Boundary-Line Approach micro-nutrient optimum concentrations and sufficiency ranges for Opuntia ficus-indica (L.) Miller fruiting

Optimum concentrations and/or sufficiency ranges of nutrients are useful for correct diagnosis and improvements of nutrient status of cultivated plants. However, Opuntia ficus-indica nutrient storage at plant and cladode levels and best fit plant requirements for fruiting remain practically unknown. Then, this research work aimed to identify the Boundary-Line Approach (B-LA) micronutrient optimum concentrations linked to maximum fruit yield per one-year old fructification cladode and sufficiency ranges at 90% maximum fruit yield for O. ficus-indica variety ‘Rojo Pelón’. Four years (2012 – 2015) data of fruit yield per cladode and micronutrient concentrations (B, Cu, Fe, Mn, and Zn) were used for the elaboration of scatter diagrams (n = 228) and selection of 7 to 10 points to estimate the B-LA quadratic functions. Then, the vertices allowed estimation of the optimum micronutrient concentrations: B = 33.62 mg kg–1, Cu =11.74 mg kg–1, Fe = 108.51 mg kg–1, Mn = 149.33 mg kg–1 and Zn = 414.91 mg kg–1 as linked to estimated maximum yield per cladode; and the sufficiency ranges at 90% maximum fruit yield: B = 24.44 to 46.25 mg kg–1, Cu = 8.68 – 15.87 mg kg–1, Fe = 73.73 – 143.3 mg kg–1, Mn = 114.89 – 183.77 mg kg–1 and Zn = 334.31 – 514.95 mg kg–1. The linked estimated maximum fruit yield per cladode varies from 1999.48 g to 2139.59 g. The proposed B-LA standards can be used to perform reliable micronutrient diagnosis and proper fertilization recommendations.