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Effect of Incubation Method and Storage Conditions on Nitrate Production of Incubated Soil Samples¹

ABSTRACT

Samples of Charlottetown fine sandy loam were incubated for 2 weeks at 30°C. and four different moisture tensions, with sand added in four different soil to sand ratios. Tension of 0.24 atm. and 1:1 soil-sand ratio was optimum for production of NO₃^--N. Incubation in an atmosphere of less than 85% relative humidity severely restricted nitrate production due to drying of the soil.

Samples of the same soil at air-dry, 10% and 20% moisture were stored at –20, –5 and +5°C. for 0.7, 3, 6, 9, 12, and 15 weeks in a complete factorial experiment, then incubated at 30°C. and 0.24 atm. moisture tension for 2 weeks. Air-drying increased nitrate production by 15 to 20 ppm. N over moist samples. Storage at 20% moisture caused a 2 to 3 ppm. decrease compared to 10% storage. Minus 20° and –5°C. storage gave constant nitrate production with changing storage time, but –20° samples were 2 to 3 ppm. N higher than –5° samples at 10 and 20% moisture.

Air-drying soil from field capacity to the wilting point had little effect on nitrate production, but further drying to the air-dry state caused a marked increase. Moisture content of soil samples during storage affected the correlation of nitrate production with ryegrass yields in the greenhouse.

¹ Contribution No. 135, Experimental Farm, Research Branch, Canada Department of Agriculture, Charlottetown, P.E.I. Presented before Div. S-4, Soil Sci. Soc. Am., Nov. 18, 1963 at Denver, Colo.

² Research Officer and Head, Soil Science Division, respectively, Experimental Farm, Research Branch, C.D.A., Charlottetown, P.E.I.

Received for publication April 14, 1964. Accepted for publication August 4, 1964.