Developing nitrogen management indicators for dryland summer-fed forage brassica species

This project activity has been a highly collaborative effort, with the group comprising members of Plant & Food Research, Forage Innovations Limited, PGG Wrightson Seeds, Beef+Lamb New Zealand, council representation through Hawkes Bay Regional Council, Environment Canterbury and Otago Regional Council and farmer triallists.

Nitrogen plays a key role in feed & food production, being among the most important crop yield-limiting factors in the world. Currently there is no information on nitrogen management practices for dryland, multi-grazed, summer-fed forage brassica crops. Without solid information for how to manage nitrogen on these crops, farmers run the risk of unnecessary costs from nitrogen applications that may not be required and potential environmental impacts from nitrate leaching from excess nitrogen applied.

In this project, scientists from Plant & Food Research are looking at how different brassica crops perform under different nitrogen management practices. In the first year of the project, four common brassica crops’ performance was investigated under two different nitrogen management practices. One management practice was using a controlled-released nitrogen fertiliser while a coated urea fertiliser was used in the other, and both practices were evaluated using crop and soil information to make decisions around the amount of nitrogen fertiliser that is applied. This first set of trials took place in the 2023-24 season on commercial farms in 3 key regions: North Otago, Mid-Canterbury & Hawkes Bay. These areas were chosen as this is where 55% of summer forage brassicas are grown. Key data on crop yield and feed quality, nitrogen uptake and soil nitrogen were collected around typical grazing times throughout the season.

In this first year, all sites experienced true dryland conditions. It was found that two of the crops, both forage rapes, performed poorly at all the sites. However, one of the multi-grazed crops, ‘Pallaton’ raphanobrassica, performed well at all sites, and was found to have the highest yields and nitrogen uptake of all the crops. It also showed that more nitrogen was retained in the system compared with other crops, which is a positive environmental outcome. However, data showed that it had low nitrogen use efficiency compared with the other crops and so nitrogen management strategies will be refined further.

Antonia Miller, business manager for this project, is excited as to how this project is progressing. “This first year had yielded interesting results which we are looking forward to expanding on. By the end of this project, we are aiming to have a set of guidelines for farmers for how to use nitrogen management indicators to maximise efficiency on the farm. By using appropriate rates of nitrogen fertiliser, ideally, costs of inputs are reduced, crop failure decreases, and support environmental stewardship.”

Trials will be repeated in each region over the next two years building on the knowledge and data from the previous year and increasing the knowledge on nitrogen management indicators.

More appropriate management of nitrogen through management indicator guidelines will benefit Aotearoa New Zealand sheep and beef farmers greatly and support the development of strategies within their own farms to uplift summer-forage brassica crops production while limiting environmental impact.