Nutritional Sufficiency Range Approach for Tifton 85 Bermudagrass Cultivated in a Subtropical Climate

Tissue analysis is an important tool for monitoring plant nutrition. However, nutritional reference values are needed to guide decisions based on the probability of achieving maximum plant yield. According to datasets and the Gaussian distribution, it is possible to model the generation of reference values that can explain the high-probability yield increase from experiments without controlled nutrient rates. The study aimed to test distribution models and propose the leaf tissue nutritional sufficiency range approach for Tifton 85 bermudagrass grown in a subtropical climate. A dataset was composed from experiments conducted in subtropical climates during three crop seasons, totaling 1320 observations. Each observations containing N, P, K, Ca, and Mg content in the leaf tissue was submitted to the sufficiency range approach (SRA) method to define the Normal, Gamma, and Weibull distribution models. Using the model with the best fit, five nutritional ranges were defined: deficient (D), low (L), sufficient (S), high (H), and excessive (E), which correspond to 2.5% (D-L), 25% (L-S), 75% (S-H), and 97.5% (H-E) of sample observations. The Gamma model showed the best fit according to the Bayesian Information Criterion in most nutrients tested. The sufficient ranges of N: 18.4–24.0, P: 2.2–3.5, K: 16.5–22.7, Ca: 1.6–2.8, and Mg: 2.2–3.6 (g kg−1) were proposed for leaf tissue. The SRA method was used to determine the nutrient sufficiency zone and can be an alternative to generate reference values that are scarce for some crops, such as Tifton 85 bermudagrass.