Some physical, chemical, and biological effects of heavy poultry manure applications on a soil ecosystem

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1977
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Virginia Polytechnic Institute and State University
Abstract

Poultry manure was applied (half plowed down in Fall, half disked in Spring) at the rates of 27, 54, 85 and 110 MT/ha/yr to field plots of Davidson clay loam soil in Virginia. Both fertilized and unfertilized control plots were included and maize was grown on all plots. After 5 years, changes in the soil were investigated, primarily in the upper 36 cm. The heavily manured plots held more moisture, especially in spring, than the controls. However, high levels of soluble salts (2,000 - 4,000 ppm) caused severe osmotic moisture stress in the maize throughout the summer on the 54-110 MT/ha plots. High levels of NH₄-N (800 ppm) and NO₂-N (60 ppm) were measured in the soil in spring. Poor emergence and high seedling mortality reduced maize grain yields from 120 Q/ha (controls) to 43 Q/ha (110 MT poultry manure). Within the two types of controls, no response to N or K was observed after 5 years without any additions of these nutrients.

Soil organic matter at 110 MT poultry manure/ha was over 7% in spring, 1976; but declined to 5.4% by November. The controls had a relatively constant 2.6 - 3.2% organic matter. Bulk density of the manured soil averaged from 0.97 to 0. 78 g/cm³ as compared to 1.07 to 1.14 g/cc in the controls. Water stable aggregation was increased by the manure from 73-76% in the controls to 94% in the 57 and 85 MT/ha plots. The increased aggregation was entirely in the 5-8 mm and 2-5 nnn sizes. Faunal activity caused the seasonal development of a very open surface structure with many vesicular pores and earthworm channels. Manure plowed down in Fall caused a plowsole layer, inhibiting downward water movement and exhibited water repellency in spring and early summer. At these times saturated infiltration rates were greatly reduced, but in November infiltration rate on the 110 MT/ha plots was near 10 times (57 cm/ha) that on the controls.

Effects on the soil biology were pronounced but complex. The most probable numbers of Nitrosomonas sp. were 100 times higher on the manured plots in spring. Nitrobacter sp. numbers were less affected by manure. Soil respiration in samples taken in November evolved 0.02 mg C day⁻¹ g⁻¹ for the controls and increased with manure rate up to 0.101 mg C day⁻¹g⁻¹ , but dropped off to 0.069 mg C day⁻¹g⁻¹ at the highest manure rate.

Disappearance of maize leaf pieces from litter bags buried in September was initially retarded on the manured plots. This effect was greatest in the large mesh bags. Disappearance of leaf pieces was generally greater in the 1.0 and 7.0 mm mesh bags than in the 0.02 and 0.1 mm meshes, indicating a significant contribution by the meso- and macrofauna.

Arthropods were extracted from soil samples taken in May, July, September and November. The manure plots were characterized by high numbers (3.8 x 10⁶ arthropods/m²) and low species diversity as measured by Simpson’s C. Acarid mites indigenous to the manure accounted for over 90% of the arthropods in the manured plots and heavily contaminated the populations of the control plots. Diversity increased and numbers declined during the summer. Correlations of between and among arthropod taxa and soil properties were investigated.

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