Responds Of Water And Nitrogen Use Efficiencies Of Cucumber To Water Supply Characteristics Of Negative Pressure Irrigation

Inadequate resources of water is a serious contradiction of agricultural development in china.How to increased mechanization and automation of irrigation technology and generalize the use of low pressure irrigation are the primary issues to be considered for modern agriculture.To further develop water-saving irrigation technologies,we should committed to the improvement and innovation of these technologies besides technical reference.These can promot the sustainable development of Chinese modern agriculture in nature.Negative pressure irrigation（NPI）is a new water-saving irrigation technology whose emitter buried under ground.The irrigation water can leach into soil from emitter by the delivery head between soil water potential and feed water pressur.The studies on negative pressure irrigation technology are still at the stage of exploration.By using negatively pressurized fertigation system,the objective of this study was to investigate effects of different combination of irrigation and fertilizer on distribution of nitrate nitrogen and water and nitrogen use efficiencies of cucumber,to research the processes and mechanisms of drought stress on photosynthesis,to study the impact of soil water content on carbon assimilation and transpiration water consumption,and to analyze the optimum rang making cucumber grow better,which would supply the reference basis about cucumber water-saving physiology under the condition of NPI.The main conclusions of this study were as follows:（1）Negative pressure of supply water had exponent relation to the soil water content which decreased as negative pressure reduced.Nitrogen application rate had no significant effect on soil water content（P>0.05）.The relationship between negative pressure of supply water and water consumption of cucumber were quadratic parabola.（2）The negatively pressurized system can keep soil water content stably within 0-25 cm soil layer.The system can keep a balance between water consumption and water supply.During cucumbers growth period,the soil water contents could keep stability essentially under the same negative hydraulic head.The average soil water content controlled by 0,-5,-10 and-10 kPa were respectively 28.7%,22.7%,20.0%and 15.6%.The change of soil water content belonged to the low intensity（Cv≤0.1）during cucumbers growth period.（3）The negatively pressurized fertigation system could extremely increase distribution uniformity of soil water and nitrogen within 0-25 cm soil layer.The difference between the minimum and maximum values of soil water content controlled by-15-0 Kpa were 3.05%-6.15%,which indicated that the soil water spatial variability was lower The average of the coefficient of variation of the distribution of soil nitrate on the vertical was decreased by 58.6-71.2 percent.（4）When RSWC was between 77.4%and 88.7%,net photosynthetic rate（P_n）and intercellular CO₂ concentration（C_i）significantly decreased with reducing water content,meanwhile,stomatal limitation（L_s）significantly increased,which indicated that stomatal limitation was responsible for reduction in P_n.When RSWC was lower than 77.4%,P_n and L_s decreased and C_i increased with reducing water content.This indicated that the main reason for restricting Pn had turn into non-stomatal limitation.There were a parabola correlation between the daily average value of P_n and leaf water use efficiency and RSWC respectively.（5）The suitable RSWC were between 77.4%and 88.7%at flowing stage and 88.7%and 103.8%at fruit stage.Carbon assimilation and transpiring water consumption had a good collaborative relationship at these conditions,which could make P_n and leaf water use efficiency（LWUE）maintain a relatively high level to accommodate water stress.（6）The primary factors affecting the quality of cucumber were fruit interior quality factor（45.38%）,amount factor（36.32%）and marketable fruit rate factor（21.10%）by the method of factor analysis and comprehensive evaluation.The above results indicated that W2N1 and W3N1 were more suitable for cucumber growth.（7）The water use efficiency and apparent N recovery under condition of-5 Kpa are 136.8%and52.32%higher than at conventional treatment.The average of plant dry weight and yield reached their maximum at the condition of-5 Kpa,which were 153 g and1406 g respectively.In view of yield,quality,water use efficiency,net photosynthetic rates,greenhouse irrigation under negative pressure for cucumber,optimal irrigation level-5 and-10kPa could be promoted.