大豆栽培密度與除草處理對雜草控制試驗

Abstract

本試驗之目的在探求不同大豆栽培密度、不同除草次數之雜草差異，供大豆雜草防除之參考。民國60年春作及夏作在苗栗農工實習農場進行。採用逢機完全區集8×3（栽培密度×除草次數）之複因子試驗設計，重複4次，小區行長2.52~3.00公尺，寬3.00~2.70公尺，小區面積為7.56m2,，行距分為50、45、40、30公分四種；株距分為20.10公分二種。除草處理分為不除草、除草一次、除草二次等三種。二次試驗之前作物均為水稻，肥料用量為20-80-60kg/ha，全部作基肥施用。玆摘錄試驗結果如下： (一) 八種栽培密度之雜草摔制效果 以行距而言：雜草之控制效果，在春作是與行距之大小成反比；夏作則僅在某種行距（如45公分，圖1.右）才能收雜草控制之效。就株距而言：春作以10公分的效果較大，20公分者較小（圖2.中）；夏作則隨行距之大小而分成二種情形，①行距較大時（如50、45公分），以較小株距（10公分）之雜草控制力大；②當行距縮小時（如40、30公分），則較大株距（20公分）之控制力較大（圖2.右）。總之，春作以密度最大之d6（30×10）之雜草控制效果最大；夏作則以密度次大之d6（45×10）之雜草控制效果較大（圖3.)。 (二) 除草次數與雜草控制之效果 一般而言，雜草之控制效果，與除草之次數成正比。除草二次之雜草控制能力，為不除草區(W0)之84%（以雜草重量計）；除草一次(W1)為不除草區(W0）之83%（圖4. 左）。故除草對雜草控制之效果極大。不同期作之除草效果，是夏作大於春作，此因春作雜草生長較夏作紫茂之故。但不除草區(W0)之雜草是夏作重，春作輕，此蓋夏作大豆生長不如春作之繁盛，雜草在生長競爭上居優勢之故。 (三) 除草次數與栽培密度對雜草控制之連合效果 不除草時，春作採用圾大密度(d8)，夏作採用中大密度d6；除草一次區(W1)春作採用密度次大之d7；夏作採用d8；除草二次區(W2)，春作採用d8；，夏作採用密度最小之d1時，對雜草之控制效果均較大（表2.及圖5.）。故概括言之，大豆採用較大之密度種植時，對雜草之控制效果均較大。 (四) 大豆田雜草之種類 春作雜草種類及株數較夏作多，重量亦較重（重23%）。春作以禾本科之毛穎雀稗草株數較多，重量較重，其次為牛筋草。夏作以禾本科之埃及指梳草株數及重量般多，其次為馬齒莧（表3.)。 (五) 除草次數與大豆產量之關係 春作在除草(W1、W2)與不除草(W0)間之大豆產量，有顯著之差異；不除草區之大豆產量為除草二次(W2)的92%，減產8%，除草一次(W1)與除草二次(W2)間則無顯著差異。夏作不除草區之大豆產量為除草二次區的74.4%，減產25.6%，差異為極顯著，除草二次與一次間之差異不顯著。其中除草二次與一次，在春、夏作之大豆產量，均無差異，故大豆田在適當密度栽培下，除草一次已足。 (六) 栽培密度與大豆產量之關係 春作除d5、d1與d6間各有顯著差異外，其他密度間概無顯著性差異。夏作則極受栽培密度之影響，以密度次大之d7及密度最大之d8之產量較高，該二密度間無顯著差異。因之春作栽培大豆宜放寬行距（如50×10，50×20公分），夏作則宜縮小行距（如40×10，30×10公分），以利增產，並收雜草控制之效果（表4.）。 (七) 除草次數與栽培密度對大豆產量之交感效應 春作時W1與d7之交感值為極顯著，W2與d1、W1與d2、W0與d6、W0與d4間均為顯著。夏作在W0與d7為極顯著，W1與d8為顯著。其中春作之W1與d7，夏作之W0與d7均係次大密度區，值得利用。 This experiment was designed to investigate the effect of weeding on weed control in various spacings of soybean in an attempt to find out the best system of weeding and spacing for soybean cultivation. The experiment was conducted in the Experimental Farm of Miaoli Agricultural Vocational School both in the Spring and Summer of 1971. A 8×3 factorial arrangement (plant density × times of weeding) in the randomized complete block design was replicated four times. The plots were 2.52-3.00m. in length and 3.00-2.70 m. in width with a size of 7.56m2. Row spacings were 50cm., 45cm., 40cm., 30cm., with plant spacings of 20 and 10 cm. The treatment of weeding was classified as no weeding (W0), weeding for one (W1), and two (W2) times. The fertilization was 20-80-60 kg/ha. used as base fertilizer with rice as precedent crop. The results of the experiment were summarised as follow: 1) Effect of weed control with spacing In the Spring crop, weed control was inversely proportional to row spacing : In the Summer crop no correlation between row spacing and weed control was observed; 45 cm. row spacing appeared to be most effective for weed control (right of Fig. 1). In the case of plant spacing, the best result was obtained in 10 cm. spacing and less effective for the spacing of 20 cm. in the Spring crop (middle, Fig. 2). In the Summer crop the result was somehow different. For the wider row spacings e.g. 50,45 cm.) weed control was most effective with smaller plant spacing (10 cm.) ; and 20 cm. for the narrower spacings (e.g. 40, 30cm. right side of Fig.2). It was concluded that the effectiveness of weed control was inversely proportional to spacing for the Spring crop whereas in the Summer crop the d6 (45×10cm.) treatment was most effective for weed control (Fig. 3). 2) Effect of weeding on weed control: The effectiveness of weed control was directly related to the number of weeding. Weeding twice (W2) was 84% more effective than without weeding (W0) ,based on the fresh weight of weed. The lack of significant difference in weed control between weeding for once (W1) and for twice (W2) indicates that only one weeding is required for sufficient weed control if proper spacing is adopted (Fig. 4). The effectiveness of weed control varied for different crop seasons ; better result was obtained in Summer crop than in Spring This was due to more luxuriant growth of weeds in Spring. In the treatment involving no weeding, weeds were more serious in Summer than in the Spring crop. This was possibly due to the less vigor of soybean growth in Summer, making better chance for weeds to profuse. 3) Interaction of weeding and spacing on weed control : Best result was obtained in no veeding plot (W0) with greatest density d8(30 × l0cm), and with midium density d6 (45 × 10cm.) for Spring and Summer crops, respectively. Better weed control was also found in weeding once plot (W1) with greater density d7 (40 × 10cm.) in Spring crop, and with greatest density d in the Summer crop. Weeding twice is similar in effect to no weeding plot but with least density d1 (50 × 20 cm.) in Summer crop. In short, the greater the density is employed, the better the weed control obtained (Table 2 and Fig. 5). 4) Weed growth in soybean field: The species of weeds grown in the soybean field were more numerious and the fresh weight of the weeds was 23% higher in the spring than in the summer crop. Most serious weeds in the spring crop were Paspalum conjugatum Berg. and Eleusine indica Garth. The most serious weeds in the summer crop were Dactyloctenium aegyptium L. and Portulaca oleracea L. (Table 3). 5) Yield of soybean and the number of weeding: There was highly significant difference in yield between treatment with weeding (W1 and W2) and those without weeding (W0). In spring crop, yield of soybean without weeding was 92% of those weeded twice (W2), i. e. 8% reduced in yield. Significant difference was also found between weeding and no weeding in the summer crop with the yield of no weeding only 74% of those weeded twice, i. e. 26% yield reduction resulted. No significant difference was observed between W1 and W2 in both crops. It is concluded that weeding has greatest effect in summer than in the spring crop, based on yield; and weeding one time is sufficient for growing soybean if adequate spacing was employed. 6) Yield of soybean and the spacing: The result showed that except between d5 (50×10cm.) and d. (45×10cm.), and between d1(50×20 cm.) and d6 in the spring crop. However, yield of soybean was affected greatly by spacings in the summer crop. Higher yield was found in the greater density d7 (40×10 cm.), and greatest density d8 (30×10 cm.). Thus, a dense cultivation of soybean in the summer crop would promise better results both in yield and in weed control. 7) Interaction of weeding and spacing on yield of soybean: The data from statistical analysis that there was highly significant difference between W1-d7 and other combinations in the the spring crop, and between W0-d7 and other combinations in the summer crop (Table 5.). It is concluded that the combinations W1-d7 and W0-d7, gave benefit not only in yield of soybeans but also on weed control in field of soybeans.