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The economic feasibility of using composted manure from KwaZulu-Natal midlands feedlots in combination with commercial N in production of dryland grain maize [Zea mays (L.)] was evaluated. Effective disposal of large quantities of manure from large scale feedlots is a concern. Yield data from Cedara experiment station were used to estimate a quadratic production function where maize grain yield is a function of manure and commercial fertiliser N application rates. Four rates of commercial N (0, 50, 100 and 200 kg ha-1) and five rates of composted feedlot manure (0, 5, 10, 20 and 30 t ha-1, as is basis) in a factorial arrangement were applied to dryland maize. The production function estimate was used to determine the combination of composted manure and commercial N, which maximized net returns. The results suggest that a compost application rate of 15 t ha-1 with 20 kg ha-1 of commercial N would be economically feasible when the price of commercial N, including application charges, is R4.50 kg-1 and the price of compost R77.20 t-1. Once the price of compost reaches R95.00 t-1 compost use is no longer economically feasible.


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