The Support And Regulation Of Root Layer Nutrient,Water To The Overground Populations Of Rainfed Wheat In Different Cultivation Modes

The arid and semi-arid region of Loess Plateau has less rainfall and lower soil fertility in general.Under the current high output of grain in this regions,how to further regulate the nutrients/water-use（absorption）in the root layer through reasonable cultivation modes,would be great meaningful to improve the support and regulatory effects for the overground population,which further increase the grain yields and water use efficiency,and promote sustainable development of dry land agriculture in Loess Plateau.The experiment was carried out in typical dryland farming region-Shaanxi Changwu area.By using the measures of increasing density,reducing nitrogen and phosphorus,applying nitrogen fertilizer by stages and applying organic fertilizer and biochar,four kinds of cultivation models were constructed.We studied the relationships among soil nutrients/water and root distribution,and their effects on the support of overground populations and the regulation of yield formation of rainfed wheat under these four different cultivation modes.Moreover,the change regularity of each conversion ratio in different growth stages of winter wheat and the regulative ability of different cultivation modes were discussed.The main results of this study are as follows:1.Compared to the Traditional Farmer Model（FP）(4752 kg·hm²;12.44 kg·hm^-2·mm^-1),the High-yield/efficiency Mode（manure/biochar）（HEM/HEB）yield increased by 23%and16%,respectively,water use efficiency（WUE）increased by 18%and 14%;Compared to the High Nitrogen Mode（HN）(5132 kg·hm^-2;13.37 kg·hm^-2·mm^-1),HEM/HEB yield increased by 14%and 8%,water use efficiency increased by 10%and 6%,nitrogen fertilizer efficiency（PFP_N）increased 59%（38.9 kg/kg N）and 26%（30.7 kg/kg N）in the case of a reduction of 14%-29%nitrogen.2.HEM/HEB maintain a relatively high soil nitrate nitrogen content during the growth period to meet the nutrient requirements of winter wheat.The root density in the shallow（0-60 cm）and deep（100-200 cm）soil is also significantly larger than FP and HN,which is beneficial to the absorption of soil nutrients and water,especially to the deep soil water utilization in the later stage of growth（HEM/HEB consume more 11-35 mm soil water（100-300 cm）than FP and HN）.The good interaction between nutrients,roots and water makes HEM/HBM maintain better population culms during growth period of winter wheat,and ensure higher spike number at harvest time,and eventually increase yield.3.The characteristics of soil water consumption in different modes can be divided into two stages（sowing to regreening period,regreening to harvest period）,and the soil moisture of HEM/HEB is the equilibrium replenishment stage from sowing to regreening period, consumed more than FP and HN during the regreening to harvest period.Through the above results,we can conclude the available water content in shallow soils（0-60cm）is greatly influenced by the available water storage of initial stage and the precipitation,and transition layer（60-100 cm）can be obviously affected by the available water storage.When the available water storage in the 100-300 cm soil layer is too high（≥239 mm）before sowing,it will cause the loss of available water in the deep soil from sowing to regreening stage;If it is moderate（≈200 mm）,available water in the deep soil remains unchanged;If it is lower（170-200 mm）,available water can be supplemented to 200 mm,approximately.4.The less precipitation in the year,the lower the precipitation retention rate（SWe/P）,while the precipitation absorption rate（SW/SWe）,the water consumption on cropland （ET/SW）and the precipitation use efficiency（PUE）are higher.In other words,ET/SW（from jointing stage to harvest stage）is higher because of less rainfall in the growth period of winter wheat,lead to less invalid evaporation before the sowing period,and the winter wheat annual water use efficiency can be enhanced.Compared to FP and HN,SWe/P of HEM/HEB is reduced after jointing stage,while SW/SWe,ET/SW,the water use efficiency of biomass （WUE_B）,the water use efficiency of grain yield（WUE_Y）and the precipitation use efficiency（PUE）all increased.The increase rate of the WUE_B and WUE_Y is greater when there is more precipitation,while the remaining ratios are smaller.In this study,we showed that HEM/HEB promoted the growth of deep roots by improving the nutrient conditions of the root layer,which increased the utilization degree of the deep water after regreening stage,further supported overground populations,and finally increased the yield,water and nutrient utilization efficiency.The soil moisture of HEM/HEB is the equilibrium replenishment stage from sowing to regreening period,and then change into consumption stage from regreening period to harvest period,thus,the temporal and spatial distribution of soil moisture was regulated,and the water use efficiency was improved.At the same time,we found that HEM/HEB increase WUE_B and WUE_Yby reducing the ineffective evaporation from sowing to regreening stage,and the WUE_B and WUE_Ywere not improved after regreening stage because of the high transpiration.But overall,the yield and PUE are increased synchronously with the increase of transpiration rate.