Over the past few weeks, the focus on this page has been slurry.
We’ve detailed how to test slurry, how to translate the results into units per 1,000 gallons, shown some of the results from the Footprint Farmers’ samples, placed a monetary value on that slurry and the last thing left to do is to decide where to target this slurry.
The first thing some will say is that slurry needs to be agitated to be sampled and tested.
This was done but then slurry was spread before the results came back. This happened with help from certain assumptions.
Slurry from animals being fed a substantial amount of compound feed will most likely have a higher phosphorus (P) content than other slurry.
Going on cross compliance guidelines, 5kg of P is present for every 1t of meal fed.
Slurry from animals on a mainly grass silage diet is likely to have a higher potassium (K) content than other slurry. This should be targeted at lower K soils and the slurry high in P should be targeted at the lower P soils.
However, we should never assume slurry nutrient content so testing is a must. It can be a very valuable tool, as we saw huge variability in the slurry samples shown last week.
These results showed many samples with lower or higher nutrient content than had been expected.
With fertiliser prices being extremely high this season, it makes little financial sense to try to build soil nutrient indices using artificial fertiliser.
However, this is also not a time to neglect P and K levels in our soils as this could work out to be much more expensive in the long run. It is much easier to maintain soil P and K indices than to build them. So this year may need to be about feeding the crop.
Looking at the tables
The tables below will take you through how the average slurry sample from the Footprint Farms can be used in some different situations. Tables 1 and 2 show the N, P and K requirements for a 5t/ha crop of grass silage and a 6.5t/ha crop of spring barley, respectively.
The Index 3 level shows the N, P and K needed to replace offtakes from the crop. Table 3 shows how much N, P and K is applied at different rates of slurry, while tables 4, 5 and 6 show the balance of N, P and K needed following an application of slurry.
It should be noted that at Index 4 for P and K, no additional P and K is needed and zero application will help to bring soils back to the optimum of Index 3. However, regular testing is needed in this case to ensure that indices do not fall too far.
Farmers should also take account of soil type and soil pH. Some soils can lock up P or K. For this reason, where a soil has a P index of 4 and pH of over 7, 20kg P/ha (16 units/ac) is allowed on a crop of spring barley.