Using rotation crops to improve soil quality

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Soil quality issues are being researched within two crop rotation experiments that started in 1994 at Narrabri. They compare several crop rotations that include or exclude legume phases. The data presented here relate to the most recent 2-year cycles of these experiments. Following cotton harvest at the end of the previous cycle, rotation crops are sown (winter cereal, faba beans (grain) or vetch (green manured). Cotton is sown in the following October across all systems. The cropping systems also include continuous (annual) cotton in one experiment, with or without green-manured vetch each winter and a cereal-vetch treatment is included in each experiment.

Soil health has become more topical as some growers perceive a decline in their soil’s fertility and as soil-borne diseases impact on cotton cropping systems. Soil health relates not just to the presence or absence of the pathogens, but to soil characteristics that promote vigorous and healthy crop growth. Soil structure, the supply of nutrients and abundance of microbial communities can give some measure of the soils’ physical, chemical and biological properties.

Crop yield and N fertiliser response

Initially, these experiments aimed to examine whether legume crops could supply enough N to enable farmers to reduce the amounts of N fertilisers needed to maximise lint yield. The responses to applied N can be seen in Figure 1. It quickly became apparent that the cotton yields we measured in the legume systems exceeded those gained from comparable non-legume systems. For example, less N fertiliser was required by the oats-vetch system because of the N input from the vetch, but importantly, the oat-vetch treatment had a significantly higher yield. The elevated lint yields in the oat-vetch system were consistent at all N fertiliser levels. This effect is due not just to the N input from the legume, but also to the improved soil environment created by growing the vetch. Our current aim is to evaluate these rotation crops and examine how they improve the soil environment.

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