Grain Yield Formation And Nutrient Use Of Winter Wheat Under Soil Surface Mulching On Dryland

In China agriculture production, dry farming not only occupies a large proportion atpresent, and is also considered to be an important part and the front edge in the future. Innorthwest China, where large areas of lands can be used for agriculture, shortage of watersupply and poor soil fertility limit agricultural development. Mulching soil surface by strawand plastic film can not only promote the natural precipitation use by crops, but also affectenvironment conditions related to crop growing, such as soil temperature and nutrientbioavailability. Therefore, how to manage the nutrients in soil and crop system under soilsurface mulching, is still an important issue to realize high grain yield and high efficiency ofresources in these dryland areas. In order to understand the crop grain yield formation andnutrient use under soil surface mulching, a long-term field experiment with winter wheat astest crop was conducted at sub-humid to drought area in the southern part of the Loess Plateau,and main results obtained are as follows:1. With no N fertilization, grain yield of winter wheat was not observed to be promotedby soil surface mulching, and especially dry matter synthesis after anthesis and itstranslocation to grains, grain yield and harvest indices were greatly decreased by strawmulching. Plastic film mulching combined with application of N fertilizer, or strawmulching at N rate up to240kg hm^-2were able to enhance wheat growth before and afteranthesis and translocation of dry matter synthesized post anthesis to grain, and thus increaseshoot biomass, grain yield and harvesting indices. Compared to mulching soil surface byplastic film, straw mulching was able to promote dry matter synthetic and its translocation tograin after anthesis, and then increase the grain yield at only high rate of N fertilizer.2. At low rate of N fertilizer (120kg hm^-2), straw mulching did not increase Nabsorption, its translocation and utilization yet, while plastic film mulching was found topromote N translocation, N uptake of shoot and grain and N harvest indices at harvest, Nproductivity and utilization efficiency were therefore increased. When N rate was increased to240kg hm^-2, soil surface mulching not only promoted N translocation, but also increased Nuptake after anthesis. At harvest, N uptake of shoot and grain and N harvest indices wereincreased significantly. Therefore, Soil surface mulching can improve grain N uptake and N utilization only under reasonable N fertilization rates.3. At low rate of N fertilizer (120kg hm^-2), straw mulching still could not promote Pabsorption and utilization. Plastic film mulching combined with application of N fertilizer andstraw mulching at high N rate (240kg hm^-2) not only increased P uptake before and afteranthesis, but also improved P translocation from vegetative organs to grain, significantlyincreasing the productivity of P fertilizer and plant P accumulation. Therefore, rates of Nfertilization was the main factor determining whether the soil surface mulching wouldimprove P uptake, accumulation, distribution and utilization or not.4. No matter how much N fertilization was used, soil surface mulching by straw orplastic film was observed to be able to improve K accumulation before anthesis, increase Ktranslocation and translocation efficiency, and also the loss and loss efficiency of K. Therefore,soil surface mulching could not improve K uptake of shoot and grain at harvest and K harvestindices. Crop K productivity could be increased by plastic film mulching with application ofN fertilization and by straw mulching only at high N rate (240kg hm^-2).5. Whether N fertilizer was applied or not, soil moisture in0to40cm soil layers wasincreased by mulching straw or plastic film at reviving and flowering stages. At harvest,although plastic film mulching combined with application of N fertilizer could increase nitrateN accumulation to10cm soil layers, soil surface mulching with plastic film or crop straw,nitrate N accumulation in0to40cm soil layers were all decreased.6. At harvest, soil moisture and nitrate N accumulation in40to300cm soil layers wereall decreased by plastic film mulching, and the decreasing altitudes was increased with Nrates. Mulching with crop straw only showed a trend to increase soil moisture in deep soillayers at N rates below120kg hm^-2, and at high N rate (240kg hm^-2), it significantlydecreased soil moisture. Whether N fertilizer was applied or not, straw mulching could allreduce nitrate N accumulation in deep soil layers. Therefore, mulching soil surface combinedwith application of N fertilizer not only promoted crop growth and uptake of N, but alsoremarkably decreased the amount of nitrate N accumulation in soil profile and then preventednitrate N from leaching into deep soil layers.