Effects Of Rice Straw Returning On Soil Nutrition Balance And Nitrogen Utilization In Wheat And Its Ecological Mechanism

Straw incorporation is an important ways of utilization of straw,and affects nutrient balance of soil and crop yield and nitrogen utilization efficiency.Verifying the effects of straw incorporation on soil nutrient banlance and nitrogen utilization in wheat and its ecological mechanism is important for improving wheat yield,benefit and protect environment.A field experiment(2010-2013)was initiated on a sandy loam soil to examine the effect of rice straw management and nitrogen rates on the temporal-spatial distributions of soil inorganic N,nitrogen accumulation during different growth stages,soil nitrogen apparent surplus amount,the growth,yield and fertilizer-N use efficiency of wheat and soil character.Rice straw was enclosed in nylon bags and returned to wheat field under nitrogen applications to study the decomposition characteristics and nutrient releas patterns of ric straw.The major results as follows:1.Grain yield and nitrogen utilization efficiency were increased after straw returned.The grain yield of wheat in the high fertility soil is higher than that in the lower fertility soil.Grain yield increased significautly with the increasing of nitrogen rate tilled 180 kg hm-2.Grain yield significantly increased under RS treatments than that under RSO treatments in 2011-2012 and 2012-2013.Compared with rice straw remove treatments,tiller number,plant N uptake and dry matter accumulation of wheat was lower at early growth stage under straw incorporation treatments.However,with the wheat growth,many nutrients released from rice straw,so the spike rate was increased,and plant N uptake and dry matter accumulation was higher at maturity stage under straw incorporation treatments.The rice straw incorporation shortened the grain filling period,but enhanced the maximum grain filling rate and mean grain filling rate,then increased 1000-grain weight.There was a lower effective panicle number but higher kernel per spike and weight of 1000 kernels,favorable to improve the wheat yield.The nitrogen utilization was higher under low soil fertility than that under high soil fertility,but nitrogen utilization efficiency decreased with the increasing of nitrogen rate.The appropriate nitrogen rate were 223-229 kg hm-2? 247-286 kg hm-2 for high-yield in high and low soil fertility level,and 233-252 kg hm-2 ? 238-256 kg hm-2 for RS treatment and RSO treatment.The straw incorporation treatments showed the nitrogen recovery efficiency lower from sowing to jointing than no straw incorporation treatments,but significantly higher at the period of jointing to maturity,and also increased agronomic use efficiency of fertilizer-N and physiology use efficiency.2.This study made clear the effects of straw incorporation and nitrogen fertilizer on the regulation of soil inorganic nitrogen migration and apparent soil nitrogen budget.NO3--N and NH4+-N contents in the 0-40 cm soil layer increased with increasing N rate.Nitrogen fertilizer application increased soil nitrogen content during different growth stages.Under the condition of same N fertilizer application amount,The straw incorporation treatments usually had lower contents of NH4+-N and NO3--N in soil at the early growth stage,but had higher soil inorganic N content,plant N uptake at the later growth stages compared with the corresponding the straw removal treatments,suggesting that rice straw provides nutrients to wheat at the later growing stages.Apparent N deficit was found throughout wheat growth stages in soil without N fertilizer application,but Apparent N deficit and surplus were different at different growth stages with N fertilizer application treatments.Apparent N surplus occurred during sowing to jointing stage when N rate was above 120 kg N hm-2,and increased with nitrogen rate increasing.During the whole growth season,the straw retained treatments had lower apparent N surplus than straw remove treatments.The appropriate nitrogen rate were 184-199 kg hm-2 and 229-253 kg hm-2 for high-yield,high nitrogen utilization and low apparent N surplus(ANS)in high and low soil fertility level,and 188-206 kg hm-2 and 191-210 kg hm-2 for RS treatments and RSO treatments.RS treatments had higher the grain yield,NAE and had lower ANS at appropriate nitrogen rate than RSO treatments.Appropriate reduction of basal N with straw incorporation could decrease the NO3--N leaching at the early stages.3.Straw incorporation impoved soil character.Soil temperature,water content increased and the value of pH decreased significantly,while increased the content of soil organic matter under Straw incorporation.The mass of soil total nitrogen increased with increasing N rate,but there was no effect of N fertilization on soil organic matter.The straw incorporation increased the activities of hydrogen peroxidase,phosphatase and urease,and significantly increased the microbial quantity.The N fertilization application rate had significant effect on activity of enzymes and quantity of microbial in wheat season,but effects of nitrogen application rates on different soil enzymes activities are different.The activities of hydrogen peroxidase,phosphatase increased with applied N rates until 180 kg N hm-2,but urease activity increase with increasing N rate.Compared with no straw incorporation,the maximum increase of population of microbial under straw returned treatments was recorded with 240 kg N hm-2.4.This study made clear the characteristic of decomposing and nutrient releasing of rice straw.The decomposition rate of rice straw was much faster within the first 30 days and then slowed down at late stage.Nitrogen applications significantly affected decomposition of rice straw,and increased with nitrogen rate increasing.The rice straw cumulative decomposition rates were 49.78-65.18%after one wheat season.The sequence nutrients release rate of rice straw increased with nitrogen rate increasing.C release rate of rice straw were 52.04-66.05%,N were 48.20-64.08%,P were 61.78-80.65%,K were 94.73-97.10%after 210 days of straw incorporation.The sequence of nutrient release rates were K>P>C>N.As a result,nitrogen fertilizer can promote the rice straw to decompose and release the nutrients.In conclusion,the appropriate nitrogen rate for high-yield and high-yield,high-NAE and low-ANS was lower under RS treatments than that under RSO teatments.All rice straw return treatments increased wheat yield,decreased the apparent nitrogen surplus amount,maintained nitrogen balance,enhance nitrogen utilization efficiency,soil enzyme activity and biological characteristics and inproved soil physic-chemical properties character.