Potassium–calcium antagonistic interaction under tomato magnesium deficiency and magnesium fertiliser regulation in solar greenhouse

Abstract

This study sought to clarify the antagonistic interactions of potassium (K) and calcium (Ca) to magnesium (Mg) under a deficiency of Mg in tomato. Tomato leaves and soil samples that had differing levels of Mg deficiency were collected to study the relationship between symptoms of Mg deficiency and contents of soil K and Ca. Four different Mg fertiliser treatments were conducted to analyse the regulation of Mg for soil K, Ca and Mg. The results showed the following: (1) The yield of tomatoes decreased significantly with an increase in Mg deficiency, and the yield of tomatoes with moderate (MD) and severe (SD) Mg deficiency decreased by 38.02% and 59.53%, respectively, compared with treatments without Mg deficiency (ND). (2) The cation saturation ratio of K+ (CSRK+) was significantly higher with MD and SD compared with ND, while the CSRMg2+ was lower. The soil K/Mg and Ca/Mg values were higher than the critical value of imbalance. (3) The soil exchangeable K, CSRK+, Ca/Mg and K/Mg under SD increased significantly when compared with that under ND. (4) The content of Mg in tomato leaves and its yield were significantly negatively correlated with soil exchangeable K, CSRK+ and K/Mg. (5) With the increase in application of Mg fertiliser, the soil exchangeable K content, K/Mg and CSRK+ decreased significantly, while the Ca/K increased. The soil exchangeable K content, K/Mg and CSRK+ with 90 kg/ha MgSO4 and 234 kg/ha K2O applied (M2K1 treatment) were the lowest among all treatments. (6) The yields of tomatoes and uptake of Ca and Mg increased as supply of Mg increased. (7). Reducing the application of K was a much more efficient way to decrease soil K/Mg and restore cation imbalance than providing Mg fertiliser in calcareous soil.