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Improvement for weed controls in organic paddy fields
本研究於2000年一、二期作分別在中興大學農場（台中市）及中興大學農業試驗場（台中縣霧峰）兩地進行田間試驗，探討覆蓋方法對有機稻田雜草之控制效果，及其對水稻生育之影響。水稻品種為台稉9號和台中秈10號。試驗採完全逢機設計（CRD），處理包括田面覆蓋稻殼、紙膜、滿江紅（大里種和利馬種）及對照共五種處理。四重複。滿江紅處理區於插秧後隨即接種滿江紅，接種量0.2 kg/m2。稻殼處理區施用稻殼0.5 kg/m2。紙膜敷蓋處理於插秧時同時進行。對照區不加任何處理。為瞭解滿江紅及稻殼最適用量，另外在中興大學校本部農場進行不同等級用量試驗。滿江紅以利馬種為試驗材料，三個接種量分別為0.1、0.2及0.3 kg/m2，稻殼三個施用量分別為0.4、0.8及1.2 kg/m2，皆於插秧後隨即施用。由於一期作稻殼覆蓋處理對雜草的抑制效果不佳，所以二期作增加煙燻稻殼處理，施用量0.6 kg/m2。
試驗結果顯示，一期作施用滿江紅處理，由於滿江紅生長快速，使得土壤氧化還原電位下降最快。二期作水稻生育初期高溫，加速紙膜、稻殼及煙燻稻殼的分解，亦使土壤氧化還原電位下降。一期作處理間以紙膜覆蓋抑制雜草效果最佳，抑制效果達99％以上， 50％紙膜在插秧後約45∼50天分解。滿江紅抑制雜草效果次之，兩參試品種以利馬種生長迅速，疊層覆蓋田面，抑制雜草效果較佳。利馬種三個接種量（0.1、0.2及0.3 kg/m2）皆能有效抑制雜草族群。大里種則僅單層覆蓋，且不耐高溫，無法有效抑制雜草族群。稻殼覆蓋抑制效果最差，主要原因可能是殘存不飽滿稻穀招來大量麻雀等鳥類啄食，鳥糞中帶來大量雜草種子所致。二期作以紙膜敷蓋處理對於雜草的防治效果最佳，50％紙膜在插秧後約30∼40天分解，但此時水稻植冠已能遮蔽大半田面，減少陽光照射地面，仍能有效抑制雜草生長。由於滿江紅生長迅速，一個月即能覆蓋整個田面，阻斷陽光照射地面，且滿江紅會與雜草競爭，所以雜草抑制效果亦佳。煙燻稻殼處理對雜草控制效果不佳，其原因可能是自製的煙燻稻殼過度燃燒灰化，施到稻田遇水即溶解，不但沒有覆蓋抑制雜草效果，反而成為雜草養分來源，致使雜草生長旺盛，抑制效果不佳。
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.
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