Nutrient Flows in Crop Production on Smallholder Farms : a Study of Nutrient Balances and Management in a Farmer’s Cooperative in Son La, Vietnam

Sammanfattning

Farm nutrient management is important in the cultivation of healthy, abundant crops whilst avoiding the unintended effects on the environment. Proper nutrient balances achieve sufficient crop nutrient supply while avoiding the pitfalls of either over- or under-application. This study analyzed a cooperative in Son La Province, Vietnam to estimate nutrient balances and track trends amongst crop species. A series of interviews and field surveys were carried out with members of the Hợp Tác Xã Thành Cường Cooperative in Mòn, Son La, Vietnam. Thirteen farms were studied to track all nutrient inputs and outputs of each agroecosystem to assess the flows and balances. There was a clear correlation between type of crop and nutrient balance. The results show that crops of specific categories, such as fruit-bearing vegetables and tree fruits, receive large excesses of inputs, whereas those like grains and sugarcane have large deficits. Nitrogen often had a large surplus, whereas phosphorus and potassium greatly varied between surplus and deficit. Leafy vegetables and roots had intermediate surpluses. These balances were driven by a combination of differing fertilization and residue removal regimes. Mineral fertilizers were found to be the primary nutrient import, while harvestable goods were the primary export. The farm-gate balances indicated generally positive nutrient budgets per hectare. Nitrogen and phosphorus balances were positive, with a single exception to the former. Long-term excessive nutrient applications or negative balances can cause crop wilting and even mortality. Potassium balances showed a deficit in one-third of farms. Over half of farms had a surplus of over 100kg N/ha/yr, and one-quarter had a surplus of over 100kg P/ha/yr. Further, excesses can cause environmental degradation, such as acidification, eutrophication, and greenhouse gas emissions, and needless monetary expenditures in an already poor region. These findings can inform local farmers, local authorities, and organizations on more efficient nutrient management by adjusting both application rates and residue management.