Soil quality assessment of greenhouse vegetable production in Ningxia—A low-contaminated and high-quality crop base

Abstract

Declining soil nutrients and increasing total metals impair optimum land productivity. Understanding the spatial and temporal variabilities of soil properties helps researchers and farmers to determine the soil's ecological status and provide science-based recommendations for fertilization, crop suitability, and land use. Ningxia has less industrial waste gas and water pollution, good ecological environment, and is an important green vegetable planting base in China. This study was conducted to investigate the spatial and temporal variabilities of soil nutrients and metal elements in greenhouse conditions. All soil samples were alkaline. The concentration of soil nutrients and metal elements was concentrated in the soil surface (0–30 cm) and increased with cultivation years. A significant difference was observed between the soil planted for more than 11 years and that planted for 0 year (open field). A total of 76.8% of the soil samples’ organic matter concentration had relatively low (10–20 g/kg) and medium grades (20–30 g/kg). And 100% and 84.5% of soil samples’ total nitrogen and available nitrogen concentrations were <40 and <200 mg/kg, respectively, at 0–30 cm. And 68.3% and 95.1% of soil samples’ available potassium (>120 mg/kg) and phosphorus (>20 mg/kg) contents were relatively high and high, respectively. Nearly all soil samples have low metal element concentrations. The soil properties in the Yellow River irrigation region were higher than those in the other areas of principal component 1 (PC1). Comprehensive soil quality in Ningxia showed alkaline conditions and high potassium and phosphorus, along with suitable amounts of available nitrogen and zinc, making it ideal for high-quality greenhouse vegetable production.