Evaluation of secondary macronutrients in mango ( Mangifera indica L.) Orchard of various districts of Sindh

of in Abstract This study was carried out to evaluate the soil and leaf tissue status of mango orchards of Matiari, Hyderabad, Tando Allahyar and Mirpurkhas districts of Sindh. In this regard, soil samples were analyzed for some physic-chemical properties (texture, EC e , pH 1:5 , calcium carbonate, organic matter, ammonium acetate extractable Ca, Mg and calcium chloride extractable S) at two soil depths (0-15 and 15-30 cm). The mango orchard soils of Hyderabad, Tando Allahyar and Mirpurkhas were silty clay loams except Matiari soils which were clay loams. The average pH values at surface and sub-surface soils falling in medium category. Organic matter content of 0-15 cm soil was higher (1.32, 1.32, 1.15 and 1.25 %) compared to 15-30 cm soil (0.87, 0.79, 0.86 and 0.86 %) respectively. Calcium carbonate contents of the study area varied from slightly calcareous (0-13%) to moderately calcareous (13-26%). The ammonium acetate extractable Ca, Mg and calcium chloride extractable S contents were 3016, 2971; 1127, 1228; and 42, 47 mg kg -1 in Matiari, 2921, 2721; 1215, 1389 and 45, 66 mg kg -1 in Hyderabad, 2740, 2583; 1424, 1478 and 207, 263 mg kg -1 in Tando Allahyar and 2866, 2882; 1244, 1222 and 285, 482 mg kg -1 in Mirpurkhas at 0-15 and 15-30 cm soil depth respectively. Total Ca, Mg and S contents in mango leaf tissue were 2.51, 0.64 and 0.54% in Matiari, 2.48, 0.69 and 0.37% in Hyderabad, 2.51, 0.67 and 0.62% in Tando Allahyar and 2.51, 0.61 and 0.60% in Mirpurkhas respectively. It can be concluded from this study that the Ca and Mg contents in soil were adequate and sufficient, and high in leaf tissues respectively. Generally there was no problem regarding S contents in soil and leaf tissues, however, 33% leaf tissue samples were low in each Tando Allahyar and Mirpurkhas.


Introduction
Pakistani mangoes are considered as a best and fetch a good price in international market due to their taste and flavor. Currently mango (Mangifera indica L.) is grown in more than 80 countries. Pakistan stands fourth largest mango producer and exporter in the world [1]. Sindh is a major mango growing province producing most of the varieties in district Matiari, Hyderabad, Tando Allahyar, Mirpurkhas, including Sukkhar, Karachi and some other districts [2,3]. Approximately, 62% of total mango production comes from Sindh province. Crop yield efficiency depends on the available nutrient status of soil [4]. Therefore an optimum supply and nutrients uptake shows a good response in growth of the plant and nutrient export. Sindh province is blessed with good climatic conditions, which not only can increase the production but improve the fruit quality to get better position in international market. Nutrients play vital role in the plants' growth, development, production and quality of fruit and mango is no exception to this. The major nutrients required by mango tree include macronutrients like nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S). These nutrients are required for different tree functions at different times. Nitrogen is required for mango tree vigor, vegetative and floral growth [5], P for cell division, growth and formation of sugarphosphate molecules, K for resistance against pathogens and insect pests, regulating water uptake [6] and fruit quality [7]. Whereas Ca provides membrane stability and strengthens cell walls, Mg is main part of chlorophyll and S is part of enzymes and proteins [8]. The optimum supply of these macronutrients at right time forms the basis for mango production on sustainable basis and ensures the fruit quality [9]. The secondary macronutrients i.e. Ca, Mg and S play a significant role in the production and quality of mango. Ca is greatly required in new flushes right after the harvesting of mango and in maintaining the fruit firmness which may disturb the Ca: N ratio in soil and leaf [10]. Calcium is considered as a secondary plant nutrient. Magnesium is the constituent of chlorophyll molecule. It is very important for the formation of seeds rich in oil. It supports in translocation of starches and regulates other nutrients uptake. Sulphur is the main and basic component of amino acids (cysteine and methionine) and therefore is indispensable part for synthesis (photosynthetic) of proteins, the vitamins (thiamine and biotin) and coenzyme-A which are used in the breakdown and synthesis of fatty acids [11].

Materials and methods
The present study entitled "evaluation of secondary macronutrient (Ca, Mg and S) in mango orchards of lower Sindh" comprised of four mango growing districts i.e. Matiari, Hyderabad, Tando Allahyar and Mirpurkhas. The details relating to soil and plant sample collection, processing and analytical methods applied are discussed in this chapter. Soil collection, processing and analysis District Tando Allahyar was selected for mango sampling. Three mango trees of same age and appearance were randomly selected from an orchard and tagged for soil and leaf sampling. Soil samples were collected at 0-15 and 15-30 cm depth. In order to have a representative soil sample from each tree four cores were dug around the tree canopy and composited depth-wise. Soil samples were preserved in labeled polythene bags and brought to the soil Fertility Research Laboratory, Department of Soil Science, Sindh Agriculture University, Tandojam. Leaf tissue collection, processing and analysis Leaf samples were collected from the same tagged trees of same district during the growth period when the nutrients were most stable (i.e. about two weeks after the emergence of flower panicles) [12]. About 25 recently matured leaves (3 rd leaf from top) of fruit bearing branches were collected around each tree and composited to one sample [13]. The samples were placed in a paper envelop, labeled and delivered to laboratory within 10 hours. Leaf samples were cleaned with tap water and then with distilled water using the method as described by [14]), oven-dried at 68 o C for 48 hours, ground to 20 mm mesh in stainless agate mill and stored. The ground mango leaf samples were subjected to total Ca and Mg analysis. The leaf samples were first wet digested using nitric acid-perchloric acid (HNO3 HClO4) mixture (2:1). The digests were analyzed for Ca and Mg by EDTA titration method [15]. Total S in mango leaves was determined by first digesting the leaf tissue material in an acid mixture, followed by S analysis on spectrophotometer by turbidimetric method [16].

Statistical analysis and interpretation
The Ca, Mg and S contents of mango orchards belonging to Matiari, Hyderabad, Tando Allahyar, and Mirpurkhas were subject to descriptive statistics using software Statistix 8.0. The mean leaf tissue nutrients were evaluated by comparing the analytical data with established critical levels of mango as given by [17]. Soil Ca and Mg and S in mango orchards were considered low to high according to the categorization as given by [18 and 19].

Particle size distribution (%)
The particle size analysis of various mango soils in Matiari, Hyderabad, Tando Allahyar and Mirpurkhas at two soil depths (0-15 and 15-30 cm) are presented in Figure  1. The data regarding particle size distribution showed a sand, silt and clay percent of 20.   The analytical results regarding organic matter contents as presented in Figure 4 showed that the organic matter content was high at surface as compared to the sub-surface soil horizons of all mango orchards. The minimum and maximum organic matter contents at 0-15 cm soil depth were 1.29 and 1.35 % in Matiari, 1.04 and 1.48% in Hyderabad, 0.80 and 1.39 % in Tando Allahyar and 0.94 and 1.52 % in Mirpurkhas. The average organic matter contents at surface were 1.32% in Matiari, 1.32% in Hyderabad, 1.15% in Tando Allahyar and 1.25% in Mirpurkhas. In case of sub-surface soils, minimum and maximum organic matter contents were between 0.66 and 1.02 % in Matiari, 0.32 and1.14 % in Hyderabad, 0.43 and 1.32 % in Tando Allahyar and 0.40 and 1.36 % in Mirpurkhas. The respective average organic matter contents were 0.87% in Matiari, 0.79% in Hyderabad, 0.86% in Tando Allahyar and 0.86% in Mirpurkhas According to the soil organic matter categorization as given by [17], the soil organic matter contents of surface soils were either in the range of 0.86-1.29 % categorized as medium (Tando Allahyar and Mirpurkhas) or high being >1.29% (Matiari and Hyderabad). All sub-surface soils also had organic matter contents between 0.86 and 1.29 %, categorized as medium.

Figure 4. Organic matter (%) of mango orchard soils in Sindh Calcium carbonate (%)
The data regarding calcium carbonate contents of mango orchard soils in Sindh at 0-15 and 15-30 cm depth is presented in Figure 5. The calcium carbonate contents ranged between 11.0 and 15.0 % and 4.5 and 9.5 % in Matiari, 11 Jackson (1969) categorization for calcareous soils, revealed that all the mango orchard soils belonging to four districts fall in slightly calcareous category (0-13%) except those of Hyderabad which were moderately calcareous (13-26%).

Figure 5. Calcium carbonate (%) of mango orchard soils in Sindh Ammonium acetate extractable Ca in soil (mg kg -1 )
The data regarding ammonium acetate extractable Ca in mango orchard surface soils (0-15 cm) as illustrated in Figure

Figure 8. Calcium chloride extractable S (mg kg -1 soil) of mango orchards in Sindh Leaf tissue contents (%)
Leaf tissue of mango orchards in various districts was tested for total nutrient contents. The results related to total Ca, Mg and S contents being presented in Figures 9-11. The leaf tissue Ca contents of mango orchards belonging to district Matiari, Hyderabad, Tando Allahyar and Mirpurkhas are presented in Figure 9.   Figure 11 showed lowest S contents of 0.37% in Hyderabad, followed by 0.54% in Matiari, 0.60% in Mirpurkhas and 0.62% in Tando Allahyar having wide variability in S content among districts. However, the contents were more or less similar in Hyderabad and Tando Allahyar. Sulphur leaf tissue contents varied from as low as 0.46 to 0.67 % in Matiari, 0.34 to 0.40 % in Hyderabad, 0.48 to 0.72 % in Tando Allahyar and 0.20 to 0.82 % in Mirpurkhas.

Discussion
The secondary macronutrients Ca, Mg and S are equally important as the primary nutrients N, P and K. Calcareous soils have high amounts of calcium carbonate and at pH 7.8 or more, and calcium and magnesium are abundant. Due to their abundance in our environment, they are never considered deficient or evaluated to be considered low or sufficient, especially with regard to Ca and Mg. Apart from presence of S minerals, S is mostly part of many fertilizers such as single super phosphate, ammonium sulphate and potassium sulphate [22]. This is why majority of the studies conducted on mango nutrition do not include the assessment of Ca, Mg and S in soil and plant. These three nutrients i.e. Ca, Mg and S play a significant role in the production and quality of mango. Calcium is greatly required in new flushes right after the harvesting of mango and maintaining the fruit firmness which may disturb the Ca: N ratio in soil and leaf [10]. These results regarding Ca contents in soil were in line with the results obtained by [23] on Kalan mangoes of Egypt. The result obtained by them showed mean Ca contents of 2.65 meq L -1 . Magnesium is part of chlorophyll molecule and enzymes and helps in P transport [24]. Magnesium is the constituent of chlorophyll molecule and plays an important role in facilitating the translocation of phosphorous [25]. The Mg contents in soil of four districts of Sindh were adequate and varied in leaf tissues. The results were in line with the results obtained by [23]. Sulphur, being part of volatile compounds is responsible for pungent smell or characteristic odour in many plants such as onion, mustard, garlic, etc. performing the role of an enzymatic activator [6]. The extractable S contents were in soil 67% was adequate and 33% was low. The leaf tissue S content was lowest (0.37%) in Hyderabad and highest (0.62%) in Tando Allahyar.

Conclusion
The Ca and Mg contents in soil were adequate and sufficient, and high in leaf tissue respectively. Generally there was no problem regarding S contents in soil and leaf tissue, however, 33% leaf tissue samples were low in each Tando Allahyar and Mirpurkhas. The other two districts had adequate S but were at the edge of satisfactory range which was further proved from the low status of leaf S contents. Through this study along with review of literature, it can be inferred that S stocks are being reduced with time, and unless replenished may affect the quality of mango. It is suggested that a three year consecutive sampling at various growth stages of mango will help to understand the fluctuation of these nutrients.