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Influence of VAMA and of Depth of Rotary Hoeing upon Infiltration of Irrigation Water¹

ABSTRACT

Long continued inter-row cultivation and passage of vehicles may adversely affect soil physical properties. The influence upon infiltration in peach orchards of the incorporation of vinyl acetate maleic anhydride (VAMA) with sandy loams which had been harmed by such treatments was studied during three irrigation seasons after a single addition of the VAMA polymer in 1953.

Treatments were: rotary hoe cultivation to depths of 1, 6, and 16 inches, with and without polymer incorporation; soil then undisturbed and kept weed-free. Polymer influence persisted through three seasons. Average depths of infiltered water after 1.6 hours for all cultivation depths were: without polymer, 3.1 in.; with polymer, 6.2 in. Where polymer was incorporated, increased cultivation depth gave increased infiltration; without polymer, cultivation depth appeared to have no appreciable effect. Supplementary measurements following tractor passage in 1955 showed average decrease in infiltration at 1.6 hours from 7.0 in. (without tractor) to 2.4 in. (with tractor).

Dispersing tendency, density, and moisture characteristics are presented for soil cores taken from one orchard at the end of the third season. The increased aggregate stability in water and lowered bulk density of cores taken from soils receiving polymer, persisted until the end of the experiment. Treatments considerably influenced moisture retention and hence pore volume at tensions less than 1/5 atm. but, with the exception of the tractor-compacted, deeply-tilled, with-polymer treatment, they had little effect upon these properties at higher tensions. The cumulative depths of infiltered water were clearly associated with changes in volume of coarser pores.

¹ Contribution from the Department of Soils and Plant Nutrition, University of California. Experiments conducted as part of Experiment Station Project BJ-5-1590. Presented before Div. VI, Soil Science Society of America, Nov. 20, 1957, at Atlanta, Ga. Particular acknowledgment is made of the assistance during 1953 of R. B. Campbell and, during 1954, of J. J. Twitchell. The cooperation or R. Atkinson, J. and L. Bowen, K. Gardner, L. S. Parks, and E. B. Singer who contributed the use of their land, the staff of the stanislaus County Farm Advisor's Office who helped during the experimental work, and Martin Fox of the Statistical Laboratory, University of California, Berkeley, is also gratefully acknowledged. Thanks are due to the Monsanto Chemical Company for donation of the vinyl acetate maleic anhydride polymer (VAMA) used in the experiments.

² Professor of Soil Physics and Senior Laboratory Technician, University of California, and Associate Professor of Statistics, Department of Statistics, University of Chicago, respectively.

Received for publication December 13, 1957. Accepted for publication March 13, 1958.