Runoff and soil erosion as affected by plastic mulch in a Hawaiian pineapple ®eld

The effects of plastic mulch in Hawaiian pineapple culture on runoff generation and soil erosion are poorly understood and not covered in the literature. Field rainfall simulation experiments were conducted on an Oxisol commonly used in Hawaii for pineapple production. Four treatments were no cover (hereafter called bare), plastic mulch as the sole cover (plastic), pineapple crowns as the sole cover (crown), and both plastic and crowns as covers (plastic±crown). The average slope of these plots was 4.2% and all were shaped into ridge-and-furrow con®gurations. For each treatment, three successive storms were imposed: a `dry run' with an intensity of 35 mm hÿ1 on the initially dry soil; a `wet run' with the same intensity on the following day; and a `very wet run' with an intensity of 62 mm hÿ1 that immediately followed the wet run. Runoff was measured and sampled every 5±10 min until a steady state was reached. Results indicated that plastic mulch itself substantially accelerated runoff generation and soil erosion due to its impervious nature. The simultaneous presence of plastic mulch and pineapple crowns, however, tended to retard runoff generation and reduce soil erosion. For all storms, runoff and erosion rates in the plastic±crown plot were smaller than those of the bare and the crown plots (ca. 30 50% less) due to the formed microbasins in plastic±crown system that enhanced in®ltration. Plots without plastic mulch displayed soil surface sealing that impeded in®ltration. The practical implication of the research is that the plastic mulch used in Hawaiian pineapple plantations may not necessarily increase runoff and soil erosion. # 1999 Elsevier Science B.V. All rights reserved.