Abstract
In order to assess the influence of the formulation of different Mg and Mn products on foliar absorption various field trials were carried out from 1997-2000. A further investigated aspect was the possible mutual interference of MgSO 4 and MnSO 4 on foliar absorption. Limited to some Mn products, also the influence of the application period (pre-and postbloom) was investigated. Furthermore, the incidence of necrotic leaf blotch and fruit russetting were assessed. The products tested were MgSO 4 with and without the addition of urea, Mg(NO 3) 2 , MgCl 2 , MnSO 4 with and without the addition of urea, the fungicide Mancozeb, the commercial products Mantrac, Hydromag, Mg-Humate, Manganbetter, Mn-Chelal, Brexil Mn, Wuxal Mn and Meda F2. MgSO 4 and MnSO 4 were also applied as combined treatments. Among the tested products, the mineral salts proved to be generally more efficient in increasing leaf nutrient content, both in the case of Mn and Mg. the addition of urea resulted in no additional benefit in terms of foliar absorption. as for the period of application, prebloom treatments with Mn had no significant effect on the nutrient level in leaf tissue grown later in the season. there was no negative side effect of any of the treatments in terms of fruit russetting except in the case of the chelates where a slight, but non significant increase of fruit russetting was recorded. no significant effect of any of the treatments on the incidence of necrotic leaf blotch was observed, suggesting that in these trials the primary causes for this physiological disorder were other factors than mg or Mn deficiencies. INTRODUCTION Foliar absorption of nutrients is influenced by various factors, among which plant species, leaf age, nutrient type and concentration, product formulation, climatic conditions and the nutritional status of the plant (Swietlik et al., 1984). Magnesium and manganese are two nutrients commonly applied via foliar sprays in apple orchards, not only in case of confirmed deficiencies but also in order to prevent or alleviate the incidence of leaf blotch and early leaf drop in susceptible varieties. There is, however, little information available on the comparative effectiveness of various sources of Mg and Mn in terms of foliar absorption. Formulated commercial products are often preferred to the cheaper mineral salts because of a supposedly higher efficiency and alleged negative side-effects (fruit russetting) of the mineral salts. As for the application period, from time to time the hypothesis is being formulated that early Mn sprays (prebloom) might be more efficient in preventing necrotic leaf blotch than treatments later in the season. The objective of this work was to compare the degree of foliar uptake of different sources of Mg and Mn, to assess their effectiveness for preventing leaf blotch and abscission, as well as to evaluate negative side effects on fruit quality. The effect of application period (pre-and postbloom) of Mn fertilizers was also examined. Finally, the possible mutual interference on leaf uptake of MnSO 4 and MnSO 4 , when applied in tank mixture, was investigated, as well as the effects of urea on nutrient absorption from MnSO 4 and MgSO 4.