Integration of organic amendments, crop rotation, residue retention and minimum tillage into a subtropical vegetable farming system enhances suppressiveness to root-knot nematode (Meloidogyne incognita)

Vegetable farming systems in tropical and subtropical Australia are vulnerable for several reasons: degradation of the soil resource due to excessive tillage; environmental problems associated with off-site movement of soil, nutrients and pesticides during intense rainfall events; over-reliance on increasingly expensive external inputs (e.g. fossil fuels, plastic film, nutrients and pesticides); and de-registration of the soil fumigants and nematicides normally used to control soilborne pathogens. This two-year experiment compared the performance of a conventional capsicum farming system (an annual forage sorghum rotation crop and normal tillage practices) with three farming systems considered likely to be more sustainable because reduced tillage, a leguminous rotation crop, mulched crop residues and inputs of organic amendments were integrated into the system. One of these alternatives (capsicum grown under minimum tillage in soil mulched with crop residues rather than plastic) yielded significantly less fruit in both years, while root rotting caused by Pythium recalcitrans and Rhizoctonia solani caused problems in all alternative systems in the second year, presumably because the pathogens multiplied on residues from the previous rotation crop. Nevertheless, one of the sustainable alternatives (organic inputs from amendments and direct-drilled rotation crops for 2 years, with plastic laid onto a mulch of crop residues) performed well in all other respects, enhancing suppressiveness to root-knot nematode (Meloidogyne incognita) in the second year and producing higher yields than the conventional system in both years. These results suggest that the conventional vegetable farming system could be improved by 1) incorporating annual applications of commercially-available organic amendments, 2) growing cultivars of forage sorghum and soybean with resistance to root-knot nematode as rotation crops under minimum tillage on permanent beds, 3) mulching biomass from the rotation crops onto the bed surface well before the vegetable crop is to be planted, and 4) leaving the bed undisturbed and covering those residues with plastic. Future research should therefore concentrate on fine-tuning such farming systems; optimising residue management practices to minimise losses from root rotting pathogens that are good competitive saprophytes; and developing mulch-laying equipment capable of laying plastic onto undisturbed beds covered with crop residue.