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Soil-Conditioning Properties of Modified Agricultural Residues and Related Materials: II. Persistence of Soil-Stabilizing Activity as a Function of Type and Extent of Modification¹

ABSTRACT

Agricultural residues, cotton linters, several of their chemical derivatives, and other related products were tested in the laboratory for their in-soil stability against microbial degradation for a period of 6 months in a controlled humidity cabinet. A modified Yoder wet-sieving technique was used to test the stabilizing effectiveness of a given polymer incorporated into Miami silt loam soil.

Forty- to sixty-mesh wheat straw, incorporated at a concentration of 0.5%, imparted greater stability to soil aggregates, following the first month of incubation at a temperature of 28° C., than did comparable applications of soybean and cotton stalks. Corn stover applications produced intermediate results. Twenty- to sixty-mesh cotton linters at 0.5% concentration yielded increasingly effective soil aggregation during the first 3 months of incubation, reaching a maximum aggregation value of 93%. Chemically-oxidized cellulose and corn starch showed surprising in-soil stability throughout the 6-month incubation period. In carboxymethyl cellulose samples, a degree of substitution (DS) of 0.7 or less was apparently insufficient to impart resistance to degradation by the microflora of the soil. However, carboxymethyl cellulose with a DS of 1.2 retained approximately 70% of its initial soilstabilizing activity over the 6-month test period. In the case of hydroxyethyl and methyl cellulose, data are presented which tend to show that a high degree of substitution is not an adequate criterion of resistance to microbial degradation. Rather, the susceptibility of such polymers to enzymatic hydrolysis is apparently attributable to a lack of uniformity of substitution, resulting in a relative abundance of unsubstituted units in the cellulose chain.

¹ Contribution from the Northern Utilization Research and Development Division, ARS, USDA, Peoria, Ill. Presented before Div. III, Soil Science Society of America, Atlanta, Ga., Nov. 20, 1957.

² Staff members.

Received for publication January 20, 1958. Accepted for publication April 10, 1958.