There’s not much point in doing a trial if you’re not going to measure it properly.

Changes in fertiliser rates can result in a number of important changes in crop growth and, in extreme circumstances, development. Plan when certain measurements are going to be made and to write them into your diary. To get them done without a fuss, it’s also important to have planned how you’re going to do them.

The first step is to have a basic trial measurement plan. Times of measurement are broken down into 4 stages to give basic time frames. The specifics will vary from crop to crop and season to season – you probably have a good idea of what happens when from your crop scouting programme.

As a rule, don’t trust your eyes! When it’s possible to take objective measurements with a tape measure or a set of scales, use them. Yield, biomass and quality must be measured using quantifiable and objective techniques. These are outlined for a variety of crops in Tips for Crops.

NEVER be tempted to assess yield or biomass using a visual assessment. It simply doesn’t work.

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Having established goals and objectives, and the treatments required to accomplish them, the next step is to plan the measurements that will be required.

Your guiding principle should be “what do I need to know to fulfil my objective?”

This probably seems like an overly simple question, but to really get the most from your trials you’ll probably want to think about measuring more than just the obvious variables (such as yield or cost) that relate directly to your treatments.

This is largely because cropping systems respond to factors such as climate, soil type and conditions, and management factors such as paddock history and timeliness of operation.

So there is a whole raft of factors that will influence the results of your trial, quite apart from the treatments that you apply. For this reason, and to enable you to interpret the applicability of your trial results to different circumstances (eg. paddocks, seasons or crop types), you’ll need to know what you’re dealing with. The only option here is measurement.

When should measurements be made?

Measurements are probably going to be required at several stages of a trial, not just at the final harvest.

A simple but effective aid to planning measurements is to think of them as occurring at 4 times – before, during, at the end, and after the trial. This can help to avoid missing crucial measurements and, if you attach estimated dates to each, will help to identify whether you’re going to hit trouble at pinch times. It’s a good idea to mark estimated measuring times in your diary so that you don’t miss important ones.

Use Data sheets to help you plan and make measurements at each of the 4 stages of your trial.

‘Before’ measurements can be done when you’re selecting and establishing your trial site, and might typically include:

• General notes on the trial site (crop history for previous 5 years, any problems that have occurred)
• Soil fertility tests (especially if you’re doing a fertiliser trial). This would usually include the major nutrients (nitrogen, phosphorus and potassium) and might include micronutrients if these can be an issue. Soil organic matter and pH levels can also help to interpret trial results. All these test figures are good to have as part of your farm plan in any case. You can use them to see whether you’re getting changes (good and bad) in your soil over time.
• Weed, pest or disease type and severity (especially if you’re doing a spray trial)
• Soil physical conditions (soil tilth, depth of compacted layers, etc.), especially if you’re doing a tillage trial.

‘During’ measurements can form part of your crop scouting programme, and might typically include:

• General observations of conditions at sowing and subsequent crop health, vigour and development
• Emergence and population counts
• Weed, pest or disease type and severity
• Time of key crop events such as jointing, tillering, flowering, silking, maturity, etc.
• Weather events (specific phenomena such as high winds, rainfall amounts, duration of surface ponding, etc).

Never be tempted to discontinue measurements mid-season because you can already see a difference between treatments.

‘End’ measurements are likely to occur around the time of final harvest and would typically include:

• Harvest date
• Yield
• Biomass
• Lodging

‘After’ measurements may or may not be required, and will vary with the type of trial that you do. They might include:

• Soil conditions
• Residue levels and ease of residue handling
• Quality analyses (eg. moisture, protein content, metabolisable energy, etc.)

Summary:

Planning and sticking to your trial measurement plan is integral for the success of your on-farm trial. Plan measurements that you need to make and write them in your diary. Stick to your measurement plan even if treatment differences appear to be so obvious that they don’t need confirmation.

What type of measurements should you make?

As a minimum, you need to make measurements that satisfy the aims of your trial. If your aim is to determine the effect of treatment on yield, then yield must be measured. If your aim is to determine the effect of treatment on disease incidence, then disease incidence must be measured. If you aim to determine the effect of treatment on soil ‘health’ then relevant indicators of soil health must be measured.

The key point underlying the statement above is that visual observations are fine, but that they cannot under any circumstances replace the ‘hard’ numbers gathered by objective measurement.

‘Hard’ results are quantitative measurements that are intended to give you numbers for comparison and analysis. Typical examples include emergence counts, plant populations, grain and biomass yield, grain moisture, thousand kernel mass, bulk density, or the dates at which given events occur (eg. emergence, silking, anthesis or harvest maturity).

‘Soft’ results are qualitative observations that are intended to give you data for which numbers are inappropriate or difficult to obtain or interpret. Typical examples that you may use include soil tilth (blocky, coarse, medium or fine), harvestability (easy, moderately difficult, difficult), paddock history, presence/absence of pests and diseases and your general impressions about the trial.

Eyes tells lies – objective measurements are hard to argue with.

NEVER be tempted to assess yield or biomass using a visual assessment. It simply doesn’t work, because there is no reliable or verifiable relationship between a crop’s appearance and its performance.

For example:

• Crop height has no consistent relationship with yield.
• Crop colour has no consistent relationship with yield.
• Stem diameter has no consistent relationship with yield.
• Tiller or stem number has no consistent relationship with yield.
• Ear length has no consistent relationship with yield.
• Individual yield components (such as ear mass, ear number or kernel mass) are little use in isolation because when one goes up the others usually go down. In isolation, they tell you very little about your crop.

In our experience, it’s better not to do a trial at all than it is to rely on a visual assessment of a key variable such as yield or biomass.

If you need to know the yield or biomass of a crop, measure it objectively and directly, using quantifiable methods.

A reliable head-to-head comparison of something complex like conventional and minimal tillage might involve using ‘best management practise’ for each system along with a bunch of ‘extra’ measurements.

The ‘extra’ measurements might include:

• Soil conditions. What is the soil type and physical condition? What is the soil fertility? What aspects of these are likely to impact on the relative suitability of conventional and minimal tillage? How much of which fertilisers should you apply?
• Seasonal conditions. Was it a dry or wet year? At which stages of crop growth? How might this have affected the results?
• Tillage. What is the time/cost of cultivating? How might this vary with soil/seasonal conditions?
• Sowing. Did it go OK? Was there any effect of tillage method on seed placement (depth, distance between seeds)?
• Crop emergence. Did time of 50% emergence change? Was emergence even over time? Was emergence variable within the row? What was the effect on the emerged population? If it was different, was it because of soil temperature, wetness or physical restrictions (surface capping, etc.)? How many seeds germinated but did not emerge?
• Pest, weed and disease incidence. Did these differ and did they require different control measures? What did these cost? How much time did they take? How much would these vary with soil or season?
• Crop development. Did jointing/flowering/silking/maturity occur at the same time?
• Crop biomass or yield. Did these differ? By how much?
• Trash/residue handling. How much residue was there? How much time did dealing with it take? How much did it cost? What is it likely to contribute to future crops?
• Soil conditions. What was the effect of each system on soil physical conditions and fertility at the end of the season or the start of the next? What would this be worth in dollars, time or flexibility?

Because you can’t isolate the effects of each of these factors experimentally, it’s important that they are monitored or, ideally, measured so that you can see how each affected costs and receipts. These may be measured in terms of timeliness, management time, inputs required, outputs received and effects on your system’s future value.

Do you have the tools to make the measurements as planned?

Make certain that you have the knowledge and equipment required to undertake the measurements that you’ve planned. If you need help or equipment, organise it in advance.

By this stage you should have a precise (but flexible) plan of the measurements that you’ll make

Take a couple of minutes to see how easy it will be to implement the plan.

• If you plan to measure soil physical conditions, have you decided on the best indicators to use? Measuring the depth of compacted layers is pretty simple, but how about severity of compaction? Will a bucket and spade do the job or is specialist equipment such as a penetrometer required?
• If you plan to measure soil chemical properties, have you decided which nutrients are most important? What depth will you measure to? Do you have a soil sampler?
• If seasonal conditions are important, do these need to be measured on site, or will data from the local newspaper do the trick?
• Pest, weed and disease incidence can have a big influence on crop performance and trial results. Do you recognise the important species of each?
• Will you use a weigh wagon to measure yield or will hand harvesting be required? Is a weigh wagon going to be available? If you’re hand harvesting, do you have access to a drying oven and a reliable set of scales?
• Do you have facilities (refrigerator, oven, etc.) for safely storing samples that need to be analysed at a later date?

Do you have the time to make the measurements as planned?

Reliable measurements require quality time for both planning and execution. Set this time aside, because good measurements are the foundation of good trials

Planning the measurements required and calibrating the necessary gear in a quieter time will make it easier to get the job done right. You don’t need to calibrate your equipment the day that you’re going to use it, although you should try to ensure that conditions during calibration are similar to those occurring during operation.

End of section critical decision point

Can you put a trial measurement plan into your diary, outlining what measurements need to be made, and the equipment needed to make them effectively? This is important if you are to get the best from the next section – Getting the design right.