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The Effects of Organic Matter Added to Lysimeters Containing Norfolk Coarse Sand¹

ABSTRACT

The decomposition of corn and soybean plants in Norfolk coarse sand was studied in shallow lysimeters. The percolate from the soybean-soil mixture was more concentrated in total salts and nitrogen than the percolate from the corn-soil mixture. The corn-soil mixture was initially higher in organic solids. The differences became smaller and the percolates became less concentrated as the decomposition progressed. The ether soluble materials in the percolates contained acidic compounds. The percolates did not contain carbohydrates. Both percolates were high in ammonia and organic nitrogen at first, but the concentration of these substances decreased rapidly. Large quantities of nitrate nitrogen appeared in the percolates from the soybean tank after two months and in the percolates from the corn tank after six months. The loss of carbon from the corn-soil and soybean-soil mixtures amounted to ninety per cent and seventy-seven per cent, respectively, in fourteen months, of which 2.1 per cent and 5.7 per cent were found in the percolates. Nitrogen losses from the corn-soil mixture were 76.8 per cent of that added, of which one third was leached and two thirds disappeared, presumably in volatile form. Nitrogen losses from the soybean-soil mixture were seventy per cent of that added of which two thirds appeared in the percolate and one third was "volatilized." Approximately the same amount of nitrogen was "volatilized" from both tanks. A greater quantity but a smaller percentage of the minerals added were leached from the soybean-soil mixture. The decomposition increased the acidity of the corn-soil mixture 1.17 pH units and of the soybean soil 0.89 pH units. Losses of ether, water, and alcohol soluble substances and hemicelluloses were large and similar in both materials. The soybean-soil mixture was richer than the corn-soil mixture in "lignin," "protein" and cellulose after fourteen months. In both cases, the residual "protein-lignin" ratio was about 2:1. Apparently the larger amount of ash and protein in the soybeans caused a greater conservation of lignin than occurred during the decomposition of the corn which was poorer in both ash and protein. The unfertilized soybean-soil produced a 406 gram crop of snap beans per tank, which matured earlier than the 181 grams of snap beans produced in the corn-soil.

¹ Contribution from the Office of Soil Fertility Investigations, Bureau of Plant Industry, U. S. Dept. of Agriculture, Washington, D.C. In co-operation with the South Carolina Experiment Station. Credit is due Dr. J. J. Skinner of the Bureau of Plant Industry, in charge of soil fertility investigations in the southeastern states, for advice and guidance in developing this investigation, and to A. B. Bowen for assistance in making the lysimeter observations and preparing the soil samples.

² Associate Soil Technologist and Assistant Chemist, respectively.