Effect of nitrogen source on olives growing in soils with high boron content

A greenhouse experiment was conducted to study the effects of nitrogen (N) forms ( NO3-, 2.6 mmol/ L; NH4+, 2.6 mmol/ L; NO3-, 1.0 mmol/L plus NH4+, 1.6 mmol/L) and boron (B) ( 0.025, 0.5 and 1.0 mmol/L) on the growth and mineral composition of olive plants ( Olea europaea L.). One- year- old own- rooted plants of the olive cultivars Megaritiki, Chondrolia Chalkidikis, Koroneiki and Kalamon were grown in plastic bags containing inert sand - perlite medium ( 1: 1) and were irrigated with a 50% modified Hoagland nutrient solution. The plants treated with NO3- and 1.0 mmol B/L presented higher leaf B than those treated with NH4+ and 1.0 mmol B/L, for all cultivars. The addition of ammonium form fertilisation caused a significant accumulation of B to root tissues when the latter consisted of 0.5 mmol/ L. As B was increased in the NO3 (-) N treatments, the number of leaves and the root dry weight of cv. Megaritiki as well as the plant height of cvv. Koroneiki and Kalamon were reduced. The above results suggest that in olive, addition of NH4+ to high B soils may be more beneficial for growth of olives than addition of NO3 (-). In most cases N form did not affect total leaf and root N levels. Also, the NH4 (-)(+) N treatments showed a decline in root phosphorus ( P) and an increase in leaf potassium with increased B. The general trend was a decrease of P in leaves with increasing B.