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Citrus is an important fruit and has a distinct position in fruit industry of the world as well as Pakistan. Citrus is ranked at the top in world, as it is cultivated on an area of 832.2 thousands ha with 13.9 MMT production (FAOSTAT, 2009). Share of citrus fruits is about 40% of the total fruits production in Pakistan, the area under cultivation is 193.2 thousands ha over 1.47 MMT production annually. 95% of total citrus is produced in Punjab province (Anonymous, 2010). At present, different cultivars are grown in Pakistan but the 'Kinnow' mandarin is ranked at the top in all the citrus cultivars and its share is 70% among all cultivars (Khan et al., 2009). Kinnow is used as fresh as well as processed. It is harvested from mid-February till the end of April in Pakistan.
Commercial production of fruits depends upon the nutrition management. Proper nutrients application is necessary to produce the good quality fruits (Ioannis et al., 2004). Nutritional requirements of citrus trees are different from that of annual crops. Citrus trees are long lasting, large and are deep rooted that's why they require more precise estimation of their nutrition. Soil test or plant analysis is mostly used for the identification and quantification of nutrient deficiencies which cannot be easily assessed by visual symptoms. Soil analysis does not give better results because of the tree roots penetration to a greater depth and causes variation. Plant analysis is better and more reliable method for determination of the nutrient status of fruit trees (Shah & Shahzad, 2008).
Micronutrients like zinc (Zn) and copper (Cu) are essential for plant growth and metabolism (Hazra, Maity & Mandal, 1987). Zn is involved in metabolic processes. In NSW Zn deficiency is a common occurrence in citrus orchards, especially in alkaline and acid coastal soils (Hardy & Huett, 2005). Plants absorb Zn directly through leaves in either ionic form (Zn2+) or in the form of a complex. Zn deficiency symptoms are firstly shown on the younger leaves. The deficiency of Zn causes chlorosis on leaves, affects stem growth and leaf size etc. Zn activates enzymes, involves in carbohydrates and protein synthesis, functioning of stomata and water relation (Zeidan, Manal & Hamouda, 2010).
Cu plays very important role in plant metabolism. The rate of respiration and photosynthesis process in plants is increased by the application of Cu. But plants require Cu in a very less quantity. It is a non-mobile element, activator of enzymes, involve in protein metabolism, and also necessary for lignin synthesis (Henry, 2008). When pH rises above 7.0, it becomes unavailable and surplus encourages Fe deficiency. Deficiencies are common in sandy soils. Cu can decrease Zn and Mn levels in leaves (Hardy & Huett, 2005).
Generally micronutrients activate enzymes in plants, and these are involved in specific and necessary functions in plants. All micronutrients like Cu, Mn, Zn, Mo, Fe, and B, except chlorine is required for activation of a specific enzyme that's why micronutrients are also called catalysts (Voss, 1998). Foliar application of micronutrients like Zn, Mn, Fe, Cu and B is very important to the trees grown in alkaline soil condition to overcome the effect of malnutrition.
Keeping in view all the facts, this research work will be conducted with the following objectives.
To study the effect of direct application of micronutrients on growth and fruit quality of Kinnow.
To standardize the best doses of Zn and Cu for foliar application in Kinnow.
To study the effect of foliar application of copper sulphate and zinc sulphate on vegetative and reproductive growth of Kinnow.
REVIEW OF LITERATURE
Botanically, Kinnow (Citrus reticulataBlanco.) belongs to the family Rutaceae. Kinnow is very important fruit of Pakistan. Micronutrients are directly related with growth and development of Kinnow. A lot of research on foliar application of micronutrients in the world is being started on fruit and vegetables. A brief research work on foliar application of micronutrients to enhance growth and fruit quality by different scientists around the world reviewed in the following paragraphs.
For the maintenance of healthy and productive citrus orchard, a fair amount of nutrients is necessary. Now farmers have aware about the importance of nutrition of citrus orchard and they have started the application of major elements like NPK in their orchards. The soils were deficient in major nutrients and also in micronutrients (Shah et al., 2003, Haq, 2002).
In citrus foliar application of micronutrients is the most important practice which was used. Foliar application was done because the amount of micronutrients was required in small quantity, and also to avoid adsorption of metal elements to soil colloids, hence making them unavailable for the plants. Boron should be preferably soil applied to citrus. In phloem, micronutrients like Mn, Zn, and B are very less mobile. Therefore, foliar application of micronutrients was made along with mixtures of salts and urea (Boaretto et al., 2008). Foliar application of micronutrients like Zn, Cu, Mn, B and Fe was much better than that of soil application because it was more effective, rapidly available to the plants, and to reduce toxicity symptoms, produced in soil accumulation of such nutrients (Obreza et al., 2010).
Citrus orchards in Swat were deficient in micronutrients. Zn, Mn, B and Cu were deficient 100%, 96%, 24% and 16% respectively in Swat orchards. There was no relationship between the soil and plant analysis for micronutrient in citrus orchards. The pH of soil was alkaline (7.5-8.5) due to which Zn, Cu, Fe and Mn were not available to the plant roots. However, while considering cumulative micronutrients contents, a strong correlation was present between surface soil (0-15 cm) and the soil profile (0-45 cm). Thus, the surface soil analysis can be used to measure micronutrients fertility pattern (Shah et al., 2012).
The number of leaves in sweet orange was increased when Zn and B were applied at very low concentration but leaf area was increased at high concentration of Zn with low concentration of B. By the foliar application of Zn either alone or with B, the sweet orange plants became healthy and nutrient status in leaves was increased and ultimately increase in the production and the bearing life (Tariq et al., 2007, Sajid et al., 2010).
The soil application of balance dose of NPK with multi-micronutrients increased the number of fruits as well as weight of fruit per tree. Production was also enhanced due to application of multi-micronutrients along with recommended NPK. The fruit juice, TSS, fruit girth, ascorbic acid content, reducing and non-reducing sugar enhanced by the application of multi-micronutrient and NPK either applied through soil or fertigation, but acidity of the fruit juice increased (Kazi, Ismail, & Joshi, 2012).
When boric acid and zinc sulphate were applied in Feutrell's Early mandarin at fruit setting, increased leaf Zn and B level optimum range was obtained. It also increased the fruit height, leaf size as well as fruit weight. Growth, productivity and fruit quality of Feutrell's Early mandarin was also better (Khan et al., 2012).
The plant height, stem girth and spread of canopy were significantly affected by micronutrients. Application of Mg, Cu and Zn in combination gave maximum results related to height, stem girth, fruit yield and spread of the plant but fruit parameters did not vary. Application of Mg, Cu, Zn, Fe and B in combination significantly increased the juice content, but had no effect on total soluble sugars, reducing sugars and acidity. NPK levels in leaves also affected by these treatments appreciably, whereas effect of these nutrients on TSS, total sugar, reducing sugars and acidity of fruits was non-significant (Ram & Bose, 2000).
Healthy and productive orchard are changing into low production with poor quality due to the deficiencies of micronutrients and citrus growers are not using micronutrients and hence, also causing serious physiological disorders (Tariq, et al., 2007).
Foliar application of Zn, Fe and B gave maximum fruit weight, higher number of fruit per plant and the greatest fruit retention. Zn and B applied in combination increased total soluble sugars and ascorbic acid, whereas Zn, B and Fe increased juice percentage and total sugar contents (Ghosh & Besra, 2000).
PLAN OF WORK AND METHODOLOGY
To evaluate the effect of foliar application of copper sulphate and zinc sulphate on growth and quality of Kinnow, a study will be conducted at research area of University College of Agriculture Sargodha, University of Sargodha.
Variables in the study
Doses of ZnSO4 and CuSO4.
T2= 0.5% ZnSO4
T3= 1% ZnSO4
T4= 1.5% ZnSO4
T6= 1% CuSO4
T7= 1.5% CuSO4
T8=0.5% ZnSO4+ 0.5% CuSO4
T9= 1% ZnSO4+ 1% CuSO4
T10= 1.5% ZnSO4+ 1.5% Copper sulphate
All other factors or variables will be kept constant
Research Design and Layout
The randomized complete block design (RCBD) will be followed in this experiment. There will be a total of ten treatment including control and all the treatment will be replicated three times, and a single plant will be considered as treatment unit. The field work will be carried out at Farm of M. Nawaz Maken Kot Muhammad Yar Tehsil Shah Pur District Sargodha while lab work will be performed at Horticulture Lab. University College of Agriculture, University of Sargodha, Sargodha. All the resources and facilities required for doing the research are available.
Data Collection and Analyses
The various parameters like fruit size (increment), shoot length, number of leaves per flush, fruit set percentage, fruit drop percentage will be recorded; and at the time of harvesting different physico-chemical parameters of the fruit like per fruit size, peel weight, fruit weight, rag weight, juice percentage, number of seeds per fruit,(healthy and aborted), acidity and total soluble solids will be measured. Four branches from each plant will be tagged from all four sides. Numbers of leaves will be counted from each tagged branch of the experimental trees and the shoot length will be measured by measuring tape.
At the time of harvesting, diameter of fruits will be measured using vernier caliper and 05 fruits per tree will be randomly selected from each experimental tree and average fruit diameter will be calculated. Electric balance will be used to measure average fruit weight and then average will be taken. Juice of each fruit will be extracted and weighed; average juice weight of five fruits will be calculated separately for each treatment. Peel and rag weight will be calculated from each sample and then average will be calculated. Seeds (healthy and aborted) will be counted, during fruit analysis. 2-3 drops of juice will be placed on the prism of refractometer to calculate total soluble solids (TSS).
The collected data will be analyzed using different statistical methods. For the explanation of the data of this study, it will be expressed as percentage, mean and standard deviation, etc.