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Effect of Tile Spacing on Crop Yield and Water Table Level in a Planosol Soil¹

ABSTRACT

Six years of data are presented on the effect of tile drainage in a Planosol soil (claypan soils of flat lands) at spacings of 15, 30, and 60 feet. Corn, oats, and hay yields were obtained as well as water table levels, rainfall, tile outflow, soil texture, and soil hydraulic conductivity measurements. Corn and oat yields on the 15- and 30-foot spacings varied from 3.4 to 9.1 bu. per acre higher (significant at 99% probability) than the yields on the 60-foot spacings. Water table, outflow, and hydraulic conductivity measurements seem to indicate that water movement to the tile is largely through the more permeable backfill over the drains. The initial water table midway between the drains a few hours after a rain is lower for the narrower spacings; subsequently, the rate of drop is nearly the same for all spacings. After the first day following rainfall, evapotranspiration and other losses appear to influence the rate of drop more than the tile. Between the drains the water table is nearly flat. After the soil is saturated, tile outflow increases rapidly within a few minutes after the rain starts and reaches a peak in 2 to 4 hours. Several peak flows of over 1 inch per day were recorded. The maximum tile outflow volume measured for a given storm was 55% of the rainfall; however, this percentage is influenced greatly by antecedent moisture conditions.

¹ Contribution from Departments of Agricultural Engineering and Agronomy, Iowa State College. Journal Paper No. J-3033 of the Iowa Agr. Exp. Sta., Ames, Iowa. Project No. 1003.

² Formerly Professor of Agricultural Engineering (now Professor of Agricultural Engineering, Ohio State University), Professor of Soils and Physics, and Associate in Agricultural Engineering, Iowa State College, respectively. Acknowledgement of assistance is made to R. K. Frevert, Oscar Kempthorne, M. W. Bittinger, R. P. Nicholson, and Ronald Phillips.

Received for publication September 6, 1956. Accepted for publication March 29, 1959.