Rain is the thing on everyone’s minds at this time of the year and especially this year after such a sustained dry period up until the recent rains at the end of May. In the perfect world we would be able to order up 20mm each week with some nice warm days in between to get the crops up and away and growing comfortably all season. However, we need to be realistic, we cannot influence rainfall so why don’t we focus on the things that we can influence? 

A lack of rainfall or below average rainfall doesn’t mean we should necessarily shut the gate and apply no more fertiliser for the year. It means that we need to maximise every single millimetre of rainfall that hits our paddocks, not by reducing nutrition but by ensuring that our crop nutrition is bang on. High rainfall years can be a great leveler meaning that as long as background nutrition is ok then a decent crop can be grown. Dry years are the years where nutrition becomes even more important, and where you can add the most value to your bottom line. 

Water use efficiency (WUE) is a big talking point each year and especially now. What if I told you that increasing your WUE had nothing to do with the colour of your tractor or the width of your air seeder bar but was as simple as getting your nutrition right? Don’t believe me? 

Consider these results from Wongan Hills last year (Table 1):

Table 1- Wongan Hills 2017
• Growing Season Rainfall (GSR)- 195mm
• Summer Rainfall- 140mm.

WUE calculated using the James Hunt method. 

At this time last year, the yield potential tool on the DPRID website was predicting a decile 2 season with a potential yield of 2.3 t/ha. The season ended up finishing below decile 1. 2.3 t/ha with the start we had last year? Happy days you’d lock it in and shut off the Flexi-N tap, no N and we got the predicted yield (Table 1- Trt 6) and got a WUE of 9 kg of grain per mm of effective rainfall. Or would you turn off the tap?

By maintaining our seeding N (Table 1- Trt 7) we got another 0.5t/ha of wheat and made another $99/ha. We not only increased yield but we increased our WUE by 22%, Happy days! It’s a dry season and everyone on Twitter and the radio is down in the dumps about how bad it is, it’s definitely time to turn the tap off? Or is it?

Persisting with our planned N inputs and applying another 50 L/ha at Z22 (Table 1- Trt 8) grew us an additional 0.4 t/ha. We not only maximised yield but we maximised GM/ha at $737 and we maximised our WUE at 12 kg/ha of grain per mm of effective rainfall. We grew 33% more grain from the exact same rainfall just by getting our N right following one of the worst starts on record! 

Don’t believe me yet? Let’s have a look at the results from another trial last year (Table 2):

Table 2- Tammin 2017
• GSR- 243mm
• Summer Rain: 212mm

WUE calculated using the James Hunt method.

The yield potential for a decile 5 finish which is what we eventually achieved was 2.8t/ha. We got there by overcoming  a potassium deficiency.. In this instance K was the driver to increase yield and WUE. With exactly the same rainfall we increased WUE by 50% with the addition of only 13kg/ha of K (Table 2- Trt 2) at seeding time. However, by ramping up our K inputs to 110 kg/ha (Table 2- Trt 4) we maximised yield, gross margin and WUE. Not a bad result from a season where we got 8 and 9mm respectively in May and June.

The trial in Tammin also had moisture probes installed in treatments 1 & 2 to compare the soil moisture readings over the season between no K applied and 13kg/ha of K applied at seeding time.

Figure 1.- Comparisons in soil moisture readings from 10-60cm- August and September 2017 - 13 kg/ha of K v 0 K.


Average daily sensor readings for the 13 K treatment indicated at the end of the season about 15mm less soil water (or more plant water uptake) than the control. Therefore the nil K treatment left more water behind in the 10-60cm soil profile. Soil water (mm) = (volumetric soil water % / 100) * soil depth (mm). Values have been summed up for 0-60cm soil profile.

Not only did the nil K treatment reduce yields and WUE but it also left valuable usable moisture in the ground.                                                                                                       

Now I’m not saying disregard the rainfall or seasonal conditions and apply as much fertiliser as you can. What I am saying is be realistic with seasonal conditions and yield potentials but also don’t let the attitude and moods of the many override the opportunities that you have to make the most of what rain you get and add value to your bottom line. 

Luke Dawson
By Luke Dawson
- Senior Agronomist
Luke was raised on the family farm at Warralakin east of Mukinbudin before completing a degree at the Muresk Institute of Agriculture. 

Luke started with CSBP in 2005 as a trainee Area Manager and has since worked as an Area Manager based in Hyden, Esperance, and Dalwallinu and District Manager for the Central Midlands District, now based in Kwinana as the Senior Agronomist. 

Luke brings a strong nutritional background to the role, as well as a focus adding value through CSBP's services. 

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