高强度连作下露天菜地土壤次生盐渍化及其影响因素研究

Soil secondary salinization in open vegetable fields and its influencing factors under continuous cropping of vegetables with high intensity

采集佛山市南海区露天菜地表层土壤,测定其硝酸盐含量和全盐量,分析珠江三角洲典型区域蔬菜地土壤次生盐渍化的发生现状和原因,为制定合理的施肥和管理措施提供科学依据。结果表明,1)136个土壤样本硝态氮质量分数在1.070～854.4mg/kg,平均值为194.3mg/kg,有19.9%的土壤样本硝态氮质量分数超过300mg/kg,已达到极高水平;全盐质量分数在0.02～2.7g/kg,平均值为1.2g/kg,有12.5%的土壤样本全盐质量分数已超过2.0g/kg的轻度盐化标准。2)土壤硝态氮质量分数与全盐质量分数之间具有一定的相关性,经统计检验相关系数达极显著水准(r=0.5665,n=131,P<0.01)。3)高强度连作露天菜地土壤的硝态氮质量分数和可溶性盐分浓度已经接近多年塑料大棚水平。4)综合而言,导致土壤次生盐渍化的原因有气候条件、土壤质地、地下水位、灌溉方式、不合理施肥等,而过量施肥及高强度连作可能是引起南海区露天菜地土壤次生盐渍化的主要因素。

The Pearl River Delta （PRD）, South China, characterized by rapid urbanization and increasing reliance on fertilizers in the last several decades, has formed its typical non-point source pollution in farmland ecosystems. Because of its high multiple-crop index, the violent contradiction between man and land seemed to be alleviated to some extent. However, new problems occurred at the same time. Many farmers planted vegetables all the year for economic benefit. Continuous cropping with high intensity made the vegetable soils acid and hardened. As a consequence, the sporadic white salt efflorescence on the surface of the soil, which was regarded as one of the characteristics of soil secondary salinization, could be seen clearly under abnormal climate condition （drought etc.）. In addition, the growth of vegetables was obviously affected, and the phenomenon that vegetables died often occurred. The present study chose Nanhai district of Foshan city as one of the typical cases of the PRD region, introduced the secondary salinization of vegetable soils, and analyzed its influencing factors. The results indicated that the NO3^--N accumulations and total salt concentrations of top soils for 136 open vegetable fields ranged from 1.070 mg·kg^-1 to 854.4 mg·kg^-1 and 0.02 g·kg^-1 to 2.7 g·kg^-1, respectively, and the average content of NO3-N and total salt reached 194.3 mg/kg and 1.2 g·kg^-1, respectively. There were about 19.9 % and 12.5 % of the samples with higher than 300 mg·kg^-1 NO3^--N accumulation and 2.0 g·kg^-1 total salt concentration, respectively, which came close to the levels of plastic greenhouse, especially under continuous cropping of vegetables with high intensity. Statistical analysis showed that NO3^--N accumulation was significantly and positively correlated with total salt concentration （r = 0.566 5, n = 131, P 〈,0.01）. There were several factors that caused soil secondary salinization, namely, climate, soil texture, ground water level, irritation mode, and over-fertilization, etc. Over-fertilization and continuous cropping of vegetables with high intensity might be two main factors for soil secondary salinization in Nanhai district.