Drip Irrigation Uniformity Evaluation Considering Distribution Location Of Clogged Emitters

Uniformity is one of the most important indicators for the evaluation of drip irrigation quality,and is also regarded as an important parameter for drip irrigation system design.Soil water distribution uniformity is the ultimate expression of drip irrigation uniformity,but the present drip irrigation uniformity indexes can't reflect it directly.In order to evaluate the influence of clogged emitters on the irrigation uniformity and the growth of crops during the operational process of drip irrigation system,the concept and computational method of location distribution uniformity of clogged emitters were set up based on the Christiansen uniformity,and then a new computational method of drip irrigation uniformity was proposed by using the arithmetic mean of the location distribution uniformity of clogged emitters and the flux uniformity of emitters,finally a comparison between several types of computational method of uniformity in a lateral and a subunit was made.In subsequent research,we used soil water distribution coefficient as the standard to evaluate the rationality and accuracy of 3 typical drip irrigation uniformity coefficients(Christiansen uniformity coefficient,Keller uniformity coefficient and the uniformity coefficients considering location of clogged emitters)and finally optimized the best one among these 3 coefficients.Three factors(clogged degree,proportion of clogged emitter,location of clogged emitters)influencing the drip irrigation uniformity were considered,and a total of 27 kinds of drip irrigation situations(clogged degree of 40%,60% and 80%;proportion of clogged emitter of 20%,30% and 40%;location of clogged emitters of even distribution,relative uniform and nonuniform distribution)were designed.The soil water distribution of each irrigation situation was simulated by HYDRUS-2D program and verified by an actual infiltration experiment.We matched soil water distribution coefficient and the irrigation uniformity coefficients of each irrigation situation,then compared and evaluated them by linear fitting.Soil water distribution coefficient was significantly influenced by sampling arrangement,therefore 9 kinds of sampling arrangements were set up and a desirable one was chosen through variance analysis.Results showed that both of the drip irrigation uniformity which considered the location distribution of clogged emitters and the Christiansen uniformity can reflect the influence of the amount of clogged emitter and the level of clogging on irrigation uniformity.In the meanwhile,the proposed method can also reflect the influence of location distribution of clogged emitters on the irrigation uniformity and overcome the weakness of Christiansen uniformity which only considered the influence of flow deviation.In the subsequent research,the desirable sampling interval and depth were 60 and 20 cm respectively for soil moisture monitoring under the condition of the simulation test.Based on the desirable sampling arrangement,there was a significant linear relevance between soil water distribution uniformity and irrigation uniformity.Among them,the uniformity coefficient considering location of clogged emitters could reflect the soil water distribution accurately;it had the optimal linear relationship with soil water distribution coefficient.According to this linear relationship,the uniformity coefficient considering location of clogged emitters could be optimized when the regression coefficient ratio for the content of clogged emitters' location uniformity and the Christiansen uniformity coefficient was 2:8.A field experiment was done in a solar heated greenhouse in order to verify the accuracy of the optimized uniformity coefficient considering location of clogged emitters.The field experiment result was consistent with the simulation result,both of which showed a significant linear relationship between soil water distribution coefficient and the optimized uniformity coefficient considering location of clogged emitters.With the increase of clogged emitters,the influence of clogged emitters' location on soil water distribution uniformity would also increase.If the clogged emitter accounted for a large proportion(>10%),the relationship between soil water distribution coefficient and the optimized uniformity coefficient considering location of clogged emitters was closer than it between soil water distribution coefficient and the other uniformity coefficients(R2=0.970,P<0.01).Therefore,the optimized uniformity coefficient considering location of clogged emitters was more proper when evaluating the irrigation uniformity.Its evaluation result was consistent with the soil moisture situation and could reflect the actual irrigation quality comprehensively.But in general,soil water distribution coefficient was higher than the optimized uniformity coefficient considering location of clogged emitters,indicating that the soil moisture was more uniform because of the soil matrix suction and the redistribution of soil water.