APPLICATION OF K, Ca, and Mg ON PEEL THICKNESS AND FRUIT CRACKING INCIDENCE OF CITRUS Hardiyanto* Indonesian Center for Horticultural Research and Development, Bogor, Indonesia

Citrus cv. Terigas (Citrus reticulata) genetically has a fragile fruit peel that occurs from young up to mature stage which causing farmers to suffer detrimental lost in production. The addition of K, Mg, and Ca can reduce the number of damaged fruit. This research was conducted at the Tlekung Experimental Field, Indonesian Citrus and Subtropical Fruits Research Institute (ICSFRI) in January October 2017, using 4-year-old Mandarin cv. Terigas and Tangerine cv. Pontianak citrus plants. The aims of this study was to evaluate the effect of K, Ca and Mg fertilizers on nutrient uptake in plants, fruit development, and the percentage of cracking fruit on Mandarin cv. Terigas (Citrus reticulata) and Tangerine cv. Pontianak (C. reticulata Blanco.). The experiment was carried out in a Nested Design. The I factor was the application of K, Ca and Mg through foliar spray, consisted of P1 (Control/without fertilizing), P2 (recommended fertilization), P3 (P2 + 3 g l K + 1 g l Ca + 1 g l Mg), P4 (P2 + 6 g l K + 2 g l Ca + 2 g l Mg), and P5 (P2 + 6 g l KNO3). The second one was the variety, Mandarin cv. Terigas and Tangerine cv. Pontianak as a control. The treatment was repeated 3 times with a unit treatment of 5 plants. Observations were made on macro nutrient uptake on leaves and fruit skin, development of fruit size, number of cracking fruit/plant, size of fruit diameter, and thickness of fruit peel. The results showed that the cracking incidence of Terigas fruits was caused by the thinning of the fruit peels, where the thinner the peel of the fruit, the more fruit would be cracked (Y = 20.501 to 9, 9702 X, R = 67.5%), while the thickness of the skin was not influenced by nutrients absorbed in the fruit peel. Treatment P2 to P5 was able to suppress fruit cracking on Terigas Mandarin between 22 56.1% at age of 22 weeks and 14.9 42.6% at age of 26 weeks after flowering. Moreover, P3 can prevent 50% of cracking fruit/plant less than the control (P1). All treatments did not significantly affect on the thickness of peel fruit of Tangerine cv. Pontianak. This activity has an impact on increasing the quantity and quality production of Mandarin cv. Terigas.

colour (albedo) and an external layer/flavedo (exocarp). The pressure that occurs due to the rapid expansion of the pulp when the fruit develops will trigger the formation of cracks in the flavedo and it is the beginning of the breaking of fruit on the stylar, which is the weakest part of the skin of the citrus fruit. In addition, nutritional imbalance, low Ca and K and high P, conditions of hot and humid air, irregular irrigation, and plants with heavy fruit can also trigger fruit cracking incidence in some citrus varieties starting at the time the they begin to develop. Fruit in young trees tends to be more susceptible to cracking than older plants (Goodwin, 2008;Cronje et al., 2013).
Studies showed that field flooding during the dry season followed by fertilizer application was able to improve the quality of Terigas Mandarin fruit, including reduced broken fruit, increased fruit diameter (grade), reduced acid levels (%), and increased fruit sugar levels (Purba et al., 2016). The application of organic fertilizer + inorganic fertilizers + mulch + (Ca and B) accompanied by flooding ditches can reduce the number of broken fruit to 19.4%. This is in accordance with the opinion of Goodwin (2008), that damaged fruit can be reduced by maintaining optimal environmental conditions for plant growth, including watering and adequate nutritional intake. The condition of deficiency of K elements will cause thin fruit skin which will encourage breakage on the fruit. The use of mulch and compost will also maintain the degree of moisture in the soil, while the application of slow release fertilizers will be enough to help provide food intake evenly.
According to El-Tanany et al. (2011), spraying K, Ca and Mg on leaves once to three times also increases the number of fruit set per branch and the number of fruit/plant. In addition, this treatment also increases the speed of fruit development, significantly reducing the broken fruit and increasing the quality of WNO sweet orange fruits. Also added by El-Rahman et al. (2012), that K applied in the form of 4-6 % KNO 3 significantly increases skin thickness thereby reducing the incidence of cracking, increases fruit size, and production, while the combination of KNO 3 5% + 2.4 D 20 ppm sprayed 60 days after flower blooms will increase fruit size (Boman & Hebb, 1998;Rattanpal et al., 2005;Vijay et al., 2016). Improvement of irrigation management, mulching, manure application, as well as other inorganic additions can reduce fruit cracking on lemon (Sandhu & Bal, 2013).
Fruit cracking can also be reduced by other growth regulator applications. The addition of Zn and NAA during the enlargement phase of Shatangju citrus will encourage an increase in IAA, GA 3 and tryptophan at the beginning of the development of the skin, thus inducing cell growth and division, reducing the variation in skin hardness and reduce cracking on the albedo which will reduce broken fruit (Li et al., 2016).
The justification of the research is that in less optimal conditions of citrus plants, the fruits of Terigas Mandarin tend to crack. On the other hand, the addition of K, Mg, and Ca by foliar spray on them would be reducing the number of damaged fruit. The aim of this study was to evaluate the effect of foliar spray of K, Ca and Mg fertilizer on nutrient uptake in plants, fruit development, fruit peel thickness, and percentage of fruit cracking in Terigas Mandarin (Citrus reticulata) with Pontianak Tangerine (C. reticulata Blanco) as a control variety.

MATERIALS AND METHODS OF RESEARCH
Note: V1 = Terigas Mandarin; V2 = Pontianak Tangerine Figure 1 -The layout of the treatments Experiment was done by adding minerals K, Ca and Mg by spraying on the leaves of plants. The treatment consisted of 2 factors, first factor was the treatment of spraying (P) and II was citrus varieties (V), with each treatment consisted of 5 plants and repeated 3 times ( Figure 1). Experiments were carried out in a nested design, with models: Y ijk = μ + B k + R (B) + A j + AB ij + ε ijk .
The spray dosage treatment was as follows: P 1: Control, plants were not fertilized; P2: Fertilization treatment according to field standards (1 kg/plant of Ponska and ZA); P3: P2 + Fertilizer K 3 gram/l + Fertilizer Ca 1 gram/l + Fertilizer Mg 1 gram/l (sprayed in January, February and March 2017); P4: P2 + Fertilizer K 6 gram/l + Fertilizer Ca 2 gram/l + Fertilizer Mg 2 gram/l (sprayed in January, February and March 2017); P5: P2 + KNO 3 6 gram/l (sprayed in January, February and March 2017). Observation Parameters:  The content of macro nutrient on leaves and fruit peels. Analysis on macro nutrient uptake was carried out at the Soil Analysis Laboratory, Faculty of Agriculture, Univ. Brawijaya Malang, East Java-Indonesia. Analysis of N, P, K, Ca, and Mg leaves was carried out 20 days after the final treatment;  Fruit size. Observation on development of fruit size was carried out by measuring the diameter of the fruit in 20 samples/plant. Fruit samples were determined on branches in the direction of 4 winds, 5 fruits/branches. Fruit development measurement is the increase in the average size of the diameter (fruit diameter in (n + 1) month -fruit diameter in (n) month;  Number of fruit cracking that is observed every month;  At harvest time: fruit diameter, fruit skin thickness (transversal fruit cut, thickness);  Statistical analysis. Data collected was analysed by ANOVA using Minitab 16 program.

RESULTS AND DISCUSSION
Nutrients content in the leaves and fruit peels of Terigas Mandarin and Pontianak Tangerine. In general, the average content of N, P, and Ca absorbed in the leaf level was higher than in the peel of its fruit, whereas K and Mg were not significantly different (Table 1). Coetzee (2007a) mentioned that the total N content on citrus cv. Valencia Late Orange (VLO) ranged from 700 -900 g/plant, with a composition of 40% and 20% for leaves and fruit respectively; 30 % in buds, branches, stems; and the rest (10%) in the roots. Moreover, Dalal et al. (2017) reported that the maximum N content in leaves reached 2.51% after foliar application of 3% KNO 3 , and this level was not significantly different compared to other treatments. Higher nutrient levels in the leaves are assumed to be due to differences in the way they are absorbed. According to Coetzee (2007a), Ca is absorbed by plants and then translocated passively to leaves and fruit through water flow. The process of transpiration of young leaves is much higher than that of young fruit, so that the flow of water and Ca that are carried will be even higher. The accumulated calcium cannot move to other tissues. This causes the Ca levels to be high after the application of foliar spray. The remaining calcium that is not used by plants will be deposited in the form of calcium oxalate which is not soluble in water. Calcium absorbed in 2010).
Potassium is mobile and transported to meristem tissue. caused due to relocation, i.e. mobility and always on the move before after spraying application. impact on increasing the size absorption efficiency in the field Mandarin and Pontianak Tangerine relatively higher than the others. Ruby) was higher than other macro minerals is absorbed in different  Effect of varieties and foliar nutrient levels absorbed in the dosages ( Table 3). The levels fertilized) were in the optimal condition. Under these conditions, on the leaves does not have application of mineral nutrients metabolic processes, plant growth treatment P4 where the nutrient content absorbed in the leaves RJOAS, 3(87), March 2019 48 in the fruit skin will affect the quality of the and generally enters the plant due to absorption tissue. Apart from absorption, nutrient content .e. from old to young tissue (Coetzee, 2007b move, the remaining content in the leaf tissue application. However, the addition of K application of fruit diameter compared to the control treatment, field was only ± 25% (Coetzee, 2007c). On Tangerine fruits, the average nutrient content others. Singh et al. (2015) reported that Ca in macro nutrients, as the fruits get older. Therefore different patterns ( Figure 2). in the skin of grapefruit (cv Star Ruby) (Source: Singh correlation analysis, there was no relationship between ( Table 2). The same trends was also reported differences in the levels of mineral nutrients in the leaves way they are absorbed or relocated.
between macro nutrient uptake in leaves and on foliar application of K, Ca and Mg on leaf nutrient the leaves are influenced by interaction of varieties s of N, P, K, and Mg absorbed in the leaves optimal range. This shows that the 4-year old plants conditions, it is suspected that the addition of fertilizer have much effect on the increase of absorbed nutrient nutrients through leaves is thought to be directly growth and development. This can be seen in nutrient content is raised 100% compared to P3, leaves tends to decrease. fruit (Blanco et al., absorption by the roots and in a tissue is also 2007b). Due to higher tissue is not higher than application will still have an treatment, although its the skin of Terigas content of N and Ca is grapefruit (cv Star Therefore each of these Singh et al. (2015) between nutrient uptake in reported by Coetzee  Based on the range of nutrients absorbed in the leaves, all nutrients found in Terigas Mandarin and Pontianak Tangerine were in the optimal level category. The optimal K and P levels in the leaves of citrus plants ranged between 0.10% -0.16% and 1.0% -1.5%. The same trend was also reported by Conell (2018) ( Table 4).  Effect of varieties and foliar application of K, Ca and Mg on nutrient levels in fruit peels. The interaction of aplication and varieties had significanty difference on N absorption. The N uptake was highest in the treatment of the combination of P1V1 and P3V1 namely 1.40 and 1.35%, but P3V1 was not significantly different from the 3 other treatment combinations in Terigas Mandarin; whereas in the combination of nutri Tangerine, N uptake in fruit peels tends to be lower than all treatments in Terigas Mandarin (Table 5). This difference in absorption ability may be related to the genetic traits of the plant.
The highest N level on other treatments. Suspected growth of the plants was slower This condition causes the process no competition with the same fruit skin.
N and Ca absorption was content was high but Ca was thought to be due to the genetic the vulnerability of Terigas Mandarin & Jiezhong (2017), Ca nutrient reduce the occurrence of degradation reduction in the process of fruit be caused by high N uptake in high absorption of water and Ca compete with leaves in the absorption  1.35%, but P3V1 was not significantly different from the 3 other treatment combinations in Terigas Mandarin; whereas in the combination of nutrient addition treatment in Pontianak Tangerine, N uptake in fruit peels tends to be lower than all treatments in Terigas Mandarin ). This difference in absorption ability may be related to the genetic traits of the plant. fruit skin was in P1V1 treatment due to better in P1V1 (control plants, without fertilization) slower than other plants because of lack of nutrient process of N uptake in the fruit skin to be better process in the leaves, which then increases was significantly affected by varieties. In Terigas was lower than Pontianak Tangerine (  foliar spray (P4) is that is raised 100% compared to P3 in plants that are just 4 years old. Thus, it will encourage a higher vegetative growth, resulting in uptake of N, Mg, and more water to the leave. Meanwhile, uptake in fruit peels will be reduced as occurs in other nutrient minerals .
Effect of varieties and foliar application of K, Ca and Mg on fruit growth. In general the interaction of varieties with the application of K, Ca, Mg through leaves had significantly different. Fruit size increased in the 2 nd (March) to the 5 th month (June), it was in accordance with the development of its diameter. In the combination of the spraying treatment of K, Ca, and Mg in the Pontianak Tangerine produced a larger size than that of Terigas Mandarin (Table 6). At the beginning of the treatment or observation (in February 2017), the fruit size ranged from 29-34 mm and 24-33 mm for Terigas Mandarin and Pontianak Tangerine, respectively. The increment of fruit diameter on Pontianak Tangerine was higher than that of Terigas Mandarin, so the average fruit diameter at the end of the observation (June) was also higher, 52.5 mm and 48.6 mm respectively ( Figure 5).  In Terigas Mandarin, the diameter better than the control and Ca which is applied through January to March). This is in and Dalal et al. (2017) on Washington oranges cv. Jaffa. Number of nutrient had added through foliar increase in photosynthesis, so activation also increase in influencing photosynthesis, Nevertheless, according to Morgan with the quality, size and thickness will significantly inhibit the development of fruit and thinner fruit skin, Tangerine (P1) was better than respond to the addition of P, K, Effect of varieties and foliar fruit. The incidence of fruit cracking 22 weeks after the flower blooms Lin & Chen (2017), the occurrence fruit will develop normally, where inside, and the oil gland has increase in the volume of fruit susceptible varieties, these developments the occurrence of cracks on the In Terigas Mandarin, significantly different between tends to produce more damaged foliar spray (P2 to P5) can suppress to 56.1% at the age of 22 weeks, bloom (May and June) (Table  methods and use of rootstock. In the development much related, namely cell division, cell development al., 2011). In the second phase, rapid fruit growth environmental factors. In sweet oranges, phase I is achieved at 2-6 months, while the next phase until harvest et al., 2011); whereas in lime, from phase II Suleiman, 2013). This also occurs in Terigas Mandarin Figure 5, in which the diameter increases very followed by a slowdown in phase III (June 2017). the treatment of P4 and P5 encourages the control (P1). The response is probably due to the through the leaves right at the fruit development phase accordance with a study conducted by El-Tanany Washington Navel Orange (WNO), Kinnow Mandarin of fruit/branches as well as fruit diameter increased foliar spraying. Aplication of K through foliar so that protein synthesis, carbohydrate metabolism, developing fruits (Hasanuzzaman et al., K also causes cell wall formation (Yadav Morgan et al. (2005), the P element in plants thickness of fruit peels, whereas, K is very influential. development of fruit, therefore the plant will produce skin, encouraging cracks on the skin. Fruit diameter than P5 treatment, this suggests that these K, and Ca in phase II. foliar application of K, Ca and Mg on total number cracking only occurs in Terigas Mandarin which blooms) or in phase II fruit development (Figure occurrence of cracking in citrus fruit is a gradual process. where the skin of the fruit develops normally, has a normal shape and arrangement. In stage fruit flesh, resulting in progressive changes in developments led to the fruit skin become thin the skin (Cronje et al. 2013  In treatment P3, the level of total fruit damage can be reduced to 50% compared to the control. This is in line with the results of the study El-Tanany et al. (2011) in WNO citrus plants on which he applied K, Ca, and Mg nutrients once, two, and three times with a concentration of 300 ppm K + 100 ppm Ca + 20 ppm Mg, resulting in a reduction in the percentage of broken fruit compared to controls along with the thickness increase in the skin of the fruit.
Effect of varieties and foliar application of K, Ca and Mg on fruit skin thickness. The treatment of varieties, the application of K, Ca, and Mg through leaves and their combinations did not significantly affect the skin thickness of the intact fruit. The average thickness of Terigas Mandarin and Pontianak Tangerine was 2.24 and 2.27 mm in May and 2.12 and 2.05 mm in June, respectively (Table 8). The development of fruit skin thickness in the two varieties is in accordance with the phase of growth and development which is differently intervals for each variety. According to Lu et al. (2017), in Satsuma Mandarin the development of fruit is characterized by the increase of diameter size along with the thickening of fruit skin until the age of 30 days. Then with increasing age, the size of the fruit increases but the thickness of the skin decreases until the ripening phase.
The occurrence of broken fruit in Terigas Mandarin began in May, with an average number per sample of 2.8 and 3.6 in May and June, respectively. The thickness of the fruit peel was not significantly affected by all treatments. The thickness of fruit peel on normal fruit is higher than that of broken fruit, both in May and June observations, whereas for control (P1), the fruit skin tends to be thinner than other treatments (Figure 7). Based on macro nutrient that the levels are classified absorbed nutrient levels optimally shows that nutrient factors are factors that influence it. Moreover, not followed by the absorption depletion of fruit peels when optimal, including nutrient imbalance, peel do not significantly affect occurrence of thinning on the the plant itself. The application of the skin and prevent degradation and galactose, and increase 2010). However, according to sweet orange fruit has no correlation fruit.  (Table 7), the number of (May). are not a single factor in the damage, but there Moreover, the decreasing pattern of average fruit absorption pattern of the fruit (Figure 8). According to Cronje fruit develops is because the environmental imbalance, low Ca and K and high P. If the nutrients affect the thickness of the fruit skin, it is suspected the fruit skin is much influenced by the genetic application of Ca to plants should increase levels of Ca degradation of pectin, cellulose and hemicellulose, levels of water-soluble pectin on the cell wall to Morgan (2005), the level of Ca present in the correlation with the quality, juice content and skin absorption of Ca, K, and P on the fruit peel Terigas Mandarin formed, the higher and more significant the number regression equation Y = 20, 501-9, 702 X (R2 = 67.5%).
the causes of cracking in citrus fruit is because withstand the pressure caused by the rapid expansion phase. With the decrease of the Terigas Mandarin of broken fruit also increased compared to the 0,00 0,50 number of cracking 67.5%). According to because the skin is not expansion of the pulp Mandarin skin thickness in the previous month

CONCLUSION
The incidence of fruit cracking in Terigas Mandarin is caused by the decrease of fruit skin with the equation Y = 20.501 -9.702 X (R2 = 67.5%), however the thickness of the fruit skin does not correlate significantly with nutrient content in the fruit skin. Likewise, nutrient levels in fruit peel also do not correlate with nutrient levels in leaves.
Cracking of fruit in Terigas Mandarin is caused more by genetic traits; it is more sensitive than control variety (Pontianak Tangerine) P3 treatment is able to prevent 50% of cracking fruit per plant sample compared to treatment P1 (control).