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.