Measurement of the productivity of soils under various environmental conditions
1950
Odell, R.T.
During 1946 and 1947 corn yields were determined on a series of plots, located in farmers' fields in north-central Illinois on Tama silt loam and Swygert silt loam. The purpose of this work was to measure, by objective sampling methods, the productivity of these two soil types for corn under various environmental conditions. Tama silt loam was much more productive than Swygert silt loam under all conditions studied. Weather conditions caused corn yields to be uniformly high in 1946, and low but variable in 1947. Average corn yields were higher where the surface soil (A1 horizon) was thick than where it was thin. Depth of surface soil had a greater effect upon corn yields for Swygert, which has an unfavorable subsoil, than for Tama, which has a permeable subsoil. Corn yields increased as density of stand increased on both soil types, but the yield increases were much greater in 1946, when the weather was favorable, than during 1947, when unfavorable weather prevailed. Tama and Swygert responded to applications of rock phosphate with increases in corn yield, but the response was small on both soil types in 1947 and was influenced by crop sequence and direction of slope on Swygert. Yields of first-year corn after clover or alfalfa were significantly higher than those of second-year corn after clover. Average corn yields were higher on south slopes than on north slopes but in most cases the differences were not large enough to be significant.
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