Abstract: Nodule growth characteristics of Chinese milk vetch (CMV) differ in response to different soil physical and chemical properties, especially in different paddy soils. This study aimed to analyze the relationship between nodule characteristics of CMV and soil physical and chemical properties in CMV used in crop rotations with rice in Taihu and Ning-zhen rice growing regions. Correlation analysis and path analysis were used to associate differences in nodule characteristics with particular soil conditions in rice stubble. It was found that root nodule number, nodule weight and nitrogenase activity of milk vetch in rice-CMV crop rotations were affected by soil conditions. Nodule number per plant and the nitrogenase activity in Kunshan sample point were high (86.24·plant^-1, 1362.73 nmol C₂H₄·min^-1·g^-1, respectively), while corresponding values for Danyang sample point were low (1.13·plant^-1, 9.25 nmol C₂H₄·min^-1·g^-1, respectively). Path coefficients for nitrate nitrogen, total nitrogen, organic matter and available phosphorus were generally strongly correlated with nodule number, and organic matter, nitrate nitrogen and available phosphorus were positively correlated (P₂=1.629, P₁=0.633, P₄=0.448) but total nitrogen negatively correlated (P₅=-1.138, P represents direct path coefficient of factors). Soil organic matter, nitrate nitrogen and available phosphorus had the greatest positive influence on nodule number, whereas high soil total nitrogen reduced nodule number. There is a synergistic relationship between root nodule characteristics and the soil environment. In practice, appropriate organic fertilizer and phosphate fertilizer should be used to improve the nitrogen fixation capacity in CMV, rather than nitrogen fertilizer.

Key words: rice stubble, Chinese milk vetch, root nodule characteristic, organic matter, available phosphorus, total nitrogen