| As a new irrigation mode of agricultural water and fertilizer,biogas slurry drip irrigation can not only avoid the environmental pollution caused by the direct discharge of biogas slurry,but also realize the secondary utilization of biogas slurry.The uniformity of fertilizer application is an important index of biogas slurry drip irrigation.It is the premise to ensure the same amount of water and fertilizer irrigation.It has a significant impact on the quality of crop products,yield and efficiency,economic and social benefits.There are many factors affecting the uniformity of fertilizer application in biogas slurry drip irrigation,which can be roughly divided into two categories: one is the clogging of emitter caused by the long-term operation of biogas slurry drip irrigation system,and the other is the uneven outflow of emitter caused by the unreasonable drip irrigation operation mode,that is,the uniformity of irrigation;The second is that the movement and intersection of biogas slurry in soil lead to uneven distribution of biogas slurry in soil,which can be characterized by soil moisture uniformity.In order to study the effects of clogging of biogas slurry emitter and drip irrigation operation mode on irrigation uniformity and the distribution of biogas slurry in soil under single and double point source drip irrigation,the following studies were carried out based on the experiments of clogging of biogas slurry drip irrigation and infiltration of single and double point source soil:(1)The experiment of irrigation uniformity of biogas slurry drip irrigation system was carried out,and the effects of different biogas slurry water fertilizer ratio,irrigation pressure and emitter type on irrigation uniformity were analyzed.The results showed that:with the increase of irrigation times,irrigation uniformity would go through two stages from fluctuating decline to rapid decline.Emitter type,biogas slurry water fertilizer ratio and irrigation pressure would affect the decline of irrigation uniformity;In the process of biogas slurry emitter clogging test,when the irrigation is over,the decreasing speed of the irrigation uniformity of the chip emitter is lower than that of the cylinder emitter,and the irrigation uniformity of the chip compensation emitter is the lowest;The larger the ratio of water and fertilizer,the higher the concentration of biogas slurry,the faster the decline of irrigation uniformity,and the more the number of plug plug;The higher the irrigation pressure,the less the number of emitter clogging and the higher the irrigation uniformity;According to the test results,it is recommended to apply biogas slurry fertilizer with chip emitter,and the irrigation pressure should not be less than 40 kPa.(2)A single factor experiment was carried out with the length of drip irrigation belt,irrigation gradient and irrigation pressure as experimental factors and the irrigation uniformity as experimental index.The influence rules of various parameters on the irrigation uniformity were obtained.The response surface test was carried out according to the response surface method,and the mathematical regression model was established Irrigation gradient and irrigation pressure.The results showed that:in the drip irrigation mode,the longer the length of drip irrigation belt was,the lower the irrigation uniformity was.When the length of drip irrigation belt was more than 60m,the decrease rate of irrigation uniformity was faster;Increasing the irrigation pressure can improve the irrigation uniformity,but when the irrigation pressure exceeds 120kPa,the increase of irrigation uniformity is not obvious;The larger the irrigation slope is,the lower the irrigation uniformity is.There is a negative linear relationship between them.The smaller the emitter flow is,the higher the ability of maintaining irrigation uniformity is.According to the test results,it is recommended to use 2L/h emitter under the slope condition;After optimization,the theoretical optimal irrigation pressure of citrus orchard is 90kPa.(3)The experiment of soil moisture uniformity under the condition of single point source biogas slurry drip irrigation was carried out,and the effects of different water fertilizer ratio,irrigation amount and emitter flow rate on soil moisture uniformity were obtained.The results showed that: under the condition of single point source biogas slurry drip irrigation,there was no significant difference between the surface and underground water content of different biogas slurry water and fertilizer ratios.Increasing the biogas slurry water and fertilizer ratio did not significantly change the soil moisture uniformity,and the effect of biogas slurry water and fertilizer ratio on the soil moisture uniformity was not obvious,so the ratio of biogas slurry water and fertilizer could be properly selected with reference to other factors;With the increase of irrigation amount,the soil surface water content will increase,and the underground water content contour will change from dense to sparse,extend the range of wetting front and increase the wetting uniformity.For the crops with large root range,the method of increasing irrigation amount and reducing the concentration of biogas slurry can be used for fertilization;With the increase of emitter flow rate,the surface soil moisture content increases,while the underground water content decreases.Increasing the emitter flow rate appropriately can improve the soil moisture uniformity.For the crop seedling stage,when the root system is shallow,the large flow emitter can be used for fertilization.For the mature crop,when the root system is deep,the small flow emitter should be used to ensure the biogas slurry infiltration;When the amount of biogas slurry irrigation is 3l,the limit distance of soil wetting front is about 33cm.When applying biogas slurry drip irrigation and fertilization,the crop roots should be controlled within this range;Under different conditions,the infiltration of biogas slurry is affected by different soil matrix potential,which leads to the change of infiltration rate of biogas slurry in soil and the different distribution of water content;There is a significant power function relationship between the migration distance and time of wetting front in biogas slurry infiltration.Based on this principle,the vertical infiltration migration formula of wetting front in ideal state is established.(4)The experiment of soil moisture uniformity under the condition of double point source biogas slurry drip irrigation was carried out,and the effects of different water and fertilizer ratio,irrigation amount,emitter flow and emitter spacing on soil moisture uniformity and the movement of wetting front were obtained.The results show that:Under the condition of double point source biogas slurry drip irrigation,the decrease of biogas slurry water fertilizer ratio will accelerate the formation time of intersection area,increase the water content of intersection area,and improve the soil moisture uniformity.According to the test results,1:3 is recommended as the best concentration ratio of double point source biogas slurry drip irrigation;With the increase of irrigation amount,the range of wetting front was extended,the width of soil saturated area was increased,the distribution of water content was changed,the difference of water content between intersection area and emitter was reduced,and the irrigation uniformity was improved.However,the increase was not obvious when the irrigation amount was too large.According to the test results,it was suggested that the biogas slurry irrigation amount should be kept above 2L;The increase of emitter flow rate can significantly increase the soil surface moisture content,thus reducing the formation time of intersection area and improving the soil moisture uniformity.For the early sowing stage or crop seedling stage,3L / h emitter can be used for biogas slurry fertilization to ensure sufficient moisture uniformity on the ground.For the late growth stage or crops with long roots,1L/h emitter is recommended for fertilization;The smaller the distance between adjacent emitters,the higher the uniformity of soil moisture.When the distance between emitters is 30 cm,there is no intersection.The distance between emitters should be controlled within 30 cm. |
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