cannot stimulate changes in existing cropping patterns or husbandry practices, or that farmers will
adopt only those new cultivars that are higher-yielding replicates of currently popular varieties.
Rather, researchers must consider carefully the costs and risks farmers face, before investing time
and money in developing particular types of new cultivars.


Balancing Yield and Maturity Period as Selection Criteria

Conventional varietal selection based on yield favours later-maturing cultivars, given the
correlation of yield and period of photosynthetic intake. Farmers, however, may adopt shoter-
term varieties in agroclimatic zones where long-duration cultivars offer higher biomass and
yields. The rationale for such a choice becomes apparent once the scientist's analytical
framework shifts from the individual cultivar to a multi-crop and multiple season perspective.
Rather than assume farmers will accommodate any maturity period in a high-yielding cultivar,
breeders must first assess local constraints on maturity periods and then select for high yields
within locally appropriate maturity classes.

Although farmers are skilled at managing cultivar diversity, including multiple maturity periods,
even minor departures from current types can have wide ramifications for cash flow and food
security. If land is scarce, for example, adoption of a longer-maturing cultivar may mean an
unaffordable delay in the planting of another essential food staple on the same plot. A new variety
may require earlier planting or harvesting of a previous season's crop on the same land. It may
compete for scarce labour at critical points in the production cycles of other crops. A later-
maturing cultivar may introduce a constraint in the family consumption calendar if its longer
period in the field coincides with a period when food substitutes are unavailable. It may introduce
a family cash constraint if delayed harvest prolongs a period of cash shortage. In short, single-
crop or commodity research programmes cannot ignore other crops and enterprises that compete
for farmers' land, labour and cash resources, and that help farmers meet their food and cash needs.

Under conditions of bimodal rainfall and land scarcity, single season yields may be less important
to small farmers than annual productivity. In this situation farmers may choose to plant the
combination of cultivars that gives the best yields in two growing seasons, rather than a single
cultivar that gives the best yield in one season but precludes a second crop the same year and
therefore forces the farmer to purchase food on an expensive pre-harvest market. Some examples
from areas where land is scarce and rainfall bimodal illustrate these points.


Maize Maturity Classes in Western Kenya

Farming systems research has highlighted the disadvantage of the highest-yielding hybrids in
western Kenya's densely settled, high rainfall zone. The long maturation period of the high-
yielding 600-series Kitale hybrids makes it difficult to plant a second maize crop. The hybrids
are planted in March and not harvested until mid-September. Because rainfall is unreliable from
December to February, the late-standing 600-series crop leaves only 100 days for replanting with
a second maize crop in the last months of the year. The second maize crop is essential to poorer
families who have little land because maize prices in July and August, before the new long rains


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