Farmer Demand for Soil Fertility Management Practices in Kenya’s Grain Basket
November 1, 2013 - Author: Mercy Kamau, Melinda Smale, and Mercy Mutua
IDWP 132. Mercy Kamau, Melinda Smale, and Mercy Mutua. 2013. Farmer Demand for Soil Fertility Management Practices in Kenya’s Grain Basket
Land degradation cripples smallholder crop production in Sub-Saharan Africa, including
those found in the densely populated, grain basket areas of Kenya. Research in the early
nineties already documented and rated nutrient depletion to be very high in the east African
Highlands. Whereas some of the soil related problems are inherent, smallholder farmer
practices have contributed to the degradation, including the increasing soil nutrient depletion.
Yield-increasing mineral fertilizers have long been viewed as the panacea for the low
productivity in smallholder farms. However, recent studies question augmenting fertilizer use
without adequate attention to soil quality and use of other soil amendments, especially given
the evidence that returns to use of inorganic fertilizer are low in degraded soils and because it
is often applied inefficiently.
The main policy challenge to improvement of productivity is that the adoption of practices
needed to restore soil properties and enhance response to inorganic fertilizer remains low.
The most obvious impediment is the time lag between farmer investments and observable
payoffs, and their public good nature when they involve land resource allocation. Adoption is
also limited by the amounts of land and labor required to produce, process and apply some
techniques and practices. Extending and adopting location-specific menus of practices is
knowledge-intensive, requiring substantial, innovative forms of investment in local research
and training capacity. Missing or underdeveloped markets for inorganic and organic fertilizer
are often cited as a reason for low uptake. Yet too little is known about markets for organic
fertilizer and farmer demand for interrelated combinations of soil fertility management
practices to guide policy interventions and investment decisions.
Our analysis contributes to understanding about smallholder demand for soil fertility
management practices, including organic and inorganic fertilizer (N nutrient), and other soil
amendments in Sub-Saharan Africa. Soil fertility management practices were grouped into
three bundles (categories): a) inorganic fertilizers b) other soil amendments; and c) erosion
control. Reduced-form, input demand functions were derived based on the underlying
conceptual framework of the non-separable model of the agricultural household. To examine
the binary choice among the three bundles of practices, we applied a seemingly unrelated,
multivariate probit model that addresses jointness and interdependence among soil fertility
management strategies. We then estimated demand for N with a censored variable regression.
Data used were collected by plot in 2008/9 from 1001 households in eight agro-ecological
zones of western and central Kenya.
Although soils in smallholder farms in Kenya are highly degraded, our findings showed there
was less than a 0.5 likelihood that households would apply inorganic fertilizers or other soil
amendments. The average intensity of fertilizer use among farmers surveyed was also too
low. The findings confirmed the price responsiveness of farmers, and the influence of market
infrastructure on their use of not only inorganic fertilizer, but soil erosion control, and other
soil amendments. An increasing price of fertilizer, relative to that of grain, led to a decline in
demand for N. Strong effects were observed for plot size and for land tenure, signaling the
importance of these variables and land use policy in encouraging greater adoption of
integrated soil fertility management practices. The effects of multiple cropping and more
cropping of legumes maybe a reflection of farmers objective to maximize returns from
inorganic fertilizers and the role of nitrogen-fixing crops as substitutes.
The findings also point to the important ways through which commonly used proxies for
family labor influence soil fertility management, showing that different age groups within
households have different effects. It was also evident that labor was a limiting factor in soil
fertility management during the main season and female headship reduced both the uptake of
soil fertility management measures on maize and the demand for inorganic fertilizer. The
crucial role of knowledge in uptake of integrated soil fertility management practices was also