Assessing Yield Variability

This article first appeared in The GROWER magazine.

Variability in crops shows that some parts are not performing as well as others. So what?

Variability is a major problem in the vegetable sectors. It is responsible for unknown but very significant financial losses all the way through the value chain. Variability comes in varied forms, from a variety of causes, with variable results and various appropriate management responses.

It may be a timing thing, a size thing, a quality thing or a quantity thing. It could be caused by weather events, soil differences, seed differences, pest or disease effects or some management factor. It may mean missed yield, lower yield, lower price or higher costs.

Process pea crops are a classic example of relatively minor timing variability causing major losses. If plants flower earlier or later, timing the harvest is problematic and both quantity and quality will be affected.  Some plants will not be ready when the harvesters come through. Others will be over mature and downgrade overall quality. Processing, in particular, needs uniform product and reliable supply.

Have you got crop variability? Assume you do, even if it is not at first noticeable. The key is to know if it is significant, what effect is has on your profitability, and whether it is worth fixing. Sometimes the benefits of dealing with it are not worth the cost. But often a cheap fix can avoid an expensive problem.

LandWISE partnered with Horticulture New Zealand to help growers estimate the value of crop yield variation. A spreadsheet calculates the cost of yield variation, based on measurements made in the field.

The three pieces of information needed are the product value, the area affected, and the yields achieved. A small booklet gives guidelines on determining areas and yields and the spreadsheet does the rest. You can download the calculator and guidelines from

Why a calculator? While many farmers do observe variability in crops, few spend time quantifying the value (cost). The calculator and guidelines set out a straightforward process that doesn’t take much time, and does the calculations for you. It presents the results as tonnes and dollars in a table, and as graphs showing relative performance.

The Calculator encourages growers to identify the cause of loss in identified parts of the paddock. It then summarises the relative impact each has on yield.

One of the key pieces of information is quantifying the “Yield Gap”. The Yield Gap refers to the difference between the Potential Yield and the Main Area yield. It reflects an overall penalty and often costs more than the obvious losses. But because it affects the whole paddock it is not easily noticed.

If the season has been normal, and there are no obvious seed, equipment or management problems, look to soil condition or irrigation management as possible causes.

The Yield Variability Calculator estimates the value of crop loss. Thinking about how often these losses are suffered, how to avoid them in future what the cost of remediation may be, will help growers determine what, if any, action to take.

Dan Bloomer, LandWISE

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