Climate Change Mitigation - Climate Resilient Agriculture for Ensuring Food Security - page 273

waterways, fi eld margins, and shelterbelts.
Compared to leaving fi elds fallow, they reduce
emissions and can sequester carbon during peri-
ods when primary crops are not grown. Cover
crops are usually an option on surplus agricultural
land or on cropland of marginal productivity.
Cover crops are fast-growing crops such as
winter rye and clovers that are planted between
periods of regular crop cultivation. By covering
the soil surface, they protect the soil from erosion,
and if leguminous, they fi x nitrogen. Later, when
plowed under, they provide humus and carbon to
the soil as well as nitrogen for the subsequent
crop.
Adoption of cover crops is limited because of
the many concerns of growers and the specifi city
of profi table cropping systems. Lack of knowl-
edge, incorrect choice of cover crop, and the
economic costs of planting and terminating cover
crops are all concerns of growers, and they have
led to the slow adoption of this practice. If land is
fallow for portions of the year, cover crops should
be considered. However, they need to be selected
on the basis of the growing season, protection
capacity, nitrogen-fi xing capability, and eco-
nomic feasibility. They vary from region to
region, cropping system to cropping system, and
crop season to crop season. Therefore, local
research must be conducted in order to obtain the
knowledge needed to use this practice reliably.
(i) Advantages
• A primary advantage is that by increasing
plant residues and roots, cover crops can
sequester carbon during times when the
soil surface would normally be bare and
emitting carbon due to soil respiration.
• Cover crops can alleviate nutrient defi -
ciencies and reduce artifi cial fertilizer use
by nitrogen fi xing, if leguminous. This
will save fossil fuel used in fertilizer
manufacture, although more nitrogen in
the soil can increase N 2 O emissions.
• Cover crops reduce soil erosion as well
as rainfall runoff by improving water
infi ltration and water adsorption in the
soil matrix.

• Cover crops can also reduce use of pesti-
cides and herbicides for the associated
cash crop by suppressing weed growth
and providing a substantial habitat for
benefi cial arthropods.
(ii) Disadvantages
• There are costs associated with planting
and terminating cover crops.
• If not terminated properly, cover crops
may act like weeds and compete with the
following cash crops for light, nutrients,
and water.
• The residues from cover crops can poten-
tially interfere with postemergence her-
bicides, which results in the escape of
weeds.
• In some cases, the additional water
requirement of the cover crops may make
this practice economically and environ-
mentally less viable.
Several examples have been presented show-
ing that the growing of cover crops is profi table.
In one experiment hairy vetch was grown during
the off-season for a main crop of corn. The costs
of fertilizer and of hairy vetch seed required for
the no-till zero-tillage cover crop systems were
$117.08 and $16.62 ha −1 year −1 , respectively,
while the cost of fertilizer for conventional
no-tillage system was $174.97 ha −1 year −1 . The
cover crop system produced average corn yield of
7.86 Mt ha −1 in a no-tillage conventional system.
The average gross margin (profi t) was
$238.28 ha −1 year −1 in cover crop system and
$233.27 ha −1 year −1 in conventional no-tillage
system.
Cover crops can also increase soil carbon
sequestration. Lal ( 1998 ) lists carbon sequestra-
tion rates from 0.28 to 2.60 Mg ha −1 year −1 from
growing cover crops on an eroded Alfi sol in
Western Nigeria.

13.1.2 Nutrient Management

Plant nutrient management to increase soil nutri-
ents and thus enhance crop productivity is a