| Shaanxi Guanzhong Plain is a typical winter wheat-summer maize rotation region, wherethe maize straw return to soil before winter wheat sowing is one of the main crop strawmanagement patterns. In order to increase crop yield and fertilizer utilization efficiency byoptimizing nutrient management of winter wheat under the maize straw return to soilcondition, a field experiment was conducted to study the N release characteristic of maizestraw and the effects of straw return on soil N supply and nitrogen uptake of winter wheatwithout and with nitrogen fertilization from2012to2013, using the method of nylon net bagand15N isotope cross labeled N fertilizer and maize straw. Also a two-year long location-fixedfield experiment was carried out to study the effects of maize straw return to soil on grainyield of the following wheat and its (nitrogen, phosphorus and potassium) N P K uptake andutilization at five N application rates of0,84,168,252and336kg ha-1. Main results were asfollows:1. The amount of total N remained in the straw was decreased from seeding to the periodbefore wintering of wheat, then increased until returning green stage and declined graduallylater, as a result of N departure by organic N mineralization from the returned straw and Ncapture of mineral N from the soil and fertilizer. From sowing to harvest of wheat, the amountof net N release to soil were9.4and7.2kg ha-1by the straw under no and200kg N ha-1fertilization, respectively, and they were the balance of19.7and18.3kg N ha-1released fromthe straw,10.4and7.6kg ha-1of N captured from the soil into straw, and3.5kg N ha-1onlyentered into the straw from fertilizer. At harvest, it was found that65.1%and67.7%of strawN were still left in the straw,31.5%and30.4%were released into the soil or lost, and only afew,3.4%and1.9%were absorbed and used by wheat, at respectively no and200kg N ha-1fertilization. Also,24.1%,74.1%and1.8%of fertilizer N were observed respectivelyabsorbed and used by wheat, left in the soil or lost, and captured by the returned maize strawunder straw return condition, when the N application rate was200kg N ha-1. Under strawreturn condition, soil N was shown to contribute the most to the aboveground part N uptake ofwheat, and then was the fertilizer N, while the straw N contributed the least, of which theywere98.3%and70.3%,0and29.0%,1.7%and0.7%, at no and200kg N ha-1fertilization, respectively. In the aboveground part of wheat, N derived from soil, fertilizer and straw weremainly distributed in the grain of wheat, and they were respectively98.1%,0and1.9%whenno nitrogen fertilization,69.9%,29.4%and0.7%when nitrogen fertilizer was applied into thesoil.2. Winter wheat grain yield was increased by the straw return treatment when the N ratewas over153and187kg ha-1, respectively in the first and second year, compared with themaize straw removal treatment, and the grain yield was decreased when the N rate was lowerthan that. Among the wheat yield component factors, the increased grain yield under strawreturn condition was mainly caused by the enhanced spike number per hectare at higher N rate.The amount of N, P and K uptake in aboveground of winter wheat was increased by strawreturn to soil when the N application rate was higher than275,123and213kg ha-1in the firstyear and200,165and241kg ha-1in the second year, respectively, but their harvest indexesdid not keep the increasing tendency under high levels of N rates. Also, the reduction of Pconcentration in winter wheat grain was found due to over-fertilization of nitrogen. Therefore,in Shaanxi Guanzhong Plain, the N application rate for winter wheat is suggested to be withinthe range of150to200kg N ha-1, so as to ensure a higher wheat yield and utilizationefficiency of nutrients when the maize straw is returned to soil before winter wheat sowing. |
