Crop Yields And Soil Physiochemical Properties In Response To Legume-based Cropping Rotation In North China Plain

Due to the huge population and limited land area sutable for farning,excess chemical fertilizer are often applied to raise crop yields in China.Hostorical data have shown that crop yields have increased by 54%since 1980s,but fertilizer inputs have also increased by 191%.Model simulations suggest that fertilizer application will increase 2.25-2.50 million tons per year by 2050.Long-term and excessive fertilization may lead to soil acidification and consequent environmental pollution.Leguminous crops or green manure(such as alfalfa),as nitrogen fixing plants,can fix nitrogen from the atmosphere by the rhizobia,which could increase soil fertility and crop yields.Comparison with conventional agriculture,legume-based cropping rotations can reduce the use of N fertilizer.Traditional rotation systems(wheat-maize and wheat-cotton)in North China Plain alaways require a large amount of chemical fertilizer.Therefore,sustainable cropping rotation is needed to alleviate environmental problems.In this study,two legume crops(soybean and alfalfa)were used to replace maize and wheat in summer and winter,respectively,to reduce the use and negative impacts of fertilizers on the environment.Leaf mean photosynthesis in the wheat-maize and alfalfa-maize rotation systems were equal and higher than that in the wheat-cotton and wheat-soybean rotation systems,respectively.In addition,mean leaf photosynthesis in the wheat-soybean rotation system was 11.59%,28.60%and 25.37%lower than that in the wheat-cotton,wheat-maize and alfalfa-maize rotation systems.Across the five years(2012-2016),wheat yield of the wheat-soybean was lower than those of wheat-cotton and wheat-maize cropping rotations by 65.69%and 67.91%,respectively.However,the yields of wheat in the wheat-soybean increased with year.In the alfalfa-maize system,the yield of maize was lower than that in wheat-maize cropping rotation system.The results of economic benefits of the cropping rotations showed that wheat-maize cropping rotation had the highest income(29326.39 RMB ha-1)and The wheat-soybean cropping rotation had the minimum net income(18479.16 RMB ha-1).Mean net income in the wheat-maize cropping rotation was 17.08%,65.10%and 34.89%higher than that in the wheat-cotton,wheat-soybean and alfalfa-maize cropping rotations,respectively.Leguminous-crop rotation had the lowest soil pH.Soil pH in the wheat-soybean cropping rotation were 2.37%and 2.45%lower than those in the wheat-cotton,wheat-maize cropping rotations,recpectively.Soil pH in the alfalfa-maize rotation system was 1.85%lower than that in the wheat-maize cropping rotation.High N fertilization in the conventional cropping rotations did not lead to reductions in soil pH in the short-term.Conventional cropping rotations had greater soil ammonium nitrogen content than the leguminous-crop rotations.Soil ammonium nitrogen contents in wheat-maize cropping rotation were 32.01%,73.38%and 80.18%higher than that in wheat-cotton,wheat-soybean and alfalfa-maize cropping rotations,respectively.Soil total nitrogen content was lower in leguminous-crop rotations,and soil total nitrogen in the wheat-maize was 29.27%higher than that in the alfalfa-maize cropping rotation.This study results showed legume-based cropping rotations reduced soil nutrient without applying nitrogen fertilizer,leading to decrease nitrogen use efficiency,thus the yield and income were low.However,in the legume-based cropping rotations reduced soil pH in the short-term Therefore,sustainable agriculture development should be appropriately increased farmland nitrogen in the future.