Effects of Mineralization Degree of Irrigation Water on Yield, Fruit Quality, and Soil Microbial and Enzyme Activities of Cucumbers in Greenhouse Drip Irrigation

Abstract

Water shortages and soil salinization are the bottlenecks of sustainable agricultural development in many arid and semi-arid regions of the world. Brackish water as a supplementary water source for agricultural irrigation is an important way to solve the shortage of agricultural water resources in arid regions. To study the effect of the mineralization degree of irrigation water (MIW) on the yield and quality of greenhouse fruit cucumber in arid, semi-arid, and cold regions, the effects of MIW on the photosynthesis, yield, and quality of greenhouse fruit cucumber, as well as the soil microorganisms and enzyme activity, were evaluated based on observed data from spring–summer (S−S) and autumn–winter (A−W). In this study, fruit cucumbers from Ningxia sunlight greenhouses were studied in a comparative experimental design with four MIW levels (CK, 2.8–3.0 g L−1; S1, 1.9–2.3 g L−1; S2, 1.2–1.4 g L−1; S3, 0.3–0.5 g L−1) where CK was used as the control treatment. The main indicators of fruit cucumber yield and fruit quality increased with MIW from 0.3 g L−1 to 3.0 g L−1. Compared with CK, the leaf area index (LAI) and net photosynthetic rate (A) of S3 of S−S (A−W) increased by 17.92% (26.32%) and 112.89% (17.68%), respectively. Vitamin C, soluble protein, and nitrate contents increased by 118.75% (24.92%), 41.67% (28.89%), and 43.09% (41.90%), respectively. The soil respiration rate (SRR) increased by 46.51% (90.48%). The yield and water use efficiency (WUE) increased by 35.98% (27.94%) and 12.95% (10.64%), respectively. A model of MIW and soil EC was developed and the applicability of the model was verified, with relative errors ranging from 2.7% to 7.8% (less than 10%). Within the experimental range, irrigation with lower MIW, which facilitated the increase in soil microbial load and soil respiration rate, promoted fruit cucumber growth, A, yield, and DMA, but was not conducive to fruit sugar accumulation; higher MIW was more conducive to improving fruit quality. The comprehensive assessment determined that the better MIW was 0.3–0.5 g L−1 (S3). The results of the study provide a feasible way to improve the quality and efficiency of greenhouse crops irrigated with brackish water in arid and semi-arid cold regions.