PHYSICAL CONDITION OF A DAVIDSON CLAY LOAM AFTER 5 YEARS OF HEAVY POULTRY MANURE APPLICATIONS

In this study, after 5 years of applying up to 110 metric tons of poultry manure/ha per year to corn plots, the pysical condition of the manured plots differed markedly from that of the unmanured controls. During the spring the activity of soil invertebrates created a highly channelized and aggregated structure in the surface soil. Plowlayer bulk density was reduced by the poultry manure from 1. 1 to 0. 8 g/cm**3 and the percentage water-stable aggregates increased from 73 to nearly 94%. About half of the variability in bulk density could be accounted for by differences in soil organic matter contents. The manured plots were generally more moist in plow layer. The manured plots held nearly 42% moisture at 0. 1 bar tension as compared to 32% for the control plots.; Little information is available on how soil physical properties are affected by very heavy poultry manure applications often associated with concentrated poultry production. In this study, after 5 yr of applying up to 110 metric tons of poultry manure/ha per year to corn plots, the physical condition of the manured plots differed markedly from that of the unmanured controls. During the spring the activity of soil invertebrates created a highly channelized and aggregated structure in the surface soil. Plowlayer bulk density was reduced by the poultry manure from 1.1 to 0.8 g/cm3 and the percentage water-stable aggregates increased from 73 to nearly 94%. About half of the variability in bulk density could be accounted for by differences in soil organic matter contents. The manured plots were generally more moist in the plow layer, especially in spring and early summer when a perched water table at a depth of 20 cm was caused by a water-repellent plowsole layer of partially decomposed manure. In the spring this layer resulted in infiltration rates on the manured plots as low as 0.02 cm/hr compared to a mean of 12.1 cm/hr on the controls. In November, the infiltration rate of the manured plots rose to 57 cm/hr due to the activities of earthworms. The manured plots held nearly 42% moisture at 0.1 bar tension as compared to 32% for the control plots. Incorporation of poultry manure by means other than moldboard plowing might avoid the creation of a plowsole manure layer which counteracts the potentially beneficial effects of the manure on soil structure and water-holding capacity.