Change Characteristics Of Conservation Tillage On Soil Water,Carbon And Nitrogen In Farmland

Water shortage and the lower use efficiency of water and fertilizer is the main factor limiting agriculture development in Henan province.Conservation tillage,an advanced farming technology,improves water retention capacity and soil fertility.With the consideration of actual situation in Henan province,it is necessary to investigate the effect of long-term conservation tillage on soil water,carbon and nitrogen in combination,which is important to the promotion of conservation tillage.However,with the limits of the field experiment,the variation of soil water,carbon and nitrogen and the optimal conservation tillage pattern need to be further study when the conventional tillage is transformed to the conservation tillages.Thus,based on the long term field experiment and RZWQM(Root Zone Water Quality Model)simulation,annual variation of soil water,carbon and nitrogen and vertical distribution of soil water,carbon and nitrogen during different growth period of winter wheat stages under long-term conservation tillage were studied.The RZWQM model was applied to simulate the dynamics of soil water,carbon and nitrogen when the conventional tillage was transformed to conservation tillages.The optimal conservation tillage transformation pattern was selected.This study could provide scientific basis for the application of conservation tillage in Henan province.(1)There were significant differences in soil water among different soil layer and water storage(0-100 cm)under different tillages in the same year(P < 0.05).Compared with the conventional tillage,soil water and water storage(0-100 cm)were significantly improved during key growth period for no-tillage and straw returning in double season treatments.Soil water retention capacity of no-tillage and straw returning in double season treatments was better than that of subsoiling treatment,especially for the dry years.The height,LAI,biomass and yield of winter wheat was significantly improved by conservation tillages.Grain number and thousand kernel weight of winter wheat were the key factors affecting winter wheat yield.In addition,the increment of yield under no-tillage treatment was greater than that under straw returning in double season and subsoiling treatments in dry year,the WUE was also significantly improved.And the yield of the straw returning treatment was the highest in the more rainfall year.(2)The increment of SOC content and SOC storage under straw returning in double season treatment was greater than that under other tillage treatments.Compared with conventional tillage,the mean annual variation,relative annual variation and annual cumulative variation of SOC contents was improved under no-tillage and straw returning in double season treatments.The relative annual variation and annual cumulative variation of SOC contents under straw returning in double season treatments was 0.23 g·kg-1 and 0.45 kg·m-2·a-1,respectively,which was greater than those under no-tillage treatment.Compared with SOC of the initial experiment year,SOC content and SOC storage(0-20 cm)was increased in different degrees under no-tillage,subsoiling and straw returning in double season treatments.There were significant differences in SOC contents under different tillage treatments(P < 0.05).(3)The contents of SOC and total nitrogen at depth of 0 to 100 cm were decreased along soil depth under different tillage treatments.Compared with soil surface,SOC and the total nitrogen content at depth of 60 to 100 cm was significantly decreased and reached to the stable value.Compared with the conventional tillage,the contents of SOC and the total nitrogen at depth of 0 to 40 cm was increased under no-tillage and straw returning in double season treatments.Compared with conversation tillage,soil NO3--N content(0-100 cm)was significantly increased in jointing and filling stages of winter wheat under no-tillage treatment.From emergency to jointing stage,soil NH4+-N content at depth of 0-20,20-40,40-60,60-80,and 80-100 cm was stable and lower;while NH4+-N content was increased from jointing to harvesting stage.There were significant differences in NH4+-N content among different tillage treatments after jointing stage of winter wheat.Compared with conventional tillage,NH4+-N content(0-40 cm)was significantly increased during jointing stage under straw returning in double season treatment.(4)The ratio of C/N was gradually increased with growth periods of winter wheat under different tillages.N accumulation amount was increased firstly,then decreased,and finally reached the maximum value in jointing stage for the whole greater periods of winter wheat.Compared with conventional tillage,average nitrogen accumulation amount in stem,leaf and ear was increased 44.3%?80.5%?70.9%,respectively,nitrogen accumulation of stem was significantly decreased 14.1%,while its nitrogen accumulation in ear was significantly increased during harvesting stage under 2-year no-tillage treatment.Moreover,compared with conversation tillage,nitrogen translocation amount and translocation ratio of vegetative organs,and the contribution to grain were significantly increased(P < 0.05)under no-tillage and straw returning in double treatments.However,the increment of nitrogen translocation and absorption was unstable under subsoiling treatment.Therefore,long-term effect of nitrogen translocation for different tillage treatments was in the order of no-tillage > straw returning in double treatment > subsoiling.(5)With the calibration and validation of RZWQM2,the results of soil water(0-100 cm),winter wheat biomass and yield was better than those of NO3--N contents(0-100cm)and SOC on soil surface for different tillage treatments.The variation of soil water,SOC and soil nitrogen before and after tillage transformation was also simulated by RZWQM2.Compared with conventional tillage,soil water storage(0-100 cm)was significantly increased,soil water loss was reduced,the WUE and NUE was improved,and SOC contents of soil surface and wheat yield was increased when conventional tillage was transformed to no tillage treatment.Therefore,soil water storage and soil fertility conservation of the transformation of conservation tillage to no-tillage was the best.