Mineral Nutrition of Prunus Rootstocks: Leaf Concentrations and Diagnosis by Vector Analysis

The effects of different levels of phosphorus fertilization and water provision on the mineral nutrition of two clonal rootstocks of Prunus were studied. Two-year-old Prunus seedlings, Hybrid GF677 (Prunus persica × Prunus amygdalus) (PH) and Pollizo Puebla de Soto 101 (Prunus insititia) (PI) were planted in an uncultivated calcareous soil (a Xeric torriorthent derived from marl) under greenhouse conditions. They were drip irrigated with subterranean water of slightly alkaline pH (7.63), EC 0.88 dS·m -1 , with a low chloride and high sulphate content. The experiment lasted two annual cycles. In October of the second year the leaf nutrient concentration and dry weight of the total leaf weight were determined in four trees of each combination of rootstock × irrigation level × fertilization treatment. The nutritive state of these trees was analyzed by vector analysis.The results point to a highly signifi cant infl uence of the rootstock nature on the leaf concentrations of most nutrients. Very low Zn and Cu concentrations were recorded on both rootstocks, for both irrigation levels and several fertilizing treatments. Vector analysis confi rmed the Cu defi ciency resulting from several of the fertilizing treatments and both irrigation levels in PH rootstocks. Prunus cultivation, homogenizing planta- tions and permitting higher densities as a result of the less excessive vigor (Rubio and Socias i Company, 1991). Among clonal rootstock, hybrid variants are becoming the norm in stone fruit species of the genus Prunus L for commercial plantations (Rubio and Socias i Company, 1991). Such aspects as the infl uence of rootstock type on the absorption of different minerals, productivity, root development, salt tolerance and root asphyxia, besides resistance to drought, have contributed to the expan- sion in the use of hybrid rootstock (Gomez Aparisi, 1991). The root system has a strong infl uence on the chemical composition of plants, although the nutrient absorption capacity is only part of a wealth of interactions which affect the levels of mineral elements in plant tissues (Wutscher, 1989). Most studies on the effect of the root- stock on mineral nutrition in trees are based on leaf analyses (Brown and Cuming, 1989; Said et al., 1993), despite the fact that all the plant tissues are involved (Holevas et al, 1985). Leaf element levels depend on absorption and transport processes, in which the rootstock has been seen to play an important role in the levels of micronutrients (Gomez Aparisi, 1991). In an attempt to develop a practical crite- rion for use in differential fertilization studies, vector analysis was developed for nutritional diagnosis purposes (Timmer and Stone, 1978; Timmer and Amstrong, 1987; Timmer and Teng, 1990). Vector diagnosis involves The recipients were arranged in 12 rows of 20 containers with suffi cient room between them to allow the canopy to grow. A drip line was run across all the containers with one self-compensating emitter in the center of each container. Half the emitters provided 4 L·h -1 and the other half 2 L·h -1 , fl ow rates that were periodically checked throughout the ex- perimental with coeffi cients in excess of 92% always being obtained. Eight tensiometers of 40 cm length were installed at random, 4 for each irrigation treatment to assess soil humid- ity, and water was added when measurements above 25 cb were recorded in any of them. The irrigation time for both sets of emitters (2 and 4 L·h -1 ) was the same so that half of the trees received exactly double amount of water. At the end of each irrigation period it was checked that the tensiometer readings were 0 cb. The water used came from a well and had a slightly alkaline pH 7.63, EC = 0.88 dS·m, Cl - = 1.50 mmol·L -1 , SO 4 -2 = 2.60 mmol·L -1 , HCO 3 - = 2.15 mmol·L -1 , Ca +2 = 1.80 mmol·L -1 , Mg +2