AbstractAn 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.
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