Abstract
In order to assess the effects of different carrier water volumes (1500 L/ha, 300 L/ha and 150 L/ha) of foliar sprays of MnSO 4. H 2 O (750 g/ha), Mg(NO 3) 2. 6H 2 O (7500 g/ha), CaCl 2. 2H 2 O (3750 g/ha) and urea (6000 g/ha) on nutrient absorption, field trials were carried out for two years (1999-2000) in 'Golden Delicious' apple orchards. In addition, the incidence of phytotoxic side effects was investigated. The experiments were designed as randomized blocks with four replications. Two treatments per trial were applied between May and June, leaf damage was assessed after each application, leaf samples were taken for chemical analysis 3-4 weeks after treatment and fruit samples were assessed at harvest for incidence of russetting. Leaf analysis revealed a significantly increased foliar nutrient content with decreasing spray volume in the case of Mn and Mg. None of the treatments lead to leaf scorch or increased fruit russetting. These results indicate that low volume sprays of foliar fertilizers can improve nutrient absorption without increasing negative side effects such as leaf scorch or fruit russetting. INTRODUCTION Low volume spraying in horticulture offers a number of advantages compared to high volume applications, particularly in terms of labour efficiency. For foliar fertilizer applications, there is still much uncertainty about the effects of low volume applications on foliar absorption and about possible phytotoxic side-effects due to the increased solute concentration. Field trials were carried out between 1999 and 2000 in 'Golden Delicious' apple orchards with the aim of comparing the effects of three different volumes of carrier water on foliar absorption of different foliar fertilizers and assessing possible side effects of the increased nutrient concentrations in the spray droplets. Spray products were chosen for different reasons. Manganese sulphate was chosen for the trial because it is readily absorbed by apple leaves, and differences in absorption rates are easily detectable. Magnesium nitrate was chosen due to its potential phytotoxicity at higher concentrations. This applies partially also to CaCl 2 , which, however, was chosen because it also represents, along with urea, one of the most widely used foliar fertilizers in apple orchards.