Plant Health, Planting

Investigating variability in potatoes

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Sarah SintonSarah Sinton
Plant and Food Research

Final potato crop yield is a sum of its parts; each individual plant contributes to it. Should some of these individuals perform below potential, overall yield will be reduced accordingly. Yield variation within a crop is caused by biotic and abiotic factors, which could range from the wholesale effect of soil compaction restricting root growth across the entire field or be an outbreak of patches of disease causing the early death of individual stems or plants.

Nationally, potato yields average 55- 60 t/ha, which are not economically sustaining for many growers, and well below the 80-90 t/ha potential yields predicted by crop models. This was confirmed in a Canterbury survey of 11 process crops in the 2012-13 season where the crops had different histories, management and cultivars. All crops had a similar overall rate of yield reduction, largely caused by soil borne disease and soil physical constraints.

The survey showed that individual groups of healthy plants in a crop did achieve up to 90 t/ha (Fig. 1).   However some groups of plants yielded as little as 30 t/ha, due to Spongospora and Rhizoctonia infection, soil compaction and/or inferior seed quality.

Figure 1 Final yields from groups of individual plants that were: both healthy and growing in compaction-free soils (yellow bar); had soil compaction together with Spongospora (root galls); had severe Rhizoctonia stem canker; had both diseases and were growing in compacted soils
Figure 1 Final yields from groups of individual plants that were: both healthy and growing in compaction-free soils (yellow bar); had soil compaction together with Spongospora (root galls); had severe Rhizoctonia stem canker; had both diseases and were growing in compacted soils

Last year, an intensive study of three Canterbury crops showed that some areas of the crops reached potential and that others were limited by soil borne disease infection and water supply.

A field experiment at Lincoln is currently investigating how bed shape, subsoiling and irrigation regime are affecting crop production, and future work will look at how improvements to seed tuber production could reduce yield variability.

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