Trish Fraser, Plant & Food Research
There have been significant changes in the management of arable cropping systems in New Zealand over the last 25 years. We have also seen substantial improvements to the productivity of the main crops: e.g. wheat production has increased by nearly 70% even though the land area under wheat has not changed significantly; and, although nearly 20% less land area now grows barley, the total quantity of grain produced has not declined. There has been a diversification of the cropping mix, with an especially large increase in forage crops to support the dairy sector. The duration of cropping phases has typically increased, with simultaneous reductions in restorative rotation phases and bare fallow periods. The use of cover or catch crops is increasing and stubble management practices have changed, with more stubble being returned to the soil and less being burned. Alongside all of this, we now have greater availability to smart technologies that enable precision agricultural techniques to apply fertiliser and water more strategically, and GPS technology to guide vehicles and implements across the land.
Over the last decade, FAR has coordinated a series of farmer surveys to investigate changes in cropping practices. Results (some of which will be discussed) have indicated that there has been an overall reduction in tillage intensity (number of passes, depth and degree of soil mixing), and an increase in direct drilling and non-inversion tillage practices, coupled with a reduction in the overall amount of ploughing.
All of these changes are likely to have had either direct and/or indirect impacts on soil properties; some with positive and some with negative impacts. There are varying opinions on whether soil quality has improved or deteriorated as a result of management changes. In the absence of baseline data on which to make such evaluations, speculation is unhelpful. Hence, FAR recently engaged Plant & Food Research to establish some soil quality ‘benchmarks’ for arable systems.
Initial findings from this work have shown that the majority of paddocks sampled were within the recommended range for both soil carbon and aggregate stability. However, in some paddocks results did fall below the recommended range, and to improve soil health in those paddocks, it is suggested that management practices which increase organic matter returns and reduce organic matter loss should be implemented. Such soil benchmarking data can be used by growers to monitor their soil physical health against relevant regional or national guidelines.