THE CLASSIFICATION OF NO_3~--SOIL SECONDARY SALINIZATION IN A TOMATO-BASED GREENHOUSE IN CHINA'S YANGTZE RIVER DELTA

摘要

Although greenhouse vegetable cultivation is one of the most productive industries in agriculture, it usually results in soil secondary salinization (SSS) that degrades soil quality, subsequently reducing agricultural efficiency. Therefore, it is necessary to propose some guidelines to direct the management of SSS in greenhouse agricultural areas. In this study, NO3-SSS classification was studied in greenhouses planted with tomato (Solanum lycopersi-cum L.) in Taizhou, Jiangsu province, East China. After the soils in these greenhouses were treated with different concentrations of nitrate, the SSS levels as expressed by electrical conductivity (EC) were studied at 0.91 ds m~(-1) for control (ck), 2.91 ds m-1 for treatment 1 (Tl), 3.95 ds m~(-1) for treatment 2 (T2), 4.76 ds m-1 for treatment 3 (T3) and 6.30 ds m-1 for treatment 4 (T4). The results showed that there were statistically significant relationships between NO3- contents and soil EC in the surface soils, implying that the change in soil quality resulted from the difference in nitrate contents. The level of the NO3- - SSS was also significantly related to the tomato height and yield (p < 0.05). The NO3- - SSS was divided into five levels according to the effects of SSS on the tomato height and yield (level I: 2.14 ds m~(-1) < EC < 2.87 ds m~(-1), level II: 2.87 ds m~(-1) < EC < 4.20 ds m~(-1), level III: 4.20 ds m~(-1) < EC < 5.57 ds m~(-1), level IV: 5.57 ds m~(-1) < EC < 6.94 ds m~(-1), level V: EC > 6.94 ds m~(-1)). This study provides practical guidelines for determining optimum levels of NO3-treatment and NO3—SSS in facilities agriculture, and also gives some valuable information to manage the cropping of vegetable e.g., tomato, in greenhouse by adjusting salinity in soil.