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Preliminary data are presented of some of the mineralogical characteristics of 41 soil series of Puerto Rico, which includes soils of three orders, 22 great soil groups occurring in seven physiographic provinces. Study of the constituent minerals of these soils show that there are present quartz, feldspars of the plagioclase series, and the clay minerals kaolin, illite, montmorillonite, and one called provisionally beidellite. The soils can be divided into two general groups, those with abundant feldspar and those where feldspar is absent or occurs only in traces. On the average, those soils which contain feldspar have a lower clay content, a higher total exchange capacity, and a higher productivity rating, where lack of rainfall or extreme slope are not factors, than those soils where feldspars are absent or occur only in traces. This appears to be independent of the great soil group, or province in which the soil series occur. It may be that the presence or abscence of feldspar in a soil is one of the indications of its potential fertility status.

The effect of leaving the trash as a mulch or burning it, for each of four crops of sugar cane growing in a lateritic soil with a 40 percent slope, has been compared with respect to cane and sugar yield and soil and water losses. No significant difference was found between the cane and sugar yield and the water losses between the mulched and unmulched treatments. But a highly significant difference was found between soil losses; it was about 11 times higher for the unmulched plots. The amount of water consumed per ton of cane was estimated to be 286 tons. The losses of available phosphorus, ammonium and nitrate, were very small in the eroded soil and water run-off. The mulching was not effective in raising the soil organic matter.