Study Of Water Effect In Double Cropping System On Dry-Farming Lands In Subhumid Regions Of Loess Plateau

Scientific research and production practices show that although less and uneven distribution precipitation in dryland region ,the conflict between discontinuous precipitation supply and′Continuous demand is leading to the main constraints in current production, but non-full use of water resources is root causes which causing the drought. Chinese Loess Plateau is the main implementation of dry farming regions. In subumid regions of Southeast Loess Plateau which have comparatively nice natural environment. Based on the traditional view of"by planting two crops in a year under the condition of little precipitation and poor soil, often lead to yield decrease of consecutive wheat". summer fallow became a sign of dry-farming land which areas is nearly three million ha on this region. the light and heat resources, water resources is wasted greatly. water use efficiency is low, the potential of yield are difficult to be improved. This study was designed to improve agricultural production and economic efficiency, sustainable and optimum using of agricultural resources by planting two crops in a year in subumid regions of Southeast Loess Plateau, exploring the way of using precipitation resources efficiently in summer fallow.Selecting Yangling Agricultural Hi-tech Development Zone(the average rainfall about 637 mm) as a representative of subhumid regions of Loess Plateau for study of double cropping system, water consumption only rely on natural rainfall for agricultural in this test. Take the local primary mode of"winter wheat– summer fallow"as CK,the other three treatmeat was"winter wheat–foxtail wheat","winter wheat–soybean","winter wheat–marize". Analyzing evaporation and the evapotranspiration,analyzing soil temperature,soil water dynamics,water satisfied rate,water consumption and yield of different double cropping system. compared the output of different models of biomass yield and economical yield. Using water use efficiency and output to comprehensively evaluate effect of various models. The valuable results and conclusions as follows:(1)After preceding winter wheat sowing stage, the average temperature has continued to reduce, then, rapid declining in December .the following year, reaching to the lowest valley in January and February. The two months are also a only Period which the average temperature in lower layer is higher than in top layer. then, the average soil temperature of soil the temperature increasd quickly with the temperatue gradually increased.later, Leaves area become more and more larger, the average soil temperature of soil is gradually increasing too.The average temperature of soil in July reached a peak of different double cropping systems in summer fallow. The average temperature of soil of different double cropping system is very similar, only in September because of earlier harvesting,the temperature of"winter wheat–foxtail wheat"is slightly higher than"winter wheat–soybean"and"winter wheat–marize". because of summer fallow, the temperature of CK is always higher than oter double cropping system by 0.9~1.0℃in June, 1.5~2.0℃in 7 month , 1.7~2.0℃in 8 month, 0.3~2.5℃in 9 month. This shows that planting a crop after winter wheat harvesting, effectively reduce the soil temperature in high temperature in summer, reduced the evaporation.(2)The evapotranspiration of different double cropping system are all more than CK."winter wheat–foxtail wheat","winter wheat–soybean","winter wheat–marize". Evapotranspiration of cropping foxtail wheat,soybean,marize were more than CK by 0.5 mm,25.2mm,37.2mm. But the absolute number of evaporation is lower than CK by 123.08mm,128.06mm,126.77mm. The effect of inhibition efficiency of soil evaporation are as follow:48.06%,50.00%,49.50%. This showed that double cropping system can effectively reduce the invalid evaporation, and the reduction is nearly equal to 26.82~27.91% of Precipitation in summer fallow. In addition, the evaporation of different double cropping systems is very similar the evaporation of CK is significantly more than other three treatments. This result is in line with result of the average soil temperature.Annual evapotranspiration of treatmentⅠ(CK), treatmentⅡ, treatmentⅢ, treatmentⅣare as follow:641.6 mm,642.16 mm,666.81 mm,678.84 mm. During the growth period of winter wheat soil evaporation is 129.09 mm, transpiration is 256.42mm. Evaporation of different treatment are as follow:385.19mm,262.11mm,257.13mm,258.41mm. Proportion between evaporation and evapotranspiration of different treatment are as follow:60.04%,40.82%,38.56%,38.07%. water waste enormous for farmland invalid evaporation of treatmentⅠ(CK).There a high proportion between evaporation in summer fallow and evaporation in annual ,the rate are as follow:66.49%,50.75%, 49.80%, 50.04%. In subhumid regions of Loess Plateau where precipitation of summer fallow and precipitation of annual is 50~65%. It easy to evaporate in summer fallow because of hot and abundant proportion. Double cropping system can effectively reduce the evaporation in annual.(3) The average soil moisture contents in 2m depth before sowing stage of winter wheat is 20.58%. water storage is 555.6mm, after harvest harvesting stage of winter wheat, the rate reduced to 12.63%, water storage is 340.9mm.At the end of the summer fallow, among different cropping systems in 2m depth, soil moisture content,water storage,water storage rate have followed the order to treatmentⅠ(CK)> treatmentⅡ> treatmentⅢ> treatmentⅣ, average soil moisture contents are as follow:20.14%,20.12%,19.20%,18.76%; water storage are as follow:543.7mm,543.2mm,518.5mm,506.5mm;water storage rate are as follow:44.2%,44.1%,38.7%,36.1%. This shows that through summer fallow period, soil water recovery at different levels of different treatment, planting foxtail after winter wheat harvesting have no impact to water storage, planting soybean and marize lead to a certain impact.(4)The water satisfied rate is very high of double cropping system. The water satisfied rate of treatmentⅡ, treatmentⅢ, treatmentⅣare as follow:100%,87.7%,95.6%, precipitation is adapt to Water requirements on physiology and ecology of different double cropping system. The daily water consumption of combinations are as follow : 1.80 mm ? d-1,1.80 mm ? d-1,1.87 mm ? d-1,1.90 mm ? d-1. This show that double cropping system didn′t lead to water consumption Increased significantly(5)The Earning of different double cropping system are Very different. The best economic returns and water use efficiency of multiple cropping systems is"wheat―maize". The best sustainability of soil water is"wheat―foxtail millet". The annual biomass yield of treatmentⅠ( CK), treatmentⅡ, treatmentⅢ, treatmentⅣare as follow:16683.4kg·hm-2,20752.1kg·hm-2,25625.0 kg·hm-2,35101.7 kg·hm-2;the economical yield are as follow:6840.2 kg·hm-2,8321.5 kg·hm-2,8399.4 kg·hm-2,13596.8 kg·hm-2;water use efficiency are as follow: 10.66 kg·hm-2mm-1,12.96 kg·hm-2mm-1,12.60 kg·hm-2mm-1,20.03 kg·hm-2mm-1;net income as follow:6976.6yuan·hm-2,8298.6yuan·hm-2,12001.6yuan·hm-2,14711.5yuan·hm-2.In the premise of significant economic benefits, multiple cropping systems will be sustainable developed. The optimum multiple cropping systems with efficient resources utilization and high economic benefits are"wheat―maize"and"wheat―soybean".