Improvement of nitrogen balance (land budget) in South Korea in terms of livestock manure: A review

Abstract

South Korea's nitrogen (N) balance is the highest among OECD countries. However, this figure is likely to be overestimated. Besides, there is a lack of scientific logic to persuade stakeholders (i.e., fertilizer company, livestock farmer) when these numbers are used as a basis for the N reduction policy. N balance is the residual value after subtracting the amount of N flowing out of the specific boundary from the amount of N entering the boundary. The boundaries of N balance are divided into farm budget, soil budget, and land budget. OECD uses a land budget for N balance calculation. The N inputs consist of mineral fertilizers, organic fertilizers, livestock manure, crop residues, seed and planting materials, biological N fixation, and atmospheric deposition. The N content in the crops produced corresponds to the N output. The N balance method proposed by the OECD is based on a grazing farming system. This method derives from the agricultural environment in which livestock manure is directly deposited into farmland. However, most of the livestock manure in South Korea is not used directly in farmland but is converted to compost and liquid fertilizer. N loss occurs during composting and liquid fertilizer production, which means that the amount of N loaded on the actual soil can be significantly reduced. Another concern related to N from livestock manure is the source of the N content in the crop. N absorbed by crops is not distinguished from livestock manure N, chemical fertilizer N, or soil N. If policymakers intend to reduce N by limiting mineral fertilizers or livestock manure, the N use efficiency of crops based on N sources will play an important role. Therefore, this paper discusses two uncertainties (N loss rate and crop N uptake) related to N from livestock manure and suggests ways to improve N balance.