The mango requires less water than the avocado, although young trees are benefited by frequent irrigations. In Florida, old mango trees will be found growing and fruiting in fence corners and abandoned gardens where they have to depend entirely on rainfall. They are much more successful under such conditions than the avocado. Orchards of budded or grafted trees are rarely irrigated after the trees have attained a few years' growth. In other regions treatment must be different. In California, for example, irrigation should be practiced as with citrus fruits. J. E. Higgins remarks concerning Hawaii: "Liberal moisture must be supplied to the roots, from 50 to 70 inches per year being required, according to the retentive power of the soil and the rate of evaporation. In the case of bearing trees the heaviest irrigation should be given from the time when the flower buds are about to open until several weeks after the fruiting is over, withholding large amounts of water during two or three months preceding the flowering season." Regarding India, Woodrow says: "When fruiting age is attained there need be no necessity for irrigation from the time the rain ceases in September till after the flowers have 'set,' that is, till the young fruit appears; thereafter, irrigation over the area covered by the branches once in fifteen days or so is desirable while the fruit is increasing in size, but may be discontinued when ripening approaches."
All writers point out the necessity of applying a check to vegetative growth previous to the flowering season. Ringing and hacking the trunk are two of the commonest practices, while root-pruning is occasionally performed in India. Recent experiments indicate that a liberal application of potash is extremely beneficial. Mulgoba trees at Miami, Florida, and Guanajay, Cuba, which were heavily fertilized with potash, produced much larger crops than those fertilized in the ordinary way. A standard commercial fertilizer especially prepared in Florida for use on mango trees contains:
5 to 6 %
7 to 9 %
9 to 11%
These elements are derived from ground bone, nitrate of soda, dried blood, dissolved bone black, and high-grade potash salts.
Woodrow recommends for India that young trees be fertilized liberally with barnyard manure; but he adds that as soon as they come into bearing the application of manure must be stopped, and leguminous cover-crops planted between the rows. These crops can be plowed under, thereby enriching the soil in the necessary degree and at the same time keeping down weeds. The best legumes for this purpose, according to Wood-row, are Crotalaria juncea, Cicer arietinum, Phaseolus aconiti-folius, and Phaseolus Mungo. P. J. Wester says, "The velvet bean (Stizolobium Deeringianum), Lyon bean (Mucuna Lyoni), the cowpea (Vigna Catjang) and related species may be used with good success in the Philippines. Of these the Lyon bean is preferable in the Philippines, since here it produces a greater amount of growth per acre than any other legume." In Florida velvet beans, cowpeas, and the bonavist bean (Dolichos Lablab) have been used. Growers should plant a number of different legumes experimentally to determine which are the best for their particular localities.
Numerous experiments to test the effectiveness of girdling and root-pruning have been made at the Porto Rico Agricultural Experiment Station. C. F. Kinman reports of them:
"Girdling, branch pruning, and root pruning are common practices, but they should be used with caution and moderation, as a tree may easily be so severely injured as to prevent its bearing for one or more seasons. Pruning back the ends of the branches to induce blossoming has been practiced with good results at the station. In the operation, from a few inches to a foot of the end of the branch was removed, depending upon the stage of maturity of the wood, leaving a few nodes from which the leaves had not fallen. From these nodes blossoms developed profusely, no blossoms appearing on untreated branches. To secure best results, the pruning should be done in the late summer or fall, several months before the blossoming time. This method should be employed on branches which are too low or too crowded or on those which would have to be removed later to improve the shape of the tree, as after a branch is pruned it makes little growth for several weeks or months or even for a year or more after the fruit ripens, and by this time it may be well overgrown by surrounding branches.
"As good results have been obtained from girdling as from other methods. A branch one to three inches in diameter was selected on each of a number of trees and a band of bark removed in September. These branches produced good crops the following spring, even when no fruits at all were borne on the remainder of the tree. Such favorable results, however, were obtained on varieties which are inclined to bear well and where the band of bark removed was wide enough to prevent the new bark from growing over the area too rapidly. Bands one-eighth and even one-quarter of an inch in diameter were overgrown so quickly that no effect was seen on the branch. Bands from one-half to three-quarters of an inch produce the best results, as they do not heal over until after the blossoming season, the callus growing downward over the wound at the rate of one inch a year. ... As removing enough bark to induce fruiting is very injurious to the branch, this practice is most profitably employed on undesirable branches which are to be removed later.
"Root pruning has been recommended, although no definite results have been noted from the experiments with it. It is best accomplished by cutting into the soil with a sharp spade about two feet inside the tips of the branches. In extreme cases the cutting may encircle the tree to a depth of eight or ten inches in heavy soil and even deeper in light soil where the root system is considerably below the surface. Cutting at such intervals as to sever the roots for one-half to two-thirds of the distance around the tree will induce blossoming under normal conditions without seriously checking the growth or thrift of the tree."
Experience in Florida has shown that girdling, to be effective, must be done in late summer. No one yet has had sufficient experience to recommend it as an orchard practice. Like root-pruning, the use of salt, and several other unusual practices, it may prove of decided value when its proper method of use has been determined. Every grower should conduct a few carefully arranged experiments along such lines as these, even though on a limited scale.
In India, the only pruning usually given the mango consists in cutting out dead wood. Since the fruit is produced at the ends of the branchlets, general pruning of the top cannot be practiced as with northern fruits. In Florida, however, several growers have found it desirable to prune out a certain number of branches from the center of the tree, so as to keep the crown open and admit light and air.