Relationship between chloride and nitrate and its effect on growth and mineral composition of avocado and citrus plants

Abstract

Two rootstocks of avocado (Persea americana Mill.), the salt‐tolerant ‘Degania‐113’ and the salt‐sensitive ‘Smith’, and two rootstocks of citrus, the salt‐tolerant ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tan) and the salt‐sensitive ‘Troyer’ citrange (Poncirus trifoliata x Citrus sinensis [L.] Osbeck), were grown in a sandy soil and irrigated daily with nutrient solutions containing various chloride concentrations. Increasing the concentration of chloride resulted in elevated chloride levels in all avocado plant parts, and toxic symptoms that were more pronounced in the ‘Smith’ than in the ‘Degania‐113’ avocado rootstock. When leaves of both rootstocks had accumulated similar chloride levels and showed scorching damage, the leaves of ‘Degania‐113’ abscised, while those of ‘Smith’ did not. High chloride reduced the total dry matter yield of the root more than that of the shoot, decreasing the “root: shoot”; dry weight ratio in both rootstocks. Addition of nitrate to the irrigation water reduced chloride accumulation in the plant and alleviated its adverse effects. Accumulation of nitrogen in the plant exceeded that of chloride in all cases. High nitrate reduced phosphorus levels in the plant and caused chlorosis in young leaves. High chloride partially reversed this effect. Citrus rootstocks responded similarly, but leaves of the chloride‐sensitive ‘Troyer’ accumulated more chloride than ‘Cleopatra’. High chloride resulted in scorching damage in the leaves and branches of ‘Troyer’, but not in ‘Cleopatra’. Nitrate reduced chloride accumulation and toxic symptoms as well as boron levels in the leaves. The results of this study suggests that water containing high chloride levels may be used to irrigate avocado and citrus orchards, provided that nitrate is supplied continuously at a molar concentration equivalent to half that of chloride. Our results also suggest that a nitrate supplement applied to citrus will reduce the undesirable uptake of boron. The difference in mode of resistance to chloride between avocado and citrus rootstocks is discussed.