Root Zone Reality

Around New Zealand, regional authorities are responding to the National Policy Statement for Freshwater Management and developing plans to improve freshwater quality. A common theme is the requirement that farmers should be applying agricultural good management practice. They are also expected to be developing farm environment plans to assess and manage the environmental risks associated with their farm business.

Farm nutrient budgets will increasingly be a part of the farm environment plan to provide a measure of the environmental performance of the farm. In most cases this will be an Overseer® nutrient budget.

Arable farmers have complex farm systems, they manage a number of crops and often have pastoral components to their farm businesses. They understand that there is a necessity to use models to develop nutrient budgets but they question whether these nutrient budgets are truly representing losses from their farms.

They are right to be concerned because in reality there has been little measurement of nitrogen losses from the root zones of cropping rotations and there is a dearth of data to calibrate the cropping components of the models. Having data to do this is a good start to building farmer confidence in the Overseer model and its nutrient budgets for cropping rotations.

A new MPI Sustainable Farming Fund project “Rootzone Reality” is funding the installation of a permanent network of fluxmeters on commercial cropping farms in Canterbury, Manawatu, Hawkes Bay, Waikato and Pukekohe. Data from a

range of arable and vegetable rotations will be collected, with crops including grains and seeds, onions, maize, potatoes, beetroot and process and leafy, green vegetables.

The data is being collected over a number of years so the impact of stock grazing within the rotations will also be captured. As well as drainage and nutrient loss data, the project will collect weather data, soil moisture and crop information including biomass accumulation throughout the season, final yield and the management practices associated with the crop production.

Hugh and Sharon Ritchie are former Hawkes Bay famers of the Year. Their farm (Drumpeel) is a large-scale 2050ha block which is a mix of cropping and livestock.

A minimum of the farm is given the full cultivation treatment, most is strip tilled.

Hugh says he’s looking forward to some robust science around the real impacts of how he is farming. He says Overseer is a useful tool for some purposes but he isn’t overly confident it is giving him an accurate picture of the nutrient losses under his management.

He is hoping this project will offer a far more robust picture of what is really happening to nutrient under the different kinds of rotations that take place on Drumpeel.

Paul Johnstone from Plant & Food Research says minimising nutrient losses from cropping systems makes good financial sense. It also minimises any adverse impacts on our waterways, which is important in many regions as new national water policy requirements are implemented. However, there is relatively little long-term measurement of how good management practices throughout New Zealand impact losses of nitrogen and phosphorus from the root zone of cropping paddocks.

He says there are 12 sites in the network, spanning the Canterbury, Manawatu, Hawke’s Bay, Waikato and Auckland regions. A wide range of cropping rotations, soil types, climatic conditions and management practices have been selected.

At each site 12 tension fluxmeters have been installed permanently at a depth of 1 metre. Any water from rainfall or irrigation events that drains to 1m is captured by the fluxmeters. It is then pumped to the surface and analysed for nitrogen and phosphorus concentrations. Net losses can be estimated by combining these concentrations and measured drainage volumes.

Results from the first year were recently presented at the Fertiliser Lime and Research Conference at Massey University.

Paul says results on Drumpeel are quite low but is important to remember that this is a long-term experiment and individual results need to be considered with some caution. These initial results were captured when the soil around the fluxmeters is resettling and the soil and water dynamics may not by typical during this period. Soil water balances are being used to pick up and omit any outliers.

Paul says the value of these projects is in the long-term patterns that become evident over time. As data is collected and discussed, our understanding of cropping systems and the interactions between the physical environment and the management practices associated with the cropping and grazing parts of the rotation will improve. These insights will provide opportunities to discuss and promote good management practices to growers.

Thanks to Diana Mathers, Research Manager Farm Systems, Foundation for Arable Research (FAR)