Low N apparent surplus with higher rice yield under long-term fertilizer postponing in the rice-wheat cropping system

Nitrogen(N)fertilization increases rice yield,but inappropriate N fertilizer application increases N loss and the risk of environmental pollution.Short-term fertilizer postponing(FP)generally reduces N apparent surplus and increases rice yields,but the effects of long-term FP on N surplus and rice yields remain unknown.Our study was the first to investigate the impacts of long-term FP(11 years)on N apparent surplus and rice yields.FP effects in the short term(≤6 years)did not affect rice yields,whereas FP effects in the long term(>6 years)increased rice yields by 13.9%compared with conventional fertilization(CF).FP did not affect panicles per unit area,1000-kernel weight,and filled-kernel rate,but spikelets per panicle increased over time due to spikelet formation stimulation.FP also reduced the N apparent surplus over time more strongly than CF owing to higher N accumulation and N utilization efficiency.FP effects in the long term also significantly increased soil organic matter,total N,and NH4_(+)^(-)N content.Our results were supported by a pot experiment,showing that rice yields in soils with a history of FP were significantly higher than those for soils without a history of FP,indicating that FP increased rice yields more strongly in later years mainly because of soil quality improvement.Our findings suggest that longterm FP can reduce N loss while increasing rice yields by improving soil quality.

Effects of plant density and nitrogen rate on cotton yield and nitrogen use in cotton stubble retaining fields

Increasing nitrogen(N)rate could accelerate the decomposition of crop residues,and then improve crop yield by increasing N availability of soil and N uptake of crops.However,it is not clear whether N rate and plant density should be modified after a long period of cotton stubble return with high N rate.This study seeks to assess the effects of N rate and plant density on cotton yield,N use efficiency,leaf senescence,soil inorganic N,and apparent N balance in cotton stubble return fields in Liaocheng,China,in 2016 and 2017.Three plant densities 5.25(D_(5.25)),6.75(D_(6.75))and 8.25(D_(8.25))plants m^(-2) and five N rates 0(N_(0)),105(N_(105)),210(N_(210)),315(N315),and 420(N420)kg ha^(-1) were investigated.Compared to the combination used by local farmers(D_(5.25)N_(315)),a 33.3%N reduction and a 28.6%increase in plant density(D_(6.75)N_(210))can maintain high cotton yield,while a 66.7%N reduction at 6.75 plants m^(-2)(D_(6.75)N_(105))can only achieve high yield in the first year.Biological yield increased with the increase of N rate and plant density,and the highest yield was obtained under 420 kg N ha^(-1) at 8.25 plants m^(-2)(D_(8.25)N_(420))across the two years under investigation.Compared to D5.25N315,N agronomic efficiency(NAE)and N recovery efficiency(NRE)in D_(6.75)N_(210) increased by 30.2 and 54.1%,respectively,and NAE and NRE in D6.75N105 increased by 104.8 and 88.1%,respectively.Soil inorganic N decreased sharply under 105 kg N ha^(-1),but no change was found under 210 kg N ha^(-1) at 6.75 plants m^(-2).N deficit occurred under 105 kg N ha^(-1),but it did not occurr under 210 kg N ha^(-1) at 6.75 plants m^(-2).Net photosynthetic rate and N concentration of leaves under N rate ranging from 210 to 420 kg ha^(-1) were higher than those under N rate of 0 or 105 kg N ha^(-1) at all three densities.The findings suggest that D6.75N210 is a superior combination in cotton stubble retaining fields in the Yellow River Valley and other areas with similar ecologies.

Substituting nitrogen and phosphorus fertilizer with optimal amount of crop straw improves rice grain yield,nutrient use efficiency and soil carbon sequestration

Crop straw return after harvest is considered an important way to achieve both agronomic and environmental benefits.However,the appropriate amount of straw to substitute for fertilizer remains unclear.A field experiment was performed from 2016 to 2018 to explore the effect of different amounts of straw to substitute for fertilizer on soil properties,soil organic carbon(SOC)storage,grain yield,yield components,nitrogen(N)use efficiency,phosphorus(P)use efficiency,N surplus,and P surplus after rice harvesting.Relative to mineral fertilization alone,straw substitution at 5 t ha^(-1)improved the number of spikelets per panicle,effective panicle,seed setting rate,1000-grain weight,and grain yield,and also increased the aboveground N and P uptake in rice.Straw substitution exceeding 2.5 t ha^(-1)increased the soil available N,P,and K concentrations as compared with mineral fertilization,and different amounts of straw substitution improved SOC storage compared with mineral fertilization.Furthermore,straw substitution at 5 t ha^(-1)decreased the N surplus and P surplus by up to 68.3 and 28.9%,respectively,compared to mineral fertilization.Rice aboveground N and P uptake and soil properties together contributed 19.3%to the variation in rice grain yield and yield components.Straw substitution at 5 t ha^(-1),an optimal fertilization regime,improved soil properties,SOC storage,grain yield,yield components,N use efficiency(NUE),and P use efficiency(PUE)while simultaneously decreasing the risk of environmental contamination.

Combined Applications of Nitrogen and Phosphorus Fertilizers with Manure Increase Maize Yield and Nutrient Uptake via Stimulating Root Growth in a Long-Term Experiment

Imbalanced application of nitrogen(N) and phosphorus(P) fertilizers can result in reduced crop yield,low nutrient use efficiency,and high loss of nutrients and soil nitrate nitrogen(NO_3^--N) accumulation decreases when N is applied with P and/or manure;however,the effect of applications of N with P and/or manure on root growth and distribution in the soil profile is not fully understood.The aim of this study was to investigate the combined effects of different N and P fertilizer application rates with or without manure on maize(Zea mays L.) yield,N uptake,root growth,apparent N surplus,Olsen-P concentration,and mineral N(N_(min)) accumulation in a fluvo-aquic calcareous soil from a long-term(28-year) experiment.The experiment comprised twelve combinations of chemical N and P fertilizers,either with or without chicken manure,as treatments in four replicates.The yield of maize grain was 82%higher,the N uptake 100%higher,and the N_(min) accumulation 39%lower in the treatments with combined N and P in comparison to N fertilizer only.The maize root length density in the 30-60 cm layer was three times greater in the treatments with N and P fertilizers than with N fertilizer only.Manure addition increased maize yield by 50%and N uptake by 43%,and reduced N_(min)(mostly NO_3^--N) accumulation in the soil by 46%.The long-term application of manure and P fertilizer resulted in significant increases in soil Olsen-P concentration when no N fertilizer was applied.Manure application reduced the apparent N surplus for all treatments.These results suggest that combined N and P fertilizer applications could enhance maize grain yield and nutrient uptake via stimulating root growth,leading to reduced accumulation of potentially leachable NO_3^--N in soil,and manure application was a practical way to improve degraded soils in China and the rest of the world.

Optimization of nitrogen fertilizer rate under integrated rice management in a hilly area of Southwest China

China has the world’s highest nitrogen(N)application rate,and the lowest N use efficiency(NUE).With the crop yield increasing,serious N pollution is also caused.An in-situ field experiment(2011–2015)was conducted to examine the effects of three N levels,0(i.e.,no fertilizer N addition to soil),120,and 180 kg N ha-1,using integrated rice management(IRM).We investigated rice yield,aboveground N uptake,and soil surface N budget in a hilly region of Southwest China.Compared to traditional rice management(TRM),IRM integrated raised beds,plastic mulch,furrow irrigation,and triangular transplanting,which significantly improved rice grain yield,straw biomass,aboveground N uptake,and NUE.Integrated rice management significantly improved 15N recovery efficiency(by 10%)and significantly reduced the ratio of potential15N loss(by 8%–12%).Among all treatments,the 120 kg N ha-1 level under IRM achieved the highest 15N recovery efficiency(32%)and 15N residual efficiency(29%),with the lowest 15N loss ratio(39%).After rice harvest,the residual N fertilizer did not achieve a full replenishment of soil N consumption,as the replenishing effect was insufficient(ranging from-31 to-49 kg N ha-1).Furthermore,soil surface N budget showed a surplus(69–146 kg N ha-1)under all treatments,and the N surplus was lower under IRM than TRM.These results indicate IRM as a reliable and stable method for high rice yield and high NUE,while exerting a minor risk of N loss.In the hilly area of Southwest China,the optimized N fertilizer application rate under IRM was found to be 100–150 kg N ha-1.