The latest DairyNZ Economic Farm Survey (2012/13) shows the three big items of discretionary expenditure on the average dairy farm are:
- feed (made, cropped or purchased) (21% of the total farm working expenses),
- wages (15%) and,
- fertilisers including N (about 14%)
Few opportunities exist to reduce wages, so when farm income is tight, what can be done about feed and fertiliser costs, noting that they are interrelated?
Clover-based pasture costs about 5-10 cents/kg DM. It is the cheapest feed, cheaper than N-fed grass, crops and supplements.
Therefore, to minimise input costs, attention should be directed to maximising pasture production.
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 7-10, and for sulphur (S, either sulphate S or organic S) the range is 10-12. These ranges apply to all soil groups. For phosphorus (P) the optimal range for high-producing dairy farms (1000kg MS/ ha) depends on the soil group: 35-40 Olsen units for sedimentary and volcanic soils and 40-45 for pumice and peats. Assuming the P, K and S 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 may be required are lime and perhaps molybdenum (Mo). Soil pH levels should be 5.8-6.0, except for peat soils (about pH 5.5). There is no soil test for Mo and so to
check soil Mo levels, clover-only samples are required. The Mo concentration should be > 0.1 ppm in the clover dry matter.
What options are available to reduce fertiliser costs?
- If current soil nutrient levels are all above the optimal ranges then fertiliser can be withheld without losing any pasture production.
- If Olsen P levels are within the optimal range then fertiliser P can be withheld for a year. This is because P does not leach - it ‘stays put’ in the soil and the Olsen P level will only decrease slowly (1-2 units per year) without any practical negative effect on pasture production.
- The nutrients K and S are mobile (they can leach). Withholding K and S inputs is risky because the soil nutrient levels, and hence pasture production, can decline rapidly.
- Pastures can only grow as fast as the most limiting nutrient. Therefore, targeting the most limiting nutrient will give the biggest bang for the fertiliser buck. For example if the P and S levels are adequate but the soil K levels are deficient, redirect the fertiliser dollar to correcting the soil K deficiency.
- Use the cheapest type of fertiliser to deliver the required nutrients. Essentially stick to the generic products (super, potash, urea) rather than the branded products.
- Determine the soil fertility on the various blocks on the farm (areas of similar slope, soil group, land use, history, productivity). Do not apply fertiliser to those blocks that are above the optimal nutrient levels (this may apply to the effluent block). Reduce the inputs on those areas that are less productive (e.g. steep hillsides).
- Lime is not a source of nutrients and it is not a substitute for fertiliser nutrients. If the soil pH is within the optimal range (5.8-6.0) or above, no lime is required for several years. Note that pasture responses to lime are small (0-5%) if the soil pH is in the range 5.5 to 5.8. By contrast, correcting nutrient limitations can increase pasture production by 10-30% depending on the severity of the deficiency. Liming is not a high priority.
- Review the fertiliser N policy. On clover-based pasture, nitrogen use is optimised (i.e. maximum kg DM grown per kg N applied) by using fertiliser N as a tactical input (about 25kg N/ha/application) in late winter/early spring and in late autumn, to drive out-of-season ryegrass production and hence broaden the seasonal pasture production profile.
- Note that clover is a better feed for ruminants than grasses (more kg MS/kg DM consumed) and overuse of fertiliser N can decrease pasture clover content (as a rule of thumb 3kg of clover N is lost for every 10kg fertiliser N applied).
To implement most of the options above requires good knowledge of the soil fertility of the farm. So in the first instance, ensure that you have a good soil fertility monitoring
programme in place 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 on that paddock at the same time each year. Clover-only samples should be collected and analyzed initially to check on clover Mo levels.