Clover-based pasture costs about 4-5c/kg drymatter (DM). It is cheapest feed, cheaper than nitrogen-fed grass, crops and supplements. To minimise input costs therefore, attention should be directed to maximising pasture production.
To optimise pasture production the soil fertility must be optimised.
The fertiliser inputs and optimal soil nutrient ranges required for optimal pasture production of clover-based pastures are well defined. For potassium (K) the optimal range is Quick Test K, 7-10, and for sulphur (S, either sulphate or organic) the range is 10-12. These ranges apply to all soil groups. For phosphorus (P) the optimal range (Olsen P) for high producing dairy farms (1000kg MS/ha) depends on the soil group: 35-40 on sedimentary and volcanic soils and 40-45 for pumice and peats. Assuming the phosphorus, potassium and sulphur soil nutrient tanks are full the annual inputs of nutrients to maintain the optimal levels are about 45-50kg P/ha, 80-100kg K/ha and 30-50kg S/ha.
The other inputs that might be required are lime and perhaps molybdenum (Mo). Soil pH levels should be 5.8-6.0, except for peat soils, which should be about pH 5.5. There is no soil test for molybdenum, so clover-only samples are needed to check soil molybdenum levels. The molybdenum concentration should be >0.1 ppm.
What options are available to reduce fertiliser costs?
If soil nutrient levels are all above optimal ranges, fertiliser can be withheld without losing any pasture production.
If Olsen P levels are within the optimal range fertiliser phosphorus can be withheld for a year. This is because phosphorus doesn’t leach – it stays put in the soil and the Olsen P level will only decrease slowly (1-2 units a year) without any practical negative effect on pasture production.
Potassium and sulphur are mobile – they can leach – and withholding their inputs is risky because soil nutrient levels and hence pasture production can decline rapidly.
Pastures can only grow as fast as the most limiting nutrient, so target the most limiting nutrient. This will give the biggest bang for the fertiliser buck. For example, if the phosphorus and sulphur levels are adequate but the soil potassium levels are deficient, redirect the fertiliser dollar to correcting the potassium deficiency.
Use the cheapest type of fertiliser to deliver the required nutrients. Essentially stick to the generic products, such as super, potash and urea, rather than the branded products.
Determine the soil fertility on the various blocks (areas of similar slope, soil group, land use, history, productivity) on the farm. Do not apply fertiliser to blocks that are above the optimal nutrient levels, such as the effluent block). Reduce the inputs on areas that are less productive, like steep hillsides).
Lime is not a source of nutrients and isn’t a substitute for fertiliser nutrients. If soil pH is in the optimal range (5.8-6.0) or above, no lime is required for several years. Pasture responses to lime are small (0-5%) if the soil pH is in the range 5.5 to 5.8. Correcting nutrient limitations can increase pasture production by 10-30% depending on the severity. Liming isn’t a priority.
Review the fertiliser nitrogen policy. On clover-based pasture, nitrogen use is optimised (ie optimal kg DM/kg N applied) by using fertiliser nitrogen as a tactical input (about 25kg N/ha/ application), applied in the late winter-early spring and in late autumn, to drive out-of-season ryegrass production and hence broaden the seasonal pasture production profile.
Clover is a better feed for ruminants than grasses (more kg MS/kg DM consumed) and overuse of fertiliser nitrogen can decrease pasture clover content. As a rule of thumb, 3kg of clover nitrogen is lost for every 10kg fertiliser nitrogen applied.
To implement most of these options requires a good knowledge about the soil fertility of the farm. Make sure you have in place a good soil fertility monitoring programme for the whole farm. Divide the farm into blocks (areas of similar slope, soil group, land use, history, productivity). Select a representative paddock within each block and collect soil samples annually from the same transect at the same time each year. Clover-only samples should be collected and analysed initially to check on clover Mo levels.
