Contribution of livestock excreta to nutrient balances

Livestock excreta make an important contribution to soil nutrient inputs and in many developing countries are the only significant input. However, there is little quantitative information available on excreta, manure production, and application and this makes it difficult to obtain meaningful soil nutrient balances. A model has therefore been developed to calculate the excreta produced and manure recovered at national levels. Excretion rate coefficients are developed for six farm animal categories and using information on animal numbers and weights obtained from the FAO Internet database, excreta production is calculated for 195 countries and the World for 1996. In addition, time series results for the period 1961 to 1996 are presented for Kenya and The Netherlands, representing contrasting agricultural systems, and for the World. Total livestock excreta in 1996 were estimated to contain 94 million tonnes of N, 21 million tonnes of P, and 67 million tonnes of K. Cattle are the largest contributors with 60% of the total; pigs and poultry account for 10% and 9%. Nutrients recovered as manure were estimated as 34 million tonnes of N, 8.8 million tonnes of P, and 22.9 million tonnes of K. Recovery of excreta as manure from cattle is about 30%, but for pigs and poultry, which are usually housed, recovery is nearly 80%. As a percentage of total soil nutrient inputs, for N, manure accounts for 14%, for P 25%, and for K 20%. The contribution made by manure relative to fertilizers plus manure is declining. Since 1961, the percentages have decreased; for N from 60 to 25, for P from 50 to 38, and for K from 75 to 57. For most countries, percentages will decrease further as fertilizer use increases, but for some developed countries, such as The Netherlands and Japan, with large livestock industries, the percentage of manure is expected to increase and fertilizer demand will fall. For many developing countries manure will remain the main nutrient input. The production of livestock excreta and manure, and fertilizer use in Kenya and The Netherlands are discussed.