Using nitrogen for profit

Thanks to agriculture’s importance to the New Zealand economy, and the reasonably high level of attention focused on the industry as a result of the increasing environmental concerns of regulatory bodies (and the general public), there is an awful lot of opinion floating around the media. A host of commentators – informed or just interested – offer their suggestions on various farm management options. Nitrogen fertilisers, palm kernel extract, dairy shed effluent – all incite comment from a range of parties, each approaching the issue from their own perspective. For the individual farmer, this mass of information can leave them asking ‘What should I do to boost production while also minimising any environmental impact?’ The answer is simple, ‘it depends.’

The reason ‘it depends’ is because of the diversity of conditions that farmers have to deal with. Soil types, climatic conditions, stock type and number, pasture composition, topography – all of these factors and more influence the way in which the farm unit responds to various management practices.

Using fertiliser nitrogen
Fertiliser nitrogen has been held responsible for much of the good and bad in New Zealand farming. On one hand, it can boost pasture growth and thus enable greater productivity per land unit. On the other, it is said to reduce clover growth, and cause nitrate leaching. Neither of these outcomes – good or bad – is a given. It all depends on the way fertiliser nitrogen is used. If we consider the dairy industry, the ultimate goal of using fertiliser nitrogen is to increase the production of milksolids per hectare. The basis of this is not just the quantity of feed grown, but also the quality. A poor-performing pasture treated with nitrogen will still be a poor-performing pasture – there will just be a bit more of it. To overcome the problem, other factors need to be considered, for example,  drainage, pasture species composition, and soil fertility. Until the factor(s) that limit pasture  performance are identified and corrected, using fertiliser nitrogen will not be an effective strategy for improving profitability.

Assuming you have high-performing, top-quality pasture yielding good metabolisable energy (ME) levels, then the next factor that could affect the profitability of nitrogen use is how well that pasture is utilised. If stocking rates and rotation mean that pasture is being fully utilised and cows are not hungry, then what will happen to the additional feed grown as a result of fertiliser nitrogen? Unless it is used in a constructive way to produce milk, it will be wasted, along with the money spent on buying and spreading the fertiliser nitrogen. When it is not possible to increase stocking rates or alter the rotation effectively, shutting up paddocks for silage or hay is a commonly used strategy for taking advantage of additional growth. The benefit of doing this is that you have less need to buy in feed later in the season, and this in turn will boost your profitability. Failure to use the available feed in a paddock and leave high grazing residuals, not only wastes money, it also increases the risk of accumulating dead or decaying plant material in the pasture, further depressing pasture quality.

Clover nitrogen or fertiliser nitrogen
What of the claim that using fertiliser nitrogen depresses clover growth? To a certain extent this is true, but it is important to look at the whole story, not just a small, solitary chapter. Studies commissioned by Ballance and carried out by the Southern Plant and Animal Research unit showed that using fertiliser nitrogen on spring-sown pastures did affect clover growth – but only initially. Pasture that received post-grazing fertiliser nitrogen between January and April showed a significant reduction in the number of clover nodes and stolon length in May, but by November, when the pastures were around 12 months old, there was no significant difference between the clover in the treated and untreated pasture. On the other hand, those pastures that had received nitrogen had significantly more ryegrass tillers at 12 months. Overall, it appears that new pasture does benefit from the judicious use of nitrogen fertiliser, and that there is no lasting effect on clover.

The key, of course, is to keep nitrogen applications light. In the work cited above, the greater the amount of nitrogen applied, the fewer clover nodes present and the shorter the stolon length. Least mpact came from a single post-grazing application of urea at a rate of 25 kg N/ha (approximately 50 kg n-rich urea/ha). Ultimately, you want to make the most of clover’s ability to harvest nitrogen for free, but to balance that against getting the most economically attainable feed per unit of land.

Fertiliser nitrogen or bought-in feed
Sometimes, using nitrogen to boost pasture growth is not the best strategy. If soil temperatures are too low to support grass growth, then no amount of fertiliser nitrogen will assist. Feed deficits will need to be met through supplementary feed, either purchased or grown on farm. While growing supplementary feed on farm is nearly always cheaper per kg DM than buying in feed, in some instances it might not be the most economical choice for your farm. For example, if land needs to be sacrificed to grow silage or other feed, and that sacrifice reduces milksolids production, then overall it may be better to buy in feed. It is important to analyse the numbers carefully and come up with a strategy that works for your farm, rather than simply adopting a one-size-fits-all approach.