Effects of different materials on soil quality and yield of cucumber under brackish irrigation

Irrigation water is one of the most important determinants of crop yields and agricultural production, accounting for about 70% of global freshwater extraction and consumption. However, the shortage of fresh water resources has been a major constraint in most areas of the world, especially in arid and semi-arid areas in China. It is a very urgent task to deal with the water crisis in recent years. Brackish water resources can be one of the necessary ways to alleviate the water crisis, due to the easy mining of the large reserves (2.00×1010 m3). Nevertheless, improper irrigation can easily to cause the continuous accumulation of salt in the soil, and eventually lead to the occurrence of secondary salinization of soil, due to the high salinity of brackish water. The salinization of the surface layer can often hinder the growth of crops for less yield. This study aims to improve the salinized soil after long-term irrigation with brackish water instead of fresh water. Taking the cucumber Del "del 99" as the test material, four treatments were designed via the four successive crop positioning experiments (2018-2020): Untreated soil (CK), desulphurized gypsum (DG), earthworm composting (W), earthworm composting and desulphurized gypsum (DG+W). A systematic investigation was made to clarify the effects of earthworm composting, desulphurized gypsum or their combination on the soil's physical and chemical properties, microbial community, and yield of cucumber under brackish water irrigation. The indexes were also incorporated into the Soil Quality Index (SQI) for the cucumber yield. The results show that: 1) The content of available nitrogen, Available phosphorous , available potassium, and organic matter in soil significantly increased by 61.63%, 23.46%, 55.35%, and 55.45%, respectively, whereas, the pH value and electrical conductivity (EC) of soil greatly decreased (P<0.05) in the DG+W treatment, compared with the untreated soil (CK). 2) MiSeq high-throughput sequencing system was also selected to sequence the bacterial community in the rhizosphere soil. It was found that the DG+W combination improved the richness and diversity of the bacterial community in the rhizosphere soil, indicating the highest Chao1 Index, Sobs index and Shannon index. 3) There was a significant positive correlation between the SQI and cucumber yield. The combined DG+W application increased the plant biomass by 6.52%%, 14.82%, 9.91%, and 60.12%, respectively. The yield of cucumber increased by 8.9%, 3.1%, 18.67%, and 13.71% in four successive stubble, respectively. 4) The DG+W treatment can be widely expected to serve as an effective soil improver for the soil quality and cucumber yield under continuous saline irrigation. According to the regional resource conditions, the DG+W treatment presented the low cost, environmental protection, and easy operation, particularly for the better soil properties and higher crop growth than before. Consequently, brackish water irrigation combined with the desulfurization of gypsum and earthworm composting soil improvement can be the feasible mode of production to promote resource utilization for the higher productivity of alkaline soil crops. The finding can provide a theoretical reference for the sustainable production of vegetable facilities and soil improvement of saline-alkali land in northern China.