Study On Water Effect Of Double Cropping Of Dry Farmland In The Subhumid Area Of Loess Plateau

Agricultural practices and related research had showed that precipitation shortage is the main restricted factor of the agriculture development in drought region; however, irrational utilization of the limited precipitation resources is the main source which causes water resource to be wasted. The Loess Plateau is the main Dryland Farming Region of China; in this region, the temporal distribution of rainfall is not suitable to the major crop-winter wheat. For a long time, based on the traditional view"store soil water and use rainwater of summer in the next spring", farmland was fallowed in summer to guarantee the well soil water content before seeding of winter wheat, even in the subhumid regions of Loess Plateau which have the better agricultural production condition. Many studies show that water collecting effects of summer fallow is finite; the soil store water rate is only 30%. Based on previous studies, we tried to investigate the feasibility of developing multiple cropping in subhumid area of Loess Plateau by conducting field experiment, and the main aim of the study was to provide evidence for efficient and sustainable utilization of limited available water resources, increasing farmland productivity level and farmer's income.The study was conducted at Yangling(the average rainfall about 637mm) to study the double cropping system of dry farmland. The experiment consisted of 5 treatment,"winter wheat?summer fallow"cropping pattern was used control (treatmentⅠ), while the other four multiple cropping patterns were"winter wheat?sesame"(treatmentⅡ),"winter wheat?soybean"(treatmentⅢ),"winter wheat? sorghum"(treatmentⅣ),"winter wheat?corn"(treatmentⅤ). We tested and analyzed the soil water dynamics, water consumption and its components, crop transpiration, soil evaporation, soil temperature, crop yield and economic benefit of different treatments, the main results are as follow:(1) In winter wheat growing season, all of the 5 treatment had the same water consumption, it was the 337.2mm, among them soil water consumption was 171.5mm, about 114.1mm consumed in 0-100cm soil layer; 98.8mm water was consumed during the heading and flowering stage, the winter wheat, which was the most in winter wheat growing season; before jointing stage, the water in 100-200cm soil layer was nearly no change.(2) During multiple cropping, all of the four multiple cropping patterns consumed more water than CK, compared with CK, the water consumption of treatmentⅡ, treatmentⅢ, treatmentⅣand treatmentⅤincreased by 20.6mm, 25.8mm, 53.8mm, 32.3mm; the soil evaporation with CK was 236.2mm,the other four multiple cropping treatments were lower than CK by 121.7mm, 118.9mm,115.2mm,125.8mm; the suppression rate of evaporation among multiple cropping treatments were 51.5%, 50.3%, 48.8%, 53.2%.(3) During multiple cropping, the precipitation was 410.6mm, which can completely satisfied the water needs of sesame, soybean, sorghum and corn; and the soil water content in 2m layer of all the 5 treatment were effective complement, at the end of summer fallow, the soil content in 2m layer of different treatments were 533.3mm, 512.7mm, 507.5mm, 479.5mm,501.0mm, which increased by 174.4mm, 153.8mm, 148.6mm,120.6mm and 142.1mm compared with that at harvest of winter wheat. At the end of experiment, all the four multiple cropping treatments had more soil water content in 0-40cm layer than CK; except the treatment V, the other 3 multiple cropping treatments had more soil water content in 0-100cm layer; the difference of soil water content in 2m layer between CK and the other four multiple cropping treatments was mainly from 0-100cm layer.(4) Multiple cropping patterns can significantly decrease top-soil temperature in summer fallow, which was beneficial to decrease the soil evaporation. During summer fallow, the soil temperature of 5cm, 10cm, 15cm, 20cm layer of CK were all higher than other four multiple cropping treatments, the temperature differences were more large in Clear day than that in Cloudy day.(5) The total water consumption of the 5 treatment weres 573.4mm,594.0mm,599.2mm,627.2mm,605.7mm, there were significants difference between multiple cropping treatments and CK (p<0.05). The water consuming intensity were 1.62mm·d-1,1.67 mm·d-1,1.69mm·d-1,1.77 mm·d-1,1.71 mm·d-1. this showed that multiple cropping pattern didn't increase water consuming intensity obviously.(6) The differences of productivity level and economic benefits among treatments were significant, the"winter wheat-corn"cropping pattern both had the highest productivity level and economic benefit, the best sustainability of soil water is"winter-wheat". The economic benefit of treatmentⅠ, treatmentⅡ, treatmentⅢ, treatmentⅣand treatmentⅤwere 5916.2yuan·hm2, 10122.7yuan·hm2, 11256.8yuan·hm2, 9604.8yuan·hm2, 12970.3yuan·hm2. Comprehensive analysis of economic benefit, and soil water sustainable utilization, the"winter wheat—corn"obtained the best economic yield and profit, and the"winter wheat—soybean"was the second-best, but this cropping systems consumed less soil water than"winter wheat—corn". So, the"winter wheat-soybean"was the optimum multiple cropping pattern for this region.