Testing the Accuracy of Chlorophyll Meters in Relation to Nitrogen Levels in Potatoes.

The need to determine adequate nitrogen levels for potato crops in the Southeast Idaho area during the growing season requires expensive petiole sample tests. The use of a SPAD Minolta chlorophyll meter by potato producers could reduce sampling costs and provide accurate in-season potato petiole nitrogen levels. The objective of this study is to compare the accuracy of the SPAD chlorophyll meter with petiole samples to determine nitrogen petiole levels for in-season N fertilization for potato crops.  Nitrogen treatments of 0, 112, 168, 224, and 280 kg ha^-1 with four replications in a randomized complete block design were used to establish different N levels in the potato crop. Fertilizer was split applied with 56 kg N ha^-1 applied at planting (except for the control treatment) and remainder applied in early June.  Petiole samples, chlorophyll meter readings, and soil nitrate (NO₃^-) test were taken once a week for eight weeks beginning in mid-June.  Petiole samples were analyzed for NO₃^- levels.  Chlorophyll meter readings will be compared to petiole and soil NO₃^- levels which are current methods for determining in-season N fertilization need.  Potato plots were harvested by digging 3 meters of two adjacent rows and yields were determined based on total weight and weight by quality class.  Yield data will be compared with petiole NO₃^-, chlorophyll meter data, and soil NO₃^- levels for determining which method best predicts yield.  The experiment is in its first year of a three year study.  Data collection has just begun, but results are not yet available.  It is expected that chlorophyll meter readings from potatoes will be correlated with petiole NO₃^- as has been shown in previous chlorophyll meter, therefore, chlorophyll meter readings could be used for in-season N fertilization decisions in potatoes.