Nitrogen and Phosphorus Availability and Weed Suppression from Composted Poultry Litter Applied as Mulch in a Peach Orchard

Composted poultry litter (CPL) may be applied as a mulch in fruit orchards to manage waste and to provide a slow-release nutrient source and weed control. With proper management, poultry manure and bedding (litter) can prevent environmental degradation, such as hypoxia in aquatic communities. Peach (Prunes persica L. 'Sunhigh') plots all received preemergence herbicides in May and then the following treatments in June 1998: commercial fertilizer (N at 15 g.m -2 ), low rate CPL (N at 15 g.m -2 as CPL at 2.9 kg.m -2 ), high rate CPL (N at 62 g.m -2 as CPL at 11.6 kg.m -2 ), and no fertilizer or mulch control. Weeds were completely controlled by mulch and herbicide during 1998 but not during 1999. By Sept. 1999, the high rate of CPL had only 27 % weed cover compared with 86% for the commercial fertilizer-treated plots. Soil N was highest (NH 4 -N and NO 3 -N at 16.4 and 18.6 mg.kg -1 soil, respectively) in plots treated with commercial fertilizer, 6 weeks after treatment (WAT). Soil N did not differ among the two CPL treatments and the control at any time. At the high rate of CPL, there was NH 4 -N and NO 3 -N at 3.2 and 0.7 mg.kg -1 soil, respectively, at 6 WAT. Water-extractable P (WEP) in the soil did not differ among the CPL and commercial fertilizer treatments at 6 WAT (P at 14 mg.kg -1 soil). However, at 47 WAT, plots with the high rate of CPL had significantly higher WEP, with P at 30 mg.kg -1 soil vs. 14 mg.kg -1 soil in plots treated with commercial fertilizer. High applications of CPL could elevate P in surface runoff to levels that cause environmental degradation. In general, Mehlich 1-extractable P (MEP) did not differ among the CPL- and fertilizer-treated plots (averaging P at 45 mg.kg -1 soil). MEP was lowest in control plots (averaging P at 21 mg.kg -1 soil). Results indicate that CPL could be used as a weed suppressant without adversely affecting N release to the environment; however, P concentration in soil water may be problematic.