Effect Of Long-term Application Of Fertilizer And Rice Staw On Soil Nitrogen Fertility And Soil Productivity In Reddish Paddy Soil

A long-term field experiment with the double rice and winter fallow cropping system was conducted based on the Key Field Monitoring Experimental Station for Reddish Paddy Soil Eco-environment in Wangcheng,Ministry of Agriculture,China,to study the effect of long-term application of fertilizer and rice straw on the soil N fertility and productivity in reddish paddy soil.The treatments selected in this study were:CK(no fertilizer applied),NP(N,P fertilizers),NPK(N,P and K fertilizers),NP+RS(NP plus rice straw) and NPK+RS(NPK plus rice straw).The results were as follow:1.With time over 27 years study period,the soil total N,alkaline hydrolysable N and mineralizable N change trends in all treatments were positive except CK which showed negative trend.The treatments of application combining fertilizer with rice straw showed significantly positive trend(p<0.01).Compared with CK,the content of total N hydrolyzed by 6M HCl was increased in both long-term application of fertilizer and combining application of fertilizer with rice straw.The former mainly increased the contents of ammonium N and unidentified N, however,the latter increased all forms of acid hydrolysable organic N. Fertilization increased the content of microbial biomass N(MBN) compared with CK.MBN in NP+RS treatment was increased by 23.7% over NP treatment,and NPK+RS treatment by 18.0%over NPK treatment,which showed significant differences(p<0.01).Compared with CK,long-term application with fertilizer only have little impact on content of soil fixed ammonium,however,the content of soil fixed ammonium was increased significantly in application combining fertilizer with rice straw treatments.2.Long-term application combining fertilizer with rice straw increased the content of water-stable aggregates in the 2～5mm and 0.5～2mm size fraction.Long-term application combining fertilizer with rice straw significantly increased the contents and storage of total nitrogen(TN) and mineralizable N(MN) in water-stable macroaggregates (2～5mm,0.5～2mm).This study also found that balanced fertilization treatments with N,P and K fertilizers could increased the contents and storages of TN and PMN in the water-stable macroaggregates(2～5mm, 0.5～2mm) compared with CK treatment,but increase in the range of TN and MN was lower in NPK treatment than in the treatments with combination application of fertilizer with the rice straw.Water-stable aggregate protected N were significantly greater for macroaggregates (2～5mm and 0.5～2mm) than for microaggregates(<0.25mm),indicating physical protection of N within macroaggregates.3.In all treatment,soil N was mineralized rapidly in 4～6 weeks, then slowly after 6^th week.The amount of mineralizable N release was almost zero after the 8^th week.Long-term application combining fertilizer with rice straw significantly increased N potential(N₀).Balanced fertilization treatment with N,P and K fertilizers also increased N₀ compared with CK,but N₀ value was lower than the treatments with combination application of fertilizer with the rice straw.The k decreased with the increase of N₀.Under long-term fertilization of fertilizer and rice straw,HKCl-NH₄,HKCl_HYDR,ISNT and MBN all indicated that the fraction of available N of different treatments was in the order of long-term application combining fertilizer with rice straw treatment > fertilizer use only treatment >no fertilizer treatment.All of the four indices were sensitive to the change of available N under long-term fertilization in reddish paddy soil.4.The grain yield trend with CK and NP treatment was negative both in the early and late rice,whereas with the rest treatment was positive.Long-term fertilization,especially application combining fertilizer with rice straw,improved the N uptake both in the grain and rice straw.N use efficiency and agronomic efficiency of different treatments were NP+RS>NP,NPK+RS>NPK,which revealed that long-term application of rice straw can increase the N efficiency.The values of apparent N balance in all treatments were positive except CK where the value was negative.Long-term application combining fertilizer with rice straw could adjust the value of apparent N balance to a suitable range.