High Nitrogen Application Rates Research Articles

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.

Nitrogen Application Can Optimize Form of Selenium in Soil in Selenium-Rich Areas to Affect Selenium Absorption and Accumulation in Black Wheat.

The composition and form of selenium in the soil have significant effects on the selenium content of crops. In this study, we investigated the selenium absorption pathway in plants by studying the interaction between nitrogen fertilizer and soil selenium. Our results showed that the selenium concentration enrichment factors (CEF) varied within the same region due to nitrogen fertilizer application, where they ranged from 1.33 to 5.02. The soil selenium flow coefficient (mobility factor, MF) increased with higher nitrogen application rates. The sum of the MF values for each soil layer treated with nitrogen application rates of 192 kg hm-2 and 240 kg hm-2 was 0.70, which was 64% higher than that for the control group with no nitrogen application. In the 0-20 cm soil layer, the highest summed water-soluble and exchangeable selenium and relative percentage of total selenium (12.45%) was observed at a nitrogen application rate of 240 kg hm-2. In the 20-40 cm soil layer, the highest relative percentage content of water-soluble and exchangeable selenium and total selenium (12.66%) was observed at a nitrogen application rate of 192 kg hm-2. Experimental treatment of black wheat with various concentrations of sodium selenite showed that selenium treatment at 50 μmol L-1 significantly increased the reduced glutathione (GSH) levels in the leaves and roots of seedlings, where the GSH contents increased by 155.4% in the leaves and by 91.5% in the roots. Further analysis of the soil-black wheat system showed that nitrogen application in selenium-rich areas affected the soil selenium flow coefficient and morphological composition, thereby changing the enrichment coefficient for leaves (0.823), transport capacity from leaves to grains (-0.530), and enrichment coefficient for roots (0.38). These changes ultimately affected the selenium concentration in the grains of black wheat.

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.

Effects of multispecies and monoculture forages on nutrient digestibility and fermentation responses using an in vitro rumen simulation technique (RUSITEC)

Enteric methane (CH4) emissions are a major contributor to global greenhouse gas emissions. A number of different CH4 mitigation strategies have been proposed, and the inclusion of alternative forages into grazing systems could be a practical and feasible option. Multispecies swards comprise a mixture of forage species and can increase grassland productivity, reduce nitrogen fertiliser requirements, and reduce fertiliser-associated nitrous oxide emissions. This study investigated the potential benefit of multispecies swards in reducing ruminal CH4 production. Using the in vitro rumen simulation technique, we compared the effects of different forages (perennial ryegrass, timothy, red clover, white clover, chicory, ribwort plantain and their equi-proportional mixture) on CH4 and gas production, ruminal fermentation parameters and nutrient digestibility. We also compared these responses to perennial ryegrass produced with a higher nitrogen application rate (300 N). The experiment was conducted over 21 d, with the initial 14 d allowed for dietary adaptation. Over the subsequent 7 d, there were significant effects of forage type on CH4 production, ruminal fermentation and digestibility. Ribwort plantain, chicory and white clover showed lower CH4 production; with chicory producing 73% and 57% less CH4 (mmol d−1) compared to 300 N perennial ryegrass and 150 N perennial ryegrass incubation, respectively. Chicory had 72% lower CH4 produced per gram of organic matter digested (mmol g−1) than that of 300 N perennial ryegrass. Chicory and 300 N perennial ryegrass had greater (P < 0.01) organic matter and nutrient digestibility (DM, CP, NDF, and ADF) than other forages. Greater ammonia nitrogen concentration was observed in chicory and both clover species, compared to the other forage species (P < 0.01). In general, the response of the six-species mixture was not significantly different to the average response of the six component monocultures. Thus, from these data, the performance of multispecies swards for these responses (in general) was predictable from the performance of the component monocultures. These results showed that different grassland forages, especially chicory and white clover, have the potential to reduce ruminal CH4 emissions and could be a promising anti-methanogenic alternative to chemical CH4 inhibitors and feed additives. More generally, the relatively wide variation in CH4 abatement potential across a small sample of plant species suggests the merit of wider screening to identify grassland species with high CH4 abatement potential in vitro.

Superior resistance to Phytophthora infestans in new pre-breeding potato clones under different nitrogen fertilisation regimes used in organic agriculture

ABSTRACT Late blight caused by Phytophthora infestans is the most devastating disease for cultivated potatoes, causing considerable financial loss annually due to loss of yield and costs of fungicide applications. For organic farming especially, the strict limitations on the use of fungicides makes research necessary to investigate factors that influence disease severity. Therefore, effects of nitrogen fertiliser rates on leaf and tuber blight in organically grown potato cultivars and pre-breeding clones were evaluated in the present study. It was found that the foliage of the pre-breeding clones was little, or not at all, affected by P. infestans, irrespectively of the nitrogen application rate, while the cultivars reacted differently with mild to strong late blight symptoms. Only some of the clones and cultivars showed increased infection of tubers at the higher nitrogen application rates, whilst most showed no significant differences between the N rates. Overall, the present study showed that the use of new resistant cultivars could be a suitable approach to reduce late blight in organic farming, where soil nitrogen levels may vary due to the use of different forms of nutrient inputs with varying mineralisation rates.

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.

Nitrogen Application Alleviates Impairments for Jatropha curcas L. Seedling Growth under Salinity Stress by Regulating Photosynthesis and Antioxidant Enzyme Activity

Jatropha curcas L. is a promising bioenergy source, and its seedling stage is sensitive to salinity. Nitrogen application presents an effective strategy for alleviating the adverse consequences of salinity stress. However, the responses of plant growth and physiology of Jatropha curcas L. seedlings to nitrogen application under salinity stress remain unclear. As a result, a one-year greenhouse plot experiment was conducted to investigate the effects of nitrogen application on the plant growth, antioxidant enzyme activity, and photosynthesis of Jatropha curcas L. seedlings under saline conditions. Experiment treatments consisted of three salinity stresses (mild salinity stress, S1: 2 g/kg; moderate salinity stress, S2: 4 g/kg; and severe salinity stress, S3: 6 g/kg), four nitrogen application rates (N0: 0 gN/plant; N1: 20 gN/plant; N2: 60 gN/plant; and N3: 100 gN/plant), and a control treatment (CK) which was without salinity stress and nitrogen application. The results showed that salinity stress substantially reduced plant growth of Jatropha curcas L. seedlings. As the salinity stress increased, the reduction in plant growth also increased. The S3 treatment had the lowest leaf area, leaf biomass, and total biomass, which decreased by an average of 70.4%, 66.3%, and 69.9%, respectively, compared to CK. Nitrogen application could compensate for these impairments of plant growth from salinity stress by promoting antioxidant enzyme activity and photosynthesis. As for mild and moderate salinity stresses, the maximum plant growth was found in the N3 treatment, with the maximum antioxidant enzyme activity, photosynthetic pigment, photosynthetic characteristic, and chlorophyll fluorescence. As for severe salinity stress, higher plant growth was found in N2 and N3 treatments, and there were no significant differences between N2 and N3 treatments. It also should be noted that the maximum photosynthetic characteristic and chlorophyll fluorescence were found in N2 treatment under severe salinity stress. In conclusion, nitrogen application could be an alternative strategy to improve the salinity tolerance of Jatropha curcas L. growth. The nitrogen application rate of 100 gN/plant could be recommended for low and moderate salinity stresses, while 60 gN/plant could be recommended for severe salinity stress. However, higher nitrogen application rate (&gt;100 gN/plant) under mild and moderate salinity stress and the effects of reactive oxygen species under salinity stress should be further evaluated.

Effects of long-term organic fertilizer substitutions on soil nitrous oxide emissions and nitrogen cycling gene abundance in a greenhouse vegetable field

Intensive vegetable fields, characterized by extremely high nitrogen (N) application rates, emit a large amount of the potent greenhouse gas nitrous oxide (N2O). Short-term substitution of organic fertilizers for chemical fertilizers may mitigate N2O emissions from vegetable fields. However, the long-term impacts, particularly on soil background N2O emissions (excluding effects caused by newly applied fertilizers) in vegetable fields, remain poorly elucidated. Thus, we conducted an 11-year experiment to investigate the long-term fertilization effects on soil background N2O emissions and the abundance of N-cycling genes in a greenhouse vegetable field. The soil capacity for potential denitrification activity (PDA) was further measured to evaluate denitrification potential. The field experiment comprised of four treatments: no fertilization (control, CK), only chemical N fertilizers (CF), 50 % of chemical N fertilizers substituted by organic fertilizers (OL), and 87.5 % of chemical fertilizers substituted by organic fertilizers (OH). The long-term application of chemical fertilizers alone (CF) and organic fertilizer substitutions (OL and OH) increased soil background N2O emissions 30-fold and 10-fold, respectively, with average N2O fluxes of 1.2 ± 3.8, 33.8 ± 5.1, 9.4 ± 2.3 and 10.2 ± 2.7 μg N2O-N m−2 h−1 in the CK, CF, OL and OH treatment, respectively. The CF treatment significantly decreased the abundance of AOA amoA, nirS and nosZ genes, while both the OL and OH treatments increased the abundance of AOB amoA, and the OH treatment also increased nosZ gene abundance. Soil pH was a key determinant of the contrasting responses of N-cycling genes to different fertilizer types. Compared with low fertilizer substitutions (OL), high organic fertilizer substitutions (OH) did not result in more soil background N2O emissions, despite higher potential denitrification activities and soil total N contents. This was due to increased abundance of nosZ gene and likely enhanced N2O consumption activities. Soil NO3−-N concentrations, soil pH, and the abundance of nosZ gene were three main factors in controlling the responses of soil background N2O emissions to long-term fertilization. Overall, this study suggests that in the long-term perspective organic fertilizer substitution is a beneficial practice to mitigate N2O emissions from intensive greenhouse vegetable cropping systems.

Multispecies forages in the Australian dairy feedbase: is there a biological business case?

This review considers the potential role of multispecies swards in de-risking Australian dairy systems that currently rely heavily on monocultures of perennial ryegrass and high rates of inorganic nitrogen application to be productive. Recent trends in increasing inorganic nitrogen fertiliser prices, societal pressure for increased environmental sustainability of farming practices, coupled with variable and extreme weather events have renewed interest for functionally diverse pasture mixtures. Evidence from the latest international studies either for or against the purported benefits of multispecies swards (e.g. productive, resilient, and environmentally positive) is examined. There is an ever-growing body of evidence confirming that species richness can promote high levels of productivity at low or zero rates of nitrogen fertiliser application, often with increasingly positive effects as species richness increases. However, results within and between different levels of species richness are not always consistent, suggesting that not all multispecies swards will perform alike, even at a constant level of functional diversity. A multitude of other factors is presented that interact to determine the success of one multispecies sward over another. These include soil type and fertility, species choice, functional group proportions, sward management under either grazing or cutting, fertiliser regimes, and grazing management practices. It was concluded that this complexity gives rise to a need for further research into the biological mechanisms behind multispecies mixtures to determine the factors, other than simply species richness, that will guarantee success as more farmers inevitably search for alternatives to perennial ryegrass pasture in the Australian dairy farming industry.

Plastic-shed vegetable cultivation alters soil gross nitrogen transformation rates and nitrous oxide production pathways

Plastic-shed vegetable cultivation is characterized by high nitrogen (N) application rates, frequent irrigation and multiple cropping, probably leading to different soil N transformation rates compared to open-field cultivation. However, how continuous cultivation of vegetables under plastic sheds affects soil N transformation rates and associated nitrous oxide (N2O) emissions remains unclear. Here, a 15N-tracing experiment in combination with the qPCR technique was used to investigate the effects of conversion from conventional open-field cultivation to plastic-shed vegetable cultivation, as well as the age of this shift, on soil gross N transformation rates, N2O emission pathways and associated microbial abundances. Five typical fields, including a wheat–maize rotation system field and four adjacent plastic-shed vegetable fields under cultivation for 2, 5, 12 and 20 years, were selected. Soil gross N mineralization rates increased significantly after two years after conversion from a wheat–maize rotation system to a plastic-shed vegetable system, and then decreased with an increase in plantation age, which could be attributed to decreased soil total phosphorus availability. Long-term vegetable plantation under plastic-shed decreased soil gross autotrophic nitrification rates significantly by decreasing ammonia-oxidizing bacteria abundance probably due to decreasing soil pH. Such decreased rates of autotrophic nitrification further led to decreased N2O emissions under plastic-shed cultivation. Under long-term plastic-shed cultivation (>2 years), negligible gross nitrate-N (NO3−-N) immobilization rates were observed due to the preferential use of ammonium-N by soil microbes, which was probably responsible for rapid NO3−-N accumulation in soils. Overall, these results could be of help to elucidate the mechanisms of soil N2O emission and NO3−-N accumulation in plastic-shed vegetable fields.

Carbohydrates accumulation, oil quality and yield of rapeseed genotypes at different nitrogen rates

ABSTRACT A field experiment was conducted in 2018–2020 to investigate the effect of two nitrogen application rates (N0 = 0 kg ha−1(control), N90 = 90 kg ha−1, and N180 = 180 kg ha−1) on morphological and physiological behaviours of two new rapeseed varieties; V1 = JYJS01 (semi-dwarf variety) and V2 = CY36 (tall variety). Our results indicated that N application enhanced the plant growth and seed protein content in comparison to control. Contrastingly, compared with control, sugar contents, i.e. sucrose and reducing sugars, decreased significantly in response to an increase in N. Seed oil content also decreased by 8.5% and 5.5%, 6.7% and 3.9% against N180 in V1 and V2 during 2019 and 2020, respectively. Furthermore, higher nitrogen application rates decreased seed fatty acid proportions by decreasing the sugar availability for fatty acid biosynthesis. Our results demonstrated the highest seed yield (9.4 g plant−1 in 2018/19 and 9.5 g plant−1 in 2019/20) in V2 against N180, and the lowest seed yield (3.2 g plant−1 in 2018/19 and 3.4 g plant−1 in 2019/20) in V1 at control. These findings imply that a high nitrogen application rate had increased the yield. At the same time, the carbohydrates translocation from stems to seed for fatty acid biosynthesis decreased, which played their significant role in seed physiology for fatty acid metabolisms, ultimately affected the seed quality. However, there is still a dire need to evaluate how nitrogen application affect the carbohydrate availability for fatty acid metabolism in the seed of new winter rapeseed varieties.

Characteristics and traceability analysis of nitrate pollution in the Yellow River Delta, China

The Yellow River Delta is one of the regions with the highest nitrogen application rate in China. Because of the high-intensity development and utilization of the Yellow River Delta, a large number of nitrate inorganic nitrogen pollutants have been transported offshore through rivers, which poses a threat to the ecological environment security of the region. The distribution characteristics of nitrate pollution, the source and transport characteristics of nitrate in surface water are unclear. In this study, we collected soil and surface water samples, determined stable isotopes of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3 and δ18O-NO3), and used the Isosource model to quantitatively analyze the distribution characteristics of soil nitrate-nitrogen and source characteristics of surface water nitrate. The results showed that: (1) The average content of NO3 --N in cultivated soil was 3.99 times higher than that in non-cultivated soil, in which cornfield > cotton field > soybean field > paddy field; (2) The nitrate flux of surface water increased from upstream to downstream, which was positively correlated with basin area; (3) In the middle and upper reaches of the study area, the surface water is mainly replenished from the Yellow River water and groundwater, while the lower reaches are affected by seawater intrusion; (4) The primary source of nitrate in the study area was dominated by human activities of agricultural production and residents’ lives, with a total contribution of 60.8%. This study will provide a scientific basis for the treatment of nitrate pollution in coastal areas.

Evidence for magnesium\u2013phosphorus synergism and co-limitation of grain yield in wheat agriculture

Modern crop production is characterized by high nitrogen (N) application rates, which can influence the co-limitation of harvested yield by other nutrients. Using a multidimensional niche volume concept and scaling exponents frequently applied in plant ecological research, we report that increased N and phosphorus (P) uptake in a growing wheat crop along with enhanced grain biomass is associated with more than proportional increase of other nutrients. Furthermore, N conversion efficiency and grain yield are strongly affected by the magnesium (Mg) to P ratio in the growing crop. We analyzed a field trial in Central Sweden including nine wheat varieties grown during two years with contrasting weather, and found evidence for Mg co-limitation at lower grain yields and P co-limitation at higher yields. We argue that critical concentrations of single nutrients, which are often applied in agronomy, should be replaced by nutrient ratios. In addition, links between plant P and Mg contents and root traits were found; high root number enhanced the P:N ratio, whilst steep root angle, indicating deep roots, increased the Mg:N ratio. The results have significant implications on the management and breeding targets of agriculturally grown wheat, which is one of the most important food crops worldwide.

Effects of water quality, irrigation amount and nitrogen applied on soil salinity and cotton production under mulched drip irrigation in arid Northwest China

Understanding the interaction effects of water, fertilizer, and salinity is of great environmental importance to mitigate soil salinization and improve crop production. Field experiments were conducted to evaluate the effects of water quality, irrigation amount, and nitrogen application rate on soil salt accumulation, root water and nitrogen uptake, lint yield, and water productivity during 2018 and 2019 growing seasons of cotton (Gossypium hirsutum L.) in arid region of Xinjiang, China. Four irrigation levels 75%, 100%, 125%, and 150% of crop water requirement (ETc) and four nitrogen levels 195, 255, 315, and 375 kg ha−1 were applied with groundwater and brackish water irrigation. Results demonstrated that, brackish water irrigation significantly increased the root-zone soil salt accumulation (SSA). Either increasing irrigation amount during the squaring stage or decreasing irrigation amount during the flower boll stage with higher nitrogen application rate can reduce the SSA. And with an increase in brackish water irrigation amount, a corresponding increase in nitrogen application rate is required to reduce the possible soil salt accumulation during the flower boll stage. Highest irrigation amount (150% ETc) and nitrogen application rate (375 kg ha−1) at the flower boll stage and during the whole growing season resulted in significant higher nitrogen uptake increment with an increasing rate of 25–74% and 39–65%, respectively. The integration of higher irrigation amount and highest nitrogen application rate with groundwater irrigation produced higher lint yield and water productivity. Considering soil salinity and lint yield as well as water productivity, the appropriate integration modes of water and nitrogen are higher irrigation amount and highest nitrogen application rate (125% ETc and 375 kg ha−1) for groundwater and lowest irrigation amount and lower nitrogen application rate (75% ETc and 255 kg ha−1) for brackish water.

Inorganic nitrogen fertilizer and high N application rate promote N2O emission and suppress CH4 uptake in a rotational vegetable system

Understanding the influence of management practices on greenhouse gas (GHG) emissions from greenhouse cropping is of great importance for assessing the environmental impacts of the greenhouse cropping industry and improving its sustainability. A tomato–cucumber–tomato rotation experiment was carried out in a typical solar greenhouse in northwest China with four treatments including two irrigation levels (regular (RI) and low (LI)) and two fertilizer types (organic fertilizer (N1) and inorganic fertilizer (N2)). Greenhouse gas fluxes (nitrous oxide, N2O, and methane, CH4) were measured regularly using the closed chamber method during the three growing seasons, along with soil water-filled pore space (WFPS), temperature, mineral-N concentration and nitrobacteria, nitrosomonas and denitrifying bacteria abundance. Over the rotation, the soil acted as a source for N2O and a sink for CH4, with the mean fluxes of 0.12 mg N2O-N m−2 h−1 and -0.31 mg CH4-C m−2 h−1, respectively. The stepwise multiple linear regressions indicated that WFPS and soil temperature accounted for significant portion of N2O emission and CH4 uptake variations, respectively for both fertilizer types. Fertilization rate and type resulted in much greater difference of cumulative GHG emission between treatments than the irrigation level. Inorganic fertilizer with higher nitrogen application rate usually resulted in higher cumulative N2O emission and lower CH4 uptake than organic fertilizer application. Over the rotation, total greenhouse emission (GHGt) and greenhouse emission intensity (GHGI) on average followed the same order of RIN2 > LIN2 > LIN1 > RIN1 with N2O emission as the dominant component for each treatment. Overall, organic fertilizer with proper water application under drip irrigation can effectively mitigate greenhouse gas emissions and maintain relatively high and stable vegetable yields in solar greenhouse cropping in northwest China.

High nitrogen application rate and planting density reduce wheat grain yield by reducing filling rate of inferior grain in middle spikelets

Excessive use of nitrogen fertilizer and high planting density reduce grain weight in wheat. However, the effects of high nitrogen and planting density on the filling of grain located in different positions of the wheat spikelet are unknown. A two-year field experiment was conducted to investigate this question and the underlying mechanisms with respect to hormone and carbohydrate activity. Both high nitrogen application and planting density significantly increased spike density, while reducing kernel number per spike and 1000-kernel weight. However, the effects of high nitrogen and high plant density on kernel number per spike and 1000-kernel weight were different. The inhibitory effect of high nitrogen application and high planting density on kernel number per spike was achieved mainly by a reduction in kernel number per spikelet in the top and bottom spikelets. However, the decrease in 1000-kernel weight was contributed mainly by the reduced weight of grain in the middle spikelets. The grain-filling rate of inferior grain in the middle spikelets was significantly decreased under high nitrogen input and high planting density conditions, particularly during the early and middle grain-filling periods, leading to the suppression of grain filling and consequent decrease in grain weight. This effect resulted mainly from inhibited sucrose transport to and starch accumulation in inferior grain in the middle spikelets via reduction of the abscisic acid/ethylene ratio. This mechanism may explain how high nitrogen application and high planting density inhibit the grain filling of inferior wheat grain.

Reducing environmental risk of nitrogen by popularizing mechanically dense transplanting for rice production in China

The high nitrogen (N) application rates typically used in Chinese cropping systems have led to diminishing returns for yields and have also imposed substantial environmental costs. Here, we estimate that the annual N loss from rice production in China reached approximately 2.6×109 kg from 2011 to 2015, and we demonstrate that adoption of the mechanically dense transplanting technique by producers is an effective method to reduce N loss from rice cropping systems without suffering a yield penalty.

Effects of nitrogen fertilizer rates and waterlogging on leaf physiological characteristics and grain yield of maize

ABSTRACT Nitrogen fertilizer supply and use play a vital role in determining crop growth and yield. However, the effects of nitrogen fertilizer levels on plant growth under waterlogging conditions remain elusive. The objective of this study was to investigate the effects of nitrogen fertilizer rates (0, 90, 180, 270, and 360 kg N ha−1, designated N0, N1, N2, N3, and N4, respectively) on leaf physiological characteristics and grain yield of maize (Zea mays L.) under two water regimes (WW or well-watered through the maize grown season and WL or waterlogged for six days at the sixth-leaf stage). Overall, in comparison to WW, WL treatment showed a reduction in the following traits, at all nitrogen rates: plant height, leaf area index, SPAD value, superoxide dismutase, peroxidase, and catalase activity, net photosynthetic rate (P n), transpiration rate, stomatal conductance, ears per ha, kernels per ear, 1,000-kernel weight, and grain yield. Moreover, the majority of the above parameters increased with the increase in nitrogen application rate under WL, as a result of the enhanced available nitrogen content at higher nitrogen application rates. Therefore, increasing supply levels of nitrogen fertilizer could improve antioxidant enzyme activity and P n, consequently producing increased maize grain yield under waterlogged conditions.

Soil N transformation rates are not linked to fertilizer N losses in vegetable soils with high N input

Vegetable soils under plastic shed are characterized by multiple cropping and extremely high rates of nitrogen (N) application, but the N use efficiency (NUE) is generally low and the rate of N loss is often high. The underlying mechanisms behind these N losses following long-term N fertilizer applications remain elusive. Here, a 15N tracing incubation study in conjunction with in-situ monitoring was performed to investigate the effects of different N fertilization regimes on gross N transformations, microbial abundance and N losses via NO3− leaching and N2O emissions in a vegetable soil under plastic shed subjected to 14 years of repeated N fertilization. The field experiment comprised of six treatments: no N fertilization (control, CK), and applications of chicken manure (M), chemical N plus M (CM), CM plus straw (CMS), 42 % of chemical N plus chicken manure (RCM) and RCM plus straw (RCMS). The results showed that the total gross N mineralization rates were significantly higher in CMS, RCMS and M treatments than in CK, CM and RCM treatments. The total gross NH4+ immobilization rates followed the order of CK > CM > CMS > M > RCM ≈ RCMS, indicating a decreasing NH4+ immobilization rate after N application. Gross autotrophic nitrification rate was significantly enhanced by fertilizer application in the order: CK < CM < CMS ≈ RCM < M < RCMS, mainly due to both increased mineralization rates and abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB). A significant negative relationship between gross rates of NH4+ immobilization and autotrophic nitrification suggests that higher autotrophic nitrification decreased NH4+ immobilization. Reduced chemical N input alleviated soil acidification, NO3− leaching and N2O emissions. There were significant positive relationships between rates of chemical N input and N loss but no relationships between gross N transformation rates and tomato yields, NO3− leaching losses and N2O emissions. Thus, soil N transformation rates do not reflect rate of fertilizer N losses in vegetable soil managed under plastic shed. We thus suggest that chemical N application rate could be reduced to decrease N losses while sustaining vegetable production.