The Distributions Of Water And Nitrogen In Soil And The Growth Of Spring Maize As Affected By Drip Irrigation Uniformity In North China Plain

Drip irrigation uniformity coefficient is used to quantify the uniformity of drip irrigation outflows,and it is one of the important parameters in designing and evaluating the drip irrigation systems.Drip irrigation systems should have a high uniformity coefficient to ensure the quality of drip irrigation and enhance water use efficiency.However,from the economical perspective,the high uniformity coefficient may increase the investment and running costs of drip irrigation systems.Whereas the too low uniformity coefficient might reduce the crop yield and quality,cause the loss of water and nitrogen,and increase the risk of non-point source pollution.Therefore,it has a practical significance to study the influence of irrigation uniformity coefficient on the distribution of soil moisture and nitrogen and the crop growth.Field experiments of spring corn(Zea mays L.)were conducted at the Daxing Experimental Station of the China Institute of Water Resources and Hydropower Research,in the North China Plain in 2009 and 2010 to evaluate the impacts of drip irrigation uniformity and application amount on the distribution of soil moisture and nitrogen,corn growth and yield.Three Christiansen uniformity coefficients(CU)of 0.66(low,C1)0.81(medium,C2),and 0.99(high,C3)and three levels of water application at 50%(low,I1),75%(medium,12),and 100%(high,13)of the irrigation requirement were used.During the both growing seasons,soil moisture in different depth were monitored regularly,and the dynamic changes of soil moisture,bulk electrical conductivity and temperature in the 35cm depth were monitored continuously.In the critical growth stages,the distribution of soil moisture and nitrogen were tested by the soil sampling method.Meanwhile,physiological indicators of spring corn such as plant height,leaf area index(LAI),chlorophyll meter reading(SPAD reading)and dry biomass above ground were regularly measured.When the com was harvested,the yield was recorded.The main conclusions of this study are as follows:(1)Under the three different drip irrigation uniformity treatments(CU=0.66,0.81,and 0.99),the uniformity coefficients of soil moisture during both growing seasons were maintained at a high level,higher than 0.85 in 2009 and 0.80 in 2010.For the low uniformity treatment,the uniformity of soil moisture was considerably higher than its irrigation uniformity.The uniformity coefficient of soil moisture in the growing periods for all uniformity treatments were relatively stable,the relative deviations-were within ± 10%.The influences of the uniformity of initial soil moisture were about 1.9 and 1.6 times more important than those of the drip irrigation uniformity coefficient in 2009 and 2010,respectively.The uniform soil moisture was maintained mainly through the rainfall and crop absorption.(2)The soil nitrate content and its uniformity coefficient gradually decreased with the increasing of soil depth.The soil ammonium nitrogen content and its uniformity coefficient evenly distributed across the profile.Drip irrigation uniformity and application amount imposed an insignificant influence on the uniformity coefficients of nitrate content,and on ammonium nitrogen content and its uniformity coefficient.The main influential factors of uniformity coefficient of soil nitrate in the jointing,filling,and maturity stages were the initial nitrate uniformity coefficient,the uniformity of soil moisture and application amount,respectively.The uniformity coefficient of soil ammonium nitrogen was slightly higher than the corresponding nitrate uniformity coefficient,but both were less than the uniformity of soil moisture.Rainfall greatly weakened the impacts of uneven irrigation on the distribution of soil moisture and nitrogen content.(3)The two-year location monitoring of soil moisture and bulk electrical conductivity.indicated that the uniformity coefficients of them were primarily influenced by their initial values.The uniformity coefficient of bulk electrical conductivity was lower than that of soil moisture during the growing season.The correlation of the soil nitrate content with soil bulk electrical conductivity,soil moisture and temperature could be described by a quadratic polynomial.Thus,the dynamic changes of soil nitrate can be grasped timely through the automatic monitoring of soil bulk electrical conductivity,soil moisture and temperature.But,the field calibration should be carried out in order to obtain higher prediction accuracy.(4)The uniformity of plant height,leaf area index,and leaf SPAD values for all teatments had maintained a high uniformity(CU>0.80)during both growing seasons,and the difference of uniform coefficient between treatments gradually decreased with the spring corn growing.The mean and the coefficient of dry matter and N uptake were not significant differences for all treatments.Its uniformity coefficients were more than 0.90 and 0.85 at harvest season,respectively.(5)Corn yield with high uniformity treatment was relatively high,but the differences among treatments did not reach a significant level.Furthermore,the yield did not change with the variation of emitter flows(1.05?2.6 L/h)along the drip line,and the uniformity coefficients of yield were all larger than 0.93,more than the low and medium irrigation uniformity coefficient(0.66 and 0.81).(6)This study illustrated that drip irrigation uniformity coefficient is not the main factors affecting the distribution of soil moisture and nitrogen,corn growth and yield of spring corrn in the North China Plain.Therefore,the design standard of irrigation uniformity coefficient(CU)might be fairly lowered in the semi-humid regions,such as the North China Plain.