Agriculture Reference
In-Depth Information
Legume trees act as “safety nets” and nutrient pumps as they help in closing the
nutrient cycle by taking nutrients leached into deeper layers up to the surface (Jose et al.
2004; Harawa et al. 2006). In addition, legume trees break up hardened soil layers and
help increase infiltration rates since they have deeper rooting systems (Nyamadzawo
et al. 2008a). The roots also help by bringing water and nutrients to the surface from
deeper soil layers through hydraulic lift (Jose et al. 2004; Bayala et al. 2008).
The soil fertility benefits of using fertilizer trees are a result of complex factors
that work together to provide a conducive environment for plant growth. This results
in enhanced plant growth and improved maize yields, due to, for instance, improved
N fixation and N availability in fallow crop rotations or tree-crop intercropping.
Increased SOC, a better safety net from deep-rooted tree fallows, increased P avail-
ability from increased soil AM fungi in the soil, and increased weed suppression
all result in improved soil fertility in legume tree-crop intercrops or rotations. We
concluded that the use of fertilizer trees provides a window of opportunity for small-
holder farmers to improve soil fertility and maize yields. The use of fertilizer trees is
a sustainable option that can result in improved food security in households that are
resource constrained, besides providing other goods and services such as fuelwood.
11.2.2 m
Aize
y
ield
i
ncreASeS
from
i
mProved
S
oil
f
fertility
Studies from the region have shown that fertilizer trees improve maize yields beyond
continuous maize production without fertilizers or with natural fallows. Controls
used to calculate response ratios in Table 11.3 may be fertilized or unfertilized maize
or natural fallow, and are described in the text. The cereal crop is maize unless noted
otherwise. These studies are not an exhaustive list, but are given to illustrate the
scope of possible yield benefits and to illustrate important issues in management of
these combined systems. For a more detailed treatment of maize yield increases with
agroforestry, see Sileshi et al. (2008).
11.2.2.1 Improved Fallows
Maize yields obtained after fallowing are highly variable. For example, Nyamadzawo
et al. (2012) reported maize yields that ranged between 10% and 250% higher after
fallows compared with continuous maize cropping without fertilizers (Table 11.3).
They reported yields of 1.8 and 0.7 Mg ha
−1
for
A. angustissima
and
Sesbania
under
conventional tillage (CT), while no tillage had even lower yields (1.3 and 0.8 Mg
ha
−1
) for
A. angustissima
and
Sesbania
,
respectively, in the first year of cropping
after 2 years of fallowing. However, in the second year of cropping, the maize yields
were 1.6 and 0.5 t ha
−1
for
Sesbania
and
A. angustissima
,
respectively, under CT,
while the maize yields were 1.5 and 0.3 t ha
−1
for
Sesbania
and
A. angustissima
,
respectively, under no tillage. Maize yields are also affected by additional factors
such as pests, diseases, and competition for water. In the first year after fallowing
in the same study by Nyamadzawo et al. (2012), maize after
Sesbania
was infested
by cutworms and this resulted in lower crop yields, while in the second cropping
season, there was a mid-season drought that affected the maize crop in coppicing
A.
angustissima.
This resulted in lower crop yields as a result of competition for water
and not because of N deficiencies.
