Mind your Ps and Ks

Following the successful launch of the ‘Online P and K calculator’ in 2013, the Fertilizer Association of Ireland has launched a Smart Phone App version of this simple and user-friendly P and K calculator for grassland and tillage crops.

The calculator is designed to calculate guideline P and K and fertilizer advice for a range of grassland, forage, and tillage crops from simple inputs that can be entered based on specific field information.

The App is freely available to download, and will provide a P and K recommendation for a grass or tillage crop in seconds.

The calculator takes account of a number of factors such as farm system, stocking rate, crop yields, soil test results and organic manure usage, to give simple bottom-line estimation of fertilizer P and K requirements.

It also includes useful field notes on soil test results and fertility levels, organic manures, lime, sulphur and magnesium.

How to use the Fertilizer Calculator

• Click on the link to ‘Fertilizer Calculator’ on the Fertiliser Association of Ireland’s website here

• Select crop category from the list of options (for example dairy grazing, cereals and so on)

• Enter details on soil P and K index, stocking rates, concentrate feed usage, yields, and organic manures by selecting from the lists provided

• Click submit to see the breakdown of the P and K requirements for maintenance, soil buildup, P and K applied in organic manure, and chemical P and K required.

• Note that P fertiliser rates may need to be adjusted based on Nitrates limits on your farm.

• Repeat steps 2-5 to calculate and P and K requirement for a different crop or grassland scenario.

Note 1 – To calculate stocking rate as kg/ha Org N, allow 85 kg of Org N per for every 1 LU/ha

Note 2 – To calculate concentrate feed used in t/ha, divide the total concentrate feed used on the farm (t) by the total grassland area (ha)

Note 3 – For crop yield, use DM yield for silage crops, and fresh yield for cereals, oilseed, legume and root crops

Note 4 – 1000 gallons per acre of slurry applied is equal to 11 t/ha. 1 t/acre of solid manure is equal to 2.5 t/ha

Note 5 – Multiply kg/ha * 0.8 to convert to units/acre

Fertiliser spreading on grassland. Photo O’Gorman Photography.