Tillage before planting
Preparation of lands for the planting of lucerne should preferably be started during the spring before the expected autumn planting date.
In the case of a cash crop being fitted in beforehand, at least two months must be allowed after harvesting it, before the lucerne is planted, in order to allow complete breakdown of the crop residue.
Lands which have been in use for several seasons must be deep ploughed to break up hardpan areas. The most important considerations when ploughing are to improve root penetration, drainage and aeration of the soil and to reduce soil compaction.
Furthermore, it helps to control weeds, breaks down and works into the soil any harvest residue, and breaks up large clods. Fertilizer can be added at the same time.
Early preparation of lands is recommended if there is a problem with weeds.
It is necessary to work the lands in the spring and then allow them to lie fallow for the summer, then to work them again in late summer and/or before planting in the autumn.
The advantages of soil tillage are temporary, and a heavy rainstorm can undo them.
If the pH of the soil is correct, then a fallow period (spray instead with herbicide) may be considered as an alternative. This may keep input costs under control.
Exposure of the soil stimulates the activity of micro-organisms which use organic material as a food source.
This can result in a poor carbon-oxygen ratio in the soil, which leads to soil compaction.
Another possible disadvantage of soil preparation is the increased costs.
There is the cost of petrol / diesel, as well as maintenance costs due to wear-and-tear on implements.
Moreover, as ploughing leads to structural damage of the soil, so more powerful tractors must be used.
Fertilisation before planting
Liming should be done before sowing.
During tillage and before sowing is the last chance for relatively insoluble fertilizers such as lime to be well mixed into the soil, so that chemical reactions can release nutrient elements for uptake by the plants.
Nutrients that usually need to be supplemented, other than lime, include phosphorus, potassium and sulphur.
Liming is the most important fertility factor for the establishment and maintenance of high-yield, high-quality lucerne. Guidelines for liming must be based on the exchangeable acidity in the soil and not simply on its pH and texture.The advantages of liming for lucerne include the following:
- Helps production of optimal yield
- Increases availability of other elements, e.g. phosphorous and manganese
- Reduces iron and aluminium toxicity
- Improves establishment of the stand
- Increases productive lifetime of the stand
- Nitrogen-fixing bacteria (Rhizobium) are more active
- Provides calcium and magnesium
- Improves soil texture and tillage
For maximum yields, the land should be limed to a pH of 6.7 to 6.9. Yield of lucerne drops rapidly in soil of pH less than 6.7.
Because lime reacts slowly with soil acids, it should be worked in at least 3-12 months, and preferably longer, before lucerne is sown.
The best time to apply lime is directly after the old lucerne stand has been removed, in a typical 4-6 year cycle of crop rotation.
This allows a longer period for the lime to act on the soil, and tillage for the following crops will mix it thoroughly into the soil.
This should bring the pH up to the required level by the time lucerne is re-planted.
The effectiveness of lime is determined by its chemical purity and by the particle size of the source.
The finer the particles, the more effective the action and the more quickly the desired pH will be reached.
To obtain the same change in pH with coarser lime would require its being spread a longer period before planting time as well as in greater quantities.It is, however, cheaper.
Also, coarser lime would not need to be applied as often as finergrained lime.
To compare prices, one should evaluate the liming medium on the basis of the quantity required to obtain the desired result. The relative effectiveness of the various liming media is indicated by:
- Effective calcium carbonate equivalent (ECCE)
- Effective neutralising power (ENP)
- Total neutralising power (TNP)
Agricultural lime should be broadcast on the surface of the soil and worked in with a disc plough, then ploughed in sufficiently deeply for maximum spreading and neutralising of acids in the ploughing layer (not less than 150-200 mm). Ploughs without a ploughdisc may deposit the lime in a layer at the hardpan.
To apply large quantities of lime (>6 ton/ha), half should be applied before beginning to work the land, and the other half after ploughing or other preparation.
Different liming media exist. Calcite products contain calcium-based neutralisers, while dolomitic types have both calcium and magnesium. Both are equally effective in altering soil pH. Which type is used is determined by the calcium (Ca) and magnesium (Mg) levels in the soil.
If soil magnesium is lower than the optimum, then a dolomitic lime should be used. If Mg is higher than optimal and the Ca X 0.6 is higher than the Mg, then both types may be used. If Mg is higher than optimum and Ca X 0.6 is lower than Mg, a calcitic lime should be used.
Phosphorous fertilisation is determined by soil analysis, target yield, and percentage clay particles in the soil.
Adequate phosphorus in the soil increases establishment success by improving root growth, and it is also important in flower formation and seed production.
Phosphorus is very immobile in most soil types. It is provided to the plant by diffusion.
When it is taken up by the roots, the concentration of P in the surrounding soil drops.
Uptake is passive and no metabolic energy is consumed in the process.
Research has shown that, in soils with low to moderate levels of P, correction of P concentration before planting, while soil is being prepared, is up to twice as effective as when applied as a topdressing after planting.
P can also be applied in a 12-25 mm band beside or below the seed, but it is more usually broadcast and worked deeply into the soil before planting time.
A minimum of 10 kg/ha is needed for high P soil. Rock phosphate is not recommended for lucerne, as the pH at which rock phosphate is effective is too low for lucerne production.
Guidelines for phosphorus fertilisation
|Application for yield potential (dry material) t/ha|
|Soil-P mg/kg||Phosphorus, P (Establishment and Maintenance) – kg/ha|
|Soil-K mg/kg||Potassium, K (Establishment) – kg/ha|
Legumes have a very high protein content and therefore a high requirement for sulphur. If necessary, pure sulphur can be used as a source of sulphur at planting.
Pure sulphur must be converted to sulphate before it can be used by the plant, a relatively slow process, especially if the sulphur is applied as a topdressing.
If pure sulphur is applied at planting time at a reasonably high level (50 kg/ha), it should be sufficient for the lifetime of the stand.
The cost of such an application should be compared to the cost of annual applications of sulphate.
Sulphur can be supplemented through the use of an application of single superphosphate, a sulphur-containing fertiliser, just before planting time. This would supply at the same time both the sulphate and phosphate requirements of the lucerne.
Research has indicated that small supplements of nitrogen can improve establishment and survival in the first year of a stand. 25-30 kg/ha should be applied if lucerne is sown directly onto sandy soil with a low organic matter content (>2%).
If the lucerne is sown as a mixture, 20-35 kg/ha N should be used, and 40-55 kg/ha if the other component of the mixture is to be used as silage.
- Soil requirements for lucerne
- Well drained
- pH 6.7-6.9
- P>40 mg/kg soil – Method used is Bray 1
- K>120 mg/kg soil – Method used is Bray 1
- Phosphate for seedling growth, root development and yield
- Potassium for healthy plants and winter survival
- Calcium for roots and N-fixation
- Magnesium essential for photosynthesis
- Sulphur necessary for protein synthesis
- Molybdenum important for N-fixation
More failures of lucerne establishment can be attributed to poor seedbed preparation, than to any other one factor.
Weed control should have already been begun the year before by using a disc or harrow.
Perennial weeds should be eradicated before beginning with planting. If the seedbed is rolled after liming, weed seed will germinate well, and this strategy can be used to combat weeds.
If lime is necessary, it should be well ploughed in three to four months before sowing, so that the lime can react with the soil and correct the pH.
If an autumn planting is planned, soil preparation should begin no later than January.
Soil moisture should be conserved, especially on dryland plantings. NB: the more the soil is tilled, the more moisture it loses.
Precise methods of planting will vary with the farm, but the following broad guidelines should be followed:
- Use deep ploughing to loosen the soil and combat perennial weeds.
- This is the case when harvest residue makes tillage difficult.
- P, K, Zn and B should be disked in just before planting.
- A cultivator or harrow should be used for the final preparation of the seedbed.
- Correct tillage should ensure a fine-textured and weed-free seedbed.
- The seedbed must be fine-textured and grainy, not powdery, to ensure good contact between the seed and the soil.
- Compact or roll the land to ensure a firm seedbed.
- A Cambridge roller can be used before seeding, while the soil is still dry, and after seeding, before the land is irrigated..
- Before planting, the land should ideally be even, without clods and firm-textured. A normal-sized person walking on the land should not sink in deeper than the tops of his soles.
- The ideal seedbed should be fine, with soil clods not more than 10 mm in diameter.
- The seed should be preferably be planted with an implement that will cover the seed shallowly and compact the covering soil, to make sure of good contact between seed and soil, and also to conserve soil moisture.
INNOCCULATION OF SEED
To ensure that the bacteria survive from inoculation until the seed is planted, it is best that the inoculation be done in a cool area with minimum direct sunlight.
The seed must be covered with an adhesive to ensure that the inoculant adheres to it.
The generally recommended and most-used adhesive is 2% methyl-cellulose solution.
In the past, a sugar or molasses solution was recommended, but they are not as effective as methyl-cellulose.
Although it is no longer common practice to coat seed with toxic fungicidal or insecticidal chemicals, seed which has been so treated should be washed before being inoculated.
This washing must be completed quickly, and the seed rapidly dried again, as germination may begin during the washing process.
This would be more damaging than using treated seed without washing.
After the seed is wetted, the inoculant is added and mixed thoroughly with it.
The amount of seed which can be treated with one packet of inoculant varies between 12 and 15 kg per packet, and is indicated on the packet.
If seed is sown in dry ground, irrigation should take place as quickly as possible afterwards.
It is recommended that the seed be pelleted under poor conditions, e.g. low pH and dry soil.
To protect the seed and make it more manageable, the correct ratio of seed, sticker and pelleting material, e.g. lime or betonite, must be used: 10 kg seed to 1 litre sticker and 9 kg lime.
Gum arabic (40% solution) or methylcellulose (2% solution) can be used as an adhesive.
Buying and inoculation of seed
The types of inoculants recommended for different types of legumes are freely available in the trade (seed companies and co-operatives).The RF 14 race is used for lucerne.
The ARC-Institute for Plant Protection is responsible for quality control, as well as the testing of improved races for optimal inoculation.
The handling of inoculant from production to actual use is extremely important, and the following are strongly recommended:
- Store the inoculant in a cool dry place, but not in a freezer. The maximum temperature under which the bacteria will survive differs for tropical and temperate legumes. Storage temperatures of not more than 20°C are recommended for inoculant of temperate legumes.
- Do not expose the bacteria to direct sunlight. At planting time, especially, it must be ensured that the seed is covered by soil as quickly as possible.
Good germination and establishment of lucerne are promoted by a longer growing season, sufficient soil moisture and cool temperatures.
At emergence, lucerne is extremely susceptible to cold, and late summer planting is only successful if soil moisture is adequate for sufficient growth to take place before the frosts.
Lucerne needs a minimum of 6 weeks growth after germination if it is to survive the winter.
This allows the plant to form a crown and build up sufficient root reserves for winter survival.
Only seed cleaned by a dealer, and accompanied by a label guaranteeing purity and germination, should be used.
The seed colour is important: only yellow to olive green to brown seed should be bought.
Dark-coloured seed should be avoided, as it indicates that the seed is either old or has been exposed to water.
Hardseededness (inability to take up water) is common in lucerne seed: 10% hardseededness is regarded as acceptable.
It is recommended that sowing be done in autumn (end of March) under irrigation, if a land is known to have a problem with weeds, and effective control of these is difficult or expensive.
In a frost-free area, any planting time is suitable if a registered herbicide is available and affordable.
If sowing is to be done under dryland conditions, it is important that the soil has sufficient moisture at planting time.
In this case lucerne must be planted in rows with a planter, to facilitate follow-up treatments such as weed control.
If the first sowing shows poor germination, re-planting can be done within 2-3 weeks.
However, it is sensible to rather disc out the stand and re-sow later in the season.
Advantages and disadvantages of late-summer vs. spring sowing
|Fewer weeds therefore less competition||Soil moisture may be limiting and may restrict growth|
|Seedbed preparation can be done with more care as farmer has more time||Insects in late summer may do more damage to seedlings than to mature plants|
|Reduced chance of Phytophthorarootrot infection||After effects of herbicides can occur in some farming systems|
|Less workload than in the busy spring season||Growth may be insufficient and lower winter survival|
|Full production the following year|
Broadcast sowing by hand
With this method it is very important to cover the seed as soon as possible with soil.
A chain can be used for this or a upside down harrow with the front raised 5 cm above the soil surface.
A roller must also be used to compact the soil. To obtain an even stand, it is extremely important to spread the seed evenly over the soil surface.
Broadcast sowing with an implement
The procedure after sowing is the same as for hand-sowing.
In rows with a planter
If a planter is used, care must be taken that the seed is evenly deposited.
A vegetable planter usually works well. If a pressure wheel is mounted on the planter it is not necessary to roll the land; otherwise this must be done after planting.
Wheat planters with a pressure wheel may also be used successfully – care must be taken, though, that the seed is not planted deeper than 15 mm.
Advantages of row-planting a.o.t. broadcast sowing:
- Better utilisation of soil moisture
- Less trampling and damage to crowns if used for grazing
- Secondary working of the land for, e.g. weed control, and penetration of water, is feasible.
- Quicker regrowth at start of growing season
- Longer lifespan of the lucerne
- Better utilisation of fertiliser applied in rows
- Lower seed requirement/ha
Under average conditions, about 60% of the lucerne seed will germinate and about 60-80% of the seedlings will die within the first year.
Lucerne seed is small, and should be planted shallowly, but still covered with soil.A covering of soil is also necessary as protection for the Rhizobium bacteria, as these should not be exposed to direct sunlight.
Seed should be especially shallowly planted in heavy clay soils, about 5-10 mm, while on sandy soils it can be planted at 10-20 mm depth.
If soil moisture is sufficient, or if irrigation is available, deeper planting is unnecessary. Under dryland conditions, seed should be planted deeper.
Soils that tend to form a crust should be kept wet until the lucerne has germinated and become established.
There are about 440 000 lucerne seeds per kg. In dryland sowing, 3-7 kg/ha is recommended, while a sowing density of 18-20 kg/ha is adequate under irrigation.
An important aspect, which is often neglected, is that seed size varies between cultivars and between seed lots.
It is therefore necessary to re-calibrate the planter whenever a new cultivar, seedlot or pelleted seed is to be planted.
As already stated, optimal lucerne production is dependent on optimal plant density and it is therefore important to ensure the best possible stand to reach the maximum potential of the lucerne.
Under average conditions, about 60% of the lucerne seed will germinate and about 60-80% of the seedlings will die within the first year.
A vigorous stand of lucerne is the basis for profitable production.
The choice of a well-drained land, the correct preparation of the land, the establishment of soil fertility by means of soil samples, as well as the correct nutrient supple-mentation before and at sowing, is crucial.
Selection of Land
Lucerne needs well-drained soil for optimum production.
Waterlogged soil creates favourable conditions for a range of diseases and pathogens, such as Phytophthora, Pythium, etc., which cause seedling diseases, reduce yield and thin out the stands.
Establishing lucerne on such soil should not even be considered. Poor drainage lowers the amount of soil-oxygen that reaches the roots.
Cultivars with high resistance to root diseases, as well as the use of fungicides at planting time, will reduce problems caused by poorly drained soil.
Care is needed to prevent erosion at planting time if the lucerne is planted on a slope, especially in the first year.
Level lands with a relatively shallow slope may have areas where water may collect and cause a poor stand to develop.
Soil types having a gleyed E-horizon and a shallow A-horizon, for instance Kroonstad type, should be avoided because of the possibility of poor drainage.
Soil types where the orthic A-horizon is underlaid by hard rock, such as Mispah type, should also not be used for lucerne.
Any soil type which is well-drained, and where the nutrient content can be corrected economically, can be used for cultivation of lucerne.
Soils need to have adequate depth, at least 1.2 m, if they are to hold a sufficient reserve of water. Lucerne has a long tap root – up to about 6 m – which under favourable conditions penetrates deeply into the soil.
This ability gives lucerne good drought resistance. Soil suitable for lucerne, and classified as medium to deep, usually occurs beside streams and rivers.
Medium to deep soil forms, with a clay content of not more than 35%, are considered as optimal for lucerne production.
The lands must not have any compacted layers or hardpan areas.
South African lucerne is grown in a variety of climatic zones and farming areas, where the nutrient status of the soil may vary widely.
To meet the nutritional require-ments of the plant, and to ensure optimal yield, the nutrient status must be ameliorated.
Correct soil nutrient status will ensure that the stand establishes rapidly and remains vigorous and productive.
A favourable nutrient status will also maintain the quality of the end product, and allow lucerne plants to compete with weeds which often invade.
The success and profitability of lucerne depends considerably on the original stand and the vigor of its growth.
Prevention of weeds
The lands must be free of perennial weeds such as kweek (Cynodon dactylon) before lucerne is established on them.
If thorough controls are not followed, the weeds will grow faster than the lucerne and result in poor stands.
There should also not be any carry-over of weedkillers which may affect the lucerne.
Annual weeds are often merely a temporary problem, and can be controlled by cutting.
It is well known that lucerne plants produce a chemical(s) which suppress the germination and growth of lucerne seedlings.
This phenomenon is called self- or autotoxicity.
The chemicals (including medicarpin) are produced in the leaves and released into the soil when the leaves fall, where they eventually break down.
The range of the toxicity increases with the age of the stand, its density and the amount of toxic residue present before re-seeding.
When old lucerne stands need to be resown to lucerne, it is sensible to rest the land for a season (or to plant an annual crop) so that the water-soluble toxins can either degrade or move out of the root zone of the new lucerne seedlings.
Under certain weather conditions lucerne can be re-sown as soon as 6-8 weeks after ploughing out of the old plants.
Breakdown of the toxins occurs more quickly in hot, damp conditions.
The following recommendations should be kept in mind:
Do not inter-sow to thicken up a stand.
The young plants may grow well initially, but because of competition for light and water, will soon die off.
Lands with two- or more year-old lucerne probably are autotoxic.
Select cultivars with a high level of disease resistance, especially for lands where lucerne has already been cultivated.
Diseases build up in the soil and adversely affect new seedling growth.
Weedkillers and fertilisation / nutrient depletion of the land as a result of previous harvesting or plantings, may also affect the success of lucerne establishment.
Soil Samples & Analysis
Because of the high price of fertilizers, it is necessary to sample the upper and lower horizons of the soil and to have them analysed at a reliable laboratory.
It is sensible to investigate the soil physically and to have it analysed chemically, and to request the laboratory to recommend fertiliser specifically for lucerne.
Most soil analyses check pH (acidity), lime, phosphorous (P), sodium (K) and various secondary and trace elements.
The recommended values can differ with soil type, cultivation potential and management needs. It is therefore necessary to consult with a specialist regarding your specific conditions.
Sampling the soil incorrectly has minimal value and can lead to incorrect information about its fertility.
The sample must be representative of the land.
General requirements for soil samples
A topsoil sample can be taken with a Beater soil bore, which samples to a depth of 150-200 mm.
Control carefully the depth of the samples. At least 30 samples (core samples) should be taken and mixed together, from which a final sample of about 500 g is taken.
Where there is soil acidity, it is recommended that samples also be taken of the underlying soil layers.
This can be done with a Dutch or Eykelkamp soil bore. About 5 core samples of about 200 mm diameter are taken, each from a different place on the land.
Samples are also taken at different depths, each one about 200 mm deeper than the last.
The samples of each specific depth are amalgamated to make one sample of that depth.
The samples must not be dried by heating.
If necessary, allow them to air-dry in a cool place before packing.
If a land is to be represented by a single soil sample, then this re-presents a compromise between various practical considerations.
It must be possible to lime and fertilise the land as a separate unit with respect to topography, drainage, soil type and previous management.
Small areas which obviously differ in appearance, as well as crop response, must either be sampled separately or excluded.
As a general rule not more than 50 ha should be represented by a single sample.
Frequence of sampling
When soil with a low fertility is to be improved by means of a planned fertilisation program, it is recommended that it be analysed annually.
Once the necessary nutrient status is reached (under normal management) the pH and fertility will not change rapidly, and a fertilisation program can be based on samples taken once every 3-4 years.
Time of year for sampling
A soil sample should be taken several months before sowing, to ensure sufficient time for delivery and analysis, for ordering of lime and fertilizer, and for the spreading of the lime at least a month or two before sowing.
As a general rule samples should be taken at the same time each year.
In the case of annual crops it is recommended that soil samples be taken after ploughing (after the previous crop has been harvested or ploughed in).
In this way it will be possible to correct any imbalance which may exist as a result of previous spreading of fertiliser in rows.
In planted pastures, samples should be taken between March and June, at least 6 weeks after the last application of fertilizer and before ploughing and liming.
Primary Soil Cultivation
Breaking up of compaction layers in the soil profile.
Mixes organic material, fertiliser and weed seed deep into the soil.
Facilitates above-mentioned cultivation. The action is the same.
Secondary Soil Cultivation
Weed control and breaking up of clods.
Breaking up of compaction layer at soil surface, and control of weeds.
Final seedbed preparation.
Final seedbed preparation.
Spreads lime evenly on the soil surface.
Facilitates even broadcasting of fertliser, before as well as after planting.
Broadcasting of large quantities of organic material.
Ensures good contact between seed and soil.
Ensures all seed is sown at a given depth.