BY: Jennifer McCombe-Théroux, regional variety trial agronomist, MPSG
When you’re considering which varieties will work best on your farm, the data from the Regional Variety Trials is a great place to start. These trials are spread across Manitoba and are designed to account for the unique growing conditions in different regions. This research offers data on various crop types, including yield, days to maturity and agronomic characteristics.
When looking through the many pages of data it can be overwhelming to interpret and compare varieties to determine which variety is a good fit for your farm. This is where the highlighter test comes in.
Adapted by Dennis Lange with Manitoba Agriculture, the highlighter test is a straightforward method for making sense of trial data to compare varieties based on statistical, not numerical, differences. It helps you understand if any yield differences between varieties are due to genetics and not from the environment or experimental error.
Understanding Data from the Regional Variety Trials – Soybeans
Before looking at the highlighter test, let’s break down the data you will typically see from the soybean Regional Variety Trials:
- Check variety – A check variety is a widely grown and established variety chosen to be used as a benchmark.
- Relative days to maturity +/- check – The number of days from planting to full maturity (R8 or 95 per cent brown pod). It is expressed as + or – days relative to the check variety.
- Long-term yield % of check – The average yield per variety over time. It is expressed as a per cent of the check yield.
- Site years tested – The number of sites the variety has been tested on over time.
- Agronomic characteristics – Traits like iron deficiency chlorosis rating and group, herbicide-resistance type, soybean cyst nematode and phytophthora root rot resistance.
- Annual yield information – How each variety performs each year. It is expressed as per cent of the yield of the check variety.
These trials provide extensive information on varieties, but the next step is understanding the data to compare varieties and determine if the differences in yield are statistically significant. This is where the Least Significant Difference (LSD) value comes in – the amount by which two varieties must differ to conclude with 95 per cent certainty that a true yield difference exists due to genetics. If the difference in yield between two varieties is higher than the LSD value, then the higher-yielding variety is statistically higher in yield. An LSD value won’t be present if there were no significant differences at a site, and this means that all varieties performed the same at that location.
Step-by-Step Guide to the Highlighter Test
To compare varieties through the highlighter test, start with three different colours of highlighters to compare yield data:
- Highlight the LSD Value and Check Variety – Start by looking at the bottom of the Yields by Location table. At the bottom of this table, you will find the LSD value – this is your benchmark for comparing the yield differences. Next, choose a check variety. This can be the existing check or any variety that you would like to compare against. Highlight the yields for this check variety and the LSD values.
- Highlight Varieties with Significantly Higher Yields – Grab a second highlighter with a different colour and scan the table for varieties that have yields higher than your check variety by at least the LSD value. For example, with an LSD of 10, variety yields must differ by at least 10 per cent from the check to be different.
- Highlight Varieties with Significantly Lower Yields – Take a third highlighter with a different colour and scan the table for varieties that have yields lower than your check variety by at least the LSD value.
After going through with the highlighters, “you are left with a checkerboard pattern,” as Lange puts it. It shows you by site the varieties that are statistically higher yielding than the check, those lower than the check and everything else (the unhighlighted) that is not statistically different from the check.
Example – Using the Western Herbicide Tolerant Soybean Results
First, the check variety, S003-R5X, and all data across the row, and the LSD values for each location along the bottom of the table are highlighted in yellow (see Figure 1). Then, varieties that performed significantly better than the check based on each location’s LSD are highlighted in green and varieties that yielded less at those locations are highlighted in red.
For this example, we used the check variety to keep things simple. However, you can choose any variety to compare to and highlight + or – based on the LSD at each location. S003-R5X is the check and at the Dauphin, Man. site the LSD is 6. Varieties that performed better than S003-R5X in Dauphin would have yielded 106 per cent or greater. Whereas varieties that yielded less than S003-R5X at Dauphin would have yielded 94 per cent or less. Any unhighlighted varieties are not statistically different in yield than the check.
If we were to look at another site, for example at Melita, Man. the LSD at this site was 10. Varieties that yielded 110 per cent or greater yielded better than S003-R5X and varieties that yielded 90 per cent or less yielded less than S003-R5X. Any unhighlighted varieties aren’t statistically different in yield than the check.
Looking Further at the Data: Digging Deeper into the Details
Once you have gone through to compare the statistical yield differences and you’ve narrowed down your varieties, it’s time to look further and compare maturity, stability in yields across test sites, how many years the variety was tested and the agronomic characteristics you’re looking for on your farm.
Maturity – Soybeans require anywhere from 105 to125 frost-free days from planting to maturity. To further narrow down your soybean options select varieties suited to your growing region using the Manitoba Soybean Maturity Zones map and days to maturity. Highlighting across the whole row of the check or the variety you would like to compare, helps you to see that the varieties above the check are earlier maturing and the varieties below the check are longer maturing.
Yields – Annual yields are found in the Yields by Location tables and this is the place to use the highlighter test to compare yields statistically for a single-year data set. Long-term yields are found in the Variety Description tables, which and shows how over time this variety has consistently maintained its yield stability in a longer period of time depending on the site years tested.
Site locations – When looking at sites, the first place to look is the location that most resembles your farm land. However, looking at that variety and its results at each location will also show you the yield stability of that variety in different environments.
Site-years tested – The more a variety has been tested helps give us confidence in the results as it has been grown on more site locations and years under varying environmental conditions.
Type – For the herbicide-tolerant varieties, type indicates if it’s an Xtend (glyphosate + dicamba tolerant), E3 Enlist (glyphosate + glufosinate + 2,4-D choline tolerant), Roundup Ready (glyphosate tolerant), WPX-Blended (glyphosate + dicamba tolerant) or XtendFlex (glyphosate + dicamba + glufosinate tolerant) variety. Use this information to help narrow down your options based on weed pressure in your fields.
Iron Deficiency Chlorosis (IDC) tolerance – Variety selection is the best tool to prevent IDC development. On fields with a higher risk of developing IDC (high calcium carbonate and soluble salt levels), choose a tolerant variety to minimize the impact of IDC on soybean yield.
Phytophthora Root Rot, Soybean Cyst Nematode – Consider these resistance traits based on the disease presence and risk in your fields.
The highlighter test is a tool that can be used on regional variety trial data for all crop types to evaluate any single year using the LSD value. By understanding the LSD value and its role in these evaluations, you can visualize and understand the yield data and truly distinguish between genetic differences to help make informed variety selection decisions.