Agronomic And Environmental Effects Of Partial Substitution Of Organic Manure To Chemical Fertilizers In Rice Cropping System

Rice and wheat are the main food crops in our country.Unreasonable application of chemical nitrogen fertilizer not only limited the improvement of crop yield per unit area and nitrogen use efficiency,but also caused the degradation of soil fertility and the increase in agricultural non-point source pollution.In this paper,with the two typical rice cropping systems such as rice-rice and rice-wheat cropping system,a series of field experiments were conducted to investigate the agronomic and environmental effects of partial substitution of organic manure to chemical fertilizers.The main results were as follows:1.Under the rice-rice cropping system,grain yields and shoot biomass of early rice or late rice of treatment FP?farmer practice,chemical fertilizers with normal NPK doses?,treatment CM?N??applying organic manure as a partial substitute for chemical fertilizers with the same nutrient doses as FP?and treatment CM?-N??applying organic manure as a partial substitute for chemical fertilizers with 84%nitrogen and the same phosphorus,potassium doses as FP?were significantly?P<0.05?higher than those of treatment CK?the control with no fertilizer?,treatment PK?chemical fertilizers with normal PK doses and no nitrogen?and treatment M?20%N??organic manure alone based on 20%of normal N doses?.The straw biomass?6363.4 kg/ha for early rice and 7603.0 kg/ha for late rice?,grain yield?6433.2 kg/ha for early rice and6771.3 kg/ha for late rice?and shoot biomass?13412.1 kg/ha for early rice and15126.6 kg/ha for late rice?and total grain yield?13204.5 kg/ha?of two season rices of the treatment CM?N?were not significantly different to treatment FP.The nitrogen contents in shoot organs of early rice,brown rice and rice husk of late rice of treatment CM?N?were similar to those of treatment FP,and so were the phosphorus contents in shoot organs of early rice and late rice of treatment CM?N?.Only the nitrogen contents in straw and shriveled grain of late rice was significantly?P<0.05?lower than those of treatment FP.In general,nitrogen and phosphorus contents in early or late rice of treatment CM?N?at harvesting stage were within the appropriate range.The nitrogen accumulation in shoots of early rice of treatment CM?N?was slightly higher than that of treatment FP and the nitrogen accumulation in shoot of late rice of treatment CM?N?was significantly?P<0.05?lower than that of treatment FP.There was no significant difference in shoot phosphorus accumulation between treatment CM?N?and treatment FP.Agronomic efficiency of chemical nitrogen fertilizer of treatment CM?N?was 16.58 kg/kg,being higher than 15.15 kg/kg of treatment FP,and apparent use efficiency of chemical nitrogen fertilizer was 41.0%,being higher than 37.9%of treatment FP.The application of organic manure as a partial substitute for chemical fertilizers with the same nutrient doses can meet the nitrogen and phosphorus needs of early rice or late rice,maintain the growth and grain yields of two season rices,and effectively improve the chemical nitrogen use efficiency.2.Under the rice-rice cropping system,the concentrations of soil water soluble total nitrogen and alkali-hydrolysable N of treatment FP,treatment CM?N?and treatment CM?-N?at the main growth stages of early or late rice were significantly higher than those of treatment CK and treatment PK?except soil water soluble total nitrogen of treatment FP at the harvesting stage of late rice?.The concentrations of soil water soluble total nitrogen of treatment CM?N?at the harvesting stage of early or late rice were significantly?P<0.05?higher than those of treatment FP.The concentrations of soil water soluble total nitrogen of treatment CM?N?at the tillering stage of early rice,seedling establishment and tillering stages of late rice were similar to those of FP.Only the concentration of soil water soluble total nitrogen of treatment CM?N?at seedling establishment stage of early rice was significantly?P<0.05?lower than that of treatment FP.The contents of soil alkali-hydrolysable N of treatment CM?N?at the tillering stage of early rice,seedling establishment and tillering stages of late rice were significantly?P<0.05?higher than those of treatment FP.There was no significant difference between the two treatments at other growth stages of early rice or late rice.The application of organic manure as a partial substitute for chemical fertilizers with the same nutrient doses could maintain a higher level of soil nitrogen supply.The contents of soil organic nitrogen and total acid-hydrolysable nitrogen of treatments FP,treatment CM?N?and CM?-N?at the harvesting stage of late rice were significantly?P<0.05?higher than those of treatment CK and treatment PK,and so was treatment CM?N?than that of treatment FP.Application of organic manure as a partial substitute for chemical fertilizers with the same nutrient doses could increase soil nitrogen pool.The results of statistical analysis showed that the content of soil alkali-hydrolysable N was significantly positively correlated to the contents of acid-hydrolysable mino acid-N,ammonia-N and amino sugar-N,implying that soil amino acid-N,ammonia-N and amino sugar-N were the important sources of soil available N.Soil urease and invertase activities of treatment CM?N?were higher than those of treatment FP at the main growth stages of early or late rice,even significantly?P<0.05?.Application of organic manure as a partial substitute for chemical fertilizers with the same nutrient doses can increase soil nitrogen pool,hydrolase activities,water soluble total nitrogen and soil available N,thus enhancing the nitrogen supply capacity of paddy soil.3.Under the conditions of rice-wheat cropping system,the grain yields and shoot biomass of rice or wheat of four fertilization treatments FP?farmer practice?,LRF?local recommended fertilization?,RF-OM_N?applying commercial organic manure as a partial substitute for chemical fertilizers with reduced nitrogen and phosphorus doses?and RF-S_C?applying straw as a partial substitute for chemical fertilizers with reduced nitrogen and phosphorus doses?were significantly?P<0.05?higher than those of treatment CK?the control,no fertilizer?.Rice grain yield and shoot biomass of treatment RF-OM_N were 7290.0 kg/ha and 15234.9 kg/ha respectively,which were significantly higher?P<0.05?than those of treatment LRF and treatment RF-S_C,and similar to those of treatment FP.There were no significant differences in rice grain yield and shoot biomass among the four fertilization treatments.The nitrogen contents in shoot organs of rice or wheat plants of treatment FP,treatment LRF,treatment RF-OM_N and treatment RF-S_C were significantly?P<0.05?higher than those of treatment CK.Nitrogen contents in shoot organs of rice plants of treatment RF-OM_N was not significantly different to those of treatment LRF,phosphorus contents in brown rice and husk of treatment RF-OM_N was not significantly different to those of treatment FP,and potassium contents in shoot organs of rice plants of treatment RF-OM_N and RF-S_C were higher than those of treatment FP,even significantly?P<0.05?.Nitrogen and phosphorus contents in wheat straw and grain of treatment RF-OM_N were not significantly different to those of treatment LRF.Potassium contents in wheat straw and grain of treatment RF-OM_N and RF-S_C were higher than those of treatment FP or LRF.There was no significant difference in nitrogen accumulation in rice shoots between treatment RF-OM_N and treatment LRF.There were no significant differences in phosphorus accumulation in brown rice and rice husk between treatment RF-OM_N and treatment FP.The amounts of potassium accumulated in shoot organs of rice plants were higher than those of treatment FP and LRF,even significantly?P<0.05?.The amounts of nitrogen and phosphorus accumulated in wheat straw and grain of treatment RF-OM_N was not significantly different to those of treatment LRF.The amount of potassium accumulated in wheat straw and grain was higher than those of treatment FP.The agronomic efficiency,apparent use efficiency and partial factor productivity of nitrogen fertilizer in rice and wheat of treatment RF-OM_N and treatment RF-S_C were significantly?P<0.05?higher than those of treatment FP and treatment LRF,implying that the application of organic manure as a partial substitute for chemical fertilizers could improve the utilization efficiency of nitrogen fertilizer.The concentrations of soil water-soluble NH₄⁺-N,NO₃^--N and water-soluble total nitrogen at the main growth stages of rice or wheat of treatment FP,treatment LRF,treatment RF-OM_N and treatment RF-S_C were significantly?P<0.05?higher than those of treatment CK.The concentrations of water-soluble total nitrogen at the main growth stages of rice or wheat of treatment RF-OM_N were higher than those of treatment LRF,even significantly?P<0.05?,and were similar to those of treatment FP.There were no significant differences in soil alkali-hydrolysable N and available phosphorus contents between treatment RF-OM_N and treatment LRF at the harvesting stage of rice or wheat.The contents of exchangeable potassium and slowly-available potassium of treatment RF-OM_N were higher than those of treatment FP and treatment LRF.Application of commercial organic manure as a partial substitute for chemical fertilizers can meet the nutrient requirements of rice and wheat,maintain normal growth and grain yield,improve nitrogen use efficiency,as well as maintain higher levels of soil available nutrients and improve soil fertilizer supply.4.The results of the field comparison experiment showed that the grain yields of rice and wheat of treatment CM?optimal control fertilization?were 8066.7 kg/ha and4699.8 kg/ha respectively,and were not significantly different to those of treatment FP?farmer practice?.The nitrogen,phosphorus and potassium contents in and amounts accumulated in shoot organs of rice and wheat plants of treatment CM were similar to those of treatment FP.The partial factor productivity of nitrogen fertilizer and phosphate fertilizer of treatment CM were 33.61 kg/kg and 76.83 kg/kg for rice respectively,and were 20.89 kg/kg and 44.76 kg/kg for wheat respectively,and were significantly?P<0.05?higher than those of treatment FP.Compared with treatment FP,the cumulative runoff losses of total nitrogen and total phosphorus of treatment CM in rice season were reduced by 40.9%and 22.5%,respectively,and were reduced by14.8%and 9.0%,respectively in wheat season.The annual cumulative runoff losses of total nitrogen and total phosphorus of treatment CM were reduced by 34.0%and18.6%,respectively.The reduction of runoff TN and TP loads were obvious.Optimal control fertilization could catch the nutrient needs of crops,maintain the normal growth and grain yields of crops,and improve the utilization efficiency of nitrogen and phosphate fertilizers,as well as effectively reduce the runoff loss of nitrogen and phosphorus from rice-wheat cropping system,which should be extensively applied in agricultural production.In such cases,the recommended fertilization rates are N 240kg/ha,P₂O₅ 105 kg/ha,K₂O 120 kg/ha for rice,and N 225 kg/ha,P₂O₅ 105 kg/ha,K₂O120 kg/ha for wheat,meanwhile,20%nitrogen from organic manure is used instead of chemical fertilizer nitrogen.