Ammonia volatilization losses and ^(15)N balance from urea applied to rice on a paddy soil

Ammonia volatilization loss and ^15N balance were studied in a rice field at three different stages after urea application in Taihu Lake area with a micrometeorological technique. Factors such as climate and the NH4^＋-N concentration in the field floodwater affecting ammonia loss were also investigated. Results show that the ammonia loss by volatilization accounted for 18.6%-38.7% of urea applied at different stages, the greatest loss took place when urea was applied at the tillering stage, the smallest at the ear bearing stage, and the intermediate loss at the basal stage. The greatest loss took place within 7 d following the fertilizer application. Ammonia volatilization losses at three fertilization stages were significantly correlated with the ammonium concentration in the field floodwater after the fertilizer was applied. ^15N balance experiment indicated that the use efficiency of urea by rice plants ranged between 24.4% and 28.1%. At the early stage of rice growth, the fertilizer nitrogen use efficiency was rather low, only about 12%. The total amount of nitrogen lost from different fertilization stages in the rice field was 44.1%-54.4%, and the ammonia volatilization loss was 25.4%-33.3%. Reducing ammonia loss is an important treatment for improving N use efficiency.

Balance of Manure and Farmland Load in a Breeding Farm

[Objective] The aim was to research balance between manure of breeding farm and farmland load. [Method] N balance of farmlands after manure fertilized was researched in a hoggery in Beijing （600 base sows and 647 breeding pigs）. [Result] The suitable N input in neighboring farmlands was 191.9 kg/（hm 2 ·y） and the farmland area satisfying balance between growing and breeding was 53.7 hm 2 in the hoggery. [Conclusion] The research provided a scientific method for balance between growing and breeding.

Surface N balances and reactive N loss to the environment from global intensive agricultural production systems for the period 1970-2030

Data for the historical years 1970 and 1995 and the FAO-Agriculture Towards 2030 projection are used to calculate N inputs (N fertilizer, animal manure, biological N fixation and atmospheric deposition) and the N export from the field in harvested crops and grass and grass consumption by grazing animals. In most industrialized countries we see a gradual increase of the overall N recovery of the intensive agricultural production systems over the whole 1970-2030 period. In contrast, low N input systems in many developing countries sustained low crop yields for many years but at the cost of soil fertility by depleting soil nutrient pools. In most developing countries the N recovery will increase in the coming decades by increasing efficiencies of N use in both crop and livestock production systems. The surface balance surplus of N is lost from the agricultural system via different pathways, including NH3 volatilization, denitrification, N2O and NO emissions, and nitrate leaching from the root zone. Global NH3-N emissions from fertilizer and animal manure application and stored manure increased from 18 to 34 Tg·yr-1 between 1970 and 1995, and will further increase to 44 Tg·yr-1 in 2030. Similar developments are seen for N2O-N (2.0 Tg·yr-1 in 1970, 2.7 Tg·yr-1 in 1995 and 3.5 Tg·yr-1 in 2030) and NO-N emissions (1.1 Tg·yr-1 in 1970, 1.5Tg·yr-1 in 1995 and 2.0 Tg·yr-1 in 2030).

Nitrogen Recommendations for Summer Maize in Northern China Using the N_min Test and Rapid Plant Tests

A field experiment with a split-plot design was carried out at Dongbeiwang Farm in Beijing Municipality to establish reliable N fertilizer recommendation indices for summer maize (Zea mays L.) in northern China using the soil Nmin (mineral N) test as well as the plant nitrate and SPAD (portable chlorophyll meter readings) tests. The results showed that Nmin sollwert (NS) 60 kg N ha-1 at the third leaf stage and N rate of 40 to 120 kg N ha-1 at the tenth leaf stage could meet the N requirement of summer maiz…

Mitrification－Denitrification Lossof Added Nitrogenin Flooded Rice Rhizosphere

Nitrification-denitrification losses of ￣15N-labelled nitrate and ammonium applied to the rhizosphere andnonrhizosphere of flooded rice were evaluated in 2 greenhouse rhizobox experiments. The loss of added Nvia denitrification was estimated directly by measuring the total fluxes of (N_2O+N_2)￣15N. It was found that 67% and51%-56% of ￣15N-nitrate added to rice rhizosphere were lost as (N_2O+N_)-￣15N in the 2 experiments, respectively,which were comparable to that added to nonrhizosphere soil (70%and47%, respectively), implying that tbedenitrifying activity in rice rhizosphere was as high as that in nonrhizosphere soil. However, only trace amounts(0-0.3% of added N) were recovered as (N_2O+N_2)-￣15N when ￣15N-ammonium was applied to either rhizosphere ornonrhizosphere, which seems to indicate that the nitrifying activity in the either rhizosphere or nonrhizosphere soilswas quite low. The apparent denitrification calculated from ￣15N balance studies was 10%-47% higher than the totalflux of (N_2O+N_2)-￣15N. Reasons for the large differences can not be explained satisfactorily. Though the denitrifyingactivity in rhizospbere was high and comparable to that in nonrhizosphere soil, presumably due to the low nitrifyingactivity and/ or the strong competition of N uptake against denitrification, the nitrification-denitrification takingplace in rhizosphere could not be an important mechanism of loss of ammonium N in flooded rice-soil system.

Statistical analysis of nitrogen use efficiency in Northeast China using multiple linear regression and Random Forest

Understanding the spatial-temporal dynamics of crop nitrogen(N)use efficiency(NUE)and the relationship with explanatory environmental variables can support land-use management and policymaking.Nevertheless,the application of statistical models for evaluating the explanatory variables of space-time variation in crop NUE is still under-researched.In this study,stepwise multiple linear regression(SMLR)and Random Forest(RF)were used to evaluate the spatial and temporal variation of NUE indicators(i.e.,partial factor productivity of N(PFPN);partial nutrient balance of N(PNBN))at county scale in Northeast China(Heilongjiang,Liaoning and Jilin provinces)from 1990 to 2015.Explanatory variables included agricultural management practices,topography,climate,economy,soil and crop types.Results revealed that the PFPN was higher in the northern parts and lower in the center of the Northeast China and PNBN increased from southern to northern parts during the 1990–2015 period.The NUE indicators decreased with time in most counties during the study period.The model efficiency coefficients of the SMLR and RF models were 0.44 and 0.84 for PFPN,and 0.67 and 0.89 for PNBN,respectively.The RF model had higher relative importance of soil and climatic covariates and lower relative importance of crop covariates compared to the SMLR model.The planting area index of vegetables and beans,soil clay content,saturated water content,enhanced vegetation index in November&December,soil bulk density,and annual minimum temperature were the main explanatory variables for both NUE indicators.This is the first study to show the quantitative relative importance of explanatory variables for NUE at a county level in Northeast China using RF and SMLR.This novel study gives reference measurements to improve crop NUE which is one of the most effective means of managing N for sustainable development,ensuring food security,alleviating environmental degradation and increasing farmer’s profitability.

Application of controlled-release urea increases maize N uptake,environmental benefits and economic returns via optimizing temporal and spatial distributions of soil mineral N

The creation of controlled-release urea (CRU) is a potent substitute for conventional fertilizers in order to preserve the availability of nitrogen (N) in soil,prevent environmental pollution,and move toward green agriculture.The main objectives of this study were to assess the impacts of CRU’s full application on maize production and to clarify the connection between the nutrient release pattern of CRU and maize nutrient uptake.In order to learn more about the effects of CRU application on maize yields,N uptake,mineral N (N_(min)) dynamics,N balance in soil-crop systems,and economic returns,a series of field experiments were carried out in 2018–2020 in Dalian City,Liaoning Province,China.There were 4 different treatments in the experiments:no N fertilizer input (control,CK);application of common urea at 210 kg ha^(-1)(U),the ideal fertilization management level for the study site;application of polyurethane-coated urea at the same N input rate as U (PCU);and application of PCU at a 20% reduction in N input rate (0.8PCU).Our findings showed that using CRU (i.e.,PCU and 0.8 PCU) may considerably increase maize N absorption,maintain maize yields,and increase N use efficiency (NUE) compared to U.The grain yield showed considerable positive correlations with total N uptake in leaf in U and 0.8 PCU,but negative correlations with that in PCU,indicating that PCU caused excessive maize absorption while 0.8 PCU could achieve a better yield response to N supply.Besides,PCU was able to maintain N fertilizer in the soil profile 0–20 cm away from the fertilization point,and higher N_(min)content was observed in the 0–20 cm soil layer at various growth stages,particularly at the middle and late growing stages,optimizing the temporal and spatial distributions of N_(min).Additionally,compared to that in U,the apparent N loss rate in PCU was reduced by 36.2%,and applying CRU (PCU and 0.8 PCU) increased net profit by 8.5% to 15.2% with less labor and fertilization frequency.It was concluded that using CRU could be an effective N fertilizer management strategy to sustain maize production,improve NUE,and increase economic returns while minimizing environmental risks.

Using BODIPY Unit to Design Molecular Acceptors with Absorption Wavelength of >1000 nm for Organic Photodetectors

Near-infrared(NIR)organic photodetectors(OPDs)are promising in flexible electronic and imaging sensor applications.However,high-performance NIR-II OPDs with photoresponse wavelength beyond 1000 nm are rare due to the lack of narrow bandgap molecular acceptors.In this work,an A-D-A′-D-Atype molecular acceptor with an onset absorption wavelength of 1150 nm was developed.Its narrow bandgap was benefited by the balanced resonance of the boron-nitrogen covalent bond(B–N)and boron-nitrogen coordination bond(B←N)in thienyl-fused 4-difluoro-4-bora-3a,4a-diaza-s-indacene(BODIPY)unit,as well as the strong intramolecular charge transfer(ICT)effect.The molecule showed a strong NIR absorption with an absorption peak at 1019 nm and an optical bandgap as low as 1.07 eV.Using the molecule as an electron acceptor in OPD device fabrication,a wide photoresponse wavelength range of 300 to∼1150 nm was achieved.At bias of−0.1 V,the device showed a low dark current density of 4.59×10^(−8) A cm^(−2) and high responsivity of 0.29 A W^(−1) at 970 nm,achieving a high peak specific detectivity of 2.39×1012 Jones and remaining a high specific detectivity of 1.59×10^(12) Jones at 1064 nm.These results demonstrate a feasible design of ultra-narrow bandgap molecular acceptors based on BODIPY unit induction of highly sensitive NIR-II OPDs.

Fate of Basal N Under Split Fertilization in Rice with ^(15)N Isotope Tracer

Split fertilization strategy is popularly adopted in rice to synchronize soil nitrogen(N) supply and crop N demand. Attention has been paid more on mid-season topdressing N, but limited on basal N. A clearer understanding of the basal N fate under split fertilization is crucial for determining rational basal N split ratio to improve the yield and reduce the loss to environment. A two-year field experiment with two N rates of 150 and 300 kg Nha^(-1), two split ratios of basal N, 40% and 25%, and two rice varieties,Wuyunjing 23(japonica) and Y-liangyou 2(super hybrid indica), was conducted. Labelled ^(15) N urea was supplied in micro-plots as basal fertilizer to determine the plant uptake, translocation, soil residual, and loss of basal N fertilizer. The results showed that basal N absorbed by rice was only 1.6%–11.5% before tillering fertilization(8–10 d after transplanting), 6.5%–21.4% from tillering fertilization to panicle fertilization, and little(0.1%–4.4%) after panicle fertilization. The recovery efficiency of basal N for the entire rice growth stage was low and ranged from 18.7% to 24.8%, not significantly affected by cultivars or N treatments. Soil residual basal N accounted for 10.3%–36.4% and decreased with increasing total N rate and basal N ratio, regardless of variety and year. 43.8%–70.4% of basal N was lost into the environment based on the N balance. Basal N loss was significantly linearly positive related with the basal N rate and obviously enhanced by the increasing basal N ratio for both varieties in both 2012 and 2013. The N use efficiency and yield was significantly improved when decreasing the basal N ratio from 40% to 25%. The results indicated that the basal N ratio should be reduced, especially with limited N inputs, to improve the yield and reduce the N loss to the environment.

Nitrous Oxide and Methane Fluxes During the Maize Season Under Optimized Management in Intensive Farming Systems of the North China Plain

Addressing concerns about mitigating greenhouse gas （GHG） emissions while maintaining high grain yield requires improved management practices that achieve sustainable intensification of cereal production systems. In the North China Plain, a field experiment was conducted to measure nitrous oxide （N2O） and methane （CH4） fluxes during the maize （Zea mays L.） season under various agricultural management regimes including conventional treatment （CONT） with high N fertilizer application at a rate of 300 kg N ha-1 and overuse of groundwater by flood irrigation, optimal fertilization 1 treatment （OPTIT）, optimal fertilization 2 treatment （OPT2T）, and controlled-release urea treatment （CRUT） with reduced N fertilizer application and irrigation, and a control （CK） with no N fertilizer. In contrast to CONT, balanced N fertilization treatments （OPT1T, OPT2T, and CRUT） and CK demonstrated a significant drop in cumulative N20 emission （1.70 v.s. 0.43-1.07 kg N ha-l）, indicating that balanced N fertilization substantially reduced N20 emission. The vMues of the N20 emission factor were 0.42%, 0.29%, 0.32%, and 0.27% for CONT, OPTIT, OPT2T, and CRUT, respectively. Global warming potentials, which were predominantly determined by N20 emission, were estimated to be 188 kg CO2-eq ha-1 for CK and 419-765 kg CO2-eq ha-1 for the N fertilization treatments. Global warming potential intensity calculated by considering maize yield was significantly lower for OPT1T, OPT2T, CRUT, and CK than for CONT. Therefore, OPTIT, OPT2T, and CRUT were recommended as promising management practices for sustaining maize yield and reducing GHG emissions in the North China Plain.