圆形喷灌机变量灌溉效益的田间试验评估

Field study on the benefits of the variable rate irrigation strategies for a center pivot system

科学的变量灌溉(Variable Rate Irrigation,VRI)水分管理方法是实现VRI技术适时适量适位水量空间分配功能和提高作物水分利用效率(WaterUseEfficiency,WUE)的关键。为研究变量灌溉水分管理方法的灌溉效益,以冬小麦和夏玉米为供试作物,基于土壤可利用水量(Available soil Water holding Capacity,AWC)将试验田块划分为4个管理区,每个管理区划分为4个子区,分别布置2种常规喷灌管理(Uniform Rate Irrigation,URI)方法和2种VRI管理方法,对比评估了VRI水分管理方法在节水、增产、提高WUE,以及改善作物株高、叶面积指数(Leaf Area Index,LAI)、产量和WUE空间分布均匀性方面的效果。结果表明,基于各管理区灌水上限值制定变量灌溉处方图并根据气象预报降雨量等级适当减少灌水量的VRI水分管理方法最优。与常规喷灌相比,最优VRI水分管理方法条件下,冬小麦节水36%,WUE提高12%;夏玉米节水40%,WUE提高29%。VRI与常规喷灌的冬小麦、夏玉米产量均未产生显著差异,VRI水分管理方法对作物株高、LAI、产量、WUE空间分布均匀性也无明显影响。研究可为大型喷灌机VRI管理决策支持系统的建立提供依据。

Potential production benefits can be expected to easily quantify for the Variable Rate Irrigation(VRI)over the conventional Uniform Rate Irrigation(URI)systems in a given field.An effective VRI management can greatly contribute to the investment in the systems.In this study,a field test was conducted from October 2017 to September 2018 during the growing seasons of winter wheat and summer maize in Zhuozhou(39°27’N and 115°51’E),Hebei Province,China.The mean annual temperature and precipitation were 11.6°C,and 563.3 mm,respectively,particularly with more than 70%probability between July and September.The VRI system was set as a center pivot with three-span 140 m long with an overhang.Variable-rate water was applied along the lateral and travel direction.A control system was also used to control the duty cycle of a solenoid valve ahead of each sprinkler,and the travel speed of the center pivot.One 1.64-hm~2 quadrant irrigated by the VRI system was delineated into four management zones(zones 1 to 4)with the available soil water holding capacity(AWC).Among them,two conventional sprinkler URI strategies(U1 and U2 treatments),and two VRI strategies(V1 and V2 treatments)were arranged in the four sub-zones for each management zone.The mean soil water contents were daily measured to determine the irrigation date in the treatments of U1,V1 and V2 in zone 1 with the lowest AWC values.Furthermore,the average soil water content was approximately represented at 0-0.4 m depths.Particularly,the mean soil water contents were measured for the four management zones in the U2 treatment.The irrigation was triggered,when the measured soil water content dropped close to 66%and 70%of the field capacity for the winter wheat and summer maize,respectively.The same application was adopted for the two URI treatments.Specifically,the 20 and 30 mm depths were set before and after the booting stage for the winter wheat,respectively,whereas,the 20 mm depths were for the summer maize.The application depth was equal to the consumption of soil water calculated from the upper limit value and the measured soil water content for the V1 treatments.In the V2 treatments of winter wheat,84%,99%,and 68%of the rate in zone 1 were recommended for zones 2,3,and 4,respectively,where the deliver depth for zone 1 was the same as the URI treatments.The V2 treatments of summer maize were also combined with the V1 treatments and the rain forecast.The applied water decreased by 0%,20%,and 40%for the light(less than 10 mm),moderate(between 10 and 25 mm),and heavy rain(more than 25 mm),respectively,according to the forecast report from the National Meteorological Center of China Meteorological Administration.There were some positive effects of VRI strategies on water-saving,yield,and WUE,spatial distribution of plant height,and Leaf Area Index(LAI).Results showed that the VRI strategy was an optimal way of irrigation management,according to the upper limit value and the meteorological forecast rainfall level.Compared with the URI,the irrigation amount of the optimal VRI strategy was reduced by 31%,and 40%,while the WUE values increased by 6%,and 27%for the winter wheat and summer maize,respectively.There was no significant difference between the VRI and URI strategies in the yield for the winter wheat and summer maize.Besides,no significant effect was found on the spatial distribution of plant height,LAI,yield,and WUE.Therefore,the irrigation prescription maps can be expected to serve as the VRI management,according to the soil water content and meteorological forecast about rainfall,particularly more suitable for both the semi-arid and semi-humid climates.