Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/20

 Surface treatment of native pasture with L, P, LP, LPK, and LPKN showed significant response during the first year only to the LPKN treatment. This response was evident in percentage of ground covered, percentage of desirable grasses, and in total herbage yield. The best yield, however, was only about one-third of the yield of improved kudzu-grass pasture for comparable periods.

D. K. Fuhriman, C. F. Cernuda, J. R. Hernández, E. A. Telford, and R..M. Smith

General soils studies showed some of the major variations with depth in soil profiles and with location on the island. The relatively high organic matter contents of tropical soils was measured and confirmed and some evidence was obtained as to the relatively rapid build-up of organic matter which is possible.

Practical studies on steep Utuado soil showed that much of the soil loss downhill is due to tillage and gravity. Artificially flattened benches proved to be quite productive when properly treated and managed. Steep hillside plots showed that some erosion control can be obtained with trashy culture, but many management details must be carefully considered.

A survey of the efficiency of the methods of water used in Puerto Rico was initiated and considerable data were accumulated. These data show that efficiencies generally are low and that in most cases less than 50 percent of the water applied is being utilized by growing crops.

Various items of soil physics equipment were tested under tropical soil and water conditions to determine their usefulness.

A. J. Loustalot and R.Ferrer Delgado

Sodium pentachlorophenate is a promising herbicide in pre-emergence weed control treatments. Experiments were conducted to study the effect of temperature, soil moisture, texture, and other environmental factors on persistence of sodium pentachlorophenate in the soil.

The data obtained in the temperature study showed that the toxicity of sodium pentachlorophenate decreased with the passage of time, as measured by the growth of corn and cucumber in treated soil. The rate and degree of inactivation was greater at the warm temperature than at the cold. As would be expected, the toxicity persisted longer at the higher rates of application. Toxicity of the herbicide at the lowest rate of application persisted for at least 2 months when the soil was stored at 10° C. The growth of corn and eucumbers in treated plots stored at this temperature was the poorest of all the treatments. There was some indication that the toxicity of the penachlorophenate