The effects of different upland rotation systems on soil chemical properties, microbial activity, and community structure

近年來我國稻米生產過剩，但雜糧卻必須仰賴進口，藉由水稻轉作雜糧旱作，可緩解減緩灌溉水不足的壓力，同時提高糧食自給率。本研究旨在探討嘉南地區活化稻田休耕地轉作生產雜糧作物，不同的旱作輪作系統對土壤化學與生物性質之影響，以瞭解是否有適當的旱作輪作模式。本研究共設定六種輪作系統，分別為：處理 1. 甜玉米─田菁─胡麻 (MSS)；處理 2. 甜玉米─田菁─黑豆 (MSB)；處理 3. 綠豆─田菁─甜玉米 (GSM)；處理 4. 黑豆─田菁─甜玉米 (BSM)；處理 5. 紅高粱─田菁─綠豆 (SSG)；處理 6. 薏苡─田菁─胡麻 (ASS)。採完全隨機區集設計 (RCBD)，每處理三重複。分別在輪作制度實作後第二年 (2013 年) 及第三年 (2014 年) 採集土壤樣品，進行化學及微生物性質分析。結果顯示處理間在土壤化學及微生物性質無顯著之差異，但三年試驗後，土壤pH、有機碳與總氮含量下降。試驗第三年去氫酶活性、呼吸作用及微生物生質碳與氮含量皆降低，顯示短期旱作輪作田間試驗使土壤整體微生物活性與生質量下降；然而，與土壤氮、磷、硫循環相關之酵素 (尿素酶、酸性及鹼性磷酸單酯酶、芳香基硫酸酯酶) 活性提高，由 PLFA 組成分析結果顯示土壤可能出現微生物逆境，短期旱作輪作田間試驗不利於土壤微生物族群生長，而 DGGE 分析結果中顯示不同旱作輪作處理對土壤細菌及真菌族群有不同之影響。由土壤 PLFA 組成及 DGGE 分析結果發現旱田與連續水田栽培之對照組中土壤細菌及真菌族群組成不同，顯示水分管理對微生物族群影響甚鉅。革蘭氏陽性與陰性菌族群、細菌與真菌族群之間可能存在競爭或互為消長之關係。總而言之，本試驗結果說明短期旱作輪作導致土壤 pH 值、有機碳及總氮含量下降且不利於土壤微生物族群生長。Owing to the deficiency of the irrigation water and the less anount of rice consumption, alterantive to decrease rice production is to developan an environment-friendly upland cropping systems. The objective of this study was to examine the effects of different upland rotation systems on the chemical and biological properities of soil. There were six types of one-year upland rotation systems, including: 1. Maize followed by sesbania and sesame (denoted as MSS); 2. Maize followed by sesbania and black soybean (MSB); 3. Mung bean followed by sesbania and maize (GSM); 4. Black soybean followed by sesbania and maize (BSM); 5. Sorghum followed by sesbania and Mung bean (SSG); 6. Adlay followed by sesbania and sesame (ASS). The soil samples were taken in the end of the second and the third year of cropping. The chemical and biological properities were analysized. The results showed the soil fertility decreased in all systems after three years of cropping. There was no difference in the soil microbial and chemical properties, including pH, organic carbon and total nitrogen contents of soil, between six systems. After three years of upland cropping, the soil microbial biomass carbon and nitrogen decreased. Enzyme activities of soils increased in response to soil nutrient deficiency, including acid/alkaline phosphomonoesterase, urease and arylsulphatase. However, the activity of dehydrogenase decreased. The bacteria and fungi populations were different between upland and paddy soil, which indicated that the soil microbial properties significantly affected by the soil water management. Furthermore, the microbial interaction led to the population growth and declined as the result of competition and synergism. In summary, the results indicate that short-term upland rotation resulted in the reduction of the soil nutrients and the growth of soil microbial community