Fulvic acid in foliar spray is more effective than humic acid via soil in improving coffee seedlings growth

Humic (HA) and fulvic (FA) acids improve the nutrient availability and uptake by plants but some aspects of their agronomic use still need to be clarified. The effects of HA soil application and FA foliar application on the growth, Zn and B uptake by coffee seedlings were evaluated. HA was added to an Oxisol at concentrations 0, 10, 25, 50, 75 and 100 mg kg(-1) (C-HA), in both limed (pH 6.2) and overlimed (pH 7.2) conditions. FA (0, 0.2, 0.5 and 1 g L-1 C-FA) was applied to coffee leaves in three different application modes (M): with 0.3% Zn and 0.6% B supplied via foliar (M-1), 0.6% B and 1.2% Zn supplied via foliar (M-2) and 1.2 mg kg(-1) B and 6 mg kg(-1) Zn supplied via soil (M-3). HA addition in soil significantly (p < 0.05) reduced leaf B and Zn accumulation and coffee growth in both pH conditions. In the M-1 and M-2, FA application significantly (p < 0.05) increased the shoot growth at 0.59 and 0.45 g L-1 and B accumulation at 0.96 and 0.45 g L-1 C-FA. Foliar application of C-FA, instead soil application of C-HA, is a suitable practice to improve coffee seedlings growth and nutrition on Oxisol.