Boundary-Line Approach Macro-Nutrient Standards for Opuntia ficus-indica (L.) Miller Variety “Rojo Pelón” Fruiting

The aim of this research work was to identify the Boundary-Line Approach (B-LA) macro-nutrient optimum concentrations linked to maximum yield and sufficiency ranges at 90% maximum yield per 1-year-old fructification cladode for Opuntia ficus-indica (L.) Miller variety “Rojo Pelon”. Four years’ (2012–2015) data of yield per fructification cladode and macro-nutrient concentration [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), or magnesium (Mg)] were used to elaborate bivariate scatter diagrams (n = 228). Selection from 9 to 11 points was performed to estimate quadratic functions as boundary-lines in each bivariate scatter diagram. The vertices allowed estimation of the optimum macro-nutrient concentrations: ln N = 2.32 (10.20 g kg−1), P = 3.04 g kg−1, K = 35.18 g kg−1, Ca = 36.65 g kg−1, Mg = 13.83 g kg−1. The target maximum yield per fructification cladode varies between 1901.13 and 1984.41 g. The estimated sufficiency ranges at 90% of the maximum yield are ln N = 2.07–2.59 (7.86–13.40 g kg−1), P = 2.54–3.54 g kg−1, K = 25.36–45.01 g kg−1, Ca = 27.96–45.35 g kg−1, and Mg = 10.3–17.38 g kg−1. These nutrient standards may be used as a reference for maximizing yield per fructification cladode in O. ficus-indica, specifically for the variety “Rojo Pelon”.