Research On The Fertilization Pattern And Nitrogen Use Efficiency For Middle And Low Productive Yellow Clayey Paddy Soil

Yellow clayey paddy soil is a typical soil with low productivity in southern China.It has some features such as strong acidity,lack of soil organic matter,and low available nutrient contents,making rice grain yield in a low level for many years.With increasing population and shrinking of cultivated land area,it is particularly important to improve the per-unit yields,especially in the farmland that provides low or medium yields.This study takes typical yellow clayey paddy soil in Jinqu Basin as research object.Base on field experiments including the comparison of the effects of long-term application of chemical fertilizer and different organic manures,single basal application of new types of slow/controlled release nitrogen fertilizers,and different cultivation methods and fertilization models,the following three aspects were studied:(1)the mechanism of reduction of key limiting factors and the improvement of soil fertility,(2)implementation of improving rice yield and nitrogen use efficiency together,(3)characteristics of rice growth and development and yield formation in high yield and high efficiency model.The main results were as follows:1.Compared to NPK alone,application of organic and inorganic fertilizers not only increased the five-year average single cropping rice grain yield(6.6%～11.2%),also significantly improved soil properties,such as soil organic matter(SOM),total nitrogen(TN),and microbial biomass carbon(MBC).Combined application of NPK and cattle manure showed the highest 5-year average rice grain yield(9.66 t ha-1)and the greatest increase in SOM,TN,available P and pH,and significantly deceased the soil bulk density.2.NPK with cattle manure additions showed the highest contents of TOC,KMnO4-C and MBC in 0-5 cm,5-10 cm and 10-20 cm soil depths.CMI,KMnO4-C and MBC were suitable for use as sensitive indicators for assessing changes in TOC in the 0-20 cm soil depth.POC was not sensitive to changes in management practices in the deeper soil layer.Overall,the integrated use of NPK and cattle manure was the most efficient management system for improving carbon sequestering.3.Compared to NPK alone,NPK with cattle manure addition significantly increased the 0.23,0.16,0.29 and 0.27 units(P<0.05)in 0-5 cm,5-10 cm,10-20 cm and 20-30 cm,respectively.There were no differences in soil pH between NPK alone and NPK with the other three organic manures(spent mushroom compost,milk vetch and rice straw).Long-term application of cattle manure improved the contents of exchange base cations in different soil layers,particularly in Ca2+ and Mg2+.At present,120 kg K2O hm-2 yr-1 inputs could not meet the nutrient balance.The content of available K in soil showed a trend of decreasing year by year.Long-term application of cattle manure decreased the content of exchangeable acidity and Al3+.Overall,combined application of NPK and cattle manure was the best way to ameliorate soil acidity.4.Acidobacteria and Proteobacteria were the microbial dominant groups in yellow clayey paddy soil.SOC was the greatest influence factor of soil microbial community diversity.Five consecutive years use of chemical fertilizer and organic manures enhanced the SOC content,thereby increasing the number of soil bacteria species and the community diversity.NPK with cattle manure addition showed the most profound effect.Additionally,combined application of NPK and cattle manure improved the relative abundance of Rhizobium and affected the biogeochemical processes of soil nitrogen.5.Different fertilization modes should be adopted in different rice cropping systems.Compared to PU 100%,NPU 100%significantly increased 5-year average rice grain yield by 9.7%for early rice and 9.5%for late rice,nitrogen use efficiency(NUE)by 10.3%for early rice and 10.1%for late rice,respectively.However,there were no differences in rice grain yield and nitrogen use efficiency for single rice.No obviously positive effect in SPCU 100%treatment was found in early rice,while significant improvement in yield and NUE were observed in single rice and late rice.SPCU 70%+ PU 30%significantly improved rice grain yield and NUE for different rice cropping systems.6.On average,the grain yield of controlled-release fertilizer significantly increased with TFS and TGS by 7.7%(9.9 vs.9.2 t ha-1)and 5.2%(9.9 vs.9.5 t ha-1),respectively,compared with the conventional N fertilizer split applications treatment.With the direct seeding method,a single basal application of controlled-release fertilizer resulted in a 3%decline(8,2 vs.8.5 t ha-1)in the average 4-year grain yield when compared with the split applications of urea treatment.Across both N treatments,the average grain yield of TFS and TGS were significantly higher(14.0%and 16.1%)than that obtained with DS(P<0.05).The improved leaf SPAD,leaf area index,and leaf area duration after the heading stage are hypothesized as the main reason for the greater grain yield of transplanted rice.