EFFECTS OF DIFFERENT POTASSIUM FERTILIZERS ON YIELD, FRUIT QUALITY AND NUTRITIONAL STATUS OF ´FAIRLANE´ NECTARINE TREES AND ON SOIL FERTILITY

A field trial with three sources of K (KNO₃, K₂SO₄ and KCl) applied at 300 kg K₂O ha^-1, was carried out between 1996 and 2000 to evaluate responses of early nectarines cv. Fairlane. The experiment was done in a Mollisol soil (VI Region of Chile) which was medium texture with limited internal drainage. All K treatments significantly increased fruit weight and diameter after year two of treatments. Also, all K treatments increased exchangeable K up to 60 cm depth. Leaf K concentrations increased from 10 g kg^-1 in the control to 15 g kg^-1. Total yield was increased by the treatments only in one season during which fruit set was low due to unfavourable climatic conditions. Fruit firmness at harvest or after 30 d storage at 0ºC was little affected by the treatments, but KNO₃ and KCl increased fruit firmness in some seasons. Dehydration and wooliness were decreased by the K treatments in two out of four seasons, especially with the K₂SO₄ fertilizer treatment. KCl increased chloride level in the subsoil to 7 meq L^-1, which may be harmful to sensitive crops. However, leaf Cl concentrations increased moderately and did not reach toxic levels. Based on the positive effect of K fertilizers on fruit quality at harvest and after storage, the critical level of 15 g kg^-1 in the leaves is proposed for early nectarines in Chile.