TY - JOUR
T1 - Increasing land pressure in East Africa: The changing role of cassava and consequences for sustainability of farming systems
AU - van Fermont, A.M.
AU - van Asten, P.J.A.
AU - Giller, K.E.
PY - 2008
Y1 - 2008
N2 - Increasing land pressure during the past three to four decades has transformed farming systems in the mid-altitude zone of East Africa. Traditional millet-, cotton-, sugarcane- and/or banana-based farming systems with an important fallow and/or grazing component have evolved into continuously cultivated cassava or cassava/maize-based systems. Within three to four decades, cassava cultivation increased from 1¿11 to 16¿55% of cropped fields in our six study sites. Declining soil fertility, and not labour or food shortage, was apparently the primary trigger for this transformation. The land use changes have increased nutrient offtakes and reduced nutrient recycling rates. Cassava and maize now account for 50¿90% of nutrient removal. Whereas single-season fallows were the most important source of nutrient recycling on cropped fields in the past, currently cassava litterfall and maize stover contribute roughly 70% of nutrient recycling, with 50¿70% of N, P and K recycled in cassava litterfall. This may explain why many farmers reason that cassava `rests¿ the soil. With increasing land use pressure farmers progressively use cassava as an `imitation fallow¿ throughout their farm. Farmers increasingly target cassava to poor fertility fields characterized by low pH and available P. High cassava intensities are nonetheless maintained on more fertile fields, probably to guarantee regeneration of soil fertility on all fields. Once cassava is targeted to poor fertility soils, farmers have run out of low-input management options and need to intensify management to maintain system productivity. As cassava is now used by more farmers and on a larger acreage than fallowing in the studied farming systems, cassava cropping could perhaps serve as an excellent entry point to strengthen system sustainability.
AB - Increasing land pressure during the past three to four decades has transformed farming systems in the mid-altitude zone of East Africa. Traditional millet-, cotton-, sugarcane- and/or banana-based farming systems with an important fallow and/or grazing component have evolved into continuously cultivated cassava or cassava/maize-based systems. Within three to four decades, cassava cultivation increased from 1¿11 to 16¿55% of cropped fields in our six study sites. Declining soil fertility, and not labour or food shortage, was apparently the primary trigger for this transformation. The land use changes have increased nutrient offtakes and reduced nutrient recycling rates. Cassava and maize now account for 50¿90% of nutrient removal. Whereas single-season fallows were the most important source of nutrient recycling on cropped fields in the past, currently cassava litterfall and maize stover contribute roughly 70% of nutrient recycling, with 50¿70% of N, P and K recycled in cassava litterfall. This may explain why many farmers reason that cassava `rests¿ the soil. With increasing land use pressure farmers progressively use cassava as an `imitation fallow¿ throughout their farm. Farmers increasingly target cassava to poor fertility fields characterized by low pH and available P. High cassava intensities are nonetheless maintained on more fertile fields, probably to guarantee regeneration of soil fertility on all fields. Once cassava is targeted to poor fertility soils, farmers have run out of low-input management options and need to intensify management to maintain system productivity. As cassava is now used by more farmers and on a larger acreage than fallowing in the studied farming systems, cassava cropping could perhaps serve as an excellent entry point to strengthen system sustainability.
KW - soil fertility management
KW - western kenya
KW - gradients
KW - farmers
KW - maize
KW - crops
U2 - 10.1016/j.agee.2008.06.009
DO - 10.1016/j.agee.2008.06.009
M3 - Article
SN - 0167-8809
VL - 128
SP - 239
EP - 250
JO - Agriculture, Ecosystems and Environment
JF - Agriculture, Ecosystems and Environment
IS - 4
ER -