| Based on field experiments,this paper studies the spatial distribution and variation characteristics of soil moisture and nitrogen(nitrate nitrogen,ammonium nitrogen,inorganic nitrogen)under drip irrigation in facility greenhouses.Through statistical analysis,multifractal theory and analysis of variance,the following methods are discussed:(1)The effect of drip irrigation on the spatial distribution characteristics of soil water and nitrogen,crop yield and water and nitrogen utilization efficiency,aimed at formulating the best drip irrigation fertilization system;(2)The characteristics of spatial distribution variation and temporal stability of soil water and nitrogen under long-term drip irrigation and fertilization,which aimed at proposing suitable monitoring points for soil moisture and a simplified method for measuring points.The main conclusions as follows:(1)The migration and transformation of soil water and nitrogen in the wet layer under different drip irrigation timing conditions show that within 3 days after a single irrigation and fertilization,the nitrogen in the early fertilization treatment is well coupled with the water in the planned wet layer of the soil,while the late fertilization Nitrogen treatment mainly accumulates in topsoil 0-10 cm.The irrigation after fertilization makes the nitrate nitrogen in the later fertilization treatment show a clear migration trend downward.The studies of three crop yields,water and fertilizer use efficiency have shown that in the later fertilization treatment,the output of pepper crops in two facilities increased by 2.51%-4.66% and 2.77%-15.26%,and the yield of eggplant in autumn stubble increased by 42.23%-50.86%.The agronomic utilization efficiency of nitrogen fertilizer has also been significantly improved,so it is recommended that the timing of fertilization should be shifted backward as far as possible during the drip irrigation fertilization process.(2)The results of statistical analysis and multi-fractal analysis show that the ammonium nitrogen content is low and evenly distributed throughout the longitudinal section of the entire study area.Nitrate nitrogen is mainly concentrated in the shallow 0-30 cm soil layer,showing high content and strong variability in surface,and the degree of variation gradually weakens with the increase of depth.The variation degree of spatial distribution of nitrogen is generally 0-50 cm > 0-30 cm > 30-50 cm soil layer,indicating that a single research scale is not enough to fully characterize the spatial variation characteristics of soil nitrogen.Before and after irrigation,the spatial distribution structure of soil water content did not change much.The soil water content of the shallow 0-40 cm soil layer increased significantly,the variability weakened,and the degree of variation of the 40-100 cm and 0-100 cm soil layers increased.On the scale between the two drip irrigation belts,nitrate nitrogen tends to be concentrated between the drip irrigation pipes with water movement,and ammonium nitrogen is easily adsorbed by colloidal particles,etc.,so that it is evenly distributed between the drip irrigation belts.(3)Analysis of variance and Spearman rank correlation coefficient analysis show that,on the entire greenhouse scale,it is recommended that the soil moisture monitoring points be only placed at about 3/4 of the east-west length.On the scale between the two drip irrigation belts,the appropriate monitoring area for ammonium nitrogen during the crop growth period is located in the middle of the drip irrigation belt,with a depth of 10-20 cm;The suitable monitoring area for nitrate nitrogen is mainly concentrated at 0-30 cm from the left drip irrigation zone,especially the nitrate nitrogen content in the soil layer at a depth of 10-20 cm is recommended to focus on monitoring during the crop growth period;Points at different depths of 30 cm from the drip irrigation belts on both sides are suitable monitoring areas for soil moisture. |
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