No abstract

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.

Data are presented here on the minimum rate of infiltration (eighth-hour) of 57 main soil types of Puerto Rico. The study included a total of 740 tests. Mean infiltration rates vary from a high value of 11.49 inches of water per hour in Yunque sandy loam, to a low of 0.07 in Aguirre clay, and 0.01 in Palmas Altas and Britton clay. When the soils were arranged according to a simple, practical classification system in use in Puerto Rico the mean values ranged from 0.01 in group 5w to 7.82 inches in group 11. When the soils were grouped following the latest classification system developed by the U.S. Department of Agriculture, mean values for soils included in the order Vertisol ranged from 0.07 to 3.83 inches. Mollisols, Oxisols, and Ultisols showed the highest infiltration values. Information is hereby given as to the effects of various soil treatments on infiltration rates.

A mathematical approach is presented in this paper to evaluate the influence of such factors as clay content, silt content, organic matter, Ca + Mg, and soluble sodium upon the stability of soil aggregates in a group of Vertisols from the Lajas Valley, P.R. The relationships between aggregate stability and silt and clay were not significant. When the percentage of organic matter was considered as the independent variable, a highly significant correlation coefficient of 0.66 was obtained. Therefore, almost 43 percent of the variability in aggregate stability could be explained on the basis of this single factor. Attempts to increase the percentage of the variability which could be explained in terms of the content of Ca + Mg, and also of soluble sodium, yielded correlation coefficients of 0.70 and 0.74, respectively. Thus, only a slight, but significant, additional increase could be explained when these variables were included.

Data are presented here for pH, organic matter, colloids, moisture equivalent, total and aggregated silt and clay, and dispersion, colloid-moisture equivalent and erosion ratios of various soils from Puerto Rico. The purpose of collecting the data was to evaluate the relative erosiveness of these soils. An upland Catalina clay profile with dispersion ratios of 13-20, colloid-moisture equivalent ratios of 0.97-2.26, and erosion ratios of 6-14, lost from 5.3 to 7.1 tons of soil per inch of run-off per acre per year, when in fallow or desurfaced, respectively. But when this soil was planted to sugar cane the losses were reduced to 1.5 and 0.13 tons of soil per inch of run-off when the trash was burned or kept as a mulch, respectively. This lateritic Catalina clay was classed as a non-erosive soil. Three soils of the gray brown podzolic or lithosol group, represented by the Múcara, Cayaguá, and Pandura series gave higher values for dispersion and erosion ratios and lower ones for colloids-moisture equivalent ratios, in their profiles, and consequently were classed as erosive soils. Other lateritic, alluvial and reddish prairie soils were classified similarly with respect to their relative erosiveness.