EFFECTS OF POTATO HILLING ON WATER RUNOFF AND SOIL-EROSION UNDER SIMULATED RAINFALL

The practice of planting potatoes (Solanum tuberosum) in rows and hilling the plants at some stage of growth has been universally adopted. Using a rainfall simulator and runoff-erosion plots (0.9 m wide x 1 m long), the effects of hilling on runoff, infiltration, and soil loss were examined on an Orthic Dystric Brunisol. Tests of the rainfall simulator revealed that variations in operating pressure (36.5-62.1 kPa) and soil slope conditions (0-15%) did not significantly (P < 0.05) affect the intensity and spatial uniformity of the simulated rainfall. The potato hills studied were 90 cm apart with heights of approximately 25 cm, row-sideslopes of 35 degrees and furrow widths of 10 cm, which are similar to those used in commercial production. Although not significantly different at P < 0.05, the runoff rate from the hilled plots was approximately 20% higher than that from the unhilled plots. Hilling resulted in a significant reduction in infiltration rate (P < 0.05). Average soil loss from the hilled plots was approximately four times higher than from the unhilled plots. For runoff rates below a critical value of 0.93 L min(-1), the rate of soil loss correlated linearly with the runoff rate, whereas a non-linear exponential equation was generated for the entire range of runoff with r = 0.94. The increase in soil loss as a result of hilling was adequately predicted from row-sideslope gradients using an existing equation derived from erosion data obtained from fields having conditions similar to that of potato hills.