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Alfalfa Growth as Affected by Aeration and Soil Moisture Stress under Flood Irrigation¹

ABSTRACT

Periodic lowering of oxygen content of the soil atmosphere to 13% or less for periods of 2 or 3 days appeared to have no adverse effects on alfalfa growth. If there were any adverse effects, they were entirely masked by the dominating effect of reduced soil moisture stress. When hydraulic moisture stress reached approximately 0.2 atm. at the 10-inch depth, growth rate was greatly curtailed. When combined with the osmotic component of soil moisture stress, 0.2 atm. hydraulic stress resulted in total soil-moisture stresses of about 1.9 and 2.8 atm. on leached and unleached plots, respectively.

In one series of irrigations where 17 inches of water were applied, the soil surface was sealed against diffusion of oxygen for at least 8 days. During this time the average oxygen content in the root zone dropped to 6% with individual readings as low as 3%. Alfalfa on these plots grew much better than did alfalfa on adjacent plots which received normal irrigation.

¹ Joint contribution of the Colorado Agr. Exp. Sta. and the Western Soil and Water Management Section, Soil and Water Conservation Research Div., A.R.S., U.S.D.A. Authorized by the Director of the Colorado Agr. Exp. Sta. for publication as Scientific Journal Series No. 502. This work was partially supported by funds from Regional Research Project W-29. Presented before Div. VI of the Western Society of Soil Science, Palo Alto, Calif., Aug. 27, 1957.

² Assistant Agronomist (Soils) and Associate Agronomist (Soils), respectively, Colorado State University, and Soil Scientists, A.R.S., U.S.D.A. The authors gratefully acknowledge the assistance of Behattin Oztan, an I.C.A. sponsored graduate student from Turkey, in taking the field measurements reported herein.

Received for publication May 4, 1957. Accepted for publication July 2, 1957.