Effects of natural grasses and intercropping green manure on the composition and diversity of the weed community in a citrus orchard

In this study, the weed communities under eight different treatments of nitrogen fertilizer application (0%, 70%, 85%, and 100% of local recommended nitrogen application rate) and sod culture (natural grasses and intercropping green manure) were investigated in a citrus orchard in Dangyang, Hubei Province, China. The effects of the sod culture, reducing nitrogen fertilizer application, and soil factors on the composition and diversity of weed communities were explored by Pearson correlation analysis and canonical correspondence analysis. Results showed that: (1) Based on the plot investigation, 30 weed species in 29 genera and 21 families were recorded in the eight treatments. The species were mainly from Gramineae and Composite; Echinochloa crusgalli (L.)Beauv., Oxalis corniculata L., and Geranium carolinianum L. were common species in all treatments; Echinochloa crusgalli and Gnaphalium pensylvanicum Willd. were dominant species under natural grass treatments; Oxalis corniculate was the dominant species under intercropping with Vicia villosa Roth. var. glabrescens Koch.(2) No significant differences in the Margalef, Patrick, Shannon-Wiener diversity, and Pielou evenness indices for weed communities were observed among the different nitrogen fertilizer amounts; intercropping green manure significantly reduced the species diversity index of the weed communities in the citrus orchard. (3) Available phosphorus in the soil significantly affected weed diversity. (4) The main soil factors that affected the distribution of weed species under the different treatments were available phosphorus, pH, water content, and temperature. This study indicates that whether nitrogen fertilizer is reduced or not, intercropping with Vicia villosa Roth. var. glabrescens Koch. significantly decreas weed diversity, suppresses the growth of malignant weeds, and reduces competition for fertilizer with fruit trees.