Crop rotation for managing nematode pests and improving soil health in sugarcane cropping systems.

Populations of free-living nematodes (FLN) increased and plant-parasitic nematodes (PPN) decreased at Tully, Ingham, Burdekin, Mackay and Bundaberg when a grass/legume pasture or legume crop was grown for 30–42 months before planting sugarcane. At other sites, shorter rotations also had significant effects on nematode communities. In north Queensland, a single soybean crop increased pre-plant populations of FLN and reduced populations of pest species such as Pratylenchus zeae by 44–89% compared to similar fields that had grown sugarcane. In a replicated experiment at Bundaberg, a soybean/peanut rotation increased numbers of FLN and reduced populations of two plant parasites (P. zeae and Rotylenchulus parvus) by 75% and 93% respectively. When sugarcane was planted following a legume, the ratio of FLN to PPN was generally greater than 20, whereas this ratio was often less than 2 in a plough-out/replant situation. It is possible that this change in the balance between beneficial and pest nematodes partly explains the improved early shoot growth and increased cane yields that are consistently obtained when sugarcane is planted following a legume. FLN are beneficial because they enhance nutrient cycling by grazing on soil microorganisms. They also help maintain populations of the predators that feed on nematodes. In contrast, PPN have a negative impact on sugarcane growth because they destroy fine roots, limit root elongation and debilitate root systems.