“V” is for variability – origins of variation within a crop and contributions to yield

LandWISE 2015 Presenter Bruce Searle

Bruce Searle, Crop Physiologist and Modeller Plant and Food Research

Why is a crop so variable and what can be done about it? And of that variability, how much can management practices actually affect?

Those who work with crops are well aware of this variability, but ways of addressing it are less clear.

Variability affects profitability so managing it is important. The more variable a crop is, the more the yield will be reduced compared to an even crop that produces the maximum attainable yield, and so profitability is reduced.

Increasingly, the value of a vegetable crop is dependent on providing product that meets some quality criteria – initially, usually size. This means that growing to maximise yield does not always increase profitability if the crop does not meet the quality standards. If variability is high then less of the crop will fall in the grades desired by the market and so profitability decreases.

Causes of variability are complex. It starts with the variability in seed size. Overlaid on this is variability in emergence time, variability in seedling size, variability in plant spacing and effects on competition, individual variability in relative growth rate, and differences in spatial supply of nutrients and water in the field and patchiness in pest and disease.

All these factors interact in different ways. Models are an ideal way to quantify some of this complexity and provide good insight, but the large number of measurements needed and the large number of interactions to compute can limit the value of such approaches.

Here we start to develop a conceptual framework that allows the causes of variability in a field to be identified and enables the contribution of each cause to be considered. We have called this framework the ‘V of variability’.



We group causes of variability into spread of emergence, establishment, population and growth, and examine how these factors change for crops of onions and potatoes and affect the variability of size in onions and potatoes and dry matter % of potatoes. We use this to identify how much variability is manageable and the appropriate key management practices to consider.

This framework, when linked with digital information capture at a field scale, could provide a powerful tool for management of variability.

Presentation Authors: Bruce Searle, Jeff Reid and Paul Johnstone – Plant and Food Research


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