The final disposal of sewage sludge is a growing concern worldwide as it has impacts on the water availability and quality for consumption, and economic activities. The Companhia de Saneamento Ambiental do Distrito Federal (CAESB) processes 400 t of biosolids a day that is rich in mineral nutrients and organic matter. Despite the lack of local agronomic criteria for use, biosolids has found a growing demand in grain, fruit crops, coffee and pastures cultivation. To evaluate the immediate (first year) and residual (second year) effects on corn production, humid biosolids (water content 900 g kg-1) was applied onto a dystrophic clayey Red Latosol at rates of 7.5, 15, 30, and 45 t ha-1 and compared to a mineral fertilizer mixture applied in equivalent N, P2O5 and K2O amounts. Both biosolids and mineral fertilizer were applied once before the first crop. A random block design was used with three replications. Corn yields in the first and second crops seasons amounted to, respectively, 7.41 and 5.70 t ha-1 of grains (at the rate of 30 t ha-1 of biosolids) and 7.38 and 5.88 t ha-1 (at the rate of 45 t ha-1). All grain yields were higher than average Brazilian standards for corn and showed the immediate and residual effects of biosolids as fertilizer. Based on the second degree equation adjusted to average data: Y = 768.24** + 320.56**x - 4.2335**x², R² = 0.9995 (Y, yield and x, biosolids rate), the estimated maximum corn productivity (6.84 t ha-1) would be obtained at a rate of 37.8 t ha-1. The best cost-benefit ratio (1.90, average of two growing seasons) was obtained with the application of 30 t ha-1. The biosolids were on average 21 % more efficient than mineral fertilizers. Results indicate that the CAESB biosolids have a good potential to be used as fertilizer for corn production in the Federal District.
water; sewage sludge; nutrients; fertilizer
