Composted cattle and poultry manures provide excellent fertility and improved management of gray leaf spot in maize

Gray leaf spot incited by Cercospora zeae maydis, is an important disease of maize (Zea mays L) worldwide. The objective of this research was to evaluate the effect of composted poultry and cattle manures on development of gray leaf spot and yield of maize. The effects of composted manures were compared with those of different sources of inorganic synthetic nitrogen fertilizers in two cropping seasons. Composted manures and mineral fertilizers were tested to supply the recommended rate of 60 kg N ha(-1) and at the highest rate of 90 kg N ha(-1). Fertilizer treated maize plants were more diseased than non-fertilized (control). Higher disease severity was observed in plots receiving high levels of inorganic N fertilizers. The severity of gray leaf spot varied with fertilizer types (P <= 0.05). Maize fertilized with composted cattle manure had the lowest levels of gray leaf spot, followed by composted poultry manure and urea (46%). Sulphate of ammonium (SA) (21%) and calcium ammonium nitrate (CAN) (27%) fertilized maize were more diseased and lower yielding. Overall grain yield across seasons in composted cattle manure, composted poultry manure and urea fertilization was 1.4 t ha(-1), 0.9 t ha(-1), 0.6 t ha(-1) and 4.2 t ha(-1), 3.7 t ha(-1) 3.4 t ha(-1) higher compared to CAN and non-fertilized (control) treatments respectively. Disease severity was also influenced by interactions between genotypes and fertilizers. The concentration of NH4-N and NO3-N in maize leaf tissues was associated with the degree of maize resistance to gray leaf spot. Maize fertilized with composted cattle or poultry manure and urea were more resistant to gray leaf spot with higher leaf tissue concentration of NH4-N and lower concentration of NO3-N. Plots fertilized with SA and CAN were heavily diseased with lower leaf tissue concentration of NH4-N. It is concluded that organic composted poultry and cattle manures can provide a beneficial, renewable source of crop nutrients for small scale-maize farmers in Africa. Advantages over mineral fertilizers are that they are inexpensive, and may also provide management of gray leaf spot. (C) 2011 Elsevier B.V. All rights reserved.