* Results and discussion
* Literature Cited
ABSTRACT: The orange (Citrus sinensis (L.) Osbeck) has high potassium requirements. Nutritional studies in Chile Orchards Have Identified orange leaf with contents below-the critical level (7.0 g kg-1). The Objective of this study Were to Evaluate the potassium Fertilizers KCl, KNO3, K2SO4 and K-MgSO4 (double salt of potassium and magnesium) and to determine Their effects on fruit quality and yield after three years of annual applications. Eighteen-year-old orange trees (cv. Valencia) grown on soil series La Rosa Mollisol Were classed as used. Conventional furrow irrigation with three rows Between the Furrows WAS employed. The average initial WAS leaf K concentration 5.7 g kg-1 s, which corresponds to a low level. The available K level in the WAS soil medium, from 0 to 20 cm in depth, and low, from 20 to 40 cm. INCREASED The foliar K content in the second year in the KNO3 and K2SO4 Treatments and in the third year in all the Treatments with Regard to the control. The Highest K WAS Obtained with KNO3 concentration (6.8 g kg-1). INCREASED K-MgSO4 from a low Mg concentration (2.1 g kg-1) to an optimum level (2.6 g kg-1). KCl raised the leaf chloride content of from 0.11 to 0.15 g kg-1. No increment in fruit yield Occurred But fruit size did increase. Treatments with potassium Also INCREASED juice acidity.
Key words: potassium, orange tree, Citrus sinensis, leaf analysis, fruit size.
SUMMARY: The orange (Citrus sinensis (L.) Osbeck) has high potassium requirements. Nutritional studies in Chile have identified orchards foliar contents below the critical level (7.0 g kg-1). The study objectives were to evaluate the potassium fertilizers KCl, KNO3, K2SO4 and K-MgSO4 (double salt of potassium and magnesium) and determine the effects on fruit quality and performance after three years of implementation. Trees were used cv. Valencia, 18, planted in soil for Series La Rosa, classified as Mollisol. Irrigation with conventional furrow with three furrows between the rows. The average concentration of initial foliar K was 5.7 g kg-1, which is a low level. The level of available soil K was medium to low to 0-20 cm and 20-40 cm deep. The foliar K content increased in the second year in KNO3 and K2SO4 treatments and in the third year in all treatments, compared with the control. The highest concentration of K was obtained with KNO3 (6.8 g kg-1). The K-MgSO4 Mg concentration increased from a low level (2.1 g kg -1) at an optimal level (2.6 g kg-1). KCl increased leaf chloride content from 0.11 to 0.15 g kg-1. Not submitted increased fruit yield, but the size of it. K treatments produced an increase in the acidity of the juice.
Keywords: potassium, orange, Citrus sinensis, leaf analysis, fruit size.
Nutritional studies conducted in citrus orchards in Chile by Benito and Ruiz (1975) found that a significant number of them the contents of potassium (K) leaf were low. These studies also noted that Chile did not apply K in the orange groves.
Citrus fruit within species, are identified as highly extractive K, with the particularity that the fruit is high in this nutrient. The annual removal of K in the orange (Citrus sinensis (L.) Osbeck) is about 100 kg ha-1 for a yield of 40 t ha-1 (Koo, 1985) and the export of K for the fruit is order of 40 kg ha-1, according to data cited by Kampfer (1966), which means that the fruit of the orange contains about 40% of total K absorbed.
Several publications indicate the effects of K application on citrus, which are particularly relevant in the fruit. In general, an increase in the level of K determines an increase in fruit size in the thickness of the peel and juice acidity. These effects have been cited by Smith (1966), Chapman (1968) and Embleton et al. (1978).
K fertilization in citrus is often performed with potassium sulfate in the market but there are other potash fertilizers as alternatives. In this regard, Davies and Albrigo (1994), noted that the K in citrus is usually given as chloride, sulfate or potassium nitrate. In Chile to date no research has been conducted with K applications in citrus, nor have compared different potassium fertilizers in orange.
The aim of this study was to evaluate the effects of different potassium fertilizers on the mineral nutrition, production, size and fruit quality in orange.br>
Materials and methods
In the present study orchard was selected with the following characteristics: it must correspond to the cv. Valencia, as it is the most planted in Chile, to be in full production, considering the high demand for K by the fruit; be homogeneous trees, with excellent management and disease control, besides presenting the level of the lowest leaf K. At the Hacienda La Rosa de la Sociedad Agricola La Rosa Sofruco SA found a garden with these characteristics, which was chosen for the test. The trial was established in the Garden Possessions, the Hacienda La Rosa, located in Peumo, Cachapoal Province, Region VI (34 ^0 19 ‘lat. 71 ^0 15’ W long.).
The trees correspond to orange (Citrus sinensis (L.) Osbeck) cv. Valencia grafted on Troyer citrange. The orchard was 18 at the time of the baseline and the planting distance was 7 x 7 m. The garden is watered by furrows and weeds were controlled with Harrow in the inter row work approximately three annually, and in line with herbicide. In the orchard fertilization program in the years prior to the test only applied urea at a dose of 980 g per tree in the month of September (end of the winter season), which was maintained during the period of investigation.
The soil corresponded to Serie La Rosa, classified as coarse Franca family, mixed, thermic, Calcic Haploxeroll subgroup, order Mollisol (CIREN, 1996). Alluvial soil located in one of the Cachapoal river terraces, deep, silty loam, sandy clay loam to loamy surface. Drainage is moderate to good, moderately rapid permeability, moisture regime is xeric. Average annual rainfall is 505 mm and average annual temperature 19.1 ^0 C with a frost-free period of 11 months. Some soil chemical properties are presented in Table 1.
Table 1. Some chemical properties of suelo1.
Table 1. Some chemical properties of the soil.
1 OM = organic matter, EC = electrical conductivity, CEC = cation exchange capacity.
Potassic fertilizers used corresponded to the common market and were analyzed at the Institute of Agricultural Research Laboratory Fertilizer Research Center of the Plate, in order to verify your grado.fertilizante. The results are presented in Table 2.
Table 2. Concentration of mineral elements in the fertilizers used.
Table 2. Concentration of mineral elements in the Fertilizers employed.
1 To convert percentage of K2O to K rate divided by 1.2.
2 Although the potassium and magnesium sulfate has the formula K2SO4 – MgSO4, this article is abbreviated as K-MgSO4. Corresponds to the double salt of potassium sulfate and magnesium sulfate, with a small amount of sodium chloride.
The treatments were: 1. Control (without application of potassium). 2. Potassium chloride (KCl). 3. Potassium nitrate (KNO3). 4. Potassium sulfate (K2SO4). 5. Potassium and magnesium sulfate (K-MgSO4). Fertilizers were applied by hand in mid October each year (1990, 1991, 1992) in two rows, one on each side of the projection of the tree, the depth of 25 cm. Every year we used a dose equivalent to 3 kg of K2O per tree.
The experimental design was a randomized complete block with five treatments and six repetitions. The experimental unit (a tree) was completely isolated for eight untreated trees as a border.
To characterize the soil, in September 1990 composite samples were taken at four points of the garden with borehole to the depth of 0-20 cm and 20-40 cm for the composite sample taken 15 samples in the projection of the top of trees before the test set.
Analyses were performed at the Laboratory of Soil and Water Chemistry, Faculty of Agricultural Sciences, University of Chile. The methods were: pH by the potentiometric method in the supernatant of a suspension of soil: water 1:2.5, organic matter (OM) by the method of wet oxidation Walkley-Black, electrical conductivity (EC) by conductivimetria in the extract of saturation, cation exchange capacity (CEC) by the method of saturation with 1 M sodium acetate at pH 7.0, using percolation exchangeable cations by the method of percolation with 1 M ammonium acetate at pH 7.0, Na and K were measured by flame photometry and Ca and Mg by atomic absorption spectrometry (AAS).
Foliar analysis were performed before setting the trial and then annually, for which samples were taken from leaves with petioles in each experimental unit in the first week of March for the outbreak of spring. Shoots were chosen fruitless and new growth. Individuals were collected 50 leaves per tree, taken in the shape of the tree at a height of about 2 m, as recommended by Embleton et al. (1978). They took the second and third leaf from the shoot tip to the base as standard approach.
Leaf samples were analyzed in the Leaf Analysis Laboratory at the same college. The samples were dried at 65 ^0 C and ground in a mill mark mesh Wiley 20. The N was determined by micro-Kjeldahl method and the Cl-specific electrode method. The K was determined by the method of flame photometry and Mg by atomic absorption spectrometry after the sample calcined at 525 ^0 C and dilution with concentrated HCl.
To determine the effects of K application on yield and quality of fruit each year following measurements were made per tree, number and weight of fruits at harvest fruit size in the line of “packing” thick peel and juice acidity by titration with 0.1 M NaOH The latter two variables were determined in a representative sample of 60 fruits per tree, taken at random.
The results were submitted to ANOVA and when significant differences were found between treatments (P lb 0.05) were tested by Duncan multiple comparison.
Results and discussion
Table 1 shows some properties of garden soil. The values of the CIC and MO indicate that this is a good soil fertility and chemical properties. Ca saturation is high and low Na, a condition favorable for this kind of fruit.
The EC is slightly high (2.7 dS m-1); for orange notes and recommended a lower value of 2.4 dS m-1 (Ayers and Westcot, 1987). The content of exchangeable K on the surface is medium, but 20 – 40 cm level is low by the standards cited by Cottenie (1984).
The low content of exchangeable K in depth could explain the lower foliar concentrations of K (initial values lower than 7.0 g kg-1). This as a result of mechanical tilling the soil is handled in this garden, which has led to the development of roots at the bottom of the profile. Foliar Mg concentrations also were at the low range, according to standards established by Embleton et al. (1978), who noted as low range for Mg concentrations between 1.6 and 2.5 g kg-1, deficiency has also been characterized in orange orchards in Chile (Benito and Ruiz, 1975; Razeto, 1985).
Yield and fruit number per tree
Table 3 shows the yield per tree and fruit number. As can be seen, no significant differences between treatments. Assuming an average yield of 220 kg per tree, the estimated yield for the orchard is 45 t ha-1, is considered high and very similar to those reported by Koo (1985) for U.S. conditions
Table 3. Effect of treatments on yield, fruit number and average fruit weight in the third year of implementation.
Table 3. Effect of Treatments on yield, fruit number and mean fruit weight at the third year of application.
1Letras different in each column indicate significant differences between treatments (P <0.05).
Embleton et al. (1978) noted that K can increase fruit yield and number of fruits harvested when the concentrations of it in the leaves are very low (in the range of 3.0 to 5.0 g kg-1). About 7.0 g kg-1 K in the leaves is unlikely to increase performance. Alva and Tucker (1999) indicated a low concentration level of 7.0 g kg-1 of K. The lowest concentration found in the trees of the garden at baseline was 5.0 g kg-1. On the other hand, the orchard had a high production potential, indicating that K was not limiting the performance and only affected the fruit size, as was shown with the results of this study.
Foreign recommendations indicate the desirability of K with levels above 7.0 g kg-1 K in the leaves only when the fruit is small and comes puffing (“creasing”) (Embleton et al., 1978). The puffing corresponds to a soft shell that collapses when pressed with fingers. This is also indicated by Davies and Albrigo (1994), who noted that a low level of K in leaves relates to a small-sized fruit with thin skins. The thin skin predisposes to the parting of the fruit, a breakdown of the shell in the area of the pedicel at harvest and puffing. In the garden where a study was performed revealed a low presence of puffing and, therefore, not assessed.
Average fruit weight
The average fruit weight increased significantly (P <0.05) in the third year of implementation (Table 3), indicating the K as a factor in the problem size (size of the fruit). This coincides with Embleton et al. (1978), who found that low a concentration of 13.0 g kg-1 K in the leaves, the application of K increased fruit size. Koller and Schawarz (1995) in Citrus sinensis x Citrus reticulata also found that high levels of K fertilizer increased the mean fruit weight.
Potassium chloride (KCl) and potassium nitrate (KNO3) increased significantly (P <0.05) the average fruit weight. The values in the treatments with potassium sulfate (K2SO4) and magnesium potassium sulfate (K-Mg SO4), even higher than the control were not significant, suggesting that the effect of fertilizers on the last two weight the result would be slower. These results are related to K concentrations in leaves in the third year (Table 6).
Table 4 shows the calibration values expressed as a percentage per treatment. The gauge number is the number of fruit packed in a box of 18 kg, therefore a higher value corresponds to a smaller fruit. According to the results, the treatment showed the highest percentages of smaller fruit, while KNO3 and KCl treatments the highest percentage of large fruit. In general, confirms the significant effect with K applications in citrus fruit size (Smith, 1966, Chapman 1968, Embleton et al., 1978).
Table 4. Certain fruits gauge line “packing” in the third year of implementation, expressed as a percentage of total fruit.
Table 4. Fruit caliber in the packing line at the third year of application as Percent of total fruit.
Shell thickness, percentage of juice and juice acidity
Albrigo Davies (1994) reported that fruit size and shell thickness increased with increasing levels of K and the juice content decreases slightly.
In this essay, the shell thickness increased slightly in all treatments with K in the third year, but the differences were not significant with the control and the percentage of juice did not change, being the order of 40%. The acidity of the juice was higher in all treatments with K and significantly higher (P <0.05) in treatments KNO3, K2SO4 and K-MgSO4 (Table 5).
Table 5. Shell thickness, percentage of juice and juice acidity in the third year of implementation. Table 5. Rind thickness, juice and titratable acidity percentaqe in the third year of application.
1 Different letters in each column indicate significant differences between treatments (P <0.05).
Potassium concentrations in leaves
In Table 6 we can see that in the first year, applications of K did not significantly increase concentrations of this element in the leaves. In the second year the highest values corresponded to the treatments KNO3 and K2SO4. In the third year levels in all K application treatments were significantly (P 0.05) higher than in the control, which would confirm the slow response that usually have fruit trees to applications of K to soil ( Razeto, 1999). This slow response could be due to a fixation of K by the clay of this soil (25% clay). Wolf (1999) indicates that the exchangeable potassium in soil with 25% clay to be ten times higher compared to a sandy soil (2.5% clay) to have an adequate concentration of K in the soil solution .
Table 6. Potassium concentration in leaves for each year. Outbreak spring sample taken in March.
Table 6. Each year foliar potassium concentration. Spring shoot, sample Obtained in March.
1 Different letters in each column indicate significant differences between treatments (P <0.05).
The concentration in the control treatment was decreased to approach a value close to critical can affect performance. This suggests that the natural supply of soil K, together with an annual contribution in the irrigation water of about 23 kg K ha-1 was insufficient to compensate for making the tree removals, especially through the fruit. In fact, the lowest value of yield was obtained in the control (Table 3). There is a difference of almost 12 t ha -1 between the highest and the control.
For cv. Valencia, Carranca et al. (1993) reported a range of optimal K outbreak leaves without fruit between 4.0 and 5.3 g kg-1. In this experiment, in the third year only the control had a value close to the lowest level of foliar K optimal. However, according to standards used in California (Embleton et al., 1978), the witness would be at a low level, trees treated with KCl, K2SO4 and K-MgSO4 in the medium to low, and only those treated with KNO3 at an optimum level. Moreover, by the standards of Alva and Tucker (1999), no treatment reached the optimum level of K from 12 to 17 g kg-1.
Concentration of chloride, magnesium and nitrogen in the leaves.
In Table 7 we can see that the third year of treatment with KCl increased significantly (P 0.05) Cl concentration in leaves. In fruit trees are showing signs of toxicity at concentrations above 3.0 g kg-1, so that the value achieved is well below the value indicated by Ayers and Westcot (1987). Embleton et al. (1978) reported a value of 7.0 g kg-1 as excessive in citrus.
Table 7. Concentration of chloride, magnesium and nitrogen in the leaves in the third year of implementation.
Table 7. Chloride, magnesium and nitrogen concentration in the leaves at the third year of application.
1 Different letters in each column indicate significant differences between treatments (P <0.05).
Mg increased significantly (P <0.05) in the treatment with K-MgSO4 reaching the optimal range reported by Embleton et al. (1978). In the other treatments, the Mg is in a low level by the same authors. It is interesting to note the increase in foliar levels of K and Mg fertilizer gotten with this, considering that both are antagonistic in fruit, which is explained by the simultaneous contribution of both elements.
KNO3 treatment if it has the highest concentration value of N in leaves was not significantly different from other treatments. This is probably explained by the high level of N is present on all trees of the garden, as a result of annual fertilization with urea.
From the results obtained under the conditions of this investigation was conducted the following conclusions were obtained:
In orchards under conventional irrigation in a soil with 0.5 cmol (+) kg-1 of exchangeable K in the first 20 cm and 0.25 cmol (+) kg-1 between 20 and 40 cm, and mean concentrations of low potassium in the leaves does not increase yield or fruit number per tree, after three years of K fertilizer to the soil. Instead, it increases the size of the fruit, both in weight and size in the third year.
Compared the four fertilizers (potassium chloride, potassium nitrate, potassium sulfate and potassium sulfate and magnesium), the first two appear more rapid or efficient in its effect on fruit size.
Potassic fertilizers applied to soil under conventional irrigation, are slow in action, as the level of potassium in the leaves increased significantly only in the third year of implementation, with the exception of potassium nitrate and potassium sulfate and the effect should be presented to the second year.
Foliar potassium level decreases from year to year in trees that are fertilized with this item.
Applications of double sulphate of potassium and magnesium increase significantly the concentration of magnesium in the leaves.
The applications of potassium chloride significantly increased the concentration of chloride in the leaves, but within normal levels.
The applications of potassium nitrate, potassium as input, do not raise the leaf content of nitrogen to an excessive level.
The authors thank the Agricultural Society SA La Rosa Sofruco funding and facilities provided for the development of this research.
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Original publication: Agric. Tec [online]. oct. 2001, vol.61, no.4 [cited June 12, 2007], p.479-487. Available on the World Wide Web: <>. ISSN 0365-2807.
Reproduction authorized by: Technical Agriculture Magazine, hriquelm [at] inia.cl
Jose Domingo Opazo A. 2 and Bruno Razeto M.2 –
1 Original submissions: May 11, 2000.
2 University of Chile, Faculty of Agricultural Sciences, Box 1004, Santiago, Chile.