| China has a vast territory,a large population and a lack of water resources.Water resources protection plays an important role in the construction of ecological civilization.West Liaohe Plain,which is an important commodity grain base in China,is located in the arid and semi-arid area.However,West Liaohe River is cut-off due to perennial drought.Therefore,groundwater is exploited seriously,and a large areas of falling funnel are formed.The low utilization rate of water resources has become the key problem for the sustainable development of agriculture in this area.In recent years,the utilization of agricultural water resources has become the major concern of the local agricultural departments.Agricultural water-saving irrigation has been vigorously developed.In view of the local climate conditions with more rainfall and wind during the sowing period,the soil covered drip irrigation technology,which is covering soil of 2?4 cm depth on drip irrigation belt without mulching,was developed in this area.Drip irrigation under mulch and soil covered drip irrigation technology has been widely promoted and demonstrated in a large areas.Since they are still in the stage of promotion and demonstration,the law of water demand for drip irrigation under mulch and shallow buried drip irrigation,the influence of water on yield,the law of evapotranspiration and irrigation system are not clear.Therefore,through comparing experiments of drip irrigation under mulch and soil covered drip irrigation,the influence mechanisms of film mulching and soil covering on transpiration and evaporation of maize under drip irrigation,on soil water transport and on rainfall utilization efficiency were studied to reveal water-saving mechanism of drip irrigation under mulch.The irrigation system of maize in different hydrological years has been formulated to provide a theoretical basis for the drip irrigation decision-making of maize in similar low areas.The main results of this paper are as follows:(1)The plant height and leaf area index of drip irrigation under mulch were 9%?20%and 13%?20% higher than those of soil covered drip irrigation in normal and dry years.There was no significant difference in plant height between soil covered drip irrigation and drip irrigation under mulch.However,the leaf area index was 4%?10% higher than drip irrigation under mulch.The root of drip irrigation under mulch was densely distributed in 25 cm soil layer and sharply decreased along the vertical direction.The root of drip irrigation under mulch was evenly distributed from the drip irrigation tape to 40 cm away from the drip irrigation tape in the horizontal direction.The root distribution of soil covered drip irrigation was deeper,10 cm deeper than that of drip irrigation under mulch,but the lateral distribution was narrow,and the horizontal distribution was dense from 10 cm to 30 cm away from the drip irrigation tape.(2)The total water consumption of drip irrigation under mulch was 9% lower than that of soil covered drip irrigation.In normal and dry years(2015 and 2018),the precipitation was smaller after tasseling period.The yield of drip irrigation under mulch was 7% ? 15%higher than that of soil covered drip irrigation.In normal and wet years(2015 and 2018),the precipitation was larger after tasseling period.The yield of drip irrigation under mulch was6% ?19% lower than that of soil covered drip irrigation.(3)The average soil evaporation under soil covered drip irrigation was 141.38 mm during the growth period,and drip irrigation under mulch was 98.10 mm.Soil evaporation,transpiration,and evapotranspiration of drip irrigation under mulch was 31% lower,21%higher and 11% lower than that of soil covered irrigation,respectively.Under soil covered drip irrigation,evaporation of high water was 13% higher than that of middle water,and of low water was 5% lower than that of middle water.Due to film mulching,the soil evaporation was only 0.67 mm,which accounted for 2% of the total evaporation of drip irrigation under mulch.The evaporation in the bare soil area(area II)of drip irrigation under mulch was 36.18 mm,which accounted for 98% of the total evaporation.The soil evaporation in the areas of ridges(zone II)under soil covered drip irrigation was 62% lower than that in the areas of rows(zone I).When the soil water content in the bare soil area(area II)was low,the soil water will transport from the film mulching area to the non-film mulching area,and the transported amount was about 11%.The results showed that drip irrigation under mulch had no water-saving function in bare soil area(area II),and the evaporation between trees was 11% higher than that of soil covered drip irrigation.The water saving mainly occurred in the film mulching area(area I).(4)In normal and dry years(2015 and 2018),drip irrigation under mulch treatment was 13%?32% higher than that of soil covered drip irrigation treatment.The effect of drip irrigation under mulch on soil moisture conservation is more significant.In normal and wet years(2015 and 2018),drip irrigation under mulch treatment was 10%?16% lower than that of soil covered drip irrigation treatment.More rainfall directly infiltrated into the soil,which made the soil water content of soil covered drip irrigation higher.Due to the influence of film interception,the soil water content of drip irrigation under mulch was lower than that of soil covered drip irrigation,and the effect of mulching film on soil water conservation was not significant.(5)The rainfall utilization of soil covered drip irrigation is about 25% higher than that of drip irrigation under mulch.When the rainfall is less than 20 mm,the infiltration depth is 20 cm.When the rainfall is 20?50 mm,infiltration depth is 40 cm.When the rainfall is more than 50 mm,the infiltration depth can reach 40 cm soil layer below.In the normal and dry years(2015 and 2018),the maximum infiltration depth of rainfall can only reach 40 cm soil layer.The rainfall in the shallow soil layer was used by crops.In normal and wet years(2015 and 2018),the infiltration depth of rainfall can reach 60?100 cm soil layer,the rainfall in the deep soil layer can be used by crop.The rainfall utilization rate of soil covered drip irrigation is 67%?78%,which is 29%?35% higher than that of drip irrigation under mulch.The interception of rainfall by film mulching was 26%?35%.When the rainfall is between 20 mm and 40 mm,the rainfall infiltration at the edge of the film(30 cm away from the drip irrigation belt)is 2%?6% higher than that at the outside of the film.(6)The high-efficiency irrigation decision of drip irrigation for maize was determined.In dry year,drip irrigation under mulch and soil covered drip irrigation required8 times and 9 times,and irrigation quotas of soil covered drip irrigation and drip irrigation under mulch were 315 mm and 270 mm,respectively.In normal year,soil covered drip irrigation and drip irrigation under mulch required 7 times,and irrigation quotas of soil covered drip irrigation and drip irrigation under mulch were 222 mm and 183 mm,respectively.In wet year,soil covered drip irrigation and drip irrigation under mulch required5 and 4 times,and irrigation quotas of soil covered drip irrigation and drip irrigation under mulch were 135 mm and 105 mm,respectively.For different study areas,the annual average precipitation and the annual precipitation forecast were used to calculate the precipitation in the growing period.When annual precipitation is less than 268.32 mm,it is better to use drip irrigation under mulch in the area,and when annual precipitation is more than 268.32 mm,it is better to use soil covered drip irrigation. |
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