Effect of fertilization patterns on weed community in late rice fields

【Objectives】 Effect of long-term and unreasonable chemical fertilization on ecological environment has attracted attention of scholars and the public, and application of organic fertilizer is paid more and more attention. It is difficult to reveal mechanism of organic fertilization on weed communities and forecast evolution trend of weed communities under organic farming environment. This paper was to study weed communities under different fertilization patterns in farmlands, and explore evolution trend of weed community structure in late rice fields. 【Methods】 The weed community structure features and biodiversity of five fertilization treatments in late rice growing season were studied by using the method of community ecology based on a long-term fertilization field experiment. Five quadrats each with 0.25 m2 area were set in each plot for sampling and investigation, and weed species, numbers, coverage and frequency in the quadrats were recorded and the rice yields were measured. Digital light meters were placed on the soil surface and top of the crop canopy. Soil samples were taken in each plot to analyze organic matter, available N, P and K. The importance values of each weed species in each plot were calculated, and the biodiversity of weeds was measured with the species richness S and Shannon-Wiener index H. Importance values of 11 common weed species in 15 plots were used as original matrix for principal components analysis and canonical correspondence analysis(CCA) by SPSS16.0. 【Results】 There are significant differences of soil nutrients and light transmittance in late rice fields under the different fertilization patterns. The rice yields in the treatments of combined application of organic manure and chemical fertilizers are higher than those in other treatments. Heleocharis plantagineiformis, Rotala indica, Cyperus difformis and Monochoria vaginalis are dominant weed species in the CK treatment. Paspalum paspaloides is dominant weed species in the NPK treatment. The weed species in the NPK5/5 and NPK3/7 treatments are dominated by Paspalum paspaloides and Cyperus difformis. Paspalum paspaloides, Cyperus difformis and Echinochloa crusgalli are dominant weed species in the NPK7/3 treatment. The result of PCA indicates that the 15 weed communities can be divided into three patterns: pattern 1 includes the CK treatment, pattern 2 includes the NPK3/7 fertilization treatment, and pattern 3 includes the NPK, NPK5/5 and NPK7/3 fertilization treatments. The principal component 1 is significantly and negatively correlated with organic matter, available N and P (P＜0.01), but is significantly and positively correlated with light transmittance (P＜0.01). The result of CCA indicates that Heleocharis plantagineiformis, Rotala indica and Heleocharis yokoscensis are adapted to the CK treatment, Paspalum paspaloides is adapt to the NPK7/3 treatment, and Monochoria vaginalis, Lindernia procumbens and Marsilea quadrifolia are adapt to the NPK3/7 treatment. The number of dominant species and biodiversity in the treatments that combined use organic manure and chemical fertilizers were between that in the CK and NPK treatments. There is a trend that the biodiversity is increased with the increase of organic manure proportion. The biodiversity indices of weed community are significant upward parabola correlative with organic matter and available N and P (P＜0.01), whereas are negatively correlated with available K (P＜0.05) and significantly and positively correlated with transmittance (P＜0.01). 【Conclusions】The weed community features are closely related to the contents of soil organic matter, available N, available P and light transmittance. Balanced fertilization significantly reduces the number of dominant weed species. The treatments that combined use organic manure and chemical fertilizers maintain the number of dominant species and biodiversity between the CK and NPK treatments. These results show that the weed community could be regulated by adjusting the application rate of organic manure for realizing the integrated weed management. Considering both the yield of late rice and biodiversity of weed community, the NPK3/7 treatment (chemical fertilizer 30% + organic manure 70%) is not only beneficial to obtain high yield, but also shows an advantage for keeping weed biodiversity.