Mn. Mathuva et al., IMPROVING MAIZE (ZEA-MAYS) YIELDS IN SEMIARID HIGHLANDS OF KENYA - AGROFORESTRY OR INORGANIC FERTILIZERS, Field crops research, 55(1-2), 1998, pp. 57-72
Farmers' maize (Zea mays) yields in semiarid Kenya are low because of
low and erratic rainfall and soil nutrient depletion. An experiment wa
s conducted in Machakos, Kenya, during November 1989-July 1995 to expl
ore the potential of hedgerow intercropping (HI) with Leucaena leucoce
phala as an alternative strategy to the use of inorganic fertilizers f
or improving maize yields in semiarid bimodal highlands. The study, co
nducted in a randomized block design with three replications, evaluate
d on an operational scale with four treatments: sole maize with or wit
hout fertilizer; and HI with prunings of L. leucocephala hedges used a
s green manure or with prunings and maize stover fed to oxen and manur
e returned to soil. About 1.4 t ha(-1) of L. leucocephala foliar bioma
ss and 1.2 t ha(-1) manure were incorporated each season in green-manu
re and ox-manure systems, respectively. Although sole maize responded
to inorganic fertilizer in six of 11 seasons, maize yield was improved
by HI, with prunings used as green manure, only once, 5 yrs after the
commencement of the study, when rainfall exceeded 500 mm. Over the ex
perimental period, maize yields were 15% and 30% less in green-manure
and ox-manure systems, respectively, than in unfertilized maize, prima
rily because of the competition of hedgerows with crops for water. The
fodder system of HI recycled only 27% of N and 50% of P exported from
the field in fodder, grain and stover, and depleted nutrients more th
an the other systems. The green-manure system made a positive N balanc
e, with similar P depletion as in the fodder system. No changes were d
etected in soil organic carbon or cations in any of the systems during
the experimental period while extractable P was significantly improve
d by fertilizing maize. Net present value of returns from fertilizing
maize at 40 kg N and 18 kg P ha(-1) was 10% higher than from the unfer
tilized control. Fertilizer use would be 25% more profitable, however,
if P were applied only to match the amount of P removed by crop (9 kg
P ha(-1) per season) and if maize were not topdressed (amounting to 5
0% of the recommended N) in poor rainfall seasons. Of the two HI syste
ms, only the fodder system was more profitable than either system of s
ole-cropped maize because the high value of fodder more than compensat
ed the smaller maize yield obtained in HI. However, the fodder system
may not give higher economic returns than a sole L. leucocephala fodde
r bank. Hence, HI using competitive species such as L. leucocephala an
d with the level of productivity observed in this study, is not approp
riate for semiarid climates to increase cereal yields, either directly
through green manuring or indirectly by fodder production and nutrien
t cycling through livestock. (C) 1998 Elsevier Science B.V.