[Effects of long-term applying sulfur- and chloride-containing chemical fertilizers on weed growth in paddy field].

An investigation was made at a double-rice paddy field in the Qiyang Red Soil Field Experimental Station,Hunan Province,China to study the species and biomass of weeds growing in rice(Oryza sativa L.) growth season after 34-year application of sulfur(SO42-) and chloride(Cl-)-containing chemical fertilizers under the same application rates of nitrogen(N),phosphorus(P),and potassium(K).Long-term application of Cl--containing chemical fertilizer resulted in the greatest species number of weeds and the highest biomass of floating weeds and wet weeds,compared with long-term application of SO42-and Cl-+SO42--containing chemical fertilizers.In early rice growth season,the biomass of weeds after applying Cl--containing chemical fertilizer was 51.4% and 17.6% higher than that after applying Cl-+SO42-and SO42--containing chemical fertilizers,respectively;in late rice growth season,the increment was 144% and 242%,respectively.More floating weeds were observed after applying Cl-+SO42-and SO42--containing chemical fertilizers,but few of them were found after applying Cl--containing chemical fertilizer.The total dry mass of weeds and the dry mass of wet weeds were positively correlated with soil Cl-content(r=0.764,P0.01 and r=0.948,P0.01,respectively),but negatively correlated with soil SO42--S content(r=0.849,P0.01 and r=0.641,P0.05).Soil alkali-hydrolyzable N and available P,under the co-effects of soil SO42--S,Cl-,and pH,had indirect effects on the total dry mass of weeds.By adopting various fertilization measures to maintain proper soil pH and alkali-hydrolyzable N and available P contents,increase soil SO42--S content,and decrease soil Cl-content,it could be possible to effectively inhibit the growth of wet weeds and to decrease the total biomass of weeds in double-rice paddy field.