A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Phosphorus fractions in earthworm casts and soils ofagroforestry systesms, pasture, and secondary forest in theCentral Amazon BasinChristienne N. Kuczak*, Erick C. M. Fernandes, Johannes Lehmann, and Marco RondonCornell University*address of primary author: 610 Bradfield Hall, Ithaca, NY 14853 U.S.A.; email: cnk4@cornell.eduPhosphorus is limiting to agricultural production throughout the tropics and 96%of land in the Amazon basin has been reported to be P-limited (Dematê and Dematê1997). Because P dynamics can be greatly affected by vegetation cover and nutrientcycling (Solomon et. al 2002), we investigated the effects of tree species and earthworms(Family Glossoscolecidae) on P in soils and earthworm casts. Soils and earthworm castsbeneath the agroforestry species Theobroma grandiflorum, Bactris gasipaes, Eugeniastipitata, and Bertholletia excelsa, the pasture grass Brachiaria sp., and the secondaryforest species Vismia sp. and Cecropia sp. were sequentially extracted using amodification of the Hedley fractionation (Hedley 1982; Tiessen and Moir 1993).Earthworm casts had significantly more total P, inorganic P, and organic P than soils.Soils and casts beneath agroforestry species had significantly more total P, inorganic P,and organic P than soils and casts beneath Brachiaria sp. and the secondary forestspecies; and soils and casts beneath Brachiaria sp. had significantly more total P,inorganic P, and organic P than soils and casts beneath secondary forest species. Thesoils and casts beneath the agroforestry species had significantly more P in the resinfraction than soils and casts beneath the secondary forest species. The greatest total Pwas in earthworm casts beneath Eugenia sp. with a mean of 251 µg cm -3 and in soilsbeneath Bertholettia sp. with a mean of 89 µg cm -3 . Secondary forests had the least totalP in both casts and soils with a mean of 11 µg cm -3 and 41 µg cm -3 , respectively. Giventhat bulk density of earthworm casts was 1.47 g cm 3 and the bulk density of soil was 0.96g cm -3 , casts contained 1.87 to 2.97 times more total P (g cm 3 ) than soils. Within thesystem studied, earthworm casts can contribute from 61 kg ha -1 in secondary forest to 140kg ha -1 beneath Eugenia sp. It was shown that earthworm casts and vegetation covercontributes greatly to P dynamics in agroforestry systems, pasture, and secondary forestin the Central Amazon Basin.