Fragile Lands of Latin America Strategies for ... - PART - USAID

176 Susanna B. Hecht
Table 6
Changes in Soil Fertility Elements in Kayap6, Colonist and Livestock Systems
Colonist
Ph
N%
P PPm
K
Ca
Mg
Forest Year One Year Five Year Ten
Livestock
Ph 4.70 5.50 5.20 5.00
N% 0.10 0.07 0.06 0.06
P PPm 2.00 7.00 2.00 1.00
K 0.10 0.17 0.10 0.05
Ca 1.30 1.70 0.92 0.64
Mg 0.42 0.65 0.60 0.30
Source: Data derived from soil samples taken at Gorotire (Kayapd), Nixdorf
Fazenda, located near Rendencao (livestock), and colonist agricutture of squatters
on the Nixdorf Ranch. Colonist and livestock agricutture sampled in 1982.
as "controls" and samples were collected on areas in the first, fifth,
and tenth years of production. Sampling areas were roughly 1 ha in
size, and the samples were collected randomly. Ten samples were taken
per "treatment" area.
Table 6 suggests several important trends. First, pH tends to improve
with burning, and this effect persists over time in all the systems,
mainly as the result of decomposition of larger boles. In the Kayapb
case, higher pHs are maintained for a longer time, probably due to the
continuation of field burning, cooking within the fields themselves, and
importing wood for cooking fires. Nitrogen (N) levels are very low in
all three systems, but the importance of low nitrogen is less pronounced
in Kayapb agriculture because of its emphasis on root crops rather
than grains for most of the production cycle. For example, rice requires
about 23 kgs of nitrogen per ton, while manioc and sweet potato
remove 3.7 and 4.3 kgs per ton respectively, and require little nitrogen