Excessive manure application stimulates nitrogen cycling but only weakly promotes crop yields in an acidic Ultisol:Results from a 20-year field experiment

Population growth and growing demand for livestock products produce large amounts of manure,which can be harnessed to maintain soil sustainability and crop productivity.However,the impacts of excessive manure application on crop yields,nitrogen(N)-cycling processes and microorganisms remain unknown.Here,we explored the effects of 20-year of excessive rates(18 and 27 Mg ha^(–1)yr^(–1))of pig manure application on peanut crop yields,soil nutrient contents,N-cycling processes and the abundance of N-cycling microorganisms in an acidic Ultisol in summer and winter,compared with none and a regular rate(9 Mg ha^(–1)yr^(–1))of pig manure application.Long-term excessive pig manure application,especially at the high-rate,significantly increased soil nutrient contents,the abundance of N-cycling functional genes,potential nitrification and denitrification activity,while it had a weaker effect on peanut yield and plant biomass.Compared with manure application,seasonality had a much weaker effect on N-cycling gene abundance.Random forest analysis showed that available phosphorus(AP)content was the primary predictor for N-cycling gene abundance,with significant and positive associations with all tested N-cycling genes.Our study clearly illustrated that excessive manure application would increase N-cycling gene abundance and potential N loss with relatively weak promotion of crop yields,providing significant implications for sustainable agriculture in the acidic Ultisols.

Soil organic carbon saturation deficit under primary agricultural managements across major croplands in China

Introduction:To generate information for the effective management of soil organic carbon(SOC)sequestration in Chinese croplands,we compared the additional organic carbon(C)that can be stabilized by fine soil particles(<20μm)with typical fertilization practices across soil types and climate zones.Using data from 30 long-term experimental study sites across the major agricultural zones in China,we estimated stable SOC saturation deficit(SOC_(deficit))under no fertilization(CK),chemical fertilization(CF),straw plus CF(S+CF),and manure plus CF(M+CF).Stable SOC_(deficit)was defined as the difference between potential and current SOC stabilized by fine soil particles.Outcomes:Stable SOC_(deficit)values varied from 51%to 82%.Soils dominated by 2:1 clay minerals showed larger stable SOC_(deficit)than soils dominated by 1:1 clay minerals under each treatment.For soils dominated by 2:1 clay minerals,stable SOC_(deficit)was significantly lower under M+CF(69%)than under CK,CF,and S+CF(78-82%)treatments,and it increased with increasing mean annual temperature(<10°C).In soils dominated by 1:1 clay minerals,stable SOC_(deficit)was considerably lower in paddy and paddy-upland than in upland soils,suggesting that paddies effectively stabilize C inputs.Discussion:Agricultural soils in China have considerable C sequestration potential,despite decades of fertilization practices.To manage soil C sequestration and model soil C dynamics effectively,factors such as soil mineral types,fertilization,and cropland use should be considered.Conclusion:Our results demonstrated that manure addition was the best fertilization method for improving soil fertility,whereas straw return in Chinese croplands should take into account climate mitigation in future.