Effects Of Population Size Andnitrogen Application On Winter Wheat Grain Yield And Wateruse Under Straw Mulching On Dryland

Water deficit is the major limited factor for winter wheat production in the dryland areas,population size and nitrogen management could significantly influence wheat growth andwater use pattern, and thus wheat yield and water use efficiency. The objective of thisresearch was to investigate effects of population size, N rates and N split-applications on soilwater storage, development of winter wheat, grain yield and water use efficiency under strawmulching on dryland in Weibei Plateau. There are two field experiments. One involvedseeding rates and population regulation measures, including10treatments which were highdensity with conventional tillage, normal density with conventional tillage, low density withconventional tillage, high density with mulching, normal density with mulching, low densitywith mulching, high density with root pruning under mulching, high density with defoliationunder mulching, normal density with root pruning under mulching, normal density withdefoliation under mulching. Another involved N rates and N split-applications, including8treatments which were high N rate with one application and normal N rate with oneapplication under conventional tillage, high N rate with one application, high N rate with twoapplications, high N rate with three applications, normal N rate with one application, normalN rate with two applications and normal N rate with three applications under mulching. Themain results obtained were as follows:1. During the experimental year, the fallow season was wet but the growing season wasvery dry. Soil water storage at0-3.6m depth under mulching was105mm higher than underconventional tillage at wheat sowing time, this extra water was used by wheat after thejointing stage. The depth of water use reached2.6m and3.4m under conventional tillage andmulching, respectively. The effect of sowing density on soil water storage (0-1m depth) wassignificant at jointing stage, but was not significant at other growing stages. Wheatpopulation sizes before heading stage were significantly influenced by seeding rates, but nodifferences were observed after heading. Wheat grain yield ranged from2841kg/hm2to3496kg/hm2, both seeding rate and mulching had no prominent effects on grain yield. However, asignificant lower harvest index was observed under high seeding rate than middle and low seeding rates. The water use efficiency was marked lower under straw mulching than underconventional due to the significant higher water use.2. The population regulation measures (root pruning and defoliation) were carried outfor treatments of normal and high seeding rates under straw mulching. Water storage in0-1msoil depth was influenced by population regulation measures, the general trend of watercontents in order was root pruning> defoliation> CK, but the effect in further deeper soillayers was not significant. Besides sowing density and population regulation measures had nosignificant interaction effects on soil water storage. The trend of spike numbers at harvest inorder was CK> defoliation> root pruning. Root pruning and defoliation dramaticallydecreased wheat biomass accumulation. Wheat grain yield ranged from2845kg/hm2to3496kg/hm2, both root pruning and defoliation had no significant effects on grain yield and wateruse efficiency. But defoliation under high seeding rate notably increased harvest index.3. Nitrogen management affected soil water storage in some extent. Water storage waslower under high N rate than under low N rate, especially in1-2m soil depth wheresignificant lower soil water storage was observed under high N rate than under low N rate atlate growth stage. However, N split-applications had no obvious effects on soil water storagecompared with one application. Nitrogen management and mulching had no significant effecton wheat population size, but significantly affected wheat LAI and biomass accumulation.Different N rates had no outstanding influence on degradation of chlorophyll andphotosynthetic rates of flag leaves, but high N rate accelerated wheat flag leaves senescence.Straw mulching contributed to improve photosynthetic characteristics and delay flag leavessenescence. Wheat grain yield ranged from3123kg/hm2to3714kg/hm2, both N rates andmulching had no significant effects on grain yield, but slightly increased water consumptionand decreased water use efficiency.On the whole, sowing density, population regulation measures and nitrogen managementhad no significant effects on grain yield and water use efficiency in the context of wet fallowseason and very dry growing season with freeze injury at jointing stage. Nevertheless, strawmulching improved functions of flag leaves and the harvest index was increased bycombining reasonable sowing density. Therefore, the interactions of sowing density, nitrogenmanagement and mulching on wheat yield and water use need further investigation in otherweather conditions in order to evaluate their comprehensive effects.