The Unexploited Potential of Nutrient Analysis in Potato Tissues at the Onset of Tuberization for Tuber Yield Prediction

Nutrient analysis of potato leaves in early growth is not sufficient for a reliable prediction of tuber yield. This hypothesis was verified based on a field experiment conducted during 2006–2008. The experimental factors were: nitrogen (N) rates (60, 120 kg ha−1), fertilizers (Urea, Urea + inhibitor—NBPT ([N-(n-butyl) thiophosphoric triamide]), and sulfur rates (0, 50 kg ha−1). Plant material for nutrient determination (N, P, K, Mg, Ca, Fe, Mn, Zn, Cu), which included leaves, stems, and stolons + roots (R+S), was sampled at BBCH 39/40. The marketable tuber yield (MTY) was in the ranges of 43–75, 44–70, and 24–38 t ha−1, in 2006, 2007, and 2008, respectively. The MTY and contents of N, Zn, and Cu, irrespective of the potato tissue, showed the same seasonal pattern, reaching the lowest values in the dry 2008. The N content in stems was the best tuber yield predictor. A shortage of K in stems and Mg and Cu in R+S, due to the opposite effect of Ca, reduced the N content. An N:Ca ratio in stems greater than 10:1 resulted in yield decrease. A reliable indication of nutrients limiting the tuber yield at the onset of potato tuberization requires data on the nutrient status in both leaves and stems.