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The following are some soil fertility basics.
Lime – what is the target? Optimum soil pH is between 6.2 and 6.5. Make sure you have lime right first, then top up with fertilizer after that. There is new research to suggest that lime and phosphorus availability are linked, so remember lime determines the availability of nutrients in different soils.
Get at least 2t/ac of lime applied at reseeding and work it into the top 2in. You want it where the seed is, not 12in below.
Lime – how much and how often? It will not be uncommon to need to apply up to 2t/ac every four or five years just to replace what leaves in milk/beef and what is leached.
Granulated lime – waste of money? Essentially, it is the same material as ground limestone but is ground finer and you can spread with your own spinner. It will work out five times more expensive than ground limestone.
Reseeding and surface seeding – any case then for bag lime? Not really. You’ll have to spread a lot of bags, and ground limestone spread on the surface before sowing will be at a fraction of the cost.
Looking at my soil test results, what pH is the right one, SMP pH or water-based pH? The target of over 6.3 refers to water-based pH. Heavier soils will take more lime to neutralise pH.
Reseeding on low pH – how much and when? Option 1: If ploughing, spread lime after ploughing and till it in on top. Option 2: If direct drilling, spray off, lime and then direct drill. If soils have a very low index and a very low pH, for example down around 5pH and P Index 1, then you need to be spreading 3t of lime per acre and three to five bags of 10:10:20.
What is the value of slurry? If using slurry to supply P and K, don’t overestimate how much P and K is in slurry. The rule of thumb is 1,000 gallons of slurry contains roughly the equivalent nutrients as a bag of 0:7:30. However, if animals are eating silage made from ground that is low in P and K, the slurry is also going to be low in P and K. Remember, over 50% of the soil samples analysed are from paddocks in index 1 and 2.
This means that the relative value of 1,000 gallons of slurry is now over €20/1,000 gallons, or €50 for a load in a 2,500 gallon tank. You might need to reassess the cost of transporting slurry to outside farms as the relative value has increased, but remember the price of diesel has also probably doubled.
Following reseeding, what should be my fertilizer overall plan rule of thumb? Rule of thumb for grazing – You need 20 units of P and 40 units of K just to replace what nutrient leaves the field. This could be applied as a bag of 10:10:20 in Feb/Mar and four bags of Pasture Sward across summer.
Rule of thumb for silage – For silage crops, you need at least three bags of 0:7:30 for first cut and a bag and a half of 0:7:30 for second cut. Some of this P and K requirement can be replaced with 3,000 gallons of slurry if that is possible. Aim for 100 units of nitrogen for first cut.
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