Evaluation of Nitrogen and Phosphorus Balance in Green Manure-Rice Cropping Systems without Incorporation of Green Manure Crops

BACKGROUND: The nutrient balance in Korea during 1985-2006 had continually increased and maintained the highest levels among OECD countries. The use of green manure crops such as barley and hairy vetch is common practice for reducing chemical fertilizer application and maintaining soil fertility. However, green manure crops can also be used as a livestock feeding material which may reduce nutrient balance in the national scale. We calculated nitrogen and phosphate balance under green manure-rice cultivating system where all green manure was removed and used for feeding livestock. METHODS AND RESULTS: The barley and hairy vetch grown in pure stands or in mixtures with different sowing rates were tested for rice cultivation without chemical fertilization. The conventional fertilization (NPK) for rice cultivation was selected to compare nutrient balance with green manure-rice cultivation. Nitrogen and phosphate balance were calculated according to the surface balance method of the PARCOM guidelines. Total aboveground biomass of mixture (barley and hairy vetch) was higher compared to that of pure barley or hairy vetch. Among the mixture with barley and hairy vetch, the highest aboveground biomass was observed in B75H25 (barley 75%+hairy vetch 25%). The nitrogen and phosphate balance in the B75H25 mixture was-104 kg N/ha and-50.3 kg P/ha, respectively. CONCLUSION(S): The barley and hairy vetch mixture proved to be a very effective strategy for biomass production of green manure. The amount of nitrogen and phosphate fertilizer to be applied is estimated to be 104 kg N/ha and 50.3 kg P/ha in order to maintain soil fertility if all green manure and rice straw were removed from rice field for livestock feeding.

녹비작물 무 환원-벼 작부체계에서 질소와 인산수지 평가

본 연구는 녹비작물-벼 재배 작부체계에서 볏짚과 녹비작물을 전량 회수하여 사료작물로 활용시 농경지 비옥도 관리를 위한 양분수지를 평가하였다. 녹비보리와 헤어리베치 혼파비율에 따른 녹비작물 생산량은 B75H25에서 가장 높게 나타났다. B75H25 처리구의 벼 수량은 NPK 처리구 대비 90%를 보였다. 녹비작물과 볏짚을 전량 회수시 NPK, B100, B75H25, B50H50, B25H75, H100 처리구의 질소 수지는 각각 2.0, -80.8, -104.0, -93.5, -82.9, 76.2 kg N/ha 이었다. 그리고 질소 수지가 가장 낮은 B75H25 처리구의 인산수지는 -50.3 kg P/ha로 가장 낮았다. 따라서 녹비작물-벼 재배 작부체계에서 녹비작물과 볏짚을 전량 사료로 활용시 농경지 비옥도 유지를 위해서 각각 약 90 kg N /ha, 50 kg P/ha의 질소와 인산 시비가 필요한 것으로 나타났다. 그리고 금후 녹비작물을 사료로 활용하고자 할 경우 화학비료 시용량과 적정 녹비작물의 회수량에 관한 연구가 필요한 것으로 판단된다.