Nitrogen value of stockpiled cattle manure for crop production

Cattle manure is a common source of fertilizer throughout Sub-Saharan Africa given problems with supply and pricing of inorganic fertilizers. The optimum rate of manure to use is often unknown and further compounded by variable N contents arising from long periods of stockpiling. This study investigated the rates of cattle manure required to optimize plant growth at different N contents arising from different storage times. A field experiment was established using cattle manure stored in the open for 4, 12 and 13 months (N content of 1.31, 1.18and 0.32%, respectively). Plant shoot dry weight and N uptake of canola (Brassica napus L) was compared to equivalent rates of inorganic N (urea) to 200 kg N ha-1at two sampling points over two growing seasons. Linear models of the form y = a + bx were fitted to the data where y is yield (dry matter or N uptake) to enable the N equivalent value (NEV) of cattle manure treatments to be compared to inorganic fertilizer. The NEV of cattle manure stored for 4 months averaged 30% for shoot dry weight and 24% for N uptake and decreased with storage. Impractical volumes of cattle manure are required for plant production in aged stockpiles, thus necessitating better options for N management. Key words: Sub-Saharan Africa, cattle manure, nitrogen fertilizer, N equivalent value, stockpiled manure.