Winter blocks can be at more risk of nitrate leaching

MEDIA RELEASE 23rd April 2012

Winter blocks can be at more risk of nitrate leaching

Greg Costello of Ravensdown looks at practical steps to reduce nitrate leaching

It’s a familiar picture of winter grazing. Groups of cows feeding on narrow ‘breaks’ of winter forage crops. What’s not so obvious is the potential for nitrogen (N) losses from these activities. Wet, cold soils, pugging and winter rain increases the risk of nitrate leaching and emissions of nitrate oxide from the multitude of urine patches deposited.

These intensive systems are managed differently to the traditional rotational grazed pasture system. In the South, it’s common practice for stock to be grazed on forage crops for between one and two months, due to low pasture growth during the winter months.

Intensification often means keeping animals in a smaller space – especially in winter. Most nitrate leaching can be attributed to losses from the animal’s urine patch. Urine patches of lactating dairy cows are shown to have up to 1,000 kg N/ha. These ‘stacks’ of nitrogen are much more vulnerable to leaching, especially in the winter drainage months.

In the winter ‘break feeding’ scenario, the urine patches are within a confined space so can be more easily targeted with a nitrification inhibitor such as eco-n. Nitrification inhibitors are sprayed on as a soil treatment to slow the nitrification process, or the conversion of ammonium to nitrate.

These products like Ravensdown’s eco-n are not fertilisers, but will help reduce the nitrate leaching by slowing the bacteria which breaks down the nitrogen in urine into its leachable nitrate form. In the Government-funded Nitrous Oxide Mitigation Research trials, three years of data from different parts of the country showed that the active ingredient in eco-n cut leaching from urine patches by a consistent 40%. The research also found that nitrous oxide emissions could be cut in half.

Lincoln University’s own studies also found eco-n made up to 70% reductions in nitrate leaching in the urine patch under intensive winter ‘break feeding’ conditions. Because eco-n comes with an economic benefit (in terms of pasture response due to retained nitrogen) eco-n pays for itself during the season, so it is a practical and cost-effective way to take action on nitrate leaching today.

Five other things to consider when tackling the risk of nitrate leaching are:
1. Irrigation type: moving from an inefficient type of border dyke to spray irrigation can significantly reduce leaching losses outside the drainage period.

2. Feed pads: use of feed pads in the shoulders of the season going into or out of the drainage period will reduce nitrogen losses from the paddock. Effluent disposal can be managed outside of the drainage period.

3. Spreading efficiency: always ask if the spreader is using differential GPS so varied amounts of nitrogen can be placed more precisely.

4. Spreading timing: timing nitrogen inputs outside of high risk months will reduce losses, however research has shown the nitrogen fertiliser only account for 5-10% of N losses from a grazed pasture.

5. Nutrient Management Plans: analysis of soil fertility, fertiliser inputs, supplements and timings to ensure pastures are growing optimally, that inputs are in fact matching outputs and mitigation actions or management changes are taken where nutrient loss factors are identified.

The Fertiliser Manufacturers’ Research Association (FMRA) and Dairy NZ have just developed regional distribution graphs for nitrate leaching, as estimated from OVERSEER nutrient budgets undertaken by fertiliser company representatives. The 12 regions are Northland, Waikato, Bay of Plenty, Central Plateau, East Coast, Taranaki, Manawatu, Nelson, Canterbury, West Coast, Otago and Southland. This means, for example, a farmer in Waikato can benchmark against others in that region. These farmers can then work with their co-operative’s account manager for rounded advice on fertiliser inputs and mitigation strategies to minimise leaching risks.

International buyers of NZ’s farm products are increasingly putting pressure on suppliers to meet quality assurance and environmental footprint standards for their own consumers, while at home, Regional Councils are addressing the issues around surface and groundwater quality with respect to nitrate leaching in their Regional Plans, all of which will require action from farmers on reducing N loss. Luckily, there are mitigations like eco-n that are ready today.

ENDS

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