Spring phosphorus essential to set up grass growth for the season

For the first installment of the Soil Fertility Series in association with Grassland Agro, AgriLand met Denis Bushe who farms just outside Avoca in Co. Wicklow.

Denis milks 100 spring-calving cows with a mix of Holstein, British Friesian, and Montbeliarde genetics in the herd. Two years ago, he decided to start using Fleckvieh straws and the first heifers, which are on the point of calving, will enter the milking herd this spring.

On the day of AgriLand’s visit in early February, the cows were out grazing. The milking platform is leased and in order to increase the amount of grass grown, Denis has invested in reseeding and soil fertility.

William Keane, a Grassland Agro agronomist in the Co. Wicklow and North Wexford area, has been working together with Denis on the fertiliser plan for the farm for the past three years.

Also Read: Sustainability: Developing a bespoke fertiliser plan to suit your farm

“The plan gets the best use out of fertiliser for my farm to grow the most grass. The PHYSALG 27 is helping to build my P [phosphorus] and because it’s a straight fertiliser I can hit the paddocks at different fertiliser rates based on William’s plan, without complicating the programme,” Denis explained.

Denis wants to maximise grass in the diet and believes that this is crucial to the profitability of his system.

I want a good cow with milk and a good calf. I want to look after my cows and feed them well but make the most out of grass as part of the system.

Spring grass has benefits for the sward, the cow, the farmer and the environment

1. The sward

One of the biggest advantages is for the grass sward. Over the winter, the grass plant goes through a physiological process known as senescence (natural dying off of old leaves).

Senescence is the process where the grass plant enters dormancy due to cold weather. The first round of grazing is essential to regenerate the sward from dormancy.

Removing dead material and setting the residual for the year is critical for a successful grazing season. The life cycle of the main perennial rye grass (PRG) tiller is one year and the PRG plant will only tiller in spring or autumn.

Because we build covers in the autumn to carry over to spring there will be some heavy covers on the farm. The key is to graze these paddocks to allow light into the base of the sward which will promote tillering.

2. The cow

The cow will benefit from the inclusion of fresh grass in the diet, which has higher quality and intake characteristics than ensiled grass.

Cows can often be stiff from cubicles and concrete over the winter housing period and the return to the field can help to reduce stress on animals.

In the first round, it is essential to condition the cow to grazing to the residual for the whole year.

3. The farmer

The advantages for the farmer are that they will benefit from an increase in milk production from the inclusion of grass in the diet.

Teagasc estimates a value of €2.70/day for each extra day at grass in spring. There is also a labour reduction which is included in this figure.

4. The Environment

The environment will also benefit from cows at grass. The land spreading and storage of animal manures is an area which significantly contributes to ammonia generated by livestock. Reducing this has a positive impact on Irish emissions.

Phosphorus

P is very immobile in the soil, and soil temperature has a big impact on the availability of phosphate from the soil reserves.

P plays an important role in the plant as it contributes to energy provision, root development, root stimulation and tillering.

When we look at these functions we must remember that lower soil temperatures have an impact on P availability and so spring is the optimum time for P application.

Slurry or FYM are good sources of organic P. However, as the P is in organic form it is not immediately available for plant uptake.

While P from slurry and FYM is valuable and useful for maintaining and building soil P levels, it can be limited in providing immediately available P for early season growth.

Slurry applied to grazing ground in spring may not be ideal where slurry would be better targeted towards areas cut for silage to balance the high off-takes of potassium (K) in silage crops.

Many farmers will be familiar with the practice of applying early nitrogen (N), but if we can stimulate the root system to be more active it will increase N use efficiency while increasing spring growth.

There are many positives to spring grazing, but it is a huge challenge and there is often a reluctance to turn cows out due to the potential to damage land.

Having an early P application will also help overcome any damage that is caused, as P will help to tiller out where poaching may have occurred and aid the recovery of the sward.

The challenges of phosphorus

P is a complex nutrient and can be fixed in the soil. Unlike N, it is unlikely that P will be lost due to leaching to any significant extent.

At low pH, P can be fixed by aluminium (AI) and iron (Fe), and at high soil pH P can be fixed by calcium (Ca) in the soil.

This is a problem on every farm in the country, but one that is an even harder task in most mineral soils, including those common in counties Wicklow and Wexford, where elevated levels of both Fe and AI can be found in the soil.

Due to the tendency of soils to fix P, it is a complex issue when attempting to build soil P indexes and can be a slow process. Correcting soil pH is a crucial step for improving soil P levels and it is advisable to investigate different P solutions which may be more efficient.

Back to the farm

Calving is going well with just over 40 cows calved. There is a high emphasis on animal welfare on the farm with every calf (bull or heifer) being placed in a calf jacket. The herd is high-producing and the spring diet includes maize silage, beet and 28% balancer.

The cows are being well fed to prevent ketosis, but the inclusion of spring grass in the diet is crucial for the system. Denis is aiming to set the cows and the grass up well for the year.

The autumn soil sampling was done by Grassland Agro agronomist William Keane, who then developed a fertiliser plan with Denis.

If you would like Grassland Agro to provide you with a free fertiliser plan, simply email: [email protected] or click here

The first round of N is urea at a rate of 23 units/ac. The plan is to go with a straight protected P (Physalg 27) as this can be varied based on soil samples and is protected from fixation in the soil. This is a decision to try and increase N use efficiency of spring N as well as promoting tillering.