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t
his article is the 23rd of a series of articles highlighting a
specific crop species that can play an imperative role in con-
servation agriculture (CA)-based crop-pasture rotations.
Besides improving the physical, chemical, hydrological and
biological properties of the soil, such species, including an-
nual or perennial cover crops, can successfully be used as
animal feed.
Livestock production systems are in many ways dependant on the
utilisation of forage species, in this case as an annual cover 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 restoration.
This article focuses on a tuber cover crop with crop potential
used to improve soil conditions and to provide high quality forage
for ruminants.
Brassica rapa L.,
turnip or
raap
Fodder turnips are a member of the mustard family. They have large
bulbous (round) or tapered roots of which a large percentage of the
root is exposed above the soil and is available to grazing animals.
These turnips are very attractive forages to ruminants as they are
rich in carbohydrates. The turnips’ foliage is erect and succulent and
is normally grazed in the first grazing cycle, followed by the roots.
The two most popular cultivars grown in South Africa are
Mammoth Purple Top and Green Globe. Turnips are biennial crops
which generally form seed the second year or even late in autumn
if planted early in spring. Turnip leaves are usually light green, thin
and sparsely pubescent (hairy).
In addition, a white-fleshed, large bulbous or tapered root develops
at the base of the leaf petioles. The storage root varies in size but
usually is 7,5 cm to 10 cm wide and 15 cm to 20 cm long.
Agro ecological distribution
Turnips are known to be cold-hardy and drought tolerant. The
most vigorous root growth takes place when low temperatures are
prevalent. Turnips are resistant to moderate frost and short periods
of moisture stress. The leaves of these plants maintain their nutri-
tional quality even after repeated exposure to frost. This species
can produce a good crop even when receiving a rainfall as low as
350 mm - 500 mm per annum. Higher production yields can be ob-
tained if irrigation is applied.
Turnips grow best in a moderately deep loam, fertile and slightly
acid soil. Turnips do not do well in a soil that has a high clay content,
is wet or poorly drained. For good root growth turnips need a sandy
to loam soil that is loose and well aerated.
Soil fertility and weed control are crucial for high productivity.
Nitrogen (N) and phosphorous (P) are the most important elements
in forage production, levels of 75 kg to 120 kg N/ha and 60 kg P/ha
for the growing season is normally recommended. If soils are low in
potassium (K), application of 30 kg/ha to 60 kg/ha is recommended.
Turnips will grow well in soils that have a pH range of 5 to 6,5.
The sowing density of turnips is 2 kg/ha to 4 kg/ha which can result
in yields of between 5 t/ha to 10 t/ha depending on environmental
and management conditions. The higher seeding rate will result in a
higher proportion of leaves to roots in turnips. Turnips can be drilled,
broadcast or aerial seeded. Oats and other small grains can be seed-
ed with Brassicas as a cover crop mix.
Management and utilisation
Turnip seed is very small and it is critical that it is planted into a
fine, firm and weed free seedbed with adequate moisture for ger-
mination and emergence. This species can also be seeded into the
stubble of a previous crop with minimum- or no-tillage. When seed-
ing into an existing crop, be sure to suppress the crop, since turnips
do not compete with other species like grasses.
As with any crop, weed control is very important, especially dur-
ing drought years when weeds compete with crops for water. Turnip
seed does not germinate well in soils with too high temperatures
and prefers temperatures of around 10°C to 15°C. This supports
the planting of turnips into stubble as soil temperatures beneath
plant material are lower.
Turnips can provide grazing at any time during the winter and au-
tumn depending on the seeding date. This species can be used as
a good foggage crop, which means it retains its forage quality well
into the early winter even after extreme cold temperatures have
occurred.
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 23
AGRICULTURE
Conservat ion
Series
ON FARM LEVEL
Conservation agriculture
Februarie 2016
44