不同茬口大豆根圈土壤pH值和氮营养分布的变化

利用根箱系统,研究不同茬口条件下大豆根圈土壤pH值和氮营养分布,结果表明,前茬为麦茬和玉米茬的大豆根面区土壤偏碱,而前茬为休闲和豆茬的大豆根面区土壤偏酸.不同茬口土壤大豆根面区NO-3 -N含量较距根面2mm区低,表现为亏缺效应.尽管处理间NH 4 -N含量分布受茬口影响较NO-3 -N小,但NH 4 -N含量分布走向却因茬口而不同,休闲土、正茬土、迎茬土、重茬土和大豆长期连作处理条件下的大豆根圈土壤NH 4 -N含量表现为一定的累积效应,而小麦长期连作茬口土壤的大豆根圈NH 4 -N含量表现为亏缺效应.试验结果表明不同茬口的大豆根圈土壤pH值、NO-3 -N和NH 4 -N含量分布变化不同,说明大豆连作障碍的原因可能更主要的归结于大豆根圈土壤微生态环境的改变.

Effect of different rotation systems on soil pH and N nutrition distribution across soybean rhizosphere

Using rhizobox system to study the soil pH and N nutrition distribution across soybean rhizosphere with different rotation systems soils, the result showed that the soil pH of central compartment (C.C) was relatively alkaline when preceding crops was wheat and maize, and relatively acid when preceding crop was soybean or no crop (fallow soil). The NO~-_3 -N concentration of C.C in all rotation systems was lower than that of 2mm compartment, which indicated that NO~-_3 -N concentration was depleted in soybean rhizosphere. Although the NH~ _4 -N concentration across soybean rhizosphere was affected by different rotation systems less than NO~-_3 -N, the NH~ _4 -N distribution patterns were different among rotation systems, i.e. NH~ _4 -N concentration slightly depleted in the rhizosphere in the monoculture wheat treatment, and a little accumulated in Fallow, W-C-S, S-W-S, W-S-S and monoculture soybean systems. According to this experimental results, we concluded that the soil pH, NO~-_3 -N and NH~ _4 -N concentrations distributed across soybean rhizosphere were greatly influenced by different rotation systems, and suggested that the reason for the barrier of monoculture of soybean may be attributed to the micro-ecology changes in the soybean rhizosphere.