The effect of organic amendment input and crop management practices on the nematode community and suppression of root-lesion nematode (Pratylenchus thornei) in a grain-growing soil

The root-lesion nematode Pratylenchus thornei is a major pest in the northern grain-growing region of Australia, costing the wheat industry alone $38 million/year in lost production. Biological suppression is being examined as a potential method of reducing populations of P. thornei, which is complementary to the current research focus of breeding tolerant and resistant varieties and using resistant hosts in crop sequences to manage the pest. This study aimed to examine the effect of key farm practices of soil suppressiveness to P. thornei. A field trial was established to determine whether suppressiveness is enhanced by organic amendments (a single application of 0, 5, 10 and 20 t organic matter/ha incorporated into the top soil) and various cropping regimes (bare fallow with residue removed, sorghum with residue retained, sorghum with residue removed). We found that the treatments did not improve soil organic carbon levels but the results of soil nematode analyses indicated that the soil’s biological status changed when these treatments were applied. In the first year after rotation with sorghum, the suppressiveness of the soil increased compared to the fallow treatment. However, in the next year after re-applying the crop management treatments following several months of fallow, soil suppressiveness had declined and difference between treatments were not significant. With the following wheat planting, the soils showed higher suppressiveness in the sorghum residue-retained treatment but that treatment did not affect the yield of two susceptible wheat varieties. The trial also showed that intensive cropping is more likely to induce suppressiveness to root-lesion nematode than a single application of up to 20 t/ha of organic matter. © 2017, Australasian Plant Pathology Society Inc.