MOP, SOP, SSP, SOA and NPK……. Wow! I have been trying to jot down the number of fertilizer products that might be blended for a spring application. However, I might have inadvertently stumbled across my first attempt at a ‘texting’ novel!

Back to my first idea: questioning the reasons for applying the various major nutrients and considering the amounts of each required to produce good quality fodder.  My first thought is that fertilizer applications are needed to boost plant growth in the 6 weeks or so that the paddock is shut up.

But wait, there’s more!  There is a need to replace the amounts, or at least some of the amounts, of each of the major nutrients removed in the process of fodder conservation. It follows that if each of the areas expected to be treated is, in fact, below optimum levels in Phosphorus, Potassium or Sulphur, then it would be a good opportunity to also add capital amounts to improve fertility in the soil.  So what is needed?

N – Nitrogen. Generally, this is the first nutrient we think of when looking to stimulate DM production. Certainly we know that it is a soluble nutrient, so any movement of water in the soil profile will move the water soluble nitrogen.  Fortunately, in many soils, not all the Nitrogen moves out of the root zone in one rainfall event.   As the soil warms, mineralisation increases and, in the process, Nitrogen is released.  However, if the paddock is or has been low in clovers, or if urine spots are showing in the pasture, then it is most likely that a response to applied Nitrogen is possible.  If clover is around the 20 to 30% mark, then 12 to 15kg N in the blend is often sufficient to get growth started.  The more perennial grass, the more Nitrogen is usually required.

P- Phosphorus. Generally, this the first nutrient we think of when we think ‘fertilizer’. (It’s only the first half of the sentence that is repeated, so read on!) This nutrient is so important that if the amounts removed are not replaced this time, it should be replaced before next growing season.  Each tonne of hay cut from the paddock removes 3 to 4 kg of Phosphorus from the soil, so it is important that this essential nutrient is replaced.  The only exception is when the level of P in the soil has been properly measured and shown to be well above the critical value.

K – Potassium.  Generally, well no, often, this nutrient is not considered, or, at the very least, only considered at fodder conservation time. It is removed from the soil in the largest quantity of each tonne of hay – that is, somewhere between 20 and 30 kg (MOP at 40 to 60 kg)!  If the soils are marginal or lower for this nutrient, more Potassium is best applied when the paddock is shut up.  Often it is not applied at the same rate as the amount removed, because of the cost benefit. However, clovers in particular are quite responsive to K, particularly in situations when the level of Potassium in the soil is low.

S- Sulphur.  Generally, (er……. you didn’t really think my use of the English language is so limited that I could not think of another start??)  Generally, this nutrient is not given much consideration at this time of the year.  That is not to say it is not essential – it is!  Sulphur is quite soluble in its sulphate form.  However, paddocks with good organic matter levels usually have sufficient Sulphur.

So, the rain has fallen and the soil profile is full!  It is worth topping up the nutrient pool with a good measured, well-considered dose of NPKS.  These four essential nutrients will be most valuable if applied some 6 weeks prior to cutting.  However, even at 4 weeks, a fertilizer application is still worth the effort.  It will not be wasted!  What is not used this season, will be available in the soil to give the pasture a boost and allow it to get away early next season.

These are just a few thoughts of my fertile imagination!   Food for thought for you, too?

Blog by Peter Flavel