Workshops helping farmers make the most effective use of their fertiliser budget, stressed the importance of continuing to make sound fertiliser decisions in economically challenging times.
The Make Your Fertiliser Count workshops, which were a pilot collaboration between Beef + Lamb New Zealand and Ballance Agri-Nutrients, have drawn good numbers of farmers eager to find out about how to make their investment in fertiliser stretch further.
One of the most important messages delivered in the workshop was that where necessary, it was better to strategically cut back fertiliser applications than stop them all together. This protects production to a degree and allows for a faster recovery.
A trial on Ballantrae Research Farm showed that withholding fertiliser can result in a 5% per year drop in production with a potential yield gap of 4.5 tonnes DM/ha compared to where Phosphate (P) was maintained.
More recent modeling based on a typical hill country sheep and beef farm showed that withholding fertiliser applications for two years can result in a net long-term loss of $194/ha. However, applying a half-rate of Phosphate while maintaining adequate Sulphur (S) was shown to reduce this loss by 75%.
Using fertiliser placement technologies to exclude stock camps, gullies, ridges, fence lines and exclusion zones can result in 18% less product applied, which helps stretch the fertiliser budget further.
Fertiliser 101
Fertiliser drives pasture growth and vigour. It is important for legumes, sward quality and composition as well as widening the pasture growth curve. Good fertility enables pastures to start producing earlier in spring and grow for longer over summer.
Investment is P and S is an investment in the long-term productivity of the farm.
South Island soils are predominantly sedimentary while North Island soils also include pumice and ash. On sheep and beef farms, the most limiting nutrients for pastures are usually P and S, sometimes potassium (K) and molybdenum (Mo) - which are particularly important for clover production – and always nitrogen (N).
While lime isn’t a nutrient, it is important as it impacts pH, which in turn affects the availability of nutrients.
NZ has a long history of fertiliser and pasture production trials, with one long-term fertiliser trial site dating back to 1946. The accumulated scientific research is published by the NZ Fertilisier Association and provides evidence-based recommendations for farmers.
A robust soil testing programme measures trends over time and should use testing methods calibrated to NZ soils. Typical soil tests for macronutrients include Olsen P, Quick Test K, Sulphate Sulphur and Organic Sulphur. Micronutrients, including Mo, are best measured in herbage.
The optimum Olsen P on ash and sedimentary soils is between 20-30, while on peat and pumice soils it is 35–45.
Target ranges for K are 5–8 on sedimentary soils, 7–10 on ash and pumice soils and 5–7 in peat soils. For S, the target range on all soils is 10–12 and for organic S, the range is 15-20.
While these ranges represent the agronomic optimum, economic optimum levels are where farmers generate the greatest return on their fertiliser investment. This can be lower than the agronomic optimum.
If nutrients leaving the farm are not replaced, this can lead to a decline in soil fertility. For example, maintaining soil P levels typically requires approximately 1.8 kg P/ha per stock unit, so a 10 stock-unit farm will need 18 kg P (200 kg Super Phosphate). However, this can vary depending on the level of subdivision and farm policies. This is why it is important to monitor trends over time.
Nitrogen – a cheap source of feed
Nitrogen (N) is a growth multiplier, but the rate of pasture response to N will depend on soil temperature and moisture.
Responses will be smaller but longer when soil temperatures are lower, but larger and shorter duration in spring. When pasture is growing fast (50–70kg DM/ha/day), a response of 15kg DM: 1kg/N is expected. It takes five to six weeks for a full response to occur. Higher nitrogen responses are typical on hill country where legumes are absent and soil N is low.
N is still one of the cheapest forms of tactical feed to protect animal production. For example:
- $852t/urea
- $2.43/kg N applied
- $73/ha applied cost (65kg/ha)
- At a 15: 1 pasture response rate, the resulting feed costs 16ckg DM.
For best returns, consider when the feed is required, rather than when it is cheapest. Applying N in late spring will grow more grass for the same spend but may contribute to an unwanted surplus. In contrast, N applied earlier in the season to feed twinning ewes in early lactation can add 2kg of extra weight per lamb at weaning. This helps maximise the weaning draft and gives ewes the opportunity to wean in good body condition.
Strategic nutrient management
Taking a strategic approach to fertiliser applications can pay dividends. A good starting point is to separate the farm into management units or blocks of different economic efficiency.
Some parts of the farm will be intrinsically more productive, or more strategically important to the farm system, and therefore should be focus for nutrients.
For example, crops, new pastures, hay and silage paddocks typically rank highest.
Flat and easier blocks will grow approximately twice the quantity of drymatter than what is grown on steep land at the same Olsen P.
This means P is more cost-effective when applied to easy country compared to steeper country.
Once blocks have been prioritised, the next step is to assess the fertility as a percentage of maximum yield or against the economic optimum. This is where a robust soil monitoring programme, using calibrated soil tests for those nutrients which are typically limiting, can be invaluable.
The results can help identify the areas of greatest return, or areas above optimum fertility where the fertiliser spend can be reallocated.
Driving clover production
The majority of pastoral fertiliser recommendations are focused on driving clover production which, due to its ability to fix N, drives ryegrass production.
Deficiencies in K and Mo can impact clover production.
A three-year trial near Manapouri showed that where K deficiencies were detected in plant tissue analysis, clover responded to applications of K, producing an average 25 % more DM than the clover in the untreated plots.
In the South Island, alluvial soils and soils derived from greywacke are vulnerable to Mo deficiencies.
Herbage analysis of clover is a more reliable than soil testing for predicting Mo requirements.
When clover Mo is less than 0.1ppm and N less than 4.5% of pasture, then the clover will respond to Mo. The recommended application is 20g Mo/ha every four to five years.
At a trial near Riversdale, pasture yield increased by 14% over one and half years in response to Mo and there was a 25% increase in clover production.
Prioritising sulphur
Sulphur is the cheapest nutrient and shouldn’t be a limiting factor. As Sulphate-S is a very mobile nutrient, annual applications are typically required. On sedimentary soils, 30–40 kg S/ha/ year is required to prevent a deficiency occurring.
For more information about fertiliser go to B+LNZ’s Knowledge Hub .