new adoption patterns are indeed emerging, but the range of hybrids on farms in Kenya still does not reflect the large number now registered for sale.

Despite a later start, adoption of improved maize is now higher in West and Central Africa. A mere 4 percent of maize area in West and Central Africa was planted to improved maize varieties in 1981 (Alene et al. 2009). West Africa appears to have also experienced a more robust rise in the adoption of improved varieties since 1990, although it is especially difficult to reliably estimate areas under improved open-pollinated varieties<sup>4</sup> . Ghana and Nigeria were the prominent success stories of the 1980s. Impressive rates of adoption also occurred in Mali, where maize is grown in cotton-based systems, although the area is relatively small.

Despite abundant evidence of dynamic change, the data reported in Tables 4 and 5 indicate that roughly half of Sub-Saharan Africa‘s maize area continues to be planted to farmers‘ varieties, though through cross-pollination and farmer selection, breeders often suggest that many of these have been influenced by proximity to improved maize.

# _Fertilizer Use_

As shown above, even in countries where improved maize covers much of maize area, only modest yield gains seem to have been achieved. Although the use of improved maize can be a catalyst for increasing farmers‘ use of other inputs, and especially fertilizer, such broad-based change has only occurred in some parts of Sub-Saharan Africa. Most farmers do not adopt the additional production practices needed to sustain yield improvement. This is particularly noticeable with respect to practices for maintaining and enhancing soil fertility, even though the shortening of the bush fallow rotation as a consequence of population pressure has made poor soil fertility the major constraint to raising productivity in many areas.

For all of Sub-Saharan Africa, about 40 percent of fertilizer is used on maize, implying that the average dose is only about 17 kg/ha of nutrients compared to the developing country average of 100 and the industrialized country average of 270 kg/ha on the same crop (Morris et al. 2007; Heisey and Norton 2007). While it is incorrect to surmise that modern maize ―depends‖ on fertilizer, modern maize does generally trace a steeper response curve for fertilizer than do traditional farmers‘ varieties. Maize is a heavy consumer of fertilizer, leading fertilizer demand in industrialized countries among major cereals, and the second most heavily fertilized crop on a global scale, after potatoes (Heisey and Norton 2007).

Farmers grow improved varieties without fertilizer in many areas of Africa, especially in marginal areas, such as the drier zones of Kenya and Zimbabwe, but also some relatively favored areas, such as Ghana. Higher adoption rates for improved seed than fertilizer reflect the high costs of fertilizer in Africa, lack of input availability, and farmers‘ cash constraints.

Even where fertilizer is used, it is often used inefficiently. A single recommendation is provided for wide areas, which does not account for the diversity of smallholder situations and the acute cash constraints under which they operate. Mistaien‘s (2001) analysis, which employs a benchmark productivity measure computed by matching farm household survey data to optimal

> 4 Because of the difficulty in measuring areas planted to improved OPVs, in particular, estimates should be considered with caution.  Almost all of the maize area in West African countries, with the exception of Nigeria, is planted to improved open-pollinated varieties. Given that the private seed system has not been active, it is likely that farmers practice seed saving for much more than the recommended number of years and because of crosspollination, it may be difficult to differentiate improved from unimproved materials.

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