Improvement for weed controls in organic paddy fields

• Main Authors: Chi-Huai Su, 蘇啟懷
• Other Authors: Shih-Shiung Chen
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/83369954647892973704

碩士 === 國立中興大學 === 農藝學系 === 89 === Field experiments were conducted in the first and second crops of 2000 on the paddy fields at NCHU (Taichung City) and AES of NCHU (Wufeng, Taichung), to investigate effects of mulching treatments on weed control in organic rice farming. Two rice cultivars, Tai-keng 9(TK9) and Taichung sen 10(TCS 10) were used for evaluation. Experimental design was conducted by completely randomized design (CRD) with 4 replications. Treatments of mulching of rice hull, paper, and two azolla varieties (Tali and Lima) were applied with no mulching as control. Plots were inoculated with azolla (0.2 kg/m2), or applied rice hull (0.5 kg/m2) immediately after transplanting. Paper was mulched simultaneously while transplanting. In order to evaluate the optimal input of azolla and rice hull, another experiment with different amounts of azolla (Lima, 0.1, 0.2, and 0.3 kg/m2) and rice hull (0.4, 0.8, and 1.2 kg/m2) was conducted at farm of NCHU. Since weed control by rice hull showed not effective in the first crop, rice hull was substituted by smoked rice hull (0.6 kg/m2) in the second crop. Results of experiment showed that soil redox potential in the first crop dropped most sharply by azolla treatment becaused of the rapidly growth of azolla. In the second crop, high temperature in the beginning of rice growth stage accelerated decomposition of paper membrane, rice hull and smoked hull. Thus resulted in decline of soil redox potential. In the first crop, paper mulching control weeds most efficiently, more than 99% of weeds were inhibited. Half life of paper in paddy fields was about 45∼50 days. The efficiency of weed control by azolla was on the second rank. Between the two azolla varieties, Lima grown fast and mulched the field rapidly with several layers. The weed control efficiency of variety Lima was much better than that of Tali. All the three inoculation rates of azolla (0.1, 0.2, and 0.3 kg/m2) controlled weeds efficiently. Variety Tali mulched in single layer only and was not tolerant to high temperature, thus not inhibited weeds population effectively. On the other hand, mulching with rice hull inhibited weeds in very low efficiency. Paper mulching was the most effective method on weed control in the second crop. When 50% paper membrane decomposed in 30∼40 days, the canopy of rice is already shaded and intercept sunlight onto the ground, thus inhibit weed growth most effectively. Azolla grew fast and mulched the whole field in one month after transplanting of rice, and controlled the weed effectively. Smoked rice hull didn’t control the weeds effectively. It was due to over-burning of the rice hull into ash, which dissolved in water immediately after apply to the paddy fields. Azolla mulching (0.1 and 0.2kg/m2) gave the highest rice yield on the first crop, mostly owing to the increase of tiller and panicles of rice. Mulching with paper membrane gave the highest yield on the second crop. TSC 10 showed a higher contents of crude protein than TK9. Content of amylose in the second crop was higher than that of the first crop. Content of amylose in rice harvested from azolla plot was higher than that from other treatments. Rice eating qualities were not significantly affected by methods of weed control. TK9 in smoked rice hull, mulching paper, and azolla plots showed a high eating qualities. Eating qualities of TCS10 in smoked rice hull and paper mulching plots were also promoted. The heavy rainfall at the first crop caused serious lodging of rice plants. Since treatment of azolla supplied more nitrogen sources, lodging was thus enhanced. After inoculation of azolla, reducing nitrogen fertilizer application is needed to avoid surplus nitrogen supply and lodging of rice. Experimental results showed that, even mulching paper controlled weed most effectively, but its high cost and chemical components to meet regulations of organic farming are the difficulties for extension. Azolla can efficiently control weeds. In order to control weeds effectively, propagation of azolla 3∼4 weeks before transplanting of rice is needed. About 0.03 and 0.06 ha, with 3 and 6 kg azolla inoculation will meet the recommendation rates in the first and second crop, respectively.