that the measurement accuracy of CGMD was high, and that the CGMD could be used to replace ASD FH2 to measure canopy vegetation indices of early and late rice. Compared with the three canopy vegetation indices based on CGMD, the correlation between NDVICGMD and LNC and that between RVICGMD and LNA was the highest. The exponential model based on NDVICGMD could be used to accurate estimate LNC with the R2 in the range of 0.8581-0.9318, and the root mean square error (RMSE), relation root mean square error (RRMSE) and correlation coefficient (r) of model validation in the range of 0.1%-0.2%, 4.0%-8.5%, and 0.9041-0.9854, respectively. The power function model based on RVICGMD could be used to estimate LNA with the R2 in the range of 0.8684-0.9577, and the RMSE, RRMSE and r of model validation in the range of 0.37-0.89 g·m-2, 6.7%-20.4% and 0.9191-0.9851, respectively. Compared with the chemical testing method, using the CGMD could conveniently and accurately measure LNC and LNA of early and late rice, which had a potential to be widely applied for high yield and high efficiency cultivation and precise management of nitrogen fertilizer in double cropping rice production.