NUTRIENT CONCENTRATION RELATIONSHIPS BETWEEN THE 4TH PETIOLE AND UPPER-STEM OF POTATO PLANTS

Successfully evaluating the nutritional status of a crop during growth and development is dependent upon sampling an identifiable plant part . Consistently sampling a petiole of the same maturity in potatoes (So lanum tuberosum L.) is difficult. We evaluated the nutrient relationsh ips between the upper-stem and the fourth petiole from Russet Burbank plants in field studies having N, P, K, Zn or Mn variables. The upper- stem was obtained by excising the stem below the sixth leaf and removi ng all leaves and the terminal meristem. Petole NO3-N, P, K, Zn and Mn concentrations were from deficient to sufficient. The NO3-N, P and K concentrations were similar in the fourth petiole and upper-stem, whil e the Zn concentration was 40% higher in the upper-stem. Calcium, Mg a nd Mn concentrations were lower in the upper-stem than in the fourth p etiole. Copper and S relationships were not adequately defined. The fo urth petiole's NO3-N, P and K diagnostic concentrations now used to mo nitor plant nutrient status can also be used for upper-stem samples. Z inc diagnostic concentrations should be increased, while Ca, Mg and Mn concentrations should be adjusted downward in the upper-tem. Addition al data are needed to refine the Ca and Mg relationships, and to estab lish relationships for Cu, S and other essential nutrients. A signific ant advantage of using the upper-stem is the elimination of the petiol e selection problem when sampling.