Farmers considered there were two sources of nitrogen – the magnificent clover plant which fixes nitrogen and the fertiliser that was applied to paddocks, excessively in some cases.
The subject of nitrogen losses versus nitrogen efficiencies was never part of the equation, Ballance Agri-Nutrients science extension manager Ian Tarbotton says.
Today, nitrogen has gone from being a productive part of the dairy farm system to also being an environmental risk.
“In the past, nitrogen wasn’t the main focus. Clover was the main source of nitrogen in the farm system and nitrogen fertiliser was used tactically and stocking rates were moderate. Now there is less clover, nitrogen fertiliser is more widely used, stocking rates tend to be higher and there is huge external interest in what’s going on with nitrogen.”
Regulatory bodies are looking at onfarm practices, with farmers increasingly being asked to provide nutrient management data. Understanding a nutrient budget has therefore become one of the key fundamentals for any dairy farmer.
While there are limitations and restrictions being put on dairy farmers, there is also a positive outcome from scrutinising nitrogen use, Tarbotton says.
“If you understand your current status around nitrogen efficiency and losses, you can look and see the efficiency gains,” he says.
“There is a huge opportunity around efficiency and utilising nitrogen more carefully.”
In terms of nutrient management, farmers are being asked to provide dairy companies with data to model nitrogen loss and nitrogen conversion efficiencies.
The data is interpreted using the Overseer nutrient budgeting software which can estimate nutrient flows into, within and out of the farm. The results are shown in the nitrogen report sent back to dairy farmers annually. The three figures in that report farmers need to be aware of are their nitrogen leaching risk, nitrogen conversion efficiency and nitrogen surplus.
“It’s important to understand the predicted nitrogen leaching from your farm from the Overseer model to see where you can improve efficiency, and over multiple years you get a clearer picture of the situation,” Tarbotton says.
What is nitrogen?
Nitrogen is an element present in all living cells, mainly as a key component of protein, having a major effect on plant quality and growth potential. However, when nitrogen is converted to nitrate in the soil it becomes mobile and has the ability to leach out of the plant rooting zone if not taken up by plants.
For example, there will be concentrated urine patches by the gates and around water troughs where farmers won’t need to apply any nitrogen fertiliser, Tarbotton says.
There are also certain paddocks onfarm that need more or less nitrogen fertiliser. Having an accurate soil map of the farm is a good start to understand any variations in soil type on the farm and farmers can then run the farm in separate blocks and apply effluent and fertiliser accordingly.
Farmers should also treat paddocks differently that had been cropped or pugged recently, he says.
Feed use strategies to reduce nitrate leaching include increasing pasture utilisation, using lower-protein feeds, lifting rather than grazing crops, replacing winter crops with summer crops and adopting low-impact winter grazing practices. A high-protein diet increases the nitrogen content of urine and increases the risk of nitrate leaching. Using low-protein feeds helps reduce the nitrogen load in the urine and the soil.
Thinking about when and where crops are fed onfarm is something else farmers can consider. How those crops are planted can also affect nitrate leaching. Heavy cultivation creates a lot of nitrogen loss, for example, while using sprays and direct drilling can equally establish a good crop.
Farmers need to ask the hard questions about whether they really need to cultivate to grow a good crop, Tarbotton says.
“Do we need to do that? What is it going to do for nitrogen loss versus efficiency?”
Pasture species are also another tool to use. Lucerne, herbs and chicory have deeper roots than ryegrass so they can access the nitrogen deeper down in the soil.
There is less clover fixation and less clover in general in NZ pastures now, mainly because of pests, and some farming practices make it tough for clover to compete, he says.
Key points
• Cow urine is the greatest source of nitrate for nitrogen leaching
• Effluent management impacts on leaching
• Fertiliser nitrogen has only a small direct impact on nitrogen leaching
• Higher protein feeds result in higher nitrogen in urine and impact on nitrogen leaching
• You can’t control soil drainage but you can control the amount of nitrogen available for drainage
