MICROCLIMATE IMPROVEMENT AND SOIL PROTECTION ASPECTS OF INTERCROPPING SORGHUM AND PEARL MILLET WITH COWPEA.
MICROCLIMATE IMPROVEMENT AND SOIL PROTECTION ASPECTS OF INTERCROPPING SORGHUM AND PEARL MILLET WITH COWPEA.
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Date
1997
Authors
OLUWASEMIRE, KOLAPO OLATUNJI
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Abstract
A better understanding, scientifically of the optimization and sustainability of
resource use in small scale agricultural production under low rainfall, poor and
deteriorating nutrient supply situations of the semi-arid zone of Nigeria necessitated
this research. It had the objective of investigating the effects of millet, sorghum and
cowpea planted sole, at recommended optimum densities and intercropped, under
cultural practices similar to the farmers' condition. The research set out to assess the
effects of two-three crop mixtures on the microclimate, soil conditions and their
productivities in a semi-arid environment. A survey of the cereal based cropping
systems of the Sudan savanna zone of Nigeria revealed the prominence of
millet/cowpea and millet/sorghum/cowpea intercropping systems. The component
crops in these systems are relay sown at relatively wide row spacings.
Field trials were conducted at Minjibir near Kano (12° 08 N, 8° 32 E) during
the 1993, 1994 and 1995 rainy seasons to compare growth, light use, water use and
root development in relation to the yield of millet, sorghum and cowpea planted sole
at the recommended optimum densities and intercropped at farmers' planting densities
under two levels of soil fertility. Another microclimatic parameter measured was near
soil surface temperature, while the consequences of these cropping systems on
seasonal nutrient balance were assessed.
The varying amounts and distribution of rainfall during the three years of
experimentation did influence millet productivity and in the intercropping systems this
was also true for growth. Sorghum grain yield was reduced by about 50% when
rainfall did not extend beyond the first decade in September. An excessively wet
season in 1994 reduced the yields of cowpea in the various cropping systems by 20
to 70%. The soil fertility status at the start of a cropping season plus the added
pre-planting organic manure ensured adequate soil fertility in all the three years of
field experimentation for millet production. Top dressing of millet components with
inorganic fertilizer before panicle initiation (6 WAS) did not significantly (P< 0.05)
increase millet grain yield. Total dry matter accumulation was also not affected by
application of fertilizer at reproductive stage in the different cropping systems.
However, sorghum dry matter production and grain yield was improved significantly
(P< 0.05) by additional fertilizer applied at the initiation of reproductive stage (8
WAS). Dry matter production per stand of cowpea in the intercrops was significantly
(P< 0.05) reduced by the associated cereal(s) planted 2 or 3 weeks earlier, and
particularly by the high tillering and faster growing millet component, compared with
the sole cowpea. There was poor vegetative growth of the cowpea components at
relatively low total plant densities in the intercrops (26667 plants ha-1) compared to
the sole cereal systems (53333 plants ha-1). This was worsened by the wetness of
1994, partly as a direct effect of weather conditions towards the end of growing
season, and partly by pest and diseases caused by these conditions. Growth and
development of the cowpea component in the widely spaced intercrops influenced
radiation interception. At peak periods of canopy development, midday radiation
interception by the intercrops varied from 60 to 80% in the direction of cereal/cereal
association while the least interception (< 30% in 1994) occurred between sorghum
and the grain cowpea (1T89KD-374) in plots with pre-planting organic manure
application alone. The higher density of the sole cereal crops caused higher overall
peak radiation interception (about 70%) than in the intercrops. The higher amount of
cowpea vegetative growth in 1995 under adequate radiation availability increased
radiation interception within the intercrops by 5 to 20% over the sole millet at peak
canopy development (45 DAS millet). The intercrop dry matter production was
increased even at lower millet density (< 25% of sole millet) by 10 to 65% at millet
and cowpea physiological maturity.
Diurnal near surface soil temperature fluctuation on cloudless days was reduced
in all the cropped treatments compared to the bare soil. However, in 1994 with more
pronounced differences early in the season, the reduction began earlier and was more
effective until millet LAI exceeded 2.5 (55 DAS millet) in the intercrops (fluctuation
< 6.5°C) than in the sole cereals (fluctuation of 10.0- 13.0°C). About the same
period in 1995, amplitudes were much smaller and diurnal differences less
pronounced.
All the crops sown sole and intercroppped rooted beyond 1 m depth in the
loose sandy soil of our experimental site. Sorghum root production was greater than
that of millet, while both cereals produced greater root densities than cowpea. The
overlap of the roots of component crops in intercropping suggests competition for
below ground resources. Cowpea produced greater root densities and achieved deeper
rooting depths when intercropped with millet and/or sorghum than when sown sole,
suggesting a better adaptation and competitive ability under intercropping. Rooting
depths of crops were shallower in a relatively wet season than when water was
limiting. The root densities and proliferation front of cereals below the surface layer
were much higher in relatively low fertility status soils than when nutrients are readily
available.
Dry matter production and system productivity of the intercrops were higher
or equal to the sole millet when cowpea productivity was better in 1993 (LER< 1.7)
and 1995 (LER< 1.2). High soil water availability favoured the growth and
development of cereals more than the cowpea, resulting in reduced intercrop systems
productivity in the relatively wetter 1994 season. Sole millet used water more
efficiently than its intercrops with cowpea, in 1994, when annual rainfall was above
the long term average. When the rainfall amount was below normal in 1995 (typical
of the recent climate situation in semi-arid Nigeria as also found in 1993), the
intercropping systems showed better WUE of about 20% in grain production and 15%
in total dry matter production in the millet/cowpea intercrop over the sole millet. The
situation in the millet/sorghum/cowpea intercrop gave for OM + IF about 35% better
WUE in both grain and total dry matter production compared to sole sorghum (Gaya
Early). In the OM sorghum based intercrop, the grain WUE figure was about 30%
and for total dry matter, 45% better than sole Gaya Early. Millet with heavy tillering,
even at low densities in the intercrops, was the dominant crop in the intercropped
systems. Deep percolation loss accounted for 15 to 20% of the seasonal available
water in 1995 (with least annual rainfall amount) at low planting density. The farmer's
cowpea cultivar (Dan-ilia) sown sole produced higher dry matter and was a more
efficient water user than the introduced improved cowpea cultivars.
This study supports the need for the manipulation of the millet/cowpea and
millet/sorghum/cowpea intercropping systems for better resource use and increased
productivities. Appropriate suggestions for achieving these improvements are
proffered.
Description
A DISSERTATION
Presented to the Faculty of Agriculture,
Ahmadu Bello University, Zaria
in partial fulfilment of the requirements for the degree of
Doctor of Philosophy
in
Soil Science
•
BY
KOLAPO OLATUNJI OLUWASEMIRE
B.Sc (Agric.) Soil Science, Ibadan
M.Sc (Agron.), Ibadan
1997
Keywords
MICROCLIMATE,, IMPROVEMENT,, SOIL,, PROTECTION ASPECTS,, INTERCROPPING,, SORGHUM,, PEARL MILLET,, COWPEA.