The effect of plant top material on the water repellence of fired sands and water repellent soils

Abstract

Large differences in the water repellence were conferred on fired sand by adding the ground tops of a range of plant species. Contact angles of 75¦ to 90¦ were caused at 2% of most pasture and native species and at 5 % many gave contact angles > 95¦ The cereal crops gave contact angles of about 60¦ (2%) and 83¦(5 %) and were more wettable than pasture and native species. The addition of ground Geraldton subterranean clover (Trifolium subteraneum cv. Geraldton) or brown mallet (Eucalyptus astrigens (Maiden)) to water-repellent sands increased the water repellence. Addition of clover to a water-repellent mallet-hill soil increased the water infiltration rate while the mallet did not change the slow rate. Wheat (Triticum aestivm), when added to water-repellent soils, always reduced the water repellence. Attention is drawn to the importance of the relative wettability of the soil and added organic matter, and therefore the type of plant cover. Soils sampled from beneath wheat/clover rotations of various lengths showed that water repellence increased in the pasture phase and was reduced during the cropping phase. The importance of the type, as well as the amount, of organic matter in the rotations is demonstrated.