Early to Mid-Season Chemical and Organic Nutrient Application
By John Brennan – Product Manager at Grassland Agro
Optimum chemical and organic nutrient application on grassland is a critical part of farming. Nutrients, be it from slurry, manure, or chemical fertiliser, are key to maximizing grass growth early in the grass growing season once prohibited periods end and conditions allow. If there is too much of a delay with nutrient application in the first round, the deficit is sometimes made up by feeding fodder and concentrates which incur additional costs on farm. If grass has a little amount of nutrients in front of it, it will respond. First round nutrient application typically involves a straight nitrogen (N) chemical fertiliser, or slurry. For waterlogged soils, it is important to not spread nutrients until they get sufficient drying and soil temperatures are at least 6 °C. Targeting nutrients to dryer parts of the farm is most appropriate at this point.
Organic fertiliser application
Slurry has a very important role on a farm by recycling available nutrients. Even though cattle slurry is a good source of N, phosphorus (P), and potassium (K), it is the N value that is the most important nutrient in slurry for the first round. In terms of how much slurry should be applied this time of year, 1,500 – 2,000 gallons/acre is advisable. If conditions allow, areas of the farm that may be targeted with slurry this time of year could be parts of the farm that were grazed last in 2024 as these would have lower grass covers. Higher application rates of slurry (e.g., 3,000 gallons/acre) is more suited to the middle of the year, or when closing silage ground. It is important to not use up all of your slurry reserves in the first round and save some for silage ground or outside blocks later in the year. Ideally, slurry is targeted towards silage ground and fields that have low indexes for P and K as 75 % of the value of slurry is its supply of P and K. Teagasc state that slurry has enough nutrients to replace what the majority of nutrients that comes off the silage ground.
Chemical fertiliser application
Chemical fertiliser application rates don’t need to be too high this time of year. A reasonable grass growth response can be achieved by spreading on drier fields this time of year. Applying a little amount of straight N chemical fertiliser, typically 25 kg/Ha (20 – 25 units/acre) in fields that do not get slurry will help encourage grass growth. Chemical N spread now will be used by the grass plant over a period of time as soil temperatures and day length increases.
Grass growth generally takes off around the middle of March when soil temperatures increase, land becomes drier, and the days get longer. At this point, we need to have P in the soil as it is the energy source that will escalate grass growth. For the second round of nutrient application, if there is a P allowance, it is good to target low P and K index soils with a compound fertiliser if no slurry was applied in the first round. Any farmer without a fertiliser plan or soils samples will have no chemical P allowance. Fields that didn’t receive slurry already could get 30 – 35 units of a straight N fertiliser per acre in the second round.
It is important to keep a sulphur nitrogen ratio in the sward of about 10:1. The soil has the potential to supply sufficient sulphur early in the season when growth rates are low. However, once we get to March and growth takes off, the N uptake of grass goes up with the demand for sulphur rising. Hence, sulphur will need to be applied in March, especially if fertiliser doesn’t go out until the second half of March. It is important to get sulphur out then and drip feed it in every 2 or 3 rounds until the end of June.
Top tips
Have a nutrient management plan in place
Target slurry to low P and K paddocks at the correct rate
Keep enough slurry for your silage fields
Apply nutrients when the conditions are right
