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

The practice of planting potatoes (Solanum tuberosum) in rows and hill ing the plants at some stage of growth has been universally adopted. U sing a rainfall simulator and runoff-erosion plots (0.9 m wide x 1 m l ong), the effects of hilling on runoff, infiltration, and soil loss we re examined on an Orthic Dystric Brunisol. Tests of the rainfall simul ator revealed that variations in operating pressure (36.5-62.1 kPa) an d soil slope conditions (0-15%) did not significantly (P < 0.05) affec t 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 ar e similar to those used in commercial production. Although not signifi cantly different at P < 0.05, the runoff rate from the hilled plots wa s approximately 20% higher than that from the unhilled plots. Hilling resulted in a significant reduction in infiltration rate (P < 0.05). A verage soil loss from the hilled plots was approximately four times hi gher than from the unhilled plots. For runoff rates below a critical v alue of 0.93 L min(-1), the rate of soil loss correlated linearly with the runoff rate, whereas a non-linear exponential equation was genera ted 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-sideslo pe gradients using an existing equation derived from erosion data obta ined from fields having conditions similar to that of potato hills.