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Soil Respiratory Activity and Organic Matter Depletion in an Arid Nevada Soil¹

ABSTRACT

Incorporation of mature crop residues of alfalfa (Medicago sativa), oat (Avena sativa), and sudan (Sorghum vulgare) into a fine sandy loam soil in southern Nevada stimulated the soil respiratory activity. A close correlation was observed between respiration rate and organic matter content; both decreased steadily over a 6-month test period.

Four mature crop residues (alfalfa, cotton (Gossypium hirsutum), oat, and sudan) were added to the same soil type in laboratory tests at 1, 2, 3, and 4% (weight/weight). Respiratory activity of these soils was followed for 10 weeks at 2-week intervals. A maximum activity was noted at the first 2-week period for the 2, 3, and 4% additions of all four residues.

The respiration rate was proportional to the residue concentration but the increments were not additive. A linear relationship was noted when the reciprocal of the rate was plotted against the reciprocal of the residue concentration, similar to that of a first-order reaction during the period of maximum activity. It was suggested that a given soil could become saturated with organic matter and reach a maximum respiratory activity; other factors would become rate limiting.

¹ Contributions from Plant, Soil and Water Science Division. University of Nevada, Reno. Max C. Fleischmann College of Agricultural Research, p. J67.

² Former Associate Professor, Plant Science, University of Nevada, now Associate Professor, Plant Sciences, Texas A&M University, and Associate Agronomist, University of Nevada, Southern Nevada Field Laboratory, Logandale.

Received for publication November 22, 1967. Accepted for publication August 15, 1968.