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Conservation agriculture
t
his article is the 21st of a series of articles highlighting a spe-
cific pasture crop species that can play an imperative role
in conservation agriculture (CA)-based crop-pasture rota-
tions. Besides improving the physical, chemical, hydrological
and biological properties of the soil, such species, including
annual or perennial cover crops, can successfully be used
as animal feed.
Livestock production systems are in many ways dependant on the
utilisation of pasture species, in this case as a pasture ley crop, and
can therefore become an integral component of CA-based crop-
pasture rotations.
It is imperative to identify a plant species fulfilling the requirements
of a dual purpose crop, i.e. for livestock fodder and/or soil restora-
tion. This article focuses on a cover crop with pasture crop potential
used to improve soil conditions and to provide a high quality grazing
for ruminants.
Mucuna pruriens
(L.), velvet bean or
fluweelboon
Velvet bean is a twining, annual legume that can reach 7 m in length.
There are two common varieties
M. pruriens
var.
pruriens
and
var.
utilis
. This species is a very well-known green manure and
cover crop.
Velvet bean is very vigorous and its growth suppresses companion
species. If velvet bean is grown in intercropping system, it should
preferably be sown at least 45 days after the other crop – especially
a crop such as maize – to overcome interspecies competition.
Agro ecological distribution
Mucuna pruriens
can either be sub-tropical or tropical. This species
is known to grow in many different habitats which include pastures,
forest edges, roadsides, riverbanks or even woodlands.
M. pruriens
can adapt to well-drained sandy soils as well as clay soils.
This species is not drought tolerant since it has a shallow root sys-
tem, and is also known to not tolerate waterlogged conditions. Vel-
vet bean requires a long growing season and is sensitive to frost and
therefore requires at least 180 frost free days. Since the species does
not succeed on cold, wet soils, when grown as a crop it should not be
planted before the soil has reached warm temperatures.
Since velvet bean cannot tolerate temperatures below 5
o
C, tempera-
tures of 20
o
C - 30
o
C are recommended during the growing season.
An ideal soil pH to grow velvet bean successfully is 5 - 6,5 on light,
sandy loam soils.
M. pruriens
is adaptable to a wide rainfall range as
low as 400 mm - > 1 200 mm.
Management and utilisation
Mucuna pruriens
is known to be a common forage crop with great
value. This species is known for its amazing weed control abilities.
The most common use of velvet bean is as a cover crop and green
manure.
It has been widely used to reclaim land that has been infested with
weeds. When planting velvet bean, it does not require a high degree
of land preparation. The best method to plant velvet bean is by drill-
ing it into the soil with about 1 m between rows and 20 cm - 80 cm
between plants (20 kg/ha - 40 kg/ha seed). Seeds are large, so seed-
ing depth can be as deep as 10 cm but not less than 3 cm. Seed does
not require scarification or inoculation with rhizobia prior to planting.
This species has also frequently been intercropped with maize and
left to grow after maize has been harvested to maintain and increase
the soil’s fertility before establishing the following season’s crop.
There are two options to manage velvet bean in such a situation
and that is to incorporate it just before the next planting season, or
partially graze it together with some maize residues to sustain rumi-
nants through the dry winter season in a subtropical area.
Velvet bean has a high dry matter production for a subtropical leg-
ume. Yields range from 5 t/ha - 13 t/ha depending on the rainfall. As
it is known that soil phosphorus (P) is an important growth element
for legumes, velvet bean can produce high yields even in marginal
soils that have a low available P value.
Soil conservation and health benefits
Velvet bean has proven to be resistant to the attack of certain pests
and diseases due to its content of toxic secondary metabolites,
which gives this species the ability to outcompete weeds. Research
has shown a significant increase in organic matter when velvet bean
biomass was incorporated into the soil. The soil moisture content
also increased by 20% to 30%, and showed a higher cation exchange
capacity, lower pH, lower apparent density and a reduction in
micronutrient recycling.
WAYNE TRUTER,
University of Pretoria,
CHRIS DANNHAUSER,
Grass SA,
HENDRIK SMITH,
Grain SA and
GERRIE TRYTSMAN,
ARC-Animal Production Institute
Integrated crop and pasture-based
livestock production systems
– Part 21
AGRICULTURE
Conservat ion
Series
ON FARM LEVEL
December 2015