Soil fertility during shifting cultivation in the tropical Karst soils of Yucatan

As the bush fallow portion of shifting cultivation in Yucatan is shortened from the traditional 25-30 years to 6-12 years, soil productivity declines. Soil properties associated with this decline have not been documented because of the extreme short-range soil variability on Yucatan's limestone shield with its mosaic of black and red soils. We examined soil fertility and organic matter in sites representing stages of shifting cultivation in the context of pedogenic differences. Black soils contained twice as much organic matter, more total P and three times more available P than red soils. At the end of the cultivation cycle both soils had lost one quarter of their organic matter relative to the longest fallow. Available P was 40% lower in the red, but similar in the black soils. All organic matter and nutrient levels were higher than in non-calcareous semiarid tropical soils elsewhere, and the productivity decline was attributed to interactions between P and K supply and available water.