CITRUS CULTURE IN PORTO RICO 



The soil at Plantaje, both surface and subsoil, in which the first 

 commercial grove on the island was planted, consists of shell sand. 

 With the formation of land at this point, silt was deposited in the 

 lower places, whereas the slight ridges remained practically pure 

 sand. A heavy hammock growth developed, especially in the silt- 

 covered areas, and after it was removed considerable humus re- 

 mained. The difference between the poorest and the best soils in 

 these groves is readily discernible by the color of soil. Analyses 

 show a difference of 2 to 3 per cent in colloid content, practically 

 all of which is organic matter. In the better grade of this soil tree 

 growth is excellent, and even in the poorest grade the trees develop 

 much better than they do under different conditions. 



The water table in these groves reaches within 3 to 4 feet of the 

 surface in the rainy season, and supplies abundant moisture most of 

 the time to the citrus trees even on the poorer soil. On the other 

 hand, the high water table is the main limiting factor in root forma- 

 tion. The depth of the root system is naturally limited by the 

 water level, and although a distance of 3 feet is ample for root 

 development it is not sufficient to allow for the changes in water 

 level that take place periodically. For example, the water may not 

 reach beyond the 3-foot limit in a certain section for several years, 

 but during a period of heavy rain it may come to within 2y 2 feet of 

 the surface. Unless this excess water is drained off, the immersed 

 roots will decay and the trees may die. At times, especially during 

 prolonged droughts when the water table subsides 12 inches or more 

 below normal, the trees may suffer from a severe shortage of mois- 

 ture. Evidently the pore space in the subsoil is too great to allow for 

 much capillary rise of water. A lack of moisture can be remedied 

 cheaply by irrigation; but since the water has an alkalinity equal 

 to 0.16 gram CaC0 3 per liter and a pH of 8 to 8.4, it may not be 

 suitable for the purpose. In the surface soil with a humus content 

 of about 2 per cent, the pH seldom reaches above 7.4. Whether or 

 not a pH of 8.4 through the entire soil mass world be detrimental is 

 not yet known. 



The sandy soils in all the other groves in the above-mentioned 

 region consist of silica sand mixed with clay silt and organic matter. 

 The poorest grade of this sand is exemplified by the narrow ridge 

 west of Dorado, which broadens out into a plain of several hundred 

 acres between Vega Baja and Lake Tortuguero. This sand is several 

 feet deep and is so pervious that water percolates through it readily. 

 It is practically devoid of clay and humus, and consequently all 

 fertilizers applied leach out immediately following a rain. To main- 

 tain plant growth, such sand must be given frequent fertilization 

 and irrigation. Even were this treatment practicable it could not 

 be satisfactorily used because citrus trees do not thrive well in a 

 soil that is entirely devoid of humus and soil organisms. Obviously 

 this extreme type of soil is unsuitable for cultivation, and large 

 areas of it can not profitably be made suitable. Often, however, 

 small areas in citrus groves may be improved without great expense. 

 Clay, when available, may be applied to good advantage at the 

 rate of 50 tons per acre. The clay should preferably be dry and 

 pulverized, or at least granulated, so that it will readily mix with 

 the sand. 



