Effects of foliar treatments with urea and nano-urea on the cell walls of Monastrell grape skins

Cell wall composition can be affected by nitrogen availability in the vineyard. Foliar application of urea is effective in supplying nitrogen needs and increasing the nitrogen content of musts. Due to the low recoveries of urea fertilisation, more effective application methods such as the use of nanotechnology are needed. In this work, the effect on the composition of Monastrell grape skin cell walls, after foliar application of urea and amorphous calcium phosphate nano-particles doped with urea was studied. The treatments with urea and nano-urea, although the urea content in the nano-treatment was eight times lower than in the conventional treatment, produce an equivalent modification of the cell wall. In fact, both treatments produced an increase in cell wall thickness and in cell wall composition, contents of proteins, hemicellulose and uronic acids also increased. However, phenolic compounds were not affected and cellulose showed lower concentrations than control grapes. Regarding the spectrophotometric parameters of the wine studied, the anthocyanins content and colour intensity were reduced in wines with both treatments and the total polyphenol index was slightly affected.