The Effect Of Maize Straw Return On The Bio-availability Of Nitrogen In Farmland Soil

This paper use nitrogen fertilizer and straw labeled by 15N separately to study 1) straw nitrogen mineralization at short time; 2) soil nitrogen and nitrogen bio-availability change under different straw and fertilizer application, then suggest nitrogen application advicePot experiments,1) straw return pot experiment under two different nitrogen soils, including CK, straw return only (S), middle nitrogenous fertilizer application(150kgN/hm2,Nl), high nitrogenous fertilizer application(300kgN/hm2,N2), straw return matched with middle nitrogen application (N1S), straw return matched with high nitrogen application (N2S); 2) straw decomposition pot experiment, including straw return matched with middle nitrogen application (N1S),straw return matched with high nitrogen application (N2S). Two pot experiments answer the following questions lthe rule of straw-N mineralization and immobilation after straw return, and the utilization extent in a short time; 3) nitrogen change and nitrogen bio-availability after long-term straw return, then suggest nitrogen application advice. The main results are as follows:1 15N tracing shows that:1) Fertilizer-N is the main source of wheat nitrogen accumulation in pot experiment. N1 treat, above 60% wheat nitrogen accumulation derive from nitrogen fertilizer in high nitrogen content soil, while above 68% in poor nitrogen content soil. N2 treat, above 75% nitrogen accumulation derive from fertilizer in two soils. Straw nitrogen offer 8%-30%, which decreased with nitrogen application adding. S treat, straw-N offered 30% of nitrogen accumulation, N1S, straw-N offered 10%, N2S,7.6%.2 Pot experiment with 15N tracing showed that: N recovery for winter wheat and residual rate in soil decreased with nitrogen application increasing, while N recovery for winter wheat decreased and residual rate in soil increased when nitrogen fertilizer applied with straw. Poor nitrogen content soil, Nl treat, N recovery for winter wheat was 41.0%, residual rate in soil was 16.9%, Compared with N1 treat, N recovery of N2 treat decreased by 5.4percent, residual rate decreased by 2.2 percent.Compared with N1 treat, N recovery of N1S decreased by 15.7 percent. The utilization of straw-N increased with nitrogen application. S treat, wheat use 4.2% of straw-N, N1S,13.5%, while N2S,14.5%.3 Nitrogen applications and straw return improved soil microbial biomass nitrogen (SMBN), and the content in high nitrogen soil is higher than that in poor nitrogen soil at the same fertilizer application and straw. S treat, MBN is 32.3mg/kg, N1 treat,35.5mg/kg, N1S 52mg/kg, in poor nitrogen soil. The trend in high nitrogen soil is the same. We can distinguish the source of SMBN by 15N tracing,15N tracing show that:1) fertilizer-N account fod more proportion with nitrogen level increasing. Mature period in poor nitrogen soil,12% SMBN derive from fertilizer-N in Nl treat,21% MBN derive from fertilizer-N in N2 treat.2) soil microbial biomass use more straw-N with nitrogen fertilizer level rising. Microbial biomass in high nitrogen soil use more straw-N than in poor nitrogen soil under the same nitrogen and straw condition. S treat, straw in poor and high nitrogen content soil provide 22.5mg and 35.5mg in returning green stage, account for 11.1% and 17.3%, respectively. When straw applied with middle nitrogen, straw provide 36.5mg and43mg in returning green stage, account for 17.7% and 20.7%, respectively.3) soil nitrogen is the main source of microbial biomass.the proportion decreases with nitrogen fertilizer application.N1 N2 treat, soil-N provide more than 75%.4 Straw burying show that:buried straw adsorbed or immobiled and released nitrogen process, seedling stage, buried straw showed net immobilization, straw fixed 11.3kg/hm2 and 20.3kg/hm2 nitrogen under middle and high nitrogen application in poor nitrogen content soil, respectively, while fixed 12.0kg/hm2 and 22.7kg/hm2 in high nitrogen content soil, then released in the following developing period. Harvesting period, buried straw net mineralized 17.5kg/hm2 and 8.5kg/hm2,33.3% and 16.2% of the straw-nitrogen application, respectively, while net mineralized 22.9kg/hm2 and 20.9kg/hm2, accounting for 43.6% and 39.8% of the straw-N, respectively.5 This paper choosed soil total nitrogen content and soil micrial bimass nitrogen as index to analyze soil after longterm straw return and nitrogen application, then conbined with nitrogen application in northchina and the results of pot experiment, we found soil need extra nitrogen application under straw return (9000kg/hm2) and middle nitrogen level (150kg/hm2) condition, and soil donot need more nitrogen fertilizer under straw return (9000kg/hm2) and high nitrogen level (300kg/hm2) condition...