Study On The Effects And Its Mechanism Of The Combination With Organic Materials On Soil Fertility Under Rice-rice-vegetable Rotation System

As one of the most important grain crops,rice(Oryza.sativa L.)is widespread all over the country.In recent years,we are confronted with the condition with gradual increasing in the number of population every year,continuous declining of arable area and relative shortage of nature resources.Thus,the improvement of farmland quality is one of the important measures to ensure the food security in China.Southern China is characterized by a multiple cropping,where is suitable with the cropping system of rice-rice-vegetables.However,series problems such as soil acidification,the decline of soil fertility and the slow effect of single straw returning result from high intensive planting under this rotation system,are becoming more and more serious.Therefore,on the premise of ensuring food security,it is of great significance to make full use of agricultural organic resources,especially to optimize the combination management of organic materials to improve soil acidification and harden and soil fertility,which could provide technical and theoretical support for the sustainable development of agriculture and the security of ecological environment.According to the systematic research,we have obtained the following results and conclusions.(1)Rice straw returning(SR)and its combination with organic materials effectively improved crop yield.The SR treatment improved the average of relative yield by 13.5%in comparison to treatment without rice straw returning(CK).From the perspective of whole test,the annual yield of treatment with rice straw combined with peanut bran(SRPB)was the highest,4054 kg ha^-1 which was 9.24%higher than SR treatment.Besides,the number of effective spikes and thousand kernel weights were the dominant factors of yield components in this research.Besides,the nutrient(N,P,K)uptake of crops showed obvious seasonal variation that the nutrient uptake of rice was higher than vegetable,and the nutrient demand of early rice was greater than late rice.The absorption of N,P,and K is at the ratio of 1:0.2:1.25 for rice and 1:0.2:2 for vegetable.(2)The soil organic carbon and total nitrogen content in all fertilization treatments were increased with the increase of particle size aggregate.Compared with the SR treatment,SRBC and SRBM treatment effectively increased>2 mm particle size aggregate and reduced<0.25 mm particle size aggregate,and the former also enhanced the carbon and nitrogen ratio(C/N)in soil aggregate.In general,SR and integration of rice straw with organic materials appreciably improved soil structure by the decrease of soil bulk density and improvement of soil porosity,as well as the change of soil aggregates in different sizes,distribution of carbon and nitrogen nutrients and improvement of soil structure.(3)The results of statistic analyzing showed that the soil environment of root growth is conducive to the increase of soil p H value,soil organic carbon and soil available nutrients.Compared with CK treatment,SR treatment significantly increased SOC,alkali hydrolyzable nitrogen(AN),AK and urease(UE)activity by 5.26%,8.33%,53.4%respectively.Compared with the SR treatment,the SOC of SRPB,SRBC and SRBM treatment also obviously increased by 5.71%,43.93%and 12.14%respectively.After six seasons of cultivation,SRBC and SRBM improved soil p H value by 5.53%and 3.85%compared with SR treatment,and the former was significantly higher than SR treatment.However,SRPB significantly decreased soil p H value by 5.53%in comparison to SR treatment.All the treatments combined with organic materials significantly increased AK content and UE activity.It deserved to be mentioned that rice-rice-vegetable planting system belongs to a typical dry and wet alternation process,and soil biochemical properties varied with the season and soil humidity.Soil p H value and UE activity gradually decreased,while the microbial biomass carbon and nitrogen content and the effective potassium content increased during the process from wet to dry process.Similarly,soil p H value increased slightly while soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and AK content decreased during the process from dry season to wet season.(4)In this study,11 key indexes of soil fertility under rice-rice-vegetable cropping system were selected to evaluate soil fertility quality by factor analysis method.And the effects of different fertilization measures on soil fertility finally were determined by the comprehensive score of factors.Results showed that the trend of soil fertility is:SRBC>SRBM>SRPB>SR>CK,indicated that the effect of rice straw returning combined with organic materials treatment on improving soil fertility was better than SR treatment.Besides,the improvement of soil fertility by the application of biochar in straw was mainly attributed to the increase of soil aggregate C/N ratio,soil p H value,SOC,MBC,MBN,AK content and soil UE activity.(5)The research of soil microbial showed that the SR treatment obviously improved the number of soil microorganisms,including bacteria,fungi and actinomycetes.SRPB and SRBM treatment were benefit to promote the increase of soil microbial population while the SRBC treatment reduced soil microbial population instead.Canonical correspondence analysis demonstrated that the variation of soil microbial species abundance could be well explained by soil chemical properties,and the first two axes explained 47.41%of the total variation.N_min and AK value explained 27.2%and 13.7%of the microbial population changes respectively,indicating that the changes in microbial community structure in organic ameliorant treatments were mainly driven by the changes in soil AK and N_min.