Abstract

Chemical constituents, NH4-N, NO3-N, urea-N, Mg, Ca, Na, K, Cl and SO4 in the precipitation at University Field Station, St. Augustine, Trinidad, were determined for a period of three years. Total annual loads of the constituents varied from year to year. The range of annual accretion of NH4-N, NO3-N and urea-N was estimated to be 5.3–8.7, 5.4–7.8 and 2.5–3.1 kg ha−1 year−1, respectively; that of Mg, Ca, Na, K, Cl and SO4 was 3.9–7.2, 20.7–35.8, 22.7–41.7, 14.7–15.3, 25.4–49.0 and 21.4–37.6 kg ha−1 year−1, respectively. The amount of all the constituents was significantly correlated with the amount of precipitation. The amount of constituent load due to dry fallout, estimated from constituent load-precipitation relationship, was significant for NO3-N, Mg, K and SO4 during the dry period (monthly precipitation <75 mm), and for urea-N, Na and Cl during dry as well as wet periods (monthly precipitation > 75 mm). The amount of all the constituents was significantly correlated with sunshine hours, evaporation, wind velocity and relative humidity (except K). Since most of these meteorological parameters were interrelated, the effect of these parameters on constituent load and constituent concentration was complex. The Mg/Na ratio in precipitation was close to that in sea water, whereas those for Ca/Na and K/Na were near to those in soil and the average earth crust. The possible mechanisms of the deviation in ionic ratios in precipitation from those of sea water are discussed.

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