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ON FARM LEVEL
Conservationagriculture
Under rainfed conditions it grows better on soils with a relatively
shallowwater table of between 2m to 6m, but especially not on a
soil that is oftenwater-logged.
It is of utmost importance that soil analyses are conducted to en-
sure that the soil’s pH is in the order of 6 - 7, soil phosphorus (P)
levelsat least at 35mg/kg, andpotassium (K) 120mg/kg - 150mg/kg.
It is often expected that the soils will have a molybdenum (Mo)
deficiency, and it is highly recommended that Mo is provided
either in a coatingor pelletingprocess. Lucerne also thrives on soils
high in calcium (Ca) and therefore this specieswill benefit immense-
ly from calcitic liming if soil pH is too low.
Maintenance fertilisation is important; especially on sandy soil, K
and P can often be limited due to harvesting lucerne as hay. One
tonof hay removes about 20 kgof K/ton and 3,5 kgof P/ton. Grazing
however recycles most of these elements back to the soil via the
dungof the animals.
Lucerne as a legume has the ability to fix its own nitrogen (N). This
is a remarkable characteristic which makes this plant so efficient
and valuable. For this process however to be possible, it is impera-
tive that the seed that is tobe planted, is inoculatedwith the correct
strain of Rhizobium bacteria. If this process is done correctly, the
plant root will be infected and noduleswill develop on the root sys-
tems of theplant andwill start fixatingN.
Other than producing hay from lucerne, consideration can be given
to producing silage in higher rainfall areas. Haymaking of lucerne
can often be difficult due to unforeseenwet and cloudy conditions,
and silage however is possible under these conditions. The sugar
content of lucerne is rather lowand it isadvisable tomix itwithother
crops, such as sorghumormaize and/or the additivemolasses.
Management challenges
The highest risk that exists when utilising lucerne is the possibility
of ruminants developing the condition termed bloat. This condition
occurs because of a specific protein in the plant that is eventually
responsible for the suffocationof the ruminant.
Toprevent bloat it is advised tograze the pasture at amature stage,
provide dry hay and enough drinking water and not to graze with
hungryanimals.Bloat guard isalso regardedasaproduct that canbe
given to animals toprevent the condition fromoccurring.
From a production perspective, with the intensive cropping of lu-
cerne, disease resistance is of high importance and many of the
higher dormancy types are known for this characteristic. Lucerne
shouldnever beovergrazed, as thiswill lead tograss invasion.
Low soil P levels are also regarded as a reason for grasses to invade
lucerne fields, andonewill need tomakeuseof theherbicides avail-
able to control grassweeds in lucerne fields.
Soil conservation and health benefits
This perennial legume pasture has been successfully planted all
over the country. Not only does it produce good quality roughage,
but becauseof its deep root system, it has the ability to return a sig-
nificant amount of organicmaterial back into the soil.
This species’ most common characteristic is to capture atmos-
pheric nitrogen and convert it into high quality plant proteinwhich
indirectly increases soil N-levels beneficial to succeeding crops.
Residual soil N in theorder of 130 kg/ha to 350 kg/ha (all depending
on the way the lucerne was managed) can be available for a suc-
ceeding crop.
According to Crocker (2003), growing lucerne for 3,5 years elimi-
nates the need for fertiliser nitrogen (N) in the next five crops.
Lucerne improves other factors, such as soil organic carbon and ag-
gregate stability, comparedwith continuous grain and long fallow.
Animal production aspects
Lucerne is regarded as the best legume crop to be planted in South
Africa, and is commonly used to produce good quality hay, espe-
cially under irrigation.
When lucerne isused forgrazingpurposes, the followingaspectsare
important tobear inmind:
Don’t allow animals tograze formore than 24hours at a time.
Do not let unconditioned animals graze lucerne – give them
some time to adapt to thehighqualitygrazing.
Never allowhungryanimals tograze lucerneandensure that suf-
ficient water is available for animals todrink.
The first year of lucernemust be lightlygrazed.
While grazing lucerne, it is recommended that medium quality
hay is provided at the same time so that tannins in this hay can
precipitate the protein responsible for bloat, therefore lowering
the risk of it occurring.
It is often advised that lucerne is safer to graze at a full bloom
stage.
Some animals, such as Merino sheep, are less susceptible to
bloat.
From a quality point of view, a crude protein of as low as 19%
and as high as 25% can be obtained, with a digestibility of
65% - 75% respectively.
Grain crop production
After establishing a typical ley crop system using lucerne for a pe-
riod of around three to five years, the soil should be sufficiently re-
stored tocultivateannual graincropsunder aCA-system.Herbicides
kill the pasture quickly and the pasture residues remain on the soil
surface providing cover that limits erosion, enhance water infiltra-
tion and reduces their rateofmineralisation.
Onceadecision ismade to terminate the ley, all pasturecomponents
should be considered as “weeds” that need to be removed. They
shouldno longer be regarded as a sourceof fodder for livestock.
Usually lucerneshouldbekilledaseasonbeforeplantinggraincrops
to allow the soil profile to be replenished with water. Maize can be
planted in the following summer, or grown in succession (“stacked”,
normally twice) followed by a long break with a two-year legume
(such as soybeans).
A suitable no-till planter should be used to plant the grain crops
directly into the residues of the pasture crop, without any other
cultivation practice disturbing the soil. Normal weed and pest con-
trol practices should be followed. However, due to the residual
soil N-levels, the following maize crop’s N fertiliser levels could be
cut with 50% for at least the following two years (i.e. in the stacked
rotation).
Conclusion
This legume species has a proven track record, and can be used
as a multi-purpose crop with significant benefits. Not only does it
CONSERVATIONAGRICULTURE
Oktober 2014
