EFFECT OF LONG-TERM APPLICATION OF ANIMAL MANURE ON PHYSICAL-PROPERTIES OF 3 SOILS

Surface soil samples to 15 cm depth were taken from replicated plots i n an ongoing long-term field experiment involving application of anima l manure on three soils in Virginia. The sampled plots had received ei ther no manure or the equivalent of 289,000 kg ha(-1) of manure as dry weight. The manure was applied annually at the beginning of each spri ng for 15 years from 1978 through 1992. The plots were cropped similar ly since 1978. Soil textures were a fine sandy loam at Holland in the Atlantic Coastal Plain region, a silt loam at Blacksburg in the Appala chian region, and a clay loam at Orange in the Piedmont region of Virg inia. The following measurements were made on subsamples: liquid and p lastic limits, wet aggregate stability, aggregate size distribution, d ispersible clay percentage, water retention at 0.03, 0.1, 0.3, 0.5, 1. 0, and 1.5 MPa tension, and modulus of rupture of moulded briquettes a t a water content corresponding to 0.1 MPa tension. Organic matter con tent by the Walkley-Black method was significantly higher in the manur e-treated soils at all three locations. Increases were 3% for the sand y loam and 25% for the silt loam and clay loam. From these values it w as estimated that at least 95% of the total applied manure had been de graded over the 15 years. Results showed that the liquid and plastic l imits for all three soils were higher (p<0.05) for the manure - treate d samples. However, the differences in the limits were only 2 to 3%. T he modulus of rupture values were lowered by addition of the animal ma nure. Decreases (p<0.05) occurred for the silt loam and clay loam samp les. The wet aggregate stability increased and the dispersible clay de creased in the manure-treated soils. Increases (p<0.05) in wet aggrega te stability occurred for the sandy loam and silt loam samples. Decrea ses (p<0.05) in dispersible clay were measured for the sandy loam and clay loam samples. Water retention was consistently, but only slightly , increased by manure addition. The increases, in the order of sample texture, were clay loam > sandy loam approximate to silt loam. Increas es tended to be higher at the lower values of tension. Manure addition consistently increased the weight percentages of aggregates passing a given mesh size. Increases, in order of sample texture, were silt loa m > clay loam > sandy loam. In their entirety, these results show that the manure produced measurable changes in the soil physical propertie s. The magnitude of the changes, in most cases, were small and depende d on the soil texture. Given the high total amount of manure applied, the results indicate that manure-induced physical changes in the soil were small and evidently did not accumulate over time. Rapid microbial degradation of the manure could be responsible for the lack of marked changes in the soil physical properties.