Effects of the rate of protein hydrolysis and spray concentration on growth of potted kiwifruit (Actinidia deliciosa) plants

Products obtained by hydrolysis of proteins have been recently used as foliar fertilisers in several fruit growing areas. In this study we have assessed the effects of the rate of protein hydrolysis and that of the N concentration in the sprayed solution on the vegetative growth of potted kiwifruit plants. Protein hydrolysates were obtained by enzymatic hydrolysis of "peptone from gelatine". The four fractions obtained (with nominal molecular weights of < 1, 1-3, 3-10 and > 10 kDa), the unhydrolysed peptone and the peptone hydrolysed but not subjected to separation were sprayed at three different concentrations (240, 400 and 800 mg N L-1). Each product was sprayed five times at ten day intervals. Control, untreated, plants and plants treated with urea were present as well. After one month from the first treatment application, the fractions with lowest nominal molecular weights stimulated, especially at lowers rates, shoot growth. The application at highest rate of the fractions with nominal molecular weight 3-10 kDa and > 10 kDa induced shoot growth and biomass increments higher than those caused by urea sprays. The hydrolysed-unfractionated peptone, regardless the rate applied, adversely affected vegetative growth and canopy biomass after two months from the beginning of treatment application, while the unhydrolysed peptone stimulated in the short term vegetative growth when applied at highest rate and performed better than urea. Root growth and biomass linearly increased with the rate of organic N when applied with fraction of 1-3 kDa and > 10 kDa. Data of nitrogen concentrations and content in leaves suggest that vegetative growth effects of the products evaluated are not only due to increase of N nutrition.