Structure and impact of cattle manure trade in crop-livestock systems of Vietnam

Cattle manure value chains play important biological and economic roles in smallholder crop-livestock systems in developing countries, but relative to other livestock products our understanding of the nature and impact of manure sales is limited. In regions with an active manure trade, farmers face a choice between manure use on-farm and sales, which affects nutrient flows and participant incomes. We analyzed the manure value chain operating in south-central Vietnam as an example of the function and role of manure trade in crop-livestock systems. Lowland cattle farmers sell manure through a network of chain participants, including small-scale collectors, lowland and highland traders, to pepper, coffee, dragon fruit and rubber farms in the central highlands and southeast coast. We collected and summarized quantitative data (e.g., manure-related labor, manure transactions, and fertilizer and manure use) gathered in semi-structured interviews with value-chain participants [lowland cattle owners (n = 101), traders (n = 27) and end users (n = 72)]. Lowland cattle owners were selected by stratified random sampling, and subsequent participants were identified in preceding interviews. One key finding concerns the seasonality of the manure value chain: most manure flowed between February and August (lowland dry season and period of peak highland demand) from lowland communes to highland coffee and pepper farms for use as organic soil amendments. Fewer sales occurred, at a lower price, to southeast coastal dragon fruit farms and rubber companies. Value addition to manure occurred via drying, bagging, collection, transport and composting. The presence of local traders facilitated market sales for smallholder cattle owners, and prices through the value chain generally reflected costs for value addition. The geographic distribution of cattle relative to agricultural land influenced the flow of manure, with net outflows from regions with higher animal density to regions with lower density and higher value crop production. Manure trade was an important source of supplementary income for farmers and a primary livelihood activity for traders. Value chain participant net incomes ranged from near US$100 yr^-1 for lowland farmers to over US$13,000 yr^-1 for traders, and returns to labor were just over US$0.50 h^-1 for lowland farmers and US$2 h^-1 for traders. The quantitative information generated during our descriptive assessment provides an important first step toward manure value chain improvement, indicates survey methods that can be applied in other areas, and identifies next steps necessary to evaluate chain evolution and resilience.