How to remediate sulfate-nitrate salinized greenhouse soil? An optimal combination of organic amendment, fertilizer and irrigation

Abstract

Greenhouse soil secondary salinization is a widespread problem along the lower-middle reaches of the Yangtze River basin, which seriously deteriorates the yield and quality of vegetables. High multiple-cropping index of the greenhouse management needs intensive application of agrochemicals and frequent irrigation which led to significant soil salinization in this area. In this study, we investigated how to remediate the salinized plastic shed soils and improve the yield and quality of vegetables using various measures, including two types of irrigation (intermittent irrigation and 80% water-holding capacity), four types of organic matter (cow manure, mushroom residue, fermented sawdust, and half-fermented sawdust) with two application rates (2 g C kg−1 soil and 8 g C kg−1 soil), and two types of inorganic fertilizers (compound fertilizer with and without sulfate). Results showed that intermittent irrigation decreased either soil electrical conductivity from 1.55 to 0.36 mS cm−1 or the concentrations of soil nitrate from 507 mg kg−1 to 31 mg kg−1 and sulfate from 664 mg kg−1 to 114 mg kg−1 in the incubation period. This effect continued to the next two periods (before seed sowing and after the first harvest). After the second harvest, all these parameters had a recover trend but remained lower than those of the original soil. Half-fermented sawdust had the best effect for soil amelioration among the four organic amendments whilst the effects were not enhanced at higher application rate. Across the two continuous growing seasons (pak choi (Brassica rapa subsp. chinensis) in first season, cherry radish (Raphanus sativus L.) in second season), especially the second harvest season, the compound fertilizer without sulfates ameliorated soil degradation and maintained greater yield compared with sulfate-containing fertilizer. Therefore, application of 2 g C kg−1 half-fermented sawdust with intermittent irrigation and use fertilizer without sulfate was optimum for the degraded greenhouse soil remediation and vegetable yield improvement. This treatment could either decreased soil EC from 1.55 to 0.325 mS cm−1 or the concentration of soil nitrate from 507 to 89 mg kg−1 and sulfate from 664 to 266 mg kg−1 after continuous two growing seasons while the radish yield in second growing season was 71% higher than CK. These findings provided an economical and practical method to remediate sulfate-nitrate salinized greenhouse soil in a short period and designed a field management mode to maintain the efficacy.