Using slurry to grow grass in 2023

Using slurry efficiently in 2023 will be essential in controlling input costs on Irish farms.

Chemical fertiliser prices still continue to stay high and in this piece from this week's Grass 10 newsletter, William Burchill, Teagasc/Dairygold Joint Programme, discusses three key points to maximising the grass grown in 2023.

Apply slurry to silage ground to maximise its phosphorus and potassium value

There is a big temptation to use more slurry on the milking platform in 2023 in order to reduce nitrogen costs on this part of the farm. However, we need to remember that the majority of the value of slurry is from its phosphorus (P) and potassium (K) and thus slurry should be targeted to areas of the farm with the highest demand for P and K i.e. silage ground. When spreading slurry on the milking platform, target paddocks with low P and K indexes first and the lowest grass covers in spring. Trailing shoe and dribble can be using to apply slurry to cover <1,000 kg DM/ha.  It’s also important to plan out which slurry tank on the farmyard will be applied to the grazing ground versus the silage ground and at what rate per acre. Knowing what’s in your slurry will help you determine this.

Know what's in your slurry

Slurry can be tested for it nitrogen (N), P and K content relatively easily and cheaply by a number of labs across the country. In the winter of 2020/21 up to 128 slurry samples from dairy farms within Teagasc/Dairygold Joint Programme discussion groups where tested for its dry matter, nitrogen, phosphorus and potassium contents. The slurry contained 10.7units/1,000gal of N (applied using LESS in spring time), 5.3units/1,000gal of P and 27units/1,000gal of K on average and varied slightly compared to the standard Teagasc values (Table 1). An interesting outcome from the testing was the clear difference in slurry nutrient content depending on which tank the slurry came from. When taking slurry samples, we recommend you to test a number of different tanks in the farmyard for this reason. Slurry form the covered tanks with higher P and K content should be kept for the silage ground, while more watery slurry from open tanks will be sufficient to meet grazing ground P and K maintenance requirements.

Table 1: Slurry test results from dairy farms across the Dairygold catchment

Based on these results, we can also see that using a trailing shoe / dribble bar at a rate of 2,000-2,500gals/acre will deliver 22units/acre of N or the same as our half bag of urea/acre. High application rates of over 2,500 gallons per acre will supply more N than is required in early spring and can result in a lower efficiency of the slurry N. A better ploy is to spread 2,000-2,500gal/acre across a larger area of the farm to reduce your fertiliser N bill. Your slurry test results can also be inputted into Pasturebase Ireland to track N, P and K applied across your farm via slurry.

Apply slurry using dribble bar or trailing shoe at the right time

Moving from spreading with a splash plate to a dribble bar or trailing shoe will give you an extra 3units/1,000g of N from your slurry. While spreading slurry in spring has the potential to improve slurry N values, this is reliant on good grass growing conditions. Given the current value of slurry, we should be asking ourselves if we are reluctant to spread chemical N fertiliser at time points during the spring due to poor growing conditions should we be spreading slurry either if we want to maximise its nutrient value?

This article first appeared in the Grass 10 weekly newsletter. For more on the programme, click here, or subscribe to the weekly newsletter below.