New clay helps crops beat drought

NIC WHITE, SCIENCENETWORK WA

Water Corporation scientists have developed a soil amendment to help crops and native plants survive in Perth's increasingly dry climate while combating dieback. Lime-amended BioClay (LaBC) improves soil water holding capacity and uses readily available materials to create a sustainable and cost effective alternative to commercial fertiliser. Project leader Tom Long says Western Australian plants often have problems surviving their first drought because not enough of the winter rain infiltrates the ground to make it to the root system. “Our target is to modify the top 100mm of sand into a sandy loam to increase its water holding capacity and break water repellence,” Mr Long says. “It's difficult trying to get anything to [survive] an initial year of drought and to get the roots established you really need to have something that holds onto the water longer into the shoulder season but also takes advantage of the out-of-season rainfall that we're getting.” The product combines a two-to-one ratio of solid waste and Cockburn builder's lime. The lime's calcium oxide converts the nitrogen in the biosolids to ammonia and the phosphorous to calcium phosphate which acts as a slow release fertiliser. This is then mixed with 1.5 times its weight in clay which the ammonia is absorbed into.   Mr Long says clay was chosen over other materials because it effectively counteracts Perth's sandy acid soil and gives it the optimal mix of sand, silt and clay, providing the best planting environment. “One of the beauties of this is that it raises the carrying capacity of the soil,” he says. “Bassendean sand has a carrying capacity of 2.2 Dry Stocking Equivalence (DSE), but once you've amended the soil and planted it's raised to about 15 DSE.” Applied 5 kg/sqm or 50 t/ha at 20 mm thick, LaBC provides a one year supply of nitrogen to kick-start growth and seven years of slow-release phosphorous to maintain nutrient supply. Mr Long says tests conducted by dieback (Phytophthora cinnamomi) researcher Dr Elaine Davison at Curtin University have shown that LaBC not only prevented the spread of dieback but killed existing infections within six days. This side benefit according to Mr Long is because of LaBC’s pH of 12 which raises the pH of the Perth soil to about neutral, the effects of which have never before been tested on dieback. Mr long says LaBC or even just lime treatment could be used to combat the spread of dieback either with direct application to affected areas or to create barriers to further infection. Editor's Note: Original news release can be found here.