Effects of Increasing Amounts of Organic Residues on Continuous Corn: I. Yields and Soil Physical Properties

When well-fertilized corn (Zea mays L.) monocultures with large amounts of residues returned to the soil became common, the question was asked as to whether soil tilth and corn yields could be maintained at satisfactory levels in Corn Belt soils. To answer this question corn growth and soil physical properties were determined in a field experiment in which different types (alfalfa (Medicago sativa L.), cornstalks, sawdust, oatstraw (Avena sativa L.) and bromegrass (Bromus inermis Leyss)) and amounts (from O to 16 tons/ha/yr) of plant residues were added to Marshall silty clay loam (Typic Hapludoll) for 13 consecutive years. The soil was cropped to corn and large amounts of N were added. For approximately the first 9 years grain yields were lower from the check and sawdust treatments than from all others. During the last 4 years grain yields declined sharply with rate of addition of cornstalk residues and slightly from additions of alfalfa. It is suggested that the yield decline in the cornstalk treatments was due to a lowering of pH and an Al-induced Ca deficiency in the plant. An alternative explanation is that the cation balance was upset as evidenced by K/Ca and K/Ca + Mg ratios in the plant. The C content of the soil was progressively increased, as was the wet aggregate stability and water retention with rate of addition of organic material. Energy of aggregate rupture, energy to initial runoff, erosion, and infiltration were not significantly influenced. It was not visually evident that significant changes occurred in soil tilth because of treatment differences. Marshall soils are well aggregated, have favorable physical and chemical properties, and although erosive, physical problems are not usually observable in the field. Corn grain yields averaged near 7,000 kg/ha (112 bu/acre) in the later years of the experiment, again suggesting that the physical properties of the soil on all treatments were favorable.