日光温室栽培番茄镁缺乏与土壤阳离子平衡的关系

【目的】北方石灰性土壤钙、镁含量丰富，镁素供应充足，缺镁主要发生在南方高度风化的酸性土壤，但近年来北方日光温室栽培番茄等作物缺镁现象频发。因此，解析导致石灰性土壤日光温室栽培番茄缺镁的主要因素，可为日光温室番茄镁素缺乏的矫正和合理施肥提供科学依据。【方法】在陕西省杨凌示范区大寨镇日光温室栽培基地，于秋冬茬栽培番茄普遍发生缺镁的盛果期（11月份），选择番茄定植时间和品种一致，叶片形态呈现不同程度缺镁症（不缺镁：外观未观察到番茄缺镁失绿症状；中度缺镁：上部1/2叶片未表现缺镁失绿症状；严重缺镁：上、下叶片均表现缺镁失绿症状）的日光温室，分别采集温室0—20 cm耕层土样和番茄第2穗与第3穗果间的叶片（下部叶片）以及上部完全展开的新生叶片（上部叶片）样品；测定土壤pH、电导率、有机质、NO₃^--N、NH₄⁺-N、有效磷、速效钾以及交换性钾、钙、镁离子含量，番茄叶片钾、钙、镁含量，计算土壤交换性钾、钙、镁离子饱和度和K/Mg、Ca/Mg、Ca/K离子比例，并调查番茄产量；分析番茄缺镁程度不同的日光温室土壤基本性质差异，交换性钾、钙、镁离子含量及平衡状况与番茄叶片养分含量和产量的关系。【结果】番茄缺镁程度不同的温室土壤性质存在差异，番茄缺镁严重的土壤电导率、NO₃^--N、速效钾显著增加。番茄缺镁和不缺镁的土壤交换性镁含量均高于缺镁临界值（0.5 cmol·kg^-1）；随番茄缺镁程度加剧，钾离子饱和度增加，钙、镁离子饱和度降低，Ca/Mg和K/Mg离子比例升高，Ca/K离子比例下降；与不缺镁相比，番茄中度缺镁的土壤交换性钾离子饱和度、K/Mg离子比例均增加了22%，严重缺镁的则分别显著增加了56%和88%；番茄严重缺镁的土壤Ca/Mg比例较未缺镁的升高了17%；番茄中度缺镁和严重缺镁的土壤Ca/K比未缺镁的分别降低了19%和37%。番茄中度缺镁的土壤Ca/Mg略高于适宜值上限（7.0），K/Mg则高于适宜上限（0.6）47%，番茄严重缺镁的土壤Ca/Mg和K/Mg分别高于适宜值上限28%和125%。番茄上、下部叶片镁含量和番茄产量分别与土壤速效钾含量、交换性钾含量、钾离子饱和度、K/Mg均呈极显著或显著负相关，与土壤有机质和Ca/K呈极显著或显著正相关，而与土壤交换性镁含量、镁离子饱和度及Ca/Mg比例间未达显著相关性；随番茄缺镁程度加剧，产量显著降低，中度和严重缺镁的番茄产量分别降低了38%和60%。【结论】番茄缺镁程度不同的温室土壤交换性镁含量均在丰富水平，而镁离子饱和度偏低；番茄表现缺镁的土壤Ca/Mg和K/Mg均呈养分比例失调状态，特别是K/Mg严重失调。土壤中钾离子过高造成阳离子比例失调是诱导番茄缺镁症的主要因素，温室高集约栽培下过量施肥影响阳离子养分平衡是值得关注的问题。

The Relationships Between Magnesium Deficiency of Tomato and Cation Balances in Solar Greenhouse Soil

【Objective】It is generally considered that the contents of calcium and magnesium (Mg) in calcareous soil are rich. Therefore, Mg deficiency usually occurs in acidic soil in south China, where the weathering is very strong. However, Mg deficiency of tomato under solar greenhouses in calcareous soil in north China becomes common. It is urgent to understand the reason of Mg deficiency of tomato under solar greenhouses in the region, which will provide scientific knowledge to solve the Mg deficient problem in the solar greenhouse. 【Method】The different degrees of Mg deficiency of tomatoes with the same transplanting times and varieties in the greenhouses in Dazhai, Yangling, Shaanxi were chosen. The degrees of tomato Mg deficiency were divided into three types based on the severity of the symptoms. The three types of Mg deficiency included the leaves without Mg deficiency, the leaves with moderate (half of the upper leaves showed deficiency) and severe (all leaves showed deficiency) Mg deficiency. The soil samples (0-20 cm), lower leaves samples (the leaves between the second and third fruit sets) and upper leaves samples (the fully developed leaves on the top plant) were taken from different greenhouses. The basic soil properties were determined, including soil pH, electric conductivity (EC), organic matter, available nitrogen, phosphorus, and potassium, and soil exchangeable K⁺, Ca²⁺, and Mg²⁺, and their contents in tomato leaves. The ratios of exchangeable K⁺, Ca²⁺, and Mg²⁺ ions, and their saturation percentages in soil colloid were calculated. The fruit yields of different greenhouses were also surveyed. The relationships between Mg deficiency of tomato and the parameters determined were analyzed.【Result】There were significant differences in soil properties between the greenhouses with different degrees of Mg deficiency. The soil EC, contents of nitrate, readily available K in soil of tomato with severe Mg deficiency were significantly increased. The content of exchangeable Mg ions in soils was higher than the critical value of Mg deficiency both in tomatoes with and without Mg deficient symptoms. With the severity of Mg deficiency of tomato, the saturation percentage of K ion was increased and the ratios of Ca/Mg, and K/Mg also increased. On the contrary, the saturation percentages of Ca²⁺ and Mg²⁺ ions, and the ratio of Ca/K were decreased. Compared with tomatoes without Mg deficiency, the saturation percentage of K⁺ and the ratio of K/Mg in soil with moderate Mg deficiency were increased both by 22%, and soil with severe Mg deficiency increased by 56% and 88%, respectively. Compared to soil without tomato Mg deficiency, the ratios of Ca/Mg in soil with severe Mg deficiency was increased by 17%, and the ratios of Ca/K in soil with moderate and severe Mg deficiency were decreased by 19% and 37%, respectively. The soil Ca/Mg ratio of tomato with moderate Mg deficiency was slightly higher than optimum value of Ca/Mg ratio (7.0), and K/Mg ratios was higher than optimum value (0.6) by 47%. The ratios of soil Ca/Mg, and K/Mg were higher than optimum value by 28% and 125%, respectively. The Mg contents in both upper and lower leaves and fruit yield of tomato were significantly and negatively correlated with the readily available K, exchangeable K⁺, saturation percentages of K⁺, and K/Mg ratio, and positively correlated with soil organic matter content and Ca/K ratio; and their correlations with exchangeable Mg²⁺ and its saturation percentages, and the ratio of Ca/Mg were not significant. With the severity of Mg deficiency, the tomato fruit yields were decreased rapidly. The decreasing rates of fruit yields in moderate and severe Mg deficiency were 38% and 60%. 【Conclusion】 The contents of soil exchangeable Mg²⁺ was at optimum levels for tomatoes with or without Mg deficiency; however, the Mg²⁺ saturation percentages was lower. The ratios of Ca/Mg, and K/Mg in soil with different Mg deficiency were imbalance, especially for the K/Mg ratio. The high level of K resulted in imbalances of cation ions was the main reason of Mg deficiency in solar greenhouse of calcareous soil. Therefore, more attentions are needed to deal with this problem.