Assessment of magnesium deficiency in greenhouse tomato crops grown on calcareous soil

Abstract

AbstractMagnesium (Mg) deficiency in greenhouse vegetable plants affects crop yields and quality. Assessing the degree of Mg deficiency and influencing factors is necessary for evidence‐based Mg supplementation. In this study, an investigation was conducted at 71 tomato cultivation greenhouses with calcareous soil, located in the main greenhouse vegetable production area of China. Plant and soil Mg contents were analysed, as well as nitrogen (N), phosphorus (P), potassium (K) and other nutrients. The tomatoes showed Mg deficiency, with none of the farms supplementing this element. The critical leaf Mg concentration of the tomatoes was 3.40 mg kg−1. Using Ward's hierarchical cluster analysis, three clusters of Mg leaf content were obtained, which were 1.07–3.00 mg kg−1 (SD cluster), 2.56–5.64 mg kg−1 (MD cluster) and 5.12–6.88 mg kg−1 (ND cluster). Tomato yields in the SD and MD clusters were 31.4% and 16.5% lower than the ND cluster, respectively. Both soil exchangeable Mg content and soil pH in the SD cluster were the lowest, while total NPK, available NPK, K/Mg and the Ca/Mg ratio were the highest. A principal component analysis (PCA) showed that Mg leaf content was negatively correlated with the exchangeable K/Mg ratio, and positively correlated with soil exchangeable Mg content, soil pH and tomato yield. Mg deficiency in the tomatoes was attributed to the high accumulation of available K in the calcareous soil and the fact that the SD cluster with greatest Mg deficiency also had the lowest soil total Mg concentration. Considering the accumulation of NPK and the causes of Mg deficiency, foliar Mg spraying is suggested to mitigate Mg deficiency in calcareous greenhouse tomato soil.