| The lack of water resources is an important limiting factor for the sustainable development of the agricultural industry in Loess Highland,which is an important grain production base in China.The variation of rainfall between intra and inter annuals in this area are very large.And limited by the technical conditions and experiment cycle of field conditions,the long-term observation on crop growth,yield,soil moisture dynamics change of the crops under different planting densities,and the long-term experimental study on water productivity under high planting density was less in Loess Highland.The DSSAT model can make up for the shortcomings of field experiment,and carry out long-term quantitative simulation of crop growth and development,yield formation and soil water use characteristics,to optimize the field management measures and assess the soil moisture status under long-term high planting conditions of rainfed farmland.In order to analyze and evaluate the water productivity,soil water use characteristics and soil water sustainability under long-term high planting density of maize in rainfed farmland,a successive field experiment was conducted on the Dryland Agricultural Research Station of Northwest A & F University,Heyang County,Shaanxi Province,China,over four growing seasons from 2015 to 2018.The experiment was a split plots design with three replications and planting density as the main plot treatment,and cultivar as the sub-plot treatment.Four planting densities were evaluated in this experiment: D1(52,500 plant ha(-1)),D2(67,500 plant ha(-1)),D3(82,500 plant ha(-1))and D4(97,500 plant ha(-1)),respectively.The three types of cultivar applied in the experiment were Yuyu22 which had large ears and kernels that did not have a compact plant structure,Zhengdan958 and Xianyu335 which were characterized by great tolerance to high planting density.This article combined with field experiment(2015-2018),simulation experiment(2015-2018)and long-term quantitative simulation experiment(1981-2018),to study the growth and development,water productivity and soil water change characteristics of spring maize in dryland under different planting densities conditions.The main conclusions of the study are as follows:1.Effect of planting density on the growth of spring maize in drylandThe effects of planting density,cultivar and cropping season on the growth and development of spring maize in dryland reached a significant level(P<0.05).There was a positive correlation between plant height and density of spring maize in dryland,and significant differences among different cultivars(P<0.05).The regression analysis model better simulated the relationship between the mechanical index of maize stalk and the planting density,and the mechanical indexes of maize stalks decreased with the increase of planting density of spring maize in dryland.The difference of mechanical indexes of stems of different cultivars reached a significant level(P<0.05).The leaf area index(LAI)increased with the increase of planting density of spring maize in dryland,and the LAI of D2,D3 and D4 treatment increased by 21.2-80.2% compared with D1.The biomass of increased with the increase of planting density spring maize in dryland,but the proportion of biomass post flowering to maturity decreases with increasing density.The responses of LAI and biomass to planting density of different spring maize cultivars were different.The amplitude of LAI and dry matter in Yuyu22 increased with population density in the early growth stage,but this result was not the case in Zhengdan958 and Xianyu335.2.Effects of planting density on yield and yield components of spring maize in drylandPlanting density,cultivar and cropping season had significant effects on spring maize yield and yield components(P<0.05).Grain yield showed a parabolic relationship with the increase in planting density,and the average annual yield reached the maximum under D2 density of spring maize in dryland.There was a significant positive correlation between kernel number per square with planting density(P<0.05),while the 100-grain weight showed a significant negative correlation with planting density of spring maize in dryland(P<0.05).The yield of different density-tolerant cultivars had different responses to planting density.Yuyu22 showed a better yield under low-density(D1)condition,but the decreased amplitude of kernel number per ear and 100-grain weight with the increasing of planting density was greater than other cultivars carry out in our experiment.The yield components have different contributions to yield of spring maize in dryland.There were significant effects of ear number per square and kernel number per ear on yield under different density conditions(P<0.05).3.Effects of planting density on soil moisture of spring maize field in drylandThe soil water content of 0-200 cm soil layer decreased with the increasing of planting density of spring maize field in dryland.The evapotranspiration(ET)increased with the increasing of population density of spring maize in dryland,and the difference between different cultivars was significant(P<0.05),average ET were ranked as ZD335> ZD958> YY22.The results showed that increasing planting density did not cause a deep dry soil layer,but when rainfall could not supplement the soil water loss,a low soil moisture condition resulted.The water use efficiency(WUE)changes with the change of yield and showed a quadratic relationship with planting density of spring maize in dryland,average WUE were ranked as ZD958> ZD335> Yu22.4.Long-term simulation of water productivity effects under different densities of spring maize in drylandRainfall is the most important factor affecting the growth and development of crops in dryland,and the erratic distribution of rainfall between interannual and seasonal on the Loess Highland resulted significant differences in crop water productivity between different cropping seasons.There was a significant positive correlation between rainfall during the whole growth period and ET in dryland(P<0.05),and a parabolic relationship with yield and WUE.Through 38-year-old quantitative simulation experiments,we found that the planting density had a significant effect on the ET,yield and WUE of spring maize in dryland(P<0.05),and the yield and WUE were showed a parabolic relation with density,and the maximum of yield and WUE was reached at D2(67500 plants ha(-1))treatment,but the ET increased with increasing density.The water consumption of long-term simulation experiment was less than the average annual rainfall in our study site,therefore,the high planting will not cause over-consumption of soil water in rainfed farmland.In summary,combined with the results of successive field experiment(2015-2018),model simulation experiment(2015-2018)and long-term quantitative simulation experiment(2015-2018),it can be concluded that high planting in Loess Highland will not cause soil water over-consumption,and increase density will not destroy the soil water balance and affect the sustainability of soil water in dryland.However,the yield and WUE of spring maize in dryland did not increase with increasing density,but performed better under D2 treatment(67500 plants ha(-1)).Therefore,it is recommended that the compact cultivar Zhengdan958 combined with the density of 67,500 plants ha(-1) is a reasonable cultivar type and planting density suitable for the water resources in the Loess Highland. |
