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The Effect of Soil Moisture Tension on Carbon Dioxide Evolution, Nitrification, and Nitrogen Mineralization¹

ABSTRACT

Four soils were incubated at 30°C. for 14 days under soil moisture conditions varying from zero tension to airdry soil after which NO₃-N and NH₄-N were measured. Carbon dioxide evolved from the soils was collected continuously and measured at the end of the 1, 2, 3, 7, and 14 days. Carbon dioxide production during the first day increased from a minimum in air-dry soil to a maximum at tensions of from 0.50 to 0.15 bars, and then decreased with further increase in soil moisture. At the end of the incubation period there was little difference in the CO₂ evolved in the tension range from zero to 0.15 bar. Maximum nitrification occurred in the tension range of 0.50 to 0.15 bars. There was a peak in both N mineralized and N nitrified in this tension range followed by a decline in NH₄-N and NO₃-N to about zero tension where there was another peak in N mineralization. Nitrification was shown to proceed at tensions above 15 bars tension but at a very slow rate. Ammonification took place at a faster rate at both high and low tensions, indicating that NH₄-N can accumulate in soil at high tensions (up to air-dry) and low tensions (near zero bars).

¹ Contribution from Colorado Agr. Exp. Sta., Scientific Journal Series 886. This work was supported in part by funds from Western Regional Project W-31.

² Instructor and Professor, respectively.

Received for publication December 13, 1963. Accepted for publication April 21, 1964.