Comparing Chlorophyll Meter Readings to Petiole Nitrogen for N Management in Potatoes.

The need to determine adequate nitrogen levels for potato crops in the Southeast Idaho 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 compare the SPAD chlorophyll meter and petiole samples for accurately measure 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 second year of a three-year study.  It is expected that chlorophyll meter readings from potatoes will be correlated with petiole NO₃^- as has been shown in previous chlorophyll meter studies, therefore, chlorophyll meter readings could be used for in-season N fertilization decisions in potatoes.