Abstract
Net irrigation requirements (NIR) of sorghum were estimated for three crop durations (3, 3.5 and 4 months), and 5 planting dates at the Fortuna Agricultural Experiment Substation, Juana Díaz, in the south coast of Puerto Rico and the Isabela Agricultural Experiment Substation, in the north coast of Puerto Rico. Modified Blaney-Criddle model was used to estimate monthly consumptive use (CU) with the temperature and rainfall data for these two locations. CU and NIR were highest at Fortuna than at Isabela for all three crop durations. For the January planting, the monthly NIR range (in) was 2.57 to 3.83 for 90 days, 0.71 to 3.83 for 3.5 months and 2.13 to 4.24 for 120 days at Fortuna; and 1.53 to 2.76 for 3 months; 0.00 to 2.76 for 105 days; 1.18 to 3.03 for 4 months at Isabela. Seasonal NIR (in) was 9.36 for 3 months, 11.13 for 3.5 months, 12.79 for 120 days at Fortuna compared with 6.95 for 3 months, 7.40 for 105 days, 8.80 for 4 months at Isabela. At both locations minimum NIR was observed in March for 3 months and in April for 3.5 and 4 months. For all planting dares, seasonal NIR (in) ranged between 8.46 to 9.36, 10.37 to 11.13, and 11.67 to 12.79 for 3, 3.5 and 4 months at Fortuna compared with 5.34 to 6.45, 6.36 to 7.40 and 7.51 to 8.80 for 3, 3.5 and 4 months af Isabela. In both locations minimum total NIR was observed in the November planting, whereas maximum total NIR was observed in the January planting. NIR was also estimated for a 20% rainfall probability which would represent dry years.