Boron toxicity in kiwifruit plants ( Actinidia deliciosa ), treated with nitrate, ammonium, and a mixture of both

The objective of this research was to study the effects of nitrogen (N) forms (NO 3 – , 2.6 mM; NH 4 + , 2.6 mM; NO 3 – , 1 mM + NH 4 + , 1.6 mM) on the growth and mineral composition of kiwifruit plants exposed to three boron (B) levels (0.025, 0.1, 0.3 mM). The kiwifruit plants were grown in a 1:1 sand : perlite mixture and irrigated daily with nutrient solutions. Shoot height, mean shoot dry weight, the number of leaves, mean leaf dry weight, and N concentration of NH 4 ‐treated plants were significantly higher compared to the NO 3 – treatment at all B levels. The concentration of 0.3 mM B significantly reduced shoot height for all N treatments. Boron toxicity symptoms appeared 14 days after starting the experiment, when plants were treated with 0.1 and/or 0.3 mM B. The nitrate supply reduced the B concentration of roots, but B levels of different leaf parts were hardly affected by the N form. Furthermore, the NH 4 ‐N form significantly reduced the Mg concentration of the leaves.