High Nitrogen Application Research Articles

Relationships between the appearance quality and starch structure of soft rice under different nitrogen levels

AbstractThis study aims to explore the formation mechanism of starch structure and the relationships between the appearance quality and starch structure of soft rice under different nitrogen levels. We comprehensively investigated the physiological aspects, starch structure variations, and appearance quality of soft rice in response to different nitrogen applications. The results showed that under the moderate nitrogen application (270 N), the soft rice exhibited the highest AGPase activity, the highest large‐starch granule content, and the lowest chalkiness. Under the highest nitrogen application (360 N), the soft rice exhibited the highest GBSS and DBE activity and the lowest SBE activity, the highest content of long‐branched amylopectin, the lowest relative crystallinity, the fewest ordered structures, the most amorphous structures, the largest semi‐crystalline lamellar thicknesses, and the highest transparency of chalk‐free rice. In conclusion, moderate nitrogen fertilization (270 N) improved the AGPase activity, which leaded to fuller starch granules and more compact endosperm in soft rice. Thus, the grain chalkiness of soft rice decreased. Continuous nitrogen application (0‐360 N) constantly increased the GBSS and DBE activity and reduced the SBE activity in soft rice, leading a lower content of short‐branched amylopectin and a higher content of long‐branched amylopectin in soft rice. Thus, the relative crystallinity and ordered structures of soft rice were reduced. These structures improved the transparency phenotype of soft rice.

High nitrogen application in maize enhances insecticide tolerance of the polyphagous herbivore Spodoptera litura by induction of detoxification enzymes and intensification of cuticle

Nitrogen (N) is one of the most intensively used fertilizers in cropping system and could exert a variety of bottom-up effects on the ecological fitness of herbivores. However, the effects of increased N inputs on insect pesticide tolerance have not been comprehensively understood. Bioassays showed that high N (HN) applied to maize plants significantly increased larval tolerance of Spodoptera litura to multiple insecticides. Activities of detoxification enzymes were significantly higher in the larvae fed on maize plants supplied with HN. RNA-seq analysis showed that numerous GST and cuticle-related genes were induced in the larvae fed on HN maize. RT-qPCR analysis further confirmed four GST genes and larval-specific cuticle gene LCP167. Furthermore, when injected with dsRNA specific to GSTe1, GSTs5, and LCP167, the mortality of larvae treated with methomyl was about 3-fold higher than that of dsGFP-injected larvae. Electron microscope observation showed that cuticle of the larvae fed on HN maize was thicker than the medium level of N. These findings suggest that increased application of N fertilizer enhances insecticide tolerance of lepidopteran pests via induction of detoxification enzymes and intensification of cuticle. Thus, overuse of N fertilizer may increase pest insecticide tolerance and usage of chemical insecticides.

Effect of Ridge–Furrow with Plastic Film Mulching System and Different Nitrogen Fertilization Rates on Lodging Resistance of Spring Maize in Loess Plateau China

The ridge–furrow with plastic film mulching (RF) system has been widely adopted in rain-fed crop planting due to its potential to enhance crop yield and water use efficiency. However, the impact of the RF system on maize lodging resistance, particularly when nitrogen fertilizer is applied, remains uncertain. Therefore, a two-year field experiment was carried out with two planting systems (FP: flat planting and RF) and two nitrogen application rates (N180: 180 kg·N ha−1 and N300: 300 kg·N ha−1) to assess the risk of lodging in maize. The results showed that compared to FP, RF resulted in a significant increase of 78.7% in lodging rate. In addition, the lodging rate increased by 22.6% with increasing nitrogen fertilizer application. The lignin content increased by 43.4%, while the stalk bending strength rose by 42.5%, under RF compared to the FP system. These improvements in the mechanical properties of maize stalks contributed to the improved lodging resistance index of RF, which was found to be approximately 21.3% higher than that of FP. In addition, high nitrogen application rates increased the risk of lodging for different planting patterns over two years. In conclusion, fertilization of spring maize with 300 kg·N ha−1 under the RF system led to higher yields but increased lodging rates. The risk of lodging should be considered when planting maize under the RF system. The results of this study can provide scientific basis and technical support for the optimization of rain-fed maize cultivation measures in the Loess Plateau.

Effects of Applying Different N Sources on Cd Accumulation, Mineral Micronutrients, and Grain Yield of Durum Wheat

This study aimed to investigate the effects of different nitrogen sources on Cd concentration in durum wheat grains in soils with low and high Cd contamination. Triticum turgidum L. durum, cv. Balcali-2000 was sown as test plant material in plastic pots containing 3.2 kg of soil. Low (0.5) and high Cd (5.0 mg Cd kg− 1 soil) were added to the culture media in the form of 3(CdSO4).8H2O. Nitrogen was also added in the form of Ca(NO3)2.4 H2O in low, sufficient, and high concentrations. In addition, a foliar application of 0.5% urea was used as a further nitrogen supply. The results showed that the total nitrogen content and the Cd concentration of the grains increased with increasing nitrogen application. This increase was more pronounced with a combination of soil nitrogen and foliar urea. While the Cd concentration in the grains was 354 µg kg− 1 at low soil Cd concentration and insufficient nitrogen supply, the Cd concentration in the grains increased by 40% to 498 µg kg− 1 at low Cd concentration and high nitrogen supply. This increase in Cd concentration in the grains was 32% higher under high nitrogen applications than at high Cd-insufficient conditions. In addition, foliar application of urea to durum wheat leaves at low soil Cd concentrations increased the Cd concentration in the grains from 354 µg kg− 1 to 484 µg kg− 1. This study showed that different treatments and amounts of nitrogen sources can affect the uptake and accumulation of Cd in wheat grains at different Cd levels.

Effect of Different Spacing and Nutrient Management on Growth and Yield of Maize: A Review

Optimal plant density influenced by crop geometric/planting techniques factors are crucial in achieving high yield to maize. In addition, nutrient management further enhances productivity. Increasing plant density can lead to higher grain yield per unit area, but it also reduces the yield per individual plant as the competition between plant to plant will increase. From different research it indicates that plant density lower than the optimum number result in higher productivity rate per plant but lower yield per area unit. After reviewing various research articles, it was concluded that the maximum growth and yield attributes of maize obtained with spacing 60: 20-30 cm. Highest nitrogen application up to 160 kg N per ha-1 by split application at sowing, 25 DAS and tasselling is most reliable to increase the maize productivity. The combined application of 70 kg ha-1 phosphorus and 60 kg ha-1 potassium is the most suitable to obtain the maximum growth and yield attributes such as plant height, number of leaves per plant, cob length, cobs per plant, dry matter accumulation and crop growth rate. Effective nutrient management, aligned with proper planting density, played a pivotal role in maximizing maize productivity, meeting the demands of a growing population, and contributing to sustainable agriculture.

Impact of Nitrogen and Silicon Amendments on Hopper Population in Rice

Present study showed that total dry weight values of rice plants were significantly higher in the plant with high nitrogen (N) application (100kg/ ha) as compared to low nitrogen (30 kg/ ha) treatment whereas the silicon (Si) amendment had very little effect on biomass accumulation but both the elements are associated with hopper pest population densities in rice. Here the correlation coefficient values were high- r= 0.759 to 0.999 and r= 0.726 to 0.996 for brown planthopper Nilaparvata lugens (Stål) and green leafhopper Nephotettix virescens (Dist.) respectively when the calculation was made between insect population and plant biomass after application of nitrogen 0 to 100 kg/ ha. However, when calcium silicate was added 140 kg/ ha or above with high doses of nitrogen the N. lugens and N. virescens incidence reduced in comparison to others. Consequently, the interaction between nitrogen and silicon play a significant role in resistance to these hopper pests.

Root Reduction Caused Directly or Indirectly by High Application of Nitrogen Fertilizer Was the Main Cause of the Decline in Biomass and Nitrogen Accumulation in Citrus Seedlings.

Citrus is the largest fruit crop around the world, while high nitrogen (N) application in citrus orchards is widespread in many countries, which results not only in yield, quality and environmental issues but also slows down the establishment of citrus canopies in newly cultivated orchards. Thus, the objective of this study was to investigate the physiological inhibitory mechanism of excessive N application on the growth of citrus seedlings. A pot experiment with the citrus variety Orah (Orah/Citrus junos) at four N fertilization rates (0, 50, 100, and 400 mg N/kg dry soil, denoted as N0, N50, N100, and N400, respectively) was performed to evaluate the changes of root morphology, biomass, N accumulation, enzyme activities, and so on. The results showed that the N400 application significantly reduced the total biomass (from 14.24 to 6.95 g/Plant), N accumulation (from 0.65 to 0.33 g/Plant) and N use efficiency (92.69%) in citrus seedlings when compared to the N100 treatment. The partial least squares pathway model further showed that the decline of biomass and N accumulation by high N application were largely attributed to the reduction of root growth through direct and indirect effects (the goodness of fit under the model was 0.733.) rather than just soil N transformation and activity of root N uptake. These results are useful to optimize N management through a synergistic N absorption and utilization by citrus seedlings.

Effects of different nitrogen applications and straw return depth on straw microbial and carbon and nitrogen cycles in paddy fields in the cool zone

Straw is an important source of organic fertilizer for soil enrichment, however, the effects of different nitrogen(N) application rates and depths on straw decomposition microorganisms and carbon and nitrogen cycling under full straw return conditions in cool regions of Northeast China are not clear at this stage. In this paper, we applied macro-genome sequencing technology to investigate the effects of different N application rates (110 kg hm−2, 120 kg hm−2, 130 kg hm−2, 140 kg hm−2, 150 kg hm−2) and depths (0–15 cm, 15–30 cm) on straw decomposing microorganisms and N cycling in paddy fields in the cool zone of Northeast China. The results showed that (1) about 150 functional genes are involved in the carbon cycle process of degradation during the degradation of returned straw, of which the largest number of functional genes are involved in the methane production pathway, about 42, the highest abundance of functional genes involved in the citric acid cycle pathway. There are 22 kinds of functional genes involved in the nitrogen cycle degradation process, among which there are more kinds involved in nitrogen fixation, with 4 kinds. (2) High nitrogen application (150 kg hm−2) inhibited the carbon and nitrogen conversion processes, and the abundance of straw-degrading microorganisms and nitrogen-cycling functional genes was relatively high at a nitrogen application rate of 130 kg hm−2. (3) Depth-dependent heterogeneity of the microbial community was reduced throughout the vertical space. At 71 days of straw return, the nitrogen cycling function decreased and some carbon functional genes showed an increasing trend with the increase of straw return depth. The nitrogen cycle function decreased with the increase of straw returning depth. The microbial community structure was best and the abundance of functional genes involved in the nitrogen cycling process was higher under the conditions of 0–15 cm of returning depth and 130 kg hm−2 of nitrogen application.

Moderate nitrogen application facilitates Bt cotton growth and suppresses population expansion of aphids (Aphis gossypii) by altering plant physiological characteristics.

Excessive application of nitrogen fertilizer in cotton field causes soil and water pollution as well as significant increase of aphid population. Reasonable fertilization is an important approach to improve agricultural production efficiency and reduce agriculture-derived pollutions. This study was aimed to explore the effects of nitrogen fertilizer on the Bt cotton physiological characteristics and the growth and development of A. gossypii, a sap-sucking cotton pest. Five different levels of Ca(NO3)2 (0.0 g/kg, 0.3 g/kg, 0.9 g/kg, 2.7 g/kg and 8.1 g/kg) were applied into vermiculite as nitrogen fertilizer in order to explore the effects of nitrogen fertilizer on the growth and development of Bt cotton and aphids. The results showed that the medium level of nitrogen fertilizer (0.9 g/kg) effectively facilitated the growth of Bt cotton plant and suppressed the population expansion of aphids, whereas high and extremely high nitrogen application (2.7 and 8.1 g/kg) significantly increased the population size of aphids. Both high and low nitrogen application benefited aphid growth in multiple aspects such as prolonging nymph period and adult lifespan, enhancing fecundity, and improving adult survival rate by elevating soluble sugar content in host Bt cotton plants. Cotton leaf Bt toxin content in medium nitrogen group (0.9 g/kg) was significantly higher than that in high (2.7 and 8.1 g/kg) and low (0.3 g/kg) nitrogen groups, but Bt toxin content in aphids was very low in all the nitrogen treatment groups, suggesting that medium level (0.9 g/kg) might be the optimal nitrogen fertilizer treatment level for promoting cotton seedling growth and inhibiting aphids. Overall, this study provides insight into trophic interaction among nitrogen fertilizer levels, Bt cotton, and cotton aphid, and reveals the multiple effects of nitrogen fertilizer levels on growth and development of cotton and aphids. Our findings will contribute to the optimization of the integrated management of Bt cotton and cotton aphids under nitrogen fertilization.

Effect of Crop Establishment Methods and Nitrogen Levels on Phenology, Quality, Nutrient Content and Uptake of Coarse Rice

A field experiment was conducted during the kharif season of 2020 at the farm of College of Agriculture, Kaul (Kaithal) of CCS Haryana Agricultural University, Hisar. The objective of the experiment was to study the response of a short-duration non-scented rice variety called HKR-48 to nitrogen fertilization under two different methods of crop establishment. The experiment followed a randomized complete block design (RBD) factorial design with the two establishment methods (direct seeding and transplanting) as main plot treatments and six levels of nitrogen (0, 30, 60, 90, 120, and 150 kg/ha) as sub-plot treatments, with three replications. The results of the experiment showed that the transplanted crop took longer to initiate tillering, anthesis (flowering), and reached maturity slightly earlier compared to the direct-seeded crop. However, both establishment methods showed similar timing for panicle emergence. The methods of crop establishment did not have a significant effect on kernel length, kernel breadth, NPK content, and protein content of the grains. However, the transplanted crop had improved hulling, milling, and head rice recovery compared to the direct-seeded crop. With increasing nitrogen levels, there was a delay in the days taken to attain tillering, panicle emergence, anthesis, and physiological maturity, following a graded response. The kernel length and breadth were not influenced by the graded doses of nitrogen. However, the quality parameters such as hulling, milling, head rice recovery, and protein content of the grains improved significantly with increasing nitrogen levels. The phosphorus (P) and potassium (K) content in the grain and straw remained unaffected by the different nitrogen doses, except for nitrogen content. The uptake of NPK by the crop (grain and straw) showed an increasing trend with higher nitrogen application

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

ABSTRACT Although significant differences in soil nitrogen levels exist under different paddy-upland rotations, the main reason for this is unclear. The nitrogen retention capacity and loss of ammonia volatilisation, leaching, etc. of paddy soil with large differences in nitrogen levels from two long-term rotations, garlic-rice and wheat-rice, were measured using the soil column simulation method. The results showed that the loss rate of leaching was only 5.4%, whereas that of ammonia volatilisation was up to 22.8%, which was the main nitrogen loss way of paddy soil under the two rotations. The average ammonia volatilisation rates under wheat-rice rotation with high and low nitrogen application rates were 12.1% and 40.2% higher than that under garlic-rice rotation, leading to a decrease in the total nitrogen loss amount and rate through ammonia volatilisation by 29.8% and 8.8%, respectively. As a result, nitrogen retention in the soil under garlic-rice rotation increased by 12.7%. In conclusion, the long-term garlic-rice rotation could significantly inhibit ammonia volatilisation, thus improving the soil nitrogen retention capacity. The straw return may increase soil organic matter content, reduce ammonia volatilisation loss, and enhance soil nitrogen retention capacity and productivity.

An appropriate ammonium: nitrate ratio promotes the growth of centipedegrass: insight from physiological and micromorphological analyses.

Reasonable nitrogen fertilizer application is an important strategy to maintain optimal growth of grasslands, thereby enabling them to better fulfil their ecological functions while reducing environmental pollution caused by high nitrogen fertilizer production and application. Optimizing the ammonium (NH4 +):nitrate (NO3 -) ratio is a common approach for growth promotion in crops and vegetables, but research on this topic in grass plants has not received sufficient attention. Centipedegrass, which is widely used in landscaping and ecological protection, was used as the experimental material. Different NH4 +:NO3 - ratios (0: 100, 25:75, 50:50, 75:25, 100:0) were used as the experimental treatments under hydroponic conditions. By monitoring the physiological and morphological changes under each treatment, the appropriate NH4 +:NO3 - ratio for growth and its underlying mechanism were determined. As the proportion of ammonium increased, the growth showed a "bell-shaped" response, with the maximum biomass and total carbon and nitrogen accumulation achieved with the NH4 +:NO3 - ratio of 50:50 treatment. Compared with the situation where nitrate was supplied alone, increasing the ammonium proportion increased the whole plant biomass by 93.2%, 139.7%, 59.0%, and 30.5%, the whole plant nitrogen accumulation by 44.9%, 94.6%, 32.8%, and 54.8%, and the whole plant carbon accumulation by 90.4%, 139.9%, 58.7%, and 26.6% in order. As a gateway for nitrogen input, the roots treated with an NH4 +:NO3 - ratio of 50:50 exhibited the highest ammonium and nitrate uptake rate, which may be related to the maximum total root length, root surface area, average root diameter, root volume, and largest root xylem vessel. As a gateway for carbon input, leaves treated with an NH4 +:NO3 - ratio of 50:50 exhibited the highest stomatal aperture, stomatal conductance, photosynthetic rate, transpiration rate, and photosynthetic products. The NH4 +:NO3 - ratio of 50:50 treatment had the largest stem xylem vessel area. This structure and force caused by transpiration may synergistically facilitate root-to-shoot nutrient translocation. Notably, the change in stomatal opening occurred in the early stage (4 hours) of the NH4 +:NO3 - ratio treatments, indicating that stomates are structures that are involved in the response to changes in the root NH4 +:NO3 - ratio. In summary, we recommend 50:50 as the appropriate NH4 +:NO3 - ratio for the growth of centipedegrass, which not only improves the nitrogen use efficiency but also enhances the carbon sequestration capacity.

Microbial regulation of aggregate stability and carbon sequestration under long-term conservation tillage and nitrogen application

The stability of aggregates plays a significant role in soil organic carbon (SOC) sequestration in conservation agriculture soils. However, the regulation of microorganisms within aggregates on aggregate stability and SOC sequestration remains elusive. By dividing the soil into three aggregate size classes [mega-aggregates (>2000 μm), macro-aggregates (250–2000 μm), and micro-aggregates (<250 μm)], we evaluated the response of aggregate stability, SOC and microbial communities within aggregates to long-term conservation tillage, which consisted of two tillage methods (conventional tillage and no-tillage) and three nitrogen application rates (105, 180, and 210 kg N ha−1). Under no-tillage treatment, high nitrogen application rate increased SOC by 2.1–3.7 g·kg−1 within mega- and macro-aggregates but reduced the total amount of phospholipid fatty acids (PLFAs) within all aggregates. Under conventional tillage, high N application rate increased mean weight diameter (MWD) and reduced total PLFAs within all aggregates only in 0–10 cm. With the same nitrogen application rate, no-tillage increased MWD by 8.7 %–42.7 %, SOC content within mega-aggregates by 7.3 %–27.8 % and within macro-aggregates by 13.2 %–28.3 % when compared with conventional tillage. Actinobacteria were recruited by straw under no-tillage and their biomass increased 1.5–7.8 times in all aggregates compared with conventional tillage, where they might participate in aggregate formation via degradation of straw and increasing SOC within mega- and macro-aggregates. Conversely, desulfovibrio biomass within all aggregates was diminished under no-tillage compared with conventional tillage, while desulfovibrio possibly directly inhibited soil aggregate formation and decreased SOC within mega- and macro-aggregates under conventional tillage. Moreover, under no-tillage, arbuscular mycorrhizal fungi biomass increased by 0.4–1.6 nmol g−1 within all aggregates compared with conventional tillage in 0–10 cm, potentially indirectly contributing to soil aggregate formation via co-metabolic processes and increasing SOC within mega- and macro-aggregates. Overall, high nitrogen application under long-term no-tillage protects SOC within mega-aggregates by altering aggregate formation through the microbial communities, providing information that may be useful in developing management strategies to enhance carbon sequestration in agricultural soils.

Potential Risk Identification of Agricultural Nonpoint Source Pollution: A Case Study of Yichang City, Hubei Province

Potential risk identification of agricultural nonpoint source pollution (ANPSP) is essential for pollution control and sustainable agriculture. Herein, we propose a novel method for potential risk identification of ANPSP via a comprehensive analysis of risk sources and sink factors. A potential risk assessment index system (PRAIS) was established. The proposed method was used to systematically evaluate the potential risk level of ANPSP of Yichang City, Hubei Province. The potential risk of ANPSP in Yichang City was 18.86%. High-risk areas account for 4.95% and have characteristics such as high nitrogen and phosphorus application rates, large soil erosion factors, and low vegetation coverage. Compared with the identification results of the Diffuse Pollution estimation with the Remote Sensing (DPeRS) model, the area difference of the same risk level calculated by the PRAIS was reduced by 33.9% on average. This indicates that PRAIS has the same level of accuracy as the DPeRS model in identifying potential risks of ANPSP. Thus, a rapid and efficient identification system of potential risks of regional ANPSP was achieved.

Responses of wheat nitrogen uptake and utilization, rhizosphere bacterial composition and nitrogen-cycling functional genes to nitrogen application rate, planting density and their interactions

The nitrogen application rate and planting density affect soil physiochemical properties, plant physiological characteristics, and soil bacterial community composition. In this study, a two-factor randomized block design was adopted with two planting density levels (high density, HD and low density, LD), and three nitrogen application rate levels (no nitrogen application, N0, low nitrogen application, LN and high nitrogen application, HN). The results showed that the highest yield was produced by LDHN and HDLN, while HDLN had the highest nitrogen use efficiency. Root dry weight was highest in HDHN, followed by HDLN, LDHN and LDLN, while the root nitrogen content was highest in LDHN and HDLN. In the 0–20 cm soil, LDLN had the highest pH and lowest nitrate nitrogen content, HDHN had the lowest pH, and HDLN had the highest content of soluble organic nitrogen and free amino acids. In addition, compared to LDHN, the bacterial community in HDLN and LDLN had higher α diversity and a higher relative abundance of functional genes involved in nitrate reduction. However, HDHN was the opposite. Additionally, correlation analysis also found that the abundance of some bacterial modules was significantly correlated with wheat nitrogen partial factor productivity. Overall, nitrogen application rates and planting density, through changing the physicochemical properties of rhizosphere soil, bacterial composition and function, and wheat root physiological properties, changed the nitrogen utilization and yield of wheat.

Productivity and water use efficiency of summer soybean-winter wheat rotation system under limited water supply in the North China Plain

Development of novel crop rotations with superior water- and N-use efficiency will be fundamental in the quest for securing sustainable food supplies under environments that are increasingly resource limited. Here, our aim was to examine how replacing maize with soybean as part of winter wheat rotations impacted the nutrient-equivalent yield (EY), evapotranspiration (ET) and water-use efficiency (WUE) of rotation systems. We contrasted summer soybean-winter wheat (SW) and summer maize-winter wheat (MW) cropping systems under three nitrogen (N) fertilization regimes: no, medium, and high nitrogen application rates (0 N, MN, and HN, respectively). Results showed that SW not only resulted in lower annual yields, but also caused more variable inter-annual wheat productivity compared with MW. SW had similar annual productivities to MW in wet (2019–2020) and dry (2020–2021) years, but lower productivity than MW in an average precipitation year (45% reduction, 2018–2019). As well, SW had higher average annual ETs (633–854 mm) than MW, mainly was attributed to higher ETs (268–440 mm) in summer. SW reduced WUEs by 17% and 28% in average (2018–2019) and dry (2020–2021) years, respectively. Regardless of cropping system, N fertilization increased annual EYs and ETs by 10–18% and 5–18% compared with no fertilization, respectively. Together these comparable increments in EY and ET, we found that N fertilization had rare effects on annual WUE of both systems. Overall, our study demonstrated that replacing maize with soybean in winter wheat rotations increased annual ET and neither maintained productivity nor improved water productivity. Thus, we suggest that practitioners explore other drought tolerant grain legumes to generate more reliable yields and less water consumption under legume-based crop rotations.

Varietal responses of root characteristics to low nitrogen application explain the differing nitrogen uptake and grain yield in two rice varieties.

Rice root characteristics are tightly associated with high-efficient nitrogen uptake. To understand the relationship of root plastic responses with nitrogen uptake when reducing nitrogen application for green rice production, a hydroponic experiment and a soil pot experiment were conducted under high (HN) and low (LN) nitrogen applications, using two rice (Oryza sativa L.) varieties, NK57 and YD6, three nitrogen absorption traits (total nitrogen accumulation, net NH4 + influx on root surface, nitrogen uptake via apoplasmic pathway) and root characteristics were investigated. In comparison with HN, LN significantly reduced nitrogen absorption and grain yield in both varieties. Concomitantly, there was a decrease in total root length, root surface area, root number, root volume, and root cortical area under LN, while single root length, root aerenchyma area, and root lignin content increased. The expression of OsAMT1;1 and OsAMT1;2 down-regulated in both varieties. The findings revealed that YD6 had smaller reduction degree for the three nitrogen absorption traits and grain yield, accompanied by smaller reduction degree in total root length, root surface area, root cortical area, and expression of the two genes under LN. These root characteristics were significantly and positively correlated with the three nitrogen absorption traits and grain yield, especially under LN. These results indicate that a large root system, lower reduction degree in several root characters, and high expression of OsAMT genes in YD6 explains its high nitrogen accumulation and grain yield under reduced nitrogen application. The study may provide rationale for developing varieties with low nitrogen fertilizer requirements for enabling green rice production.

Effect of Nitrogen Management on Wheat Yield, Water and Nitrogen Utilization, and Economic Benefits under Ridge-Furrow Cropping System with Supplementary Irrigation

Supplemental irrigation under a ridge-furrow (RF) cropping system is a valuable cropping practice that balances resource efficiency and high crop yield. However, the effects of nitrogen management on crop growth, yield formation, and economic benefits under RF systems have not been clearly investigated. In this study, the experiment was designed with three experimental factorials, including three cropping systems (RF, RF cropping with 80 mm irrigation; TF1, traditional flat cropping with 200 mm irrigation; and TF2, traditional flat cropping with 80 mm irrigation), two nitrogen application rates (NL, 180 kg N ha−1; NH, 240 kg N ha−1), and two fertilizer application models (B, all nitrogen fertilizers were applied basally at the pre-sowing stage; BT, nitrogen fertilizer was applied at both the pre-sowing and jointing stages at a ratio of 1:1). A two-year field experiment was conducted to investigate the effects of nitrogen fertilizer management on wheat yield, water and nitrogen utilization, and economic benefits under the RF cropping system. The results showed that the RF system significantly increased the soil moisture content and improved the water productivity (WP) and grain yield of wheat. Nitrogen reduction (NL) under the RF system did not affect the water use of the wheat compared with traditional high nitrogen application (NH) but increased the nitrogen uptake and fertilizer productivity of the wheat. Although NL led to a reduction in aboveground dry matter accumulation, it did not significantly affect the yield of wheat but increased the net income of wheat cultivation. Under NL conditions, the BT nitrogen application model promoted nitrogen uptake in wheat and ameliorated the reduction in grain protein content due to plastic film mulching, and this model is an integrated planting practice that trades off wheat yield and quality. These findings suggest that NLBT is a promising and recommendable cropping practice under RF systems considering resource utilization, high yield and quality, and economic efficiency.

Improving Wheat Grain Yield and Nitrogen Use Efficiency by Optimizing the Fertigation Frequency Using Center Pivot Irrigation System

High efficient nitrogen (N) application method and proper N management strategies can further reduce the losses and enhance N use efficiency. Field experiments were conducted in the 2015–2016 and 2016–2017 growing seasons to evaluate the effects of four fertigation frequencies treatments (FT-1: all the topdressing N was applied at the jointing stage; FT-2: 67% and 33% of the topdressing N was applied at the jointing and filling stages; FT-3: 33%, 50% and 17% of the topdressing N was applied at the regreening, jointing and filling stages; FT-4: 33%, 33%, 17% and 17% of the topdressing N were applied at the regreening, jointing, anthesis and filling stages) on wheat yield, water use efficiency (WUE), partial productivity of N fertilizer (PFPN) and N harvest index (NHI). In addition, one-time topdressing by surface broadcasting at the jointing stage was set up as a control (BC-1). The results showed that FT-3 and FT-4 supplied sufficient NO3−-N in the 0–40 cm soil layer, which reduced the risk of soil NO3−-N leaching to the deeper layers. FT-4 had the highest grain yield, WUE, PFPN and NHI, with average values of 9153.4 kg ha−1, 2.1 kg m−3, 0.74 kg kg−1 and 31.3 kg kg−1, respectively, followed by these values corresponding to the FT-3 in two years. These findings suggest that topdressing N split with 3–4 times, that is to say applying approximately 16.7% of topdressing N in anthesis and filling stages, respectively by the center pivot fertigation method can significantly improve yield, WUE, PFPN and NHI.

Effects of Urea Application on Soil Organic Nitrogen Mineralization and Nitrogen Fertilizer Availability in a Rice–Broad Bean Rotation System

Rice cultivation is facing a situation where rice production stagnates while nitrogen fertilizer (NF) application continues to increase. The effectiveness of the NF residues from the rice season on the growth of rotating broad beans is unclear. High NF use in rice cultivation also affects the nitrogen supply through soil organic nitrogen (SON) mineralization (SONM). However, the rules of SONM and the NF availability in the rice–broad bean rotation system (RBRS) are unknown. A field trial of the RBRS was conducted using 15N-labeled urea (CO(15NH2)2) as the partial NF source (15N accounted for 5.3% of the total pure nitrogen applied) for the rice and no NF for the broad bean. It was found that 33.0–38.1% of NF in the rice season was utilized. NF availability was low in the broad bean season (3.6–4.0%). SONM was the most important source, providing approximately 60% of the nitrogen for rice growth. The SONM into mineral nitrogen and the fixation of mineral nitrogen into SON occurred simultaneously, with SONM dominating in most cases. SON content decreased slowly in the rice season and dramatically in the broad bean’s podding stage with a 0.64 g kg−1 (24.1%) decrease. The high nitrogen application in rice season promoted SONM and aggravated groundwater pollution. Soil urease activity, rather than catalase, phosphatase, and invertase activities, can be the main monitoring object of SONM. Furthermore, fungal abundance (especially Aspergillaceae, Neuroceae, and unclassified_o__Helotiales), rather than bacteria, was the primary target for SONM monitoring. It is unreasonable to apply large amounts of NF in the rice season but not in the broad bean season in the RBRS. N1 (135 kg N ha−1) had the best comprehensive benefits regarding crop yield, nitrogen supply by SONM, NF utilization, and nitrogen loss on the environment in the RBRS.