Hay and Silage Paddock Fertiliser.

Hay and Silage Paddock Fertiliser.

7th December 2010
Peter Burton

We receive calls and emails from customers asking what they should apply to hay and silage paddocks after harvesting.  There are a number of factors to consider before reaching an answer.
 
The potassium content of pasture is typically around 4%, with phosphorus around 0.4% or one tenth that of potassium.  Potassium is the element removed in the greatest quantity and therefore the nutrient most commonly replaced.
 
Depending on the weight of the crop somewhere between 50kg and 80kg of potassium per hectare may be removed. 
 
If this factor alone is considered then the cost of replacing at current pricing for the two most commonly used potassium fertilisers are as follows.
 
                                                50kg                            80kg
Muriate of Potash (KCl)            $97                              $155
 
Potassium Sulphate                       $130                            $208   
 
These figures do not include GST nor do they include the cost of cartage and spreading.  Potassium sulphate although more expensive contains sulphur and on low Anion Storage soils sulphur has a value.
 
The usual reaction by most farmers to these figures is to do nothing and hope that all is well and that decision may have merit.
 
Many soils have quite large natural reserves of potassium and in the warm moist climate of particularly the Waikato and Bay of Plenty natural weathering is sufficient to rapidly replace significant quantities of removed potassium.  How much depends in part on natural reserves and a Reserve Potassium soil test will help provide that information.
 
If the area from which hay and/or silage is removed is also the area on which it is fed out, most of the removed potassium will eventually be returned although the distribution will be somewhat uneven.
 
Another factor affecting potassium availability is the speed at which nutrient is actually cycling in the soil.  Where nutrient cycling is rapid high levels of pasture production can be achieved with relatively small amounts of plant available nutrient.
 
The two factors that most affect the rate of nutrient cycling are physical soil structures and biological activity, the same factors directly influenced by DoloZest and CalciZest made by Eco-Logic Soil Improvement.
 
The application of CalciZest (including boron) at 400kg/ha costs $71.20+GST/ha ex Taupo or Te Teko stores and helps ensure that clover production over summer is maximised.
 
There are valuable visual checks that can be made on farm.  If lack of plant available potassium is limiting growth then the size of clover leaf around urine patches will be significantly larger than those in other areas.
 
Ideally cover leaf size is thumbnail size or larger.  If leaves are this size close to urine patches but less than half that size elsewhere digging holes and checking for root penetration is helpful.  In well structured soils there will be significant root development to at least 25cm and roots in an ideal situation can be found deeper than 0.5m.  With these pieces of information and a recent soil test, decision making becomes easier.