綠肥作物供作芻料利用之評估

Abstract

我國每年受到梅雨及颱風等氣候因素的影響，年雨量超過2000公厘，且驟雨頻仍而集中，常造成農田長時間積水的現象，時而發生的淹水逆境使得苜蓿等高品質的豆科牧草無法正常生育，因此國內僅能零星地在排水良好的農田小規模種植苜蓿，經濟價值小，絕大部分豆科牧草的需求，須仰賴進口。近年來國際上生質能源的需求急增，帶動了玉米、甘薯等所謂能源作物的栽培生產熱潮，生質能源產業引發「與人爭糧」及「與糧爭地」問題，即能源作物排擠到糧食作物及飼料作物的栽培生產，造成世界性的糧食與飼料的價格高漲。我國由於國產芻料不足，酪農業每年必須進口逾50%的禾本科及豆科乾草才能滿足草食牲畜的餵養需求，因此飼料價格高漲對於國內酪農業的衝擊非常大。值此進口芻料價昂之際，有必要思考可以替代苜蓿供作豆科牧草餵飼，且適合國內栽培的其他豆科作物。國內已推廣栽培多年的綠肥作物，值得加以評估。近來國內進口苜蓿價格的漲幅直逼100%，已使牧草成本佔牛乳生產總成本的60%以上，所以降低牧草成本是減輕牛乳漲價壓力的一個重要途徑，而發展替代性豆科牧草為積極的方向，值得產官學界重視。為評估綠肥作物供作芻料利用的可行性，以開發替代性國產豆科牧草的來源，本研究調查田菁、綠肥大豆、油菜與埃及三葉草等國內主要綠肥作物之芻料產量及植體化學成分，並且探討這些綠肥作物的青貯調製方法及不同青貯調製處理對綠肥作物青貯品質之影響，以評估國內種植的綠肥作物利用作芻料的潛力，期對於補充國內豆科芻料來源之不足有所貢獻，進而能幫助乳酪產業降低生產成本，提高競爭力。

Manure crops are encouraged with subsidy by government to grow in the fallow land in Taiwan. The objective of this study was to determine the forage yield, chemical contents and silage quality of manure crops planted at different locations to evaluate the potential of manure crops used for forage. Plant height and dry yield of sesbania (Sesbania roxburghii) are 163-187 cm and 5.0-6.3 Mg ha-1, and content of crude protein (CP) is between 16.1-17.2 %. The Flieg’s point of sesbania silage was different with location. Silage of sesbania planted in Tainan and Hwalien had the points lower than 40, which belonged to “poor” quality. Sesbania planted in Pingtung and Taitung could make the silages with “moderate” quality. Soybean (Glycine max) cv. Tainan No. 4 and 7 both had the higher plant height and dry yield in spring than in fall for all locations. In spring, dry yields of TN4 and TN7 were 5.4-9.3 Mg ha-1 and 8.1-13.0 Mg ha-1, respectively, while were 4.2-7.0 Mg ha-1 and 4.8-8.1 Mg ha-1, respectively, in fall. The content of CP, acid detergent fiber (ADF) and neutral detergent fiber (NDF) of TN4 and TN7 were 13.8-16.4%, 33.9-37.7%, 54.4-59.0% and 14.4-16.6%, 34.2-39.5%, 51.2-57.2%, respectively. Silage of soybean planted in spring had the Flieg’s points belonged to “poor” quality, but soybean planted in fall could make the silages with “moderate” quality. Plant height and dry yield of berseem clover (Trifolium alexandrinum) at flowering period was 59 cm and 4.4 Mg ha-1, and its CP content was upper than 18%. Silage of berseem clover without any ensiling treatment has Flieg’s points lower than 20, which quality was “poor”. Wilting, adding with corn meal or mixing with napiergrass chops could raise the silage quality significantly as the pH reduced to 4.2-4.5 and the Flieg’s points lifted to 42.2-50.7. Rape (Brassica napus) had very low dry yield (2.2 Mg ha-1) at flowering period since its low dry matter percent. The CP content of rape was about 10% and content of ADF and NDF of rape was also lower than leguminous manure crops comparatively. Similarly to the berseem clover, Silage of berseem clover without any ensiling treatment has Flieg’s points lower than 20. Wilting and other ensiling treatments could raise the silage quality significantly to the “moderate” level.