If you’ve decided to look at whether or not you can reduce your rates of N application to a given crop (‘what’) in order to increase profit (‘why’), then the logical treatments are the current rate of N fertiliser and a lower rate of N fertiliser.

Head-to-head trials like this are good because you get a simple A-B, old-new comparison that you can put into action.

It’s important that the rates of fertiliser application differ enough to have a readily identifiable practical or financial effect. A good rule of thumb is to use rates that differ by at least 20%. Any less, and you will probably have trouble picking up the difference.

Because it’s a head-to-head comparison of rate of nitrogen application, you’ll need to try to keep everything else the same.

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What type of treatments should you apply?

We strongly recommend simple head-to-head trials that compare something old with something new – 2 treatments is usually plenty

Armed with your simple statement of goals and objectives, selecting the right treatments shouldn’t be difficult.

In most cases you will be comparing an existing practice or technique with a simple alternative, so you’ll need only two treatments. Until you become really familiar with running experiments it’s probably best to stick with this type of trial.

Maybe you decided that you’d compare the gross margin from “normal” and “reduced” fertiliser rates (objective) to see whether it increased gross margin (goal). Clearly, this suggests that our treatments will be the “normal” rate and a “lower-than-normal” rate.

Head-to-head comparisons of this sort are likely to be the types of trials that you perform most often – you know what you currently do, and want to see whether a simple alternative is any better. The key to success in head-to-head trials is to change only one part of each treatment and nothing else.

If your treatments are normal and lower rates, then the only difference between your trial plots should be the rate. You should apply fertiliser on the same day, ideally with the same equipment, using the same variety in the same paddock, using the same population and herbicide. If you are only changing nitrogen rates, the other nutrients (P, K, S etc.) must be the same.

If you’ve heard that higher populations need more fertiliser, or compete better with weeds, don’t be tempted to give the higher population more fertiliser or less herbicide than the normal population. If you do, you won’t be able to tell whether treatment differences were caused by population, fertiliser or herbicide. You won’t have achieved your simple objective and, by generating a false impression of the effects of population, you could be worse off than if you’d not done a trial at all.

Similarly, if you’re comparing broadcast and incorporated fertiliser with that applied down the spout, use the same rate and type of fertiliser and keep everything else the same. Don’t be tempted to apply more fertiliser to the broadcast treatment to help the seedlings off to a good start. Once you add in “extras” you lose the ability to fulfil your objective.

In a head-to-head comparison you should take changes one step at a time This doesn’t always seem to fit best with a management change that will require more than one adjustment in your system, but it’s still often the best way to go.

End of section critical decision point

Can you put together a set of instructions that outlines how many treatments there will be, how much of each treatment there will be, and how and when each treatment will be applied? This is important if you are to get the best from the next section – “Getting the measurements sorted out”.