Improving nitrogen recommendations for potatoes through estimation of determinacy of varieties
Currently, there are no objective, cost-effective ways of establishing the nitrogen (N) determinacy group of new varieties. Yet, this information is essential to determine the appropriate N application rate for a given season length and soil N supply. In consequence, during initial commercialisation new varieties are often given incorrect applications of N fertiliser resulting in increased production costs, yield loss, poor crop quality and increased wastage. Anecdotally, due to this inappropriate agronomy during initial commercialisation, some otherwise promising varieties have not achieved their full commercial potential. Mis-allocation of N determinacy group in seed crops could be detrimental to yield, skin-set and pathological loading.
Over three years, this project has shown that the four candidate metrics are correlated with one another and can be used to determine the nitrogen grouping (and in turn the nitrogen requirement) of new potato varieties. The preferred metric is to count main-axis nodes on the potato plant since this method is robust, quick, cheap and non-destructive. However, when augmented with other metrics e.g. integrated ground cover and or harvest index, the accuracy of the node counting method is improved. Factors such as excess nitrogen, extremes of climates, poor soil condition will affect the reliability of these metrics but no more than they would affect the reliability of more traditional nitrogen response experiments. This project has resulted in the development of simple protocol that will enable stakeholders in varietal development and commercialisation to quickly determine the nitrogen grouping of new varieties.