LEAF NUTRITIONAL LEVELS IN PEACH AND NECTARINE GROWN IN SUBTROPICAL CLIMATE

The study evaluated the leaf nutritional levels of peach and nectarine trees under subtropical climate in order to improve the fertilization practices. The experiment was carried out in São Paulo state University, Botucatu, São Paulo State, Brazil. The experimental design consisted of subdivided plots, in which plots corresponded to cultivars and subplots to the leaf sample periods. The evaluated peach cultivars were: Marli, Turmalina, Precocinho, Jubileu, Cascata 968, Cascata 848, CP 951C, CP 9553CYN, and Tropic Beauty, and that of nectarine was ‘Sun Blaze’. The sample periods were: after harvest, plants in vegetative period; dormancy; beginning of flowering and fruiting (standard sample). Results indicated significant variations in the levels of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn and Zn for the sampling period and in N, Ca, Mg, S, B, Fe and Mn levels for the cultivars.


INTRODUCTION
Peach production in Brazil was 239,149 tons in 2008, and the harvested area was 21,326 ha (ANUÁRIO BRASILEIRO DA FRUTICULTURA, 2010).Located in a warmer climatic region, São Paulo State contributes with around 10% planted area and 23% national production, presenting 21.5 t/ha/year mean productivity, as well as economic potential for the cultivation of peach and nectarine trees.The state has the early fruit harvest as its great advantage not only over the main Brazilian producing regions, but also over most countries located in the Southern Hemisphere, such as Chile, Argentina, Uruguay and South Africa (PEREIRA et al., 2002).
In subtropical regions, specific procedures for orchard management are necessary, especially nutritional control, in which balanced and satisfactory mineral nutrition factors are related to good harvests at the stages of plant production and formation.Fructification and production for most temperate fruit plants, including peach trees, are S. LEONEL et al.
initially associated with the suitable development of flower buds.Thus, nutritional and phytosanitary management, as well as suitable environmental conditions to break dormancy, are essential (NAVA et al., 2009).An adequate nutritional status of flowers leads to higher and effective fructification for most fruit species, and nutritional competition is also frequently associated with low fructification levels in several fruit trees.The competition for nutrients during flower bud differentiation originates malformed flowers, negatively affecting fructification (CROSSA-RAYNAUD et al., 1985).
Early defoliation is a serious and very common problem in the main peach producing regions in Brazil, especially in São Paulo State, where the temperatures of the cultivated areas are higher.According to Nava et al. (2009), early defoliation, caused by either environmental and nutritional issues or phytosanitary problems, usually decreases carbohydrate levels in the plants, affecting their fructification.Some reports in the literature consider that a suitable nutritional status of flower buds may overcome the effect of high temperatures during flowering due to the prolongation of the pistil receptivity time (GAO et al., 2002 andWOLUKAU et al., 2004).
Since nutritional management of peach and nectarine trees cultivated in subtropical regions is still little known, especially regarding leaf fertilization and different cultivar requirements, this study aimed to evaluate the leaf nutritional content for peach and nectarine cultivars at different phenological stages over the production cycle in order to provide information for fertilization techniques under those conditions.
The plants from the experimental area aged 7 years and were spaced 6.0m between plants x 4.0m between rows, in a dryland area.The rootstock 'Okinawa' was used for all canopy cultivars.To assure the good development of plants, cultural and phytosanitary procedures were performed during the whole experimental period by following technical recommendations (PEREIRA et al., 2002).
Samples of recently mature complete leaves (blade with petiole) were harvested from the medium portion of current-year branches in the different plant quadrants (Malavolta et al., 1997).Eight leaves were harvested from each plant, totaling three plants per plot, with four replicates.The total sample was composed of 96 leaves for each evaluated cultivar.The levels of the nutrients N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn were quantified, according to the methodology proposed by Malavolta et al. (1997), in the Laboratory of Plant Mineral Nutrition.Harvests occurred: 1 -after fruit harvest, at the vegetative stage (February); 2 -during the dormancy period (May); 3 -at flowering beginning (August); and 4 -from the 13 th to the 15 th week after full flowering, before harvest − fructification (October−November); this period is considered ideal to compare leaf patterns (LEECE & BARKS, 1974;JOHSON & URIU, 1989;FREIRE & MAGNANI, 2003).
The experimental design was subdivided plots, in which plots corresponded to the cultivars evaluated, and the subplots, to the leaf harvests in 2009.The obtained results were sub�ected to analysis of variance and, as for significance, means were compared by Tukey's test at 1 and 5% probability.

RESULTS AND DISCUSSION
There were significant variations in the levels of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn according to harvests (Tables 1 to 6), which confirms that the uptake of mineral elements by peach trees varies with the plant physiological stages over the production cycle.The highest levels of N, S, B, and Zn were detected at the third harvest, corresponding to the onset of flowering.As regards P levels, the highest values were obtained at the third (flowering onset) and fourth (fructification) harvests.K and Ca levels were highest in the fructification period (fourth harvest), which corroborates the statement that these elements are essential to fruit quality in this period.The highest Mg and Mn levels were observed in the dormancy period (second harvest).At the first (after collection) and third (flowering onset) harvests, Cu levels were highest.Fe was highest at the second (dormancy) and third (flowering onset) harvests.
Johnson et al. ( 2006) emphasize that, although leaf sampling is worldwide recommended during the fructification stage, when the requirement for most nutrients is highest since fruits are the strongest plant drains, other periods can lead to better uptake of different nutrients, as observed in the present study.These authors also reported that leaf sampling during fructification can be considered very late to fulfill the fertilization requirements of the annual growth season.Based on this statement, the same authors evaluated leaf harvest during the dormancy period and observed a good response for N, P, B, and Zn.In their opinion, the other nutrients did not present response because deficiency symptoms had not been induced yet.
The present results for the levels of N, P, K, Cu, Mn, Zn, and Fe were within the normal range, although there were differences regarding leaf harvests.Ca and Mg levels were below the recommended patterns, whereas B levels were above those values.S levels could not be compared since there were no reports on this element in the literature.
As regards nutrient uptake by the different evaluated cultivars, there were significant variations in the levels of N, Ca, Mg, S, B, Fe, and Mn, with different responses according to the nutrient.In general, leaf macronutrient uptake by the evaluated cultivars was in the following order: N>K>Ca>P>Mg>S.For micronutrients, the order was: Fe>Mn>B>Zn>Cu.According to Fachinello et al. (1996), nutrient export (kg/t) by fruits, pruned branches and leaves is: N (3.5),P 2 O 5 (1.05) and K 2 O (5.5), without considering the growth of peach trees.Malavolta (1980) reported that the levels of macronutrients (kg/ha) exported over peach fruit harvests (kg/ha) are: N (70); P(6); K (40); S (4); Ca (1.2); and Mg (2.4).
The results of the present study agree with those in the specialized literature, which state that nitrogen presents the highest uptake and the highest influence on peach tree productivity (Rombolá et al., 2000) since it directly affects the vegetative branch growth (Mattos et al., 1991), the number of vegetative and flower buds, and the number of fruits per plant.This nutrient can provide a longer period of leaf permanence, consequently increasing the period of reserve accumulation for the subsequent cycle (SERRAT et al., 2004).However, excessive supply can lead to oversprouting, which results in excessive shading, decreasing the fruit exposure to sunlight (MATTOS et al., 1991).Means followed by different uppercase letters in the column and lowercase letters in the line differed according to Tukey's test at 5% significance.

CONCLUSIONS
1.There were variations in the levels of N, Ca, Mg, S, B, Fe, and Mn for the different cultivars, with different responses according to the nutrient.As regards harvests at the different phenological stages of the peach tree, there was a difference in the leaf level of all evaluated nutrients.2. In general, macronutrient uptake by the evaluated cultivars was in the following order: N>K>Ca>P>Mg>S.The order for micronutrient uptake was: Fe>Mn>B>Zn>Cu.

TABLE 1 -
Nitrogen and phosphorus levels (g kg -1 ) in leaf samples of peach and nectarine cultivars at different harvests.Botucatu, 2009.Means followed by different uppercase letters in the column and lowercase letters in the line differed according to Tukey's test at 5%

TABLE 2 -
Potassium and calcium levels (g kg -1 ) in leaf samples of peach and nectarine cultivars at different harvests.Botucatu, 2009.

TABLE 3 -
Magnesium and sulfur levels (g kg -1 ) in leaf samples of peach and nectarine cultivars at different harvests.Botucatu, 2009.Means followed by different uppercase letters in the column and lowercase letters in the line differed according to Tukey's test at 5% significance.
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TABLE 5 -
Iron and manganese levels (mg kg -1 ) in leaf samples of peach and nectarine cultivars at different harvests.Botucatu.2009.Means followed by different uppercase letters in the column and lowercase letters in the line differed according to Tukey's test at 5% significance.S. LEONEL et al.TABELA 6 -Zinc levels (mg kg -1 ) in leaf samples of peach and nectarine cultivars at different harvests.