Planning nutrition for 2016

With much of the Wimmera and Mallee recovering from two very dry years, cash flow is tight and crop planning and budgeting require careful consideration. Fertiliser is one budget line item with the potential for savings, but it is important to keep sufficient flexibility in the system to realise full yield potential if 2016 is to be favorable.

TAKE HOME MESSAGES

• Soil test strategically.
• Where possible, reduce rates of phosphorus (P), sulphur (S), potassium (K) and zinc (Zn) but don’t forgo yield by dropping P rates completely; ideally keep them at 3-5kg/ha.
• Continually review nitrogen management, especially as the season progresses.

THE PROCESS

1. Fit the fertiliser to the budget

Where cash flow is tight, allocate an amount for fertiliser, then work backwards from there to derive suitable fertiliser mixes and rates. The aim is to provide the bare minimum without compromising potential yield.

Specifically:

•  P rates of 3 to 5kg/ha are usually adequate for cereals in soils that are not P deficient. Nil P can be detrimental if the season has reasonable yield potential.
•  Restrict pre-sowing sulphur (S) to areas of deficiency.
• It is low risk to defer zinc (Zn) for a season.
• Only include potassium (K) on responsive soils and after soil testing to check for need.
• Defer copper (Cu) and manganese (Mn) unless strong evidence exists to indicate that application is necessary.
• Use deep soil test results and a range of yield targets to explore nitrogen (N) requirements. Money saved in other areas can be used on N if the season is favorable.

2. Keep soil testing in the budget

Allow for soil testing costs in the budget. Spending between $1000 and $5000 on soil testing can easily be recouped in fertiliser savings. Useful soil measurements are: soil moisture, nitrate, ammonium, Colwell P, and PBI and DGT-P. Tips for turning soil test results into dollar savings are provided in sections on P, S and N.

Check that soil test depths are correct. For most nutrients, 0-10cm is sufficient in most soils in the southern region. Nitrogen (N) and sulphur (S), however, should be sampled to 60cm. This is due to their high mobility within soils.

3. Consider using variable rate applications (VRA)

If you have distinct soil variability (e.g. a dune-swale system) and the capacity to apply fertiliser to specific zones at different rates, 2016 would be a good season to use VRA technology for little additional cost. If, however, you are not set up, then it may be something to consider for the future. Long-time VRA proponents, keep up the good work, apply nutrients only where they need to be.

4. Do the maths on fertiliser blends

Compare costs when considering fertiliser blends and cost per unit of nutrients when budgeting. In most cases it is more economic when logistically possible (ie. three bin box on the seeder), to use two separate products such as urea and mono-ammonium-phosphate (MAP) rather than a blend of 27:12 (or something similar). This allows N and P rates to be further refined according to soil types and requirements (based on soil test and last season’s results).

P FERTILISER

Additional P tests such as PBI and DGT can refine the likelihood of P responsiveness. Phosphorus buffering index (PBI) estimates the soil’s ability to remove P from solution. Soils with a higher PBI are more likely to show P deficiencies, while low PBI presents the opportunity to reduce P inputs. If replacement P programs have been continually used, testing for variable PBI across the paddock could then mean saved fertiliser costs in the form of reduced inputs. Soils with higher levels of calcium, iron and aluminum are more likely to tie up P. The DGT test mimics a plant’s ability to extract P from the soil. It is a useful test to when P deficiency is suspected or when there has been unexplained poor performance despite a reasonable Colwell P level.015 BCG SEASON RESEARCH RESULTS

S FERTILISER

Trial work has proved that it is difficult to achieve S responses. Work carried out by Sean Mason (University of Adelaide) showed that, in the South Australian Mallee, critical soil test levels have been around 2.5-3mg/kg. Critical soil test ranges for a set of WA soils are also shown in Table 1. Canola crops remove the highest amount of S per t/ha (Table 2) compared with wheat, faba beans, barley and lucerne. Prioritise crops with a high S demand (such as canola) and soil test at depth. Then use the cheapest source of S available where levels are below critical thresholds. Sulphur is often a good candidate for VRA as the lighter soils are often most responsive.

Source: BFDC – Anderson et al (2013), prese nted by Sean Mason at a MPCN Lameroo workshop 2015.

Table 2. Crop removal rates of S.

Source: Sean Mason (MPCN Lameroo workshop 2015).

NUTRITION AFTER HAY

Crops cut for hay will have had more nutrients removed from the paddock than if harvested for grain and are logical choices for soil testing.

DEEP N TESTING

Invest in deep N soil tests rather than rely solely on the previous crop history. Nitrogen in the soil is heavily influenced by summer fallow rainfall, and can vary significantly from one paddock to the next.

As nitrogen is highly mobile in the soil profile, a deep soil test is recommended. Soil N differences between paddocks can vary to the tune of 50 to 100kg N/ha, which is considerable dollar difference when extrapolated to paddock scale.

Soil test results are very useful when making N decisions. Sampling that occurs closer to sowing will give a more accurate indication of the crop available N as it takes into account any mineralisation that occurred. However, logistics often dictate that sampling is done in February or March and experience shows that the results are still a very useful guide.

In-crop sampling may provide some useful information, but you will need to factor in what the crop has already taken up and that can be difficult to ascertain.

CALCULATING N SUPPLY

N supply for the entire season is based on starting soil N (from the soil test), in addition to any mineralisation that may occur between sampling and sowing, and then during the spring. Most advisers have methods for accounting for mineralisation that suit their region. Yield Prophet® is a useful tool for determining N mineralisaton. For the Mallee and Wimmera, on medium textured soil, it is usually somewhere between 5 and 40kg/ha N depending on seasonal conditions.

YIELD POTENTIAL AND N DEMAND AND MONITORING SEASONAL OUTLOOKS

Yield potential is what drives N demand: a sensible expectation of your potential yield (t/ha) is critical for N budgeting.

Tools to determine yield potential estimates include gut feel and experience; French and Schultz calculations, and crop modelling with systems such as Yield Prophet®. Starting soil water should be considered when estimating yield potential.

Without knowing seasonal outcomes, setting a range rather than an absolute target yield is suggested. Nitrogen demand and fertiliser requirements can then be calculated for either end of the range which assists with budgeting.

Understanding how to interpret seasonal outlook information and the influence of climate drivers on seasonal outcomes is an important step to estimating likely yield outcomes. Excellent resources are listed in the useful links section below.

N APPLICATION STRATEGY

In high priority N paddocks with low soil N reserves, apply sufficient up-front to ensure the low end yield potential is not compromised. Later applications can be used if necessary.

In low priority N paddocks, with medium to high soil N reserves, defer N applications to preserve cash flow.

Product choice may be a mix of logistics and cost. Check the cost per unit, particularly for topdressing options. Considering the importance of timeliness when topdressing. Availability can also influence product selection decisions.

BCG SEASON RESEARCH RESULTS

MONITOR AND EVALUATING AS THE SEASON PROGRESSES

It is important to monitor the season on a regular basis, and from this monitoring to adjust, modify or alter fertiliser decisions. Figure 1 highlights the things to consider regularly throughout the season.

Questions individuals should be asking each time they are monitoring are summarised in Table 3.

Table 3. Steps to take as the season progresses.

 

There is a time limit as to when nitrogen applications can be made; it is necessary to be aware of crop growth stage. Nitrogen scheduling is the process of delaying any unnecessary nitrogen applications in the hope that the cropping season will end before the next applications is needed. As a general rule in the Mallee, nitrogen (for wheat) should be applied no later than GS32, while in the Southern Wimmera it is GS39-45. Any nitrogen applications made after these growth stages may affect grain protein rather than yield or have no economic benefit.

Figure 1: Monitoring yield potential and nitrogen decision making (Source K Burke).

CONCLUSION

To make better use of fertiliser dollars in 2016, soil test strategically, but still do more than less. Where possible, reduce rates of P, S, K and Zn but do not forgo yield by dropping P rates completely. Ideally keep them at 3-5kg/ha. Nitrogen management should be continually reviewed, especially as the season progresses. Seasonal outlook tools and understanding climate drivers will help to gauge the likely outcome of the season.

 Fertiliser costs represent a large part of the total input costs each year; coming from the 2015 season, it is important to be conscious of the available budget and make every attempt to work within it.

 Profits can be made by planning fertiliser applications strategically.

REFERENCES

Burke K, 2014, GRDC Grains Farm Updates Southern.

USEFUL LINKS

• Soil testing for crop nutrition
• Using deep soil cores for Nitrogen, Potassium & Sulfur
• Phosphorus fact sheet
• The Very Fast Break
• CliMate App
• Bureau of Meteorology
• Guidelines for interpreting soil test results

This paper provides strategies for formulating a lowest cost fertiliser plan without restricting yield potential.