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The applied study of climate change on human activities has gained relevance in recent years. Its effect over the agricultural zones of developing countries is important to establish future adaptation strategies. In this work, current and future potential distributions under the framework of niche modeling of rice, sugarcane and pineapple for Costa Rica were evaluated. The results suggest that, for all three crops, the areas with higher probability of a negative effect due to the change in distribution of suitable areas correspond to rural environments. The point variations in mean annual temperature and annual precipitation variables did not show a defined pattern in the distribution areas of the crops. Regarding the overlapping effect between production areas and the forest area of the country, sugarcane presents the greatest overlapping in all future scenarios, while pineapple cultivation shows an inverse trend. The actual investigation proves the importance of climate change scenarios as a tool for evaluating the potential effect of this phenomenon over agricultural crops, with its repercussions at social and environmental level. [ABSTRACT FROM AUTHOR]

Temperature is one of the major climatic factors that affect growth, development and yield of the rice crop, and also can reduce the time of change of phenological stages. The beginning stages of tillering, initiation of primordia, flowering and harvest maturity were determined with the S, V and R system recently proposed by Counce et ál. (2000); it consists on counting the number of fully developed leaves; in addition, a correlation was made with accumulated degree days that the plant had at that time, in order to estimate with how many degree days the plant began a phenological stage; this parameter is related to the average daily temperature and a base temperature of 10ºC. For the start of tillering the plant needed 140.9 degree days; for primordium start, 1268.9; for bloom 1746; and completed its cycle with a total of 2333.2 degree days. This allows to conclude that, for a variety of long cycle (130-135 days), when the accumulation of degree days is equal or similar to the previous data, the plant initiates one of the above-mentioned phenological stages; however, each one of the varieties in use by farmers must be calibrated, because there are differences in crop cycle length among them. [ABSTRACT FROM AUTHOR]

An experiment of fertilization with N, P, K and S on rice (cv. CFX 18) was evaluated under flooded conditions in a Eutric Inceptisol in Guanacaste; also, the absorption curve of macro and micronutrients during the growing season was determined. The treatments were 0, 80, 120 and 160 kg.ha-1 of N; 0, 40 and 80 kg.ha-1 of P2O2; 0 and 50 kg.ha-1 of K2O, and 0 and 20 kg.ha-1 of S, for a total of 8 treatments with 4 replicates, in a randomized complete block design. Foliar analysis was performed at pre-flowering, and the yield of dry and clean grain was determined at harvest. In the treatment of 120 kg.ha-1 of N, 40 kg.ha-1 of P2O5, 50 kg.ha-1 of K2O, and 20 kg.ha-1 of S, 5 whole-plant samples were taken at 28, 43, 66, 79 and 93 days after germination, for dry weight determination and chemical analysis of nutrients and for development of the absorption curves as a function of plant age. There was a significant response in yield to N, P, K and S. The treatment of 120 kg.ha¹ of N, 40 kg.ha-1 of P2O5, 50 kg.ha-1 of K2O, and 20 kg.ha¹ of S presented the highest grain yield, in a soil that had an adequate content of P and K, but low in S. These same treatments brought about the higher foliar contents of N and P and were significantly different from treatments with no N and no P. The nutrient absorption curve was directly related to biomass production. Most of the absorption of nutrients occurred during the reproductive and ripening stages. The maximum absorption of N, P, K, Ca, Mg and S was 61, 25, 197, 17, 11 and 9 kg.ha-1, respectively. [ABSTRACT FROM AUTHOR]