168 Weed Suppression and N and P Mineralization in an Orchard Mulched with Composted Poultry Litter

Abstract

Improper management of poultry manure and bedding (litter) can cause hypoxia in aquatic communities, but poultry waste can be converted to a stable organic fertilizer by composting. Peach trees (Prunus persica L. `Sunhigh') received the following treatments in May 1998: commercial fertilizer (15 g N/m2), low-rate composted poultry litter (15 g N/m2 as 2.9 kg composted litter/m2), high-rate composted poultry litter (62 g N/m2 as 11.6 kg composted litter/m2), and no treatment control. Weeds were completely controlled during 1998, but, by Sept. 1999, the high-rate poultry litter had only 27% weed cover compared with 86% for the commercial fertilizer-treated plots. Soil N was highest in plots treated with commercial fertilizer (16.4 mg N-NH4 and 18.6 mg N-NO3 per kg soil, 6 weeks after treatment) and did not differ among the remaining treatments (in the high rate of poultry litter—3.2 mg N-NH4 and 0.7 mg N-NO3 per kg soil, 6 weeks after treatment). Water soluble P in the soil did not differ among treatments at 6 weeks after treatment (≈12 mg P per kg soil for all treatments) but, at 47 weeks after treatment, plots with the high rate of poultry litter had 30 mg P per kg soil compared with 14 mg P per kg soil in plots treated with commercial fertilizer. In general, Mehlich 1 acid-soluble P did not differ among the litter- and fertilizer-treated plots (averaging 45 mg P per kg soil). Acid-soluble P was lowest in control plots (averaging 21 mg P per kg soil). Results indicate that poultry litter could be used as a weed suppressant without adversely affecting nitrogen release to the environment. However, P mineralization may be problematic and requires further investigation.