坡地果園覆蓋種類對土壤水分肥力果實產量影響之研究

Abstract

本試驗之目的，在探討敷蓋及覆蓋作物對香蕉及柑桔生長之影響以及水分養分競爭問題，以供今後研究及推廣之依據。試驗設計採用完全逢機區集排列，重複6次，共有6種不同處理：(1)對照區（不種植覆蓋作物，亦不敷蓋任何東西，僅按一般農民之慣例行全面除草）。(2)敷蓋區（敷蓋稻草10,000公斤／公頃，再加蓋打洞PE塑膠布）。(3)多年生豆科之營多藤區(IntortumClover)。(4)多年生豆科之山珠兒豆區(Centrosema)。（5）多年生豆科之小卵葉藤區(Desmodium buergeri)。(6)多年生禾本科之巴喜亞草區（Bahia grass）。 本試驗自民國60年春開始，在南投縣集集香蕉園及臺中縣東勢柑桔園實施，時經三載，計收穫香蕉果實二期及柑桔三期，所獲結果可得如下結論： (一) 香蕉果實產量及其生育狀況，敷蓋區或豆科作物覆蓋區與對照區比較時，其差異不顯著，但禾本科之巴喜亞草區確較對照區為低。柑桔甲、乙兩地之果實產量均不規則，惟巴喜亞草覆蓋區產量有較低之趨勢。再就柑桔品質言，敷蓋區及覆蓋作物區較對照區果皮較薄而果汁較多，果實成熟期則以前兩者較後者為晚，其中尤以敷蓋區最晚。 (二) 覆蓋作物生長情形，在各種情形下均以禾本科巴喜亞草生長最旺，且產量亦高，但巴喜亞草覆蓋區之柑桔樹冠三年內擴展最慢，果實產量亦有較低之趨勢，果皮亦較薄。香蕉生長情形及產量亦見低落，同時土壤水分亦以本處理為最低，足見本草與主作物競爭水分及其肥分之情形。且巴喜亞草地下走莖密佈，開孔施肥較不便，故似不宜於作為平台面上覆蓋作物之用，但如作為堦壁護坡或山邊溝保護用，或屬理想。至於豆科覆蓋作物，在香蕉園以山珠兒豆生長情形最佳，但有攀綠性，其莖蔓易纏繞果樹，為其缺點。在柑桔園以營多藤最為良好，小卵葉藤不論在香蕉園或柑桔園均生長不良，尤以收刈後復生力甚差。 (三) 土壤理化性質分析結果，香蕉園及柑桔園各處理區土壤之有機質含量均比對照區為高。香蕉園自第三年開始以第2處理（敷蓋區）、第3處理（營多藤區）及第5處理（小卵葉藤區）均比對照區為高，差異均達顯著。柑桔甲地以第5處理（小卵葉藤）及第6處理（巴喜亞草）均比對照區高，柑桔乙地以第2處理（敷蓋區）及第4處理（山珠兒豆）、第6處理（巴喜亞草）均比對照區為高，差異均達顯著。至於有效磷、鉀乃因果樹歷年皆多量施肥而不均勻，土壤間變異甚大，處理影響不明顯。土壤之假比重，在第一年各處理間影響不大，但至第二年開始均有相當減低之趨勢，並與對照區差異顯著。土壤安定度，在香蕉園以第3處理（營多藤）為最高，柑桔園以第4處理（山珠兒豆）為最高，其餘各處理亦比對照區高。 (四) 土壤水分之測定結果，不論香蕉園或柑桔園，其土壤水分含量均以敷蓋區（第2處理）為最高，即表示敷蓋稻草及塑膠布對果園土壤水分保持效果最佳，但因現在塑膠布昂貴，稻草搬運又費工，因此成本高，目前不合經濟原則“覆蓋作物之處理區，以山珠兒豆區及營多藤區之土壤水分含量最高，小卵葉藤與巴喜亞草及對照區為較低。 The purpose of this experiment is to investigate the effects of mulching and cover cropping on the soil fertility and moisture condition as well as the growth of banana and citrus (Pongkan) so as to provide basic information for the practice of soil management in orchards The experiment was conducted with six different treatments as follows: 1. CK, Untreatment, under usual practice of cultivation. 2. 1ice straw mulching; 10,000 kg/ha of straw covered with perforated PE film. 3. Intortum clover cover cropping (Legume) 4. Centrosema cover cropping (Legume) 5. Desmodium buergeri cover cropping (Legume) 6. Bahia grass cover cropping (Herb) Treatments were replicated six times with completely randomized design and were conducted for 3 years from 1971 to 1973 The results obtained from banana plantation in Nan-tou with two crop harvests and citrus orchard in Taichung with three crop harvests may be summarized as follows: 1 Both the fruit production and growth condition of banana crop were not significantly affeced by treatments other than Bahia grass cover cropping which somewhat reduced the yield of banana. Fruit production of citrus grown in different orchard showed irregular results except a tendency of reducing yield of the plots with Bahia grass cover cropping. Concerning the quality of citrus fruits, considering two orchard as a whole, in comparison with that of check plot, peel of mulching treatment was thinner and juice contents of mulching, Desmodium buergeri, and Bahia grass cover cropping were higher. However, the fruit maturity was somewhat delayed by the treatments especially the mulching treatment. 2. Bahia grass grew vigorously resulting in high fresh grass yield in any condition, but expanding rate of canopy surface area of treatment with Bahia grass cover cropping was the lowest among treatments in a period of 3 years, and this treatment resulted in a tendency of reducing yield of citrus fruits, made its peel thinner, and the growth and yield of banana were reduced too, and soil water content was the lowest among treatments. These were the evidences of competition of water and nutrient between the grass cover cropping and main crops. In addition, dense roots of Bahia grass make fertilization inconvenience. So the grass may be an ideal protector for rise wall of bench terrace but will not be recommended as a cover crop on bench top. About legume cover crops, Centrosema grew better than other cover crops in banana plantation with a demerit of climbing twining habit on fruit trees. Intortum clover grew well in citrus orchard but Desmodium buergeri, grew poorly in both banana plantation and citrus orchard especially being poor in its regrowth vigor after mowing. 3. The effects of treatment on soil physical and chemical properties: In each experimental cite, soil organic content was higher in all treated plots than in check plot. In banana plantation, organic content of mulching, Intortum clover and Desmodium buergeri, cover cropping plots was significantly higher than that of check plot. Organic content of Desmodium buergeri, and Bahia grass cover cropping plots of citrus orchard A, and mulching, Centrosema, and Bahia grass cropping plots of citrus orchard B were all significantly higher than that of check plot. Available K2O and P2O5 content indicated a wide fluctuation and no significant difference among treatments. This may be due to uneven distribution of applied fertilizers. Soil bulk density of treated plots was significantly reduced beginning in second year of experiment in comparison with check plot. The aggregate stability of the treated soil was higher than that of the soil in check plot. Particularly, Intortum clover cover cropping of banana plantation and Desmodium buergeri, of citrus orchard were the highest in each orchard respectively. 4. Effects of treatments on soil moisture content: Moisture content of the mulching plots was the highest. It means that mulching with rice straw then covered with PE film was the best way for conserving soil moisture. But high price of PE film and cost of transportation of rice straw at present time made this way uneconomical. Of the cover cropping treatments, Centrosema and Intortum clover plots were the treatments of higher soil moisture content; and Desniodium buergeri, Bahia grass and check plots were the treatments with lower soil moisture content.