SA Graan Februarie 2016

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February 2016
ON FARM LEVEL Conservation agriculture
Turnip plants are ready for grazing or green feed when the forage is
about 30 cm tall (70 to 90 days after planting). The pasture should be
grazed for a short time and the livestock removed to allow the plants
to regrow. A strip grazing system is desirable to ensure complete
grazing.
The forage quality of turnip is outstanding with exceptionally high
protein content and can be regarded similar to concentrate feeds.
Bearing the latter in mind, precautions should be taken to prevent
any animal health problems. Livestock should not be starved when
put onto a field of turnips, as this will cause animals to over indulge
causing serious metabolic disturbances.
Animals should be conditioned to turnips so that a healthy rumen
microbial population can develop to ultimately digest the high
levels of protein in forage turnips. Feeding low quality hay with high
fibre content can facilitate optimal utilisation of turnips. Turnips
could be grazed in approximately 60 to 90 days after planting de-
pending on varieties.
Soil conservation and health benefits
Turnips just like many other Brassicas provide a 70% to 80% soil
coverage. These species are well known for their ability to capture
soil nitrogen (N) remaining after a crop harvest. Turnips produce
large taproots that can grow as deep as 1,5 m and often deeper and
can play a significant role in alleviating compaction especially when
soils are moist and easier to penetrate.
Their deep rooting also allows these crops to scavenge nutrients
from deep in the soil profile. As the large tap roots decompose,
they leave channels open to the surface that increase water infiltra-
tion and improve the subsequent growth and soil penetration of
crop roots.
Most Brassicas including turnips have been shown to release
metabolic by-products that exhibit broad activity against bacteria,
fungi, insects, nematodes and weeds. Brassica cover crops are
often mowed and incorporated to maximise their natural fumigant
potential.
Recent studies world-wide have indicated the potential use of tur-
nips and other Brassicas for pest management. Preliminary results
show that different varieties contain different amounts of bioactive
chemicals and when using these species as green manure, fewer
pests were noted. Like most green manures, Brassica cover crops
also suppress weeds in the autumn with their rapid growth and
canopy closure.
Management challenges
Regarding the use of a turnip cover crop in animal production
systems, there are a few challenges regarding animal health. Since
most Brassicas have a low amount of fibre it is extremely impor-
tant that turnips should not constitute more than 75% of the rumi-
nant’s diet.
It is therefore important that when turnips are grazed that a lower
quality roughage be supplemented. If turnips are not grazed care-
fully, health disorders such as bloat, atypical pneumonia, nitrate
poisoning and hypothyroidism can occur.
Turnip crops may suffer from a variety of diseases such as rhizoc-
tonia rot, club root, turnip mosaic virus, root knot, anthracnose,
leaf spot and white rust. Some of these diseases can lead to crop
failure if rotation or other control measures are not used. Resistant
varieties are available to some diseases. To prevent problems with
diseases, Brassicas should not be grown on the same site more than
two years in a row.
Turnips also are subject to insect damage and can include flea
beetles, common turnip louse or aphid. These insects are more com-
mon under conventional tillage practices and can be controlled with
appropriate insecticides when applied to the soil at planting.
Animal production aspects
Due to highly variable climatic conditions in South Africa produc-
tion of fodder turnip (cultivar Mammoth Purple Top) in Limpopo
and Gauteng yielded the most when planted in February and defoli-
ated late August, resulting in 5,1 t/ha and 3 t/ha of which 2,4 t/ha and
1,7 t/ha were leaves and 1,7 t/ha and 1,3 t/ha tubers, respectively.
Research has shown that turnip produces high-quality forage and
livestock eat the stems, leaves and roots of turnip plants. Above-
ground parts normally contain 15% to 25% crude protein, 65%
to 80% in vitro digestible dry matter (IVDDM) with the roots contain-
ing 8% to 14% crude protein and 80% to 85% IVDDM. The mature
forage Brassica maintains a high nutrient concentration into autumn
and early winter. Turnips can be 80% to 90% digestible. By compari-
son, high quality lucerne hay is approximately 70% digestible.
Turnips are readily grazed by cattle and sheep and provide use-
ful supplementary grazing in the mid-winter or late autumn when
warm-season grasses and cereal forages are non-productive. Due
to their nutritive value, turnips are especially useful for feeding ani-
mals with high nutritive requirements.
Such an application might include fattening lambs, flushing ewes
and feeding lactating ewes, dairy cattle and young beef cattle.
Lambs grazing turnip gained an average 214 g/day to 249 g/day,
whereas lambs fed hay, gained 186 g/day to 195 g/day.
Conclusion
The Brassica species are valuable cover and forage crops. They do
however have special management requirements especially when
it comes to utilising them for animal grazing. As a dual purpose
crop, their specific management requirements are negligible when
the soil conservation benefits are realised. It does take good plan-
ning to integrate turnips into a grain production system, but
when this crop is being used as part of a multi-functional cover
crop programme and/or mix, specifically to restore soil quality, this
system is much easier to apply with substantial soil and animal
grazing benefits.
For more information, contact Dr Wayne Truter at wayne.truter@
up.ac.za, Prof Chris Dannhauser at
Dr Hendrik Smith at or Mr Gerrie
Trytsman at
References
Evans, D.W. 1979. Cruciferous-growth and yield. Symposium proceeding: Sheep
harvested feeds for the Intermit. West, Colorado State University, Fort Collins,
Colorado., 59 - 63.
Jung, G.A., McClellan, W.L., Byers, R.A., Gross, C.F., Kocher, R.E. and Reed, H.E.
1979. Old forage crops may come back. Crops Soils 31, 17 - 19.
Kinder, C.A. 2004. Growing and utilising turnips as forages. Proceedings, Idaho
Alfalfa and Forage Conference, 24 - 25 February 2004, Twin Falls, ID. University of
Idaho Extension.
Koch, D.W., Ernst, F.C., Leonard, N.R., Heldberg, R.R., Blenk, T.J. and Mitchell. J.R.
1987. Lamb performance on extended season grazing of turnips. J. Anim. Sci. 65,
1 275 - 1 279.
Undersander, D.J., Kaminski, A.M., Oelke, E.A., Smith, L.H., Doll, J.D., Schulte, E.E.
and Oplinger, E.S. 2015. Turnips: Alternative feed crops manual.
CONSERVATION AGRICULTURE