The Effects of Water-nitrogen Coupling on Transport of Water, Salt and Nitrogen in Matrix-cultured Greenhouse Cucumber

【Background and Objective】 Matrix-culture has been increasingly used in vegetable production, but continuous irrigation and fertilization could result in salinization and degradation of the matrix. The purpose of this paper is to experimentally study the impact of different combinations of irrigation and nitrogen (N) fertilization on water, salt and nitrogen dynamics in sandy matrix of cucumber, as well as its consequence for cucumber yield. 【Method】 The experiment was conducted in a greenhouse and consisted of seven treatments which were designed using the secondary saturated D-optimal design methods. Each treatment had three replicates. All treatments were drip-irrigated. During the experiment, we measured the moisture content, EC, nitrate and ammonium contents at four layers in the matrix after each 20 days, as well as cucumber yield in each treatment. 【Result】 The irrigation amount controlled water movement in the matrix, and the irrigation water moved downwards in most treatments. Mulching the matrix surface with a membrane can suppress the detrimental effect of salt to some extent, but avoiding excessive irrigation and N application is the best way to reduce salt accumulation in the matrix. Water flow took nitrate and ammonium to move with it in the matrix, and there was a threshold for ammonium below which the cucumber roots were unable to take up. The cucumber yield increased with irrigation and nitrogen fertilization parabolically: increasing first and then declining after the irrigation or fertilization exceeded a threshold. 【Conclusion】 On average, in terms of moisture content, the optimal water-nitrogen coupling is to set the upper and low soil moisture content in the matrix for irrigation at 80.20%~89.40% and 60%, respectively, N application at 623~917 kg/hm2. These not only ensure sufficient water and N to the crop, but also reduce the risk of water and N leaching and secondary salinization of the matrix.