Chloride uptake by tropical forage grasses in two soils of Puerto Rico.

Abstract

An experiment was conducted on two dairy farms in Puerto Rico (Gurabo and Cidra) from September 1998 to July 1999 with the objective of quantifying chloride (Cl-) concentrations and uptake in grazed forage, Aif plots were fertilized with the equivalent amount of 330,110, and 220 kg/ha/yr (N, P205, K20) and the treatments consisted of four Cl- levels (0, 82,164, and 328 kg/ha/yr) split in four applications. Forage was harvested every 28 days during the seven-month experiment. Plant Cl- concentrations were determined by means of a potentiometric titration in the laboratory. Yields (fresh and dry weight) were not significantly affected by Cl- levels, which suggests that background soil concentrations were sufficiently high so as not to limit plant growth. Mean monthly Cl- concentrations in forage tissue were significantly affected by Cl- levels, increasing from 0.79 to 0.82% in Cidra and from 0.68 to 0.96% in Gurabo. Cumulative Cl- uptake by forage in the sevenmonth study period for the highest Cl- treatment was 124 and 161 kg/ha in Cidra and Gurabo, respectively. Our data suggest that excess Cl- in milk does not necessarily originate from Cl-containing fertilizer. Estimated CI consumption by dairy cows consuming tropical forages and concentrate is higher than that suggested by the U.S. National Research Council.