Management system adopted for bearing trees are quite different, especially with regard to nutrient and irrigation management, than that adopted for non bearing trees. The shift in management system could be commenced 3-4 years after planting dependin g on the tree size. The objective in managing bearing trees is to promote the tree reserve level for subsequent flowering and fruiting while at the same time trees are allowed to grow and maintain sufficient vigor for producing high yields in following years.
Tree reserve levels could be increased by two ways. That is by optimizing conditions required for high rate of photosynthesis and by controlling excessive vegetative growth that consume stored reserves unnecessarily. Photosynthesis rate and excessive vegetative growth may be manipulated by controlled N and water supply that will be discussed under nutrient and irrigation management later.
In bearing tree management the growers has to think the productivity of trees in long run to maintain the sustainability of tree production capacity. A sustainable production may be achieved only if trees are managed with a scientific tree management system based on the phenology or growth cycle of bearing trees.
Application of plant nutrients economically at correct time with right amounts in a way that nutrients could be taken up by plants efficiently with minimum losses covers the whole issue of nutrient management. Proper nutrient management has significan t effects on tree productivity. The purpose here in nutrient management is to keep mineral nutrient levels in the tree with in the desired range to have the growth and development effects and fruiting of trees as desired by the grower.
It is time to just review the functions of major plant nutrients in mango. Mango needs annual applications of Nitrogen, Phosphorus and Potassium.
Nitrogen is needed at the time of vegetative flushing to support leaf growth. Nitrogen is utilized to synthesize chlorophyll molecules found in green sub cellular organs known as chloroplasts where photosynthesis occur. In addition to this, N is used as components in many enzymes, co-enzymes, hormones, nucleic acids and many other plant proteins. N is highly mobilized and if there is a deficiency, N in older leaves may be transported to new developing leaves. Threfore, deficiency symptoms appear in o lder leaves becoming yellowish in color and early senacsence.
Phosphorus is required to synthesis ATP, cellular molecules engaged in respiration process to support plant life. P is also found in other bio-molecules such as nucleic acids, enzymes, certain proteins and in cell membrane phospholipids.
Potassium is essential mainly for food translocation within the plant. This nutrient is not generally found in plant cells as integral components of bio molecules. Potassium is found in cellular sap as K+ and are facilitating many plant physiological processes such as stomatal opening, activation of enzymes and charge balancing agent in transport of anionic nutrients such as nitrates and sulphates etc..
The most important thing in nutrient management for bearing trees is to analyze the importance of timing of nutrient application in relation to tree phenology or growth cycle. The recommended fertilizer mixture for bearing mango trees are 12-8-34 for Dry and Intermediate Zones and 11-10-25 for wet zone. Based on these mixtures, annual requirement of each nutrient are given in Table 1.
|Age of Tree=>
|Age of Tree=>
With the exception of N, the essential nutrients for growth can be applied to the soil at any time without forcing competitive, non productive vegetative flushing. This does not mean to say that some rationalization of fertilizer application is not ne eded. However,looking at tree nutrient requirements, application timing can be programmed in relation to growth cycle.
Nitrogen is one of the most important and powerful management tools currently available and learning to use it effectively is very essential to improve orchard productivity. Application of N stimulate vegetative flushing. At the same time withholding N temporarily favors fruitfulness, but we have to be careful as overall productivity declines if trees become N deficient. The timing in N application is also critical in balancing the tree between vegetative and reproductive growth. Therefore, all N req uirement should be given just after harvesting to induce growth flush immediately. Never after the growth flush is mature untill the next harvesting time !
P may be added at any time of the year. Its best, however, to apply it in rainy season under rain fed conditions. Otherwise it may be applied at any time of the year with another fertilizer to cut d requirement of plants are high during the period fro m flowering to fruit maturity for during this period trees are very active in translocating food reserves to maturing fruits. Trees need K during flush development also. Therefore K may be applied after harvesting and again during flowering to fruit matu rity.
In addition to above major nutrients, other nutrients that are important include Calcium, Magnesium, Sulphur, Zinc, Boron, Iron , Manganese and Copper. Under high tree management, the requirements of these nutrients may be increased as most of these n utrients are removed from the field with harvested fruits. Under such circumstances external applications may be required. Requirements of those nutrients may be decided by leaf analysis. Leaves are usually sampled during flowering to assess micro-nutrie nt requirements.
It is imperative to see that trees are not over fertilized with any of the major or minor nutrient as excess amounts may cause problems like excessive vegetative growth, low yields, inferior fruit quality and nutrient toxicity.
In addition to timing, the way fertilizers are placed for the trees to take up effectively is also important in nutrient management. For efficient utilization by trees, fertilizers must be equally distributed on the root zone area. Active roots are sc attered 30 cm from the trunk to drip line in small trees and in well grown trees this may extend up to about 1 – 1.5 m away from the drip line. After broadcasting equally on the root zone area, fertilizers should be incorporated to the soil by cultivatin g the top soil. Care should be taken not to damage the roots too much. If a thick mulch with under tree sprinklers are available for irrigation such mechanical incorporation is not required as a number of frequent irrigations may slowly incorporate the f ertilizers to root zone.
Especial care should be taken when appling urea as the source of N. Urea must only be applied when the soils are moist. If not trees must be irrigated immediately after urea application.
Fertilizers may also be applied as bands or in few spots around the tree to reduce application costs. however, equal broadcasting around the tree and incorporation to the root zone by mechanical ways or by irrigation is the best technique of applicati on. Band and spot application methods are less efficient than broadcasting on the root zone.
Lime application is an integral component in mango nutrient management. Mangoes prefer a soil pH of around 6.5. At this pH most soil nutrient elements become available to plants. If the soil is acidic, finely ground lime or dolomite may be applied to adjust the soil pH. These liming materials may be apply as bands along the tree raw or just around the trees on the root zone. The exact lime requirements may be estimated by using soil analysis results. For general purposes the following table can be us ed to estimate lime requirements to bring the soil pH to 6.5 under different soil conditions.
Like nitrogen, irrigation is another effective and powerful management tool to improve tree productivity in bearing trees as well as to control biennial bearing habit of trees. Irrigation is also important in enhancing the fertilizer use efficiency of trees.
In talking about irrigation management, it is necessary at the beginning to understand the critical period of irrigation requirements and required quantities of water in line with the tree growth cycles. In an annual growth cycle mango has two critica l periods of high water demand. One is after harvesting up to flushing and flush maturity. Then the second and the most important critical water demand arise with the flowering of the trees and this continues up to fruit maturity. During these periods, the quantities of water demands are very high and is determined by the variety, tree age and tree size, soil type and climatic conditions prevailing on these periods such as rain fall, temperature, ET and wind velocity. However, the research information on exact water requirements are not available and therefore it should be decided by the grower looking into the principles behind the water requirements of trees as well as taking into consideration the climatic and soil conditions. As a basic guideline to estimate water needs, as mentioned above 25 mm per week to the root zone may be followed for periods with peak water demand.
After the flush mature the irrigation water applications must be cut down significantly up to flowering time. This is because mango need 2 – 4 month dormant period before flowering as a pre condition for the development of floral primodia. If excess w ater is applied before the onset of flower primodia, unnecessary growth flushes may come out affecting the subsequent flowering and fruit production. Therefore, during the period from flush maturity to flowering, irrigation may be completely cut off. Und er extreme drought conditions if trees show signs of water deficiency, little irrigation may be required to keep the plants alive and active in photosynthesis. Usually, in areas where suitable climatic conditions are found for commercial mango production , the period from flushing to flowering must have a dry period with very little rains. In this regard, Mahawali System B climate is very ideal for variety Willard according to its phenological growth cycle.
Final irrigation may be given about one month prior to the expected date of harvesting. Variety Willard mature about 3.5 – 4 months after flowering. Other varieties may take a slightly shorter or longer period. The time taken from flowering to maturit y also may slightly vary according to the climatic conditions and locations. Growers must record observations on flowering and harvesting dates tformation are very valuable in deciding irrigation timing.
Trees must be pruned after harvesting, the objectives in pruning are to remove dead or diseased wood, to remove additional growth flushes to allow more light penetration into the leaf canopy and also to control tree height to facilitate cultural manag ement practices. Erect branches are less fruitful compared with spreading branches and these must be removed. At the same time lower branches are pruned to about 1 meter from ground level to facilitate cultivation practices such as weed control, fertili zer application and irrigation.
A light pruning is also recommended after main flush matures in order to remove suckers and excess shoots. Certain mango varieties like Willard produce 5 – 6 or more branches per shoot tip at flushing and make the canopy very dense and crowded. Other varieties may give rise to 2 – 4 shoots per terminal. Excess shoots may be removed to about 3-4 shoots per terminal. It should also kept well in mind that at this pruning, remaining shoots should not be shortened as it will affect flowering in view of th e fact that under tropical conditions only terminal flowers occur. Only additional shoots and suckers must be removed. However, under temperate conditions even machine pruning at this time is permissible shortening the remaining shoots because under such conditions, in those shoots shortened by machine pruning auxiliary flowers emerge.
Root zone area of the trees must be kept weed free all the time. Manual cultivation is not recommended as it will disturb active roots. Weed killers with a heavy mulch may be quite effective in controlling weeds. Weed control practices do not differ f rom what was explained for non bearing trees.
Thick mulch is recommended as explained previously for non bearing trees. Mulching materials may be continuously added every year.
Mulching together with chemical weed control and under tree sprinkler irrigation has the added advantage of easy tree manipulation for inducing water stress required as a precondition for excellent flowering from flush maturity to flowering. Under the se circumstances, the active root zone may be confined to the top 6 – 10 inch of soil depth and tree manipulation therefore become easy with controlled irrigation.
Pest and diseases must be effectively controlled to get a good harvest from bearing trees. Pest and disease activity must be closely monitored from flowering to fruit harvest in order to prevent major pest or disease out breaks which might destroy mos t of the crop if left unnoticed.
Major pests include Mango hoppers, Mango weevil and Fruit fly. The diseases of importance are Anthracnose and Stem end rot. Timely action is necessary to prevent economic losses from these pest and disease problems.