CITRUS CULTURE IN PORTO RICO 



33 



which no well-defined methods have as yet been perfected in Porto 

 Rico are considered on the basis of practice successfully used 

 elsewhere. 



Commercial planting of citrus in Porto Rico dates from about the 

 year 1901. The first plantings consisted mostly of orange trees, but 

 these were generally rebudded to grapefruit a few years later. The 

 more recent plantings consist almost entirely of grapefruit. 



The area devoted to grapefruit approximated 6,000 acres in 1928, 

 when the estimated yield was 1.235,000 boxes of that fruit. The 

 quantity of oranges produced fluctuates from year to year. In 1924 

 less than a quarter of a million boxes of oranges were exported, 

 whereas the previous year the exportation was nearly three-quarters 

 of a million boxes. Most of this fruit was produced by trees growing 

 in the mountain districts, where they are used as shade for coffee 

 trees. 



The commercial citrus groves are located mainly on soils ranging 

 from light beach sand to heavy clay. The sandy type of soil is 

 suitable for citrus culture, provided it contains a fair amount of 

 humus and the water table does not at any time rise to within the 

 soil area occupied by the larger portion of the root system. 



In a preliminary study of tree stocks a chemical method was de- 

 vised permitting of readily differentiating one kind of stock from 

 another by means* of the color produced when ferric chloride was 

 added to an aqueous extract of the root bark. 



The selection of seeds for the production of stock as well as of seed- 

 ling trees is emphasized, and nursery methods suitable to local con- 

 ditions are described. Bud selection, based upon recognized, de- 

 sirable trees and fruit characters, is discussed. 



Field methods, based upon practical experience in Porto Rico, 

 are outlined. These include the provision of windbreaks for the 

 citrus tree and the planting of the latter on raised mounds. Planting 

 such permanent windbreaks as the bamboo or other similar tall, 

 quick-growing plants is recommended. The use of smaller plants, 

 grown among the citrus trees as windbreaks, also is advocated, espe- 

 cially for young plantings. The purpose of the latter is primarily 

 that of maintaining as high an air humidit}^ among the trees as 

 possible. By this means scale insects, which are very destructive to 

 citrus trees, are kept in check by scale-destroying fungi. 



The planting of citrus trees on raised mounds is described. By 

 the use of this method the crown roots become exposed after the 

 mound subsides, which effectively prevents foot rot, a disease doing 

 considerable damage to citrus trees planted too deep. 



Fertilizing, based upon local field experience, is discussed. It is 

 pointed out that most local planters apply 50 pounds or more of 

 mixed fertilizer to each bearing tree annually, and that some apply 

 as much as 100 pounds to large bearing trees. The formulas of the 

 various fertilizer mixtures used are too variable to serve as a basis 

 for standardization of fertilizer formulas. The number of annual 

 applications is variable, but the practice of applying the fertilizer 

 three times a year, the first part of December, March, and June, is 

 desirable for bearing trees. 



