Nutrient Mobility in a Shifting Cultivation System, Belize, Central America

Abstract

In recent years, the pressure on shifting cultivators to reduce the fallow periods has been increasing because of the need to produce more food for an ever growing-population. Earlier studies have reported that as much as a 15 to 20 year fallow period was required to return a two-year agricultural site to its original fertility. Data on biomass changes show rapid increases in early stages of succession (Ewel, 1971; Buschbacher and Uhl, 1987), during which time the wood tissues are important in the immobilization of cations, phosphorus (P) and nitrogen (N) (Bartholomew et al., 1953; Snedaker and Gamble, 1969; Singh et al., 1985). Brubacher et al. (1989) have shown that levels of nitrogen (N), phosphorus (P) and potassium (K) allocated to leaves peaked in year-old fallows, with little further increase in 2- and 3-year-old sites. Potassium (K) accumulated rapidly in stem material, with little increase after the first year of fallow growth, whereas N and P accumulation continued at steady rates for another 2 years of fallow development. The role of weeds in nutrient accumulation during the initial stages of secondary succession has been reported by Toky and Ramakrishnan (1983) and Lambert and Arnason (1986). The more recent studies listed above have suggested that immobilized nutrients in plant tissues can reach levels similar to the surrounding, undisturbed forest within 10 years.