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Dry start highlights the value of potassium placement in Tammin

30 Jun, 2017
It is seasons like this that highlight the importance in maximising the efficiency of any applied nutrients in order to ensure that any dollar spent, is spent the right way.

By Luke Dawson, CSBP Senior Agronomist

There is no getting away from the fact that 2017 has seen much of the Western Australian wheat belt experience the driest start to the season since 2006 or 2002 depending on who you talk to!

It's seasons like this that highlight the importance in maximising the efficiency of any applied nutrients in order to ensure that any dollar spent, is spent the right way. Drier seasons tend to exacerbate nutrient deficiencies, and minor reductions in nutrient use efficiency can result in large losses in return on investment per hectare in a year where every dollar returned counts.

This has never been more evident in CSBP’s long term potassium (K) trial at Thomson’s farm, south of Tammin.

This trial was seeded on the 26 May 2017 into a duplex sand over clay, with minimal moisture in the topsoil and some subsoil moisture at depth. The aim of this trial is to compare different potassium fertiliser strategies on the basis of cost per hectare and effectiveness.

Figure 1 highlights the different K fertiliser strategies practised in the area.

Table 1
Figure 1. Thomson long term K strategies trial – K inputs over 4 years

A visit to this trial on the 20th of June really highlighted the value of K placement compared to K rate. Up until this date only 6mm of rain had been received at the trial site after all of the fertiliser applications had been applied and seeding had finished.

Figure 2
Figure 2. Banded K vs topdressed K

Figure 2 is a comparison between plot four and plot five in the trial. Plot four has received treatment two, which is the grain removal K option, which will serve to supply 13 units of K per year over four years to replicate the amount of K removed by the crop. This treatment will receive 13 units of K as K-Till Extra Plus, drilled at seeding each year.

Plot five has received treatment five, which is the capital K rundown option. This treatment will receive one application of K at 303kg/ha of MOP in the first year and we'll look to see how much of this K is available over the four year period. This treatment received no K drilled at sowing with the MOP top-dressed prior to seeding.

As figure 2 highlights there is a significant visual difference in the two plots. Plot four is much healthier and has started to tiller whilst plot five is still at 2.5 leaf stage with classic K deficiency symptoms of yellowing, and the arrow head shape of leaf chlorosis appearing on the oldest leaves. With only six mm's of rain since application of the MOP, plot five appears to have had no uptake of the freshly applied 150K from topdressing in comparison to plot four, which received only 13 units of K, however the K applied was applied near the seed which has enabled much better uptake of the applied K.

In this situation, applying a small amount of K where that plant can access it appears to be the much better option for the plant. With a potential cost difference of $109/h between the top-dressed K and drilled K it may appear to be the better option for the hip pocket as well.

This trial will be plant tested in early July and the results will be made available.