Dairy farmers in Ireland are being pushed to use the maximum allowable rate of Nitrogen/year but are we achieving the optimum response rate? Could it be used more efficiently? What impact is the use having environmentally and on our soil microbiology? (Graise Consultancy)
I feel there is still huge misconception about the role of nitrogen, the response from chemical N application and the impact of application on the soil’s own ability to fix N from the atmosphere. I need to stipulate at this point that I have no personal interest to see the reduction of N usage on farm, other than a genuine belief that farmers should be achieving greater profitability as well as reduced environmental impact from doing so, luckily the two go hand in hand.
On a recent trip to NZ I got the chance to have a better look at the reduced N trial at Lincoln University Dairy Farm (LUDF) and speak to the farm manager Peter about the impact of the reduced N use. For them, it has meant coming from the use of 300 to 340KgN/Ha/year and growing 21TDM/Ha/year down to using 140-170KgN/Ha/year and growing 18/19TDM/Ha/year.
LUDF’s objective is to maximise profit while embracing a sustainable farm system. Achieving this objective will involve maintaining production per hectare without increasing nitrogen application or purchased feed, target is less than 300KgDM/cow of purchased feed to come from off the milking platform.
There are 560 Jersey cross bred, 500-510KgLW cows milking on a milking platform of 160 hectares with production of 500KgMS/cow+, around 1800KgMS/hectare.
There is a very clear recognition in NZ of N losses through leaching and off-gassing in wet ground conditions or low soil temperatures. First N application of 25KgN/Ha was done in late August/early September to avoid leaching in wet soils (equivalent to late February/early March here) and applied every rotation at the same rate, except through the reproductive stage of the plant where N was increased to 44KgN/Ha for 2 rotations to prevent the ryegrass plant going to seed through that time. Once the ryegrass plant passes the reproductive phase and growth rates are good, it is then possible to skip N application for some rotations.
The first obvious key to reducing chemical N input is clover. At 300KgN/Ha+ there was no clover in the sward but has now been introduced back into pastures, but what surprised me about the trial was how much it relies on tetraploids. The use of tetraploids means they have changed target pre-grazing levels from 2800KgDM/Ha to around 3200KgDM/Ha and the cows are still willingly achieving target residuals as the tetraploids are more palatable than diploids.
Rotation in late spring has gone from 16-21 days out to 20-24 days which means that when N is applied every rotation, it is actually done less often.
I am highly aware of some of the differences between NZ and Ireland/UK that need to be taken into account. Soil temperatures are higher earlier in spring in NZ. There is a higher rate of evapo-transpiration due to higher sunlight hours. Soils are mostly alluvial which means some higher nutrient retention and reserves (K especially) but overall, N response works identically as it does in Ireland and the UK.
The critical thing we need to recognise is that the ability for plants to fix nitrogen is not limited to legumes, there is a diverse and abundant range of nitrogen fixing microbes, archaea and fungi that live in in our soils but it is actually the application of chemical inorganic nitrogen that depletes the microbes and fungi that fix atmospheric N, reducing carbon in our soils and effectively causing an endless circle of inorganic N requirement created by ourselves.
So what should we be doing, what’s the alternative?
One thing we can’t do is cut off chemical N application abruptly, it would be like a heroin addict going cold turkey and have massive impact on pasture growth and profitability.
Improved N use may initially mean no reduction at all but just a more targeted approach so that a higher average response is achieved which means more pasture grown and better economics, as well as being more environmentally responsible.
What we need to do first and foremost is really look at our rates of application at varying times of the year and focus on achieving the most economic response we can, avoiding the marginal use in very early spring that achieves a 5:1 response at best (5KgDM for every KgN applied) and actually has the greatest negative impact environmentally. Higher us of urease protected urea would help reduce volatisation rates.
If we aim to reduce usage by around 20%/year and ensure we focus on ensuring PH is right, use slurry and FYM more effectively and look at multi-species swards, we are more likely to build soil carbon levels, humus and organic matter which creates greater soil health, moisture balance and pasture growth/utilisation and it is more likely to contribute to improved rumen health as discussed in a previous article.
Stick to your spring rotation planner as much as you can do so, N application at low soil temperatures and high soil moisture levels is environmentally irresponsible, shows very low response rates and is an uneconomic addiction.
zdroj : foodandfarmingfutures.co.uk