Establishment of critical nutrient levels in the soil and leaf of 'Prata' banana using the boundary line.

• The boundary line (BL) method allowed defining critical levels. • Soil fertility classes and leaf sufficiency ranges were obtained for 'Prata' banana. • Diagnostic standards should be regional. Reliable standards for interpreting chemical analysis of soil and leaves are indispensable for the rational use of fertilizers and optimization of yield in banana orchards. The objective of this study was to establish critical levels, soil fertility classes and leaf nutrient sufficiency ranges for the banana cultivar 'Prata', using the Boundary Line (BL) approach. Data on fruit yield and chemical analysis of soil and leaves, collected from 2010 to 2017 in commercial plots, were used. Scatter plots relating yield to soil fertility attributes/leaf nutrient contents were created. Subsequently, BLs and equations were established to estimate fertility classes and sufficiency ranges. The fertility classes obtained were 6.8–7.2 for pH, 15.4–24.0 g dm−3 for OM, 72.5–145.5 mg dm−3 for P, 109.2–192.3 mg dm−3 for K, 3.3–6.1 cmol c dm−3 for Ca, 0.5–1.2 cmol c dm−3 for Mg, 4.7–8.2 cmol c dm−3 for SB, 6.0–9.6 cmol c dm−3 for CEC and 76.5–83.8 % for V. The appropriate ranges of leaf contents of N, P, K, Ca, Mg and S for banana were 19.8-21.9 g kg−1, 1.4–2.0 g kg−1, 26.5–35.6 g kg−1, 5.4–7.3 g kg−1, 2.0–2.6 g kg−1 and 1.3–1.6 g kg−1, respectively. The ranges of B, Cu, Fe, Mn, Zn and Na contents were 5.8–11.8 mg kg−1, 5.0–8.1 mg kg−1, 56.3–72.6 mg kg−1, 102.1–199.5 mg kg−1, 13.5–18.2 mg kg−1 and 29.8–55.4 mg kg−1, respectively. Leaf analysis is an important tool for evaluating the nutritional status of banana plants. Establishing these diagnostic standards for the current growing conditions allows the rational use of correctives and fertilizers, besides the obtaining of higher yields of 'Prata' banana in the Ceará state, Brazil. [ABSTRACT FROM AUTHOR]