| The Madagascar rainforests display some of the richest biodiversity found on earth, yet are disappearing rapidly via slash-and-burn agriculture. The main study objectives were to document soil systems of the Ranomafana National Park region, provide detailed soil characterization data, and provide soil interpretations for sustainable agriculture and forestry development.; The regional geology consists mainly of high-grade felsic metamorphic rocks and granites. Upland soils over thick saprolite generally classified as Oxic Dystrudepts. Some soils contained horizons that nearly met all criteria for an oxic horizon. Upland soils over thin saprolite possessed higher cation exchange capacities and weatherable mineral contents, and classified mainly as Typic Dystrudepts.; Alluvial soils classified into various subgroups of Humaquepts, Dystrudepts, Fluvaquents, Udifluvents, and Udipsamments.; Long-term climate data indicated a udic soil moisture regime. Soil temperature measurements indicated an isothermic soil temperature regime, and were highly correlated with elevation (r2 = 0.97). Climate data and soil temperature data suggested that mean annual air temperature equals mean annual soil temperature.; Total elemental analyses of representative rock and saprolite samples revealed extremely low levels of bases and phosphorus. Soil characterization data generally indicated pH values of 4–5, very high aluminum saturation levels, and extremely low levels of exchangeable bases and Olsen-extractable phosphorus, regardless of landscape position. With minor exceptions, the RNP area soils reflected very low available nutrients and extraordinarily low total nutrient reserves.; The combined data sets revealed that soil nutrient levels are insufficient for sustainable crop production without nutrient inputs. Those inputs must be obtained either from the rainforest biomass through burning, through biomass harvesting for compost, or from chemical fertilizers. Burning destroys the rainforest, and nutrient harvesting depletes an already fragile ecosystem. Chemical fertilizers therefore represent the only long-term solution for sustainable agriculture at present population densities. Promoting “organic” agronomic practices only creates unrealistic hopes for sustainability, because the fundamental biogeochemical constraints remain ignored. The soil data and deforestation rates unambiguously indicate that fertilizers are essential for sustainable development and associated conservation goals. |
