T he type of poultry manure determines its effects on soil pH because poultry feed contains varying amounts of calcium carbonate. All poultry rations contain some ground limestone. Broiler and turkey feed may contain less than 1% ground limestone whereas layer and breeder rations may contain 7 to 10% ground limestone. Most of this ground limestone will be passed through the bird and ends up in the manure or litter. In broiler litter (manure plus bedding), the manure and the limestone may be concentrated in the bedding as several flocks are produced on the same bedding, and it dries out.
A survey of Alabama fescue pastures showed that fields that had received repeated applications of poultry broiler litter over many years had an average surface soil pH of 6.3 (±0.1) compared to fields receiving only commercial fertilizers. These latter fields had a surface pH of 5.8(±0.1) (Kingery et al., 1993). Hue (1992) also showed that chicken manure was very effective in raising soil pH. He theorized that much of this pH increase was due to reactions of organic anions. Poultry litter can detoxify Al by increasing soil pH, complexing soluble Al with organic acids, and complexing soluble Al as it reacts with phosphorus in the litter/manure. (Typically hen manures have calcium carbonate contents of 15 to 18% (300 to 360 lb calcium carbonate per ton).
Soil pH may increase substantially with applications of hen manure because the amount of liming material added to the soil exceeds the amount of acidity released by the conversion of nitrogen. Over application of hen manure/litter could result in too high a soil pH on very sandy Coastal Plain soils. This could result in micronutrient deficiencies (e.g. Mn) on some Coastal Flatwoods soils. Soil pH's greater than 7.0 in the upper one foot of soil and nearly 7.0 in the one to two foot sampling depth, were found in a number of Piedmont fields receiving repeated applications of hen manure and no commercial limestone applications. Although no crop production problems associated with these unusually high soil pH's have been documented in these clay soils, pH values this high would likely cause problems in sandy Coastal Plain soils. The liming value of layer manure should be considered when layer manure is used as a crop nutrient source. This value is not trivial as one ton of lime per acre every three years currently costs about $30 per acre or $10 per acre per year.
Prepared by Jim Camberato and Charles Mitchell
- Hue, N.V. 1992. Correcting soil acidity of a highly weathered ultisol with chicken manure and sewage sludge. Commun. Soil Sci. Plant Anal. 23:241-264.
- Kingery, W.L., C.W. Wood, D.P. Delaney, J.C. Williams, G.L.Mullins, and E. van Santen. 1993. Implications of long-term land application of poultry litter on tall fescue pastures. J. Prod. Agric. 6:315-395.