Resumo:
Research focused on adequate nutrition of plants is essential in modern coffee production to increase yield and develop more efficient management strategies with greater environmental and economic sustainability. The objectives of this study were to establish critical and optimal levels of soil fertility properties for high yielding Arabica coffee crops using the Boundary Line method and, then, relate the macronutrient contents in the diagnostic leaf of coffee to the macronutrients available in the soil using the Quadrant Diagram of the Plant-Soil Relationship (QDpsR). The study made use of a soil chemical analysis database, leaf macronutrient contents, and Arabica coffee yield from five representative coffee-growing regions in Minas Gerais. An analysis of data consistency was performed, and relative fruit yield (RFY) was related to the soil organic matter (SOM), P, K, Ca, and Mg contents in the soil, establishing the boundary line (BL) in each graph. Equations were adjusted from the BL points, and the equation that best fit was selected. Using the QDpsR method, the response plane was divided into four quadrants, where the total leaf contents of N, P, K, Ca, Mg, and S were plotted as a function of the contents of SOM, P, K, Ca, and Mg in the soil, on the y and x axes of the Cartesian coordinate system. The regression equations were adjusted to the pairs of points (y, x) of quadrants III and I and were used to estimate the macronutrient sufficiency ranges from the critical and optimal levels in the soil. The BL method was used to determine the class of good soil fertility for SOM, P, K, Ca, and Mg. The QDpsR method allows determination of response curves for leaf content as a variable of soil contents, making it possible to estimate the sufficiency ranges in the diagnostic leaf of coffee: 33.4-35.8 g kg -1 of N, 1.4-1.6 g kg -1 of P, 24.4-27.0 g kg -1 of K, 11.9-13.6 g kg -1 of Ca, 3.8-4.5 g kg -1 of Mg, and 1.4-1.8 g kg -1 of S; which were consistent with the sufficiency ranges considered suitable for the crop. This study demonstrated the importance of leaf analysis as a tool for evaluation of the nutritional status of Arabica coffee since the technique is consistent with the theoretical principles underlying it.
