Last update: April 3, 2012 07:57:05 AM E-mail Print

 

LUCERNE-KING OF FODDER CROPS

 

G.C. de Kock

Head: Agronomy Section

Agricultural Research Institute, Grootfontein

 

LUCERNE was probably the first crop to be cultivated for hay. It is indigenous to Mesopotamia. It spread with the Persian armies from Media to Greece in 470 B.C. where it was known as "Medic". Lucerne was brought from Greece to North Africa and hence to Italy and in 100 B.C. from Italy to the rest of Europe. Apart from other parts in Europe, it was cultivated in the Lucerne region of Italy from whence it obtained its common name.

It spread from Spain to the Americas where it is known as Alfalfa, an Arabic word meaning "best fodder". It came to South Africa from South America in 1861 and was first grown in the Worcester district. From there it spread to the Little Karoo and Karoo, mainly as grazing for ostriches.

Lucerne is today the most important fodder crop grown under irrigation in the Karoo and because of the high yields obtained, its palatability and high feeding value, is known as the King of fodder crops.

Lucerne is known botanically as Medicago sativa belonging to the family Leguminosae. There are three species of the genus Medicago known as Lucerne, namely

(These two species are found mainly in the colder parts of the world.)

 

Adaptation

Lucerne has a wide adaptation ability provided sufficient water is available. Temperature plays a very minor part in the regional distribution of lucerne. Moisture is, however, the limiting factor.

Lucerne can be cultivated under dry land conditions where the annual summer rainfall is higher than 400 to 500 mm and in winter rainfall areas where the annual rainfall is higher than 350 to 400 mm. Lucerne requires large amounts of water for optimal production. (From 750 to 800 kg of water is required for every kilogram of dry matter produced.) Due to a deep root system the lucerne plant can withdraw water from deeper soil levels. An important advantage of such a deep root system lies in the fact that the plant can survive long dry periods once it has been established.

Lucerne is adapted to a series of soil conditions provided the following requirements are complied with:

1. The soil should not be acid. The poor growth of lucerne on acid soils (ph < 5,5) is usually due to manganese and/or aluminium toxicity, reduced availability of molybdenum and phosphate and inefficient nitrogen fixation. The application of lime to raise the pH to 6,0 and higher is a prerequisite for lucerne production on acid soils. The lime requirement of a soil is determined by soil analysis.

2. The soil should not be brack or alkaline brack (ph > 8,3). Lucerne is reasonably brack resistant but the growth and development of seedlings is retarded by high concentrations of salts. The availability of other plant nutrients can also be influenced by a high pH and the presence of brack salts in the soil. The high pH and brack salt content can be rectified by the application of Agricultural Gypsum. The actual amount should be determined by soil analysis.

3. The soil profile is also very important. With its well-developed root system, lucerne prefers a deep soil. The depth of the soil profile can be limited by impenetrable layers or by compaction of the subsoil or a plough sole. Under such conditions a temporary water table can develop after irrigation or during a wet season, causing the lucerne roots to rot or be penetrated by disease organisms. Lucerne therefore requires a deep and well-drained soil.

 

Soil preparation

When lucerne is to be established under irrigation, it is especially desirable to prepare a fine and firm seedbed. As the soil will be irrigated for a number of seasons, well laid out beds save costs and ensure high yields. As efficient weed control is practically impossible in new established lucerne lands, the preparation of the soil must be such that the seedbed is practically weed free at the time of establishment. It is good practice, especially with new lands, to cultivate another crop for at least a season before establishing lucerne. It enables the farmer to control the weeds and to ensure that the slope of the irrigation beds is corrected before lucerne is planted. High patches in lands cause lucerne to suffer from drought, while it becomes waterlogged in low patches. It must always be kept in mind that lucerne usually remains on the land for a number of years and that good soil preparation before establishment is of the utmost importance because this will eliminate future problems.

As fertility affects the yield and longevity of lucerne, fertilisers must be applied during the preparation of the soil. An application of supers at this stage is recommended.

 

Establishment

In the Karoo lucerne can be sown under irrigation at any time of the year except in June and July. The best time is, however, during late summer (February to April). If sown in spring, August and September would be the best months to sow.

The time and money spent on the preparation of the seedbed can be in vain due to the use of poor seed. Apart from the fact that an unsatisfactory stand is obtained, there is also the danger that weeds, especially dodder, can be introduced.

It is thus desirable to use certified seed.

Lucerne seed should be inoculated with the correct nodular bacteria before sowing in order to ensure that nitrogen fixation takes place. Traces of Rhizobium bacteria are usually found on host plants, but even where lucerne has been in a crop rotation system on the land for years, seed should still be inoculated.

High seeding rates (15-20 kg of seed per hectare) are required under irrigation, intermediate rates in high rainfall areas and low seeding rates in low rainfall areas. Lucerne seed should preferably not be sown with a so-called cover crop.

The seed can be broadcasted by hand, seed drill or cycalone spreader. The seeding depth varies with soil depth and the moisture content of the soil. The optimum depth varies from 10 to 20 mm on sandy loam soil and 5 to 10 mm on clay soils. The seed should only be lightly covered. The land can be irrigated immediately after seeding.

Unless the seedbed is well prepared beforehand, weeds often damage the young crop. Combat the weeds by cutting with a mower set high above the ground before any seed is produced.

 

Fertilisation

Lucerne is a perennial crop, which occupies the land for a number of years. The necessary nutrients must therefore be applied to the soil before establishment. Lucerne requires a large amount of phosphate, which is closely associated with the utilisation of nitrogen by the plant; it stimulates root growth and is also of importance in the flowering and seed setting processes. Super phosphate should be applied during soil preparation and worked into the soil.

A shortage of nitrogen is seldom experienced in lucerne. It may, however, be necessary to apply a small amount of nitrogen at a young stage on soils where nitrogen is limited.

The application of Potassium is only essential on certain sandy soils and can be supplied by the application of Potassium sulphate.

Fertiliser applications must preferably be based on the results of soil analyses.

 

Irrigation

Lucerne requires large amounts of moisture, but is at the same time sensitive to over irrigation, especially where the latter occurs on badly drained soils causing the accumulation of large amounts of free water.

The first irrigation is applied before establishment of the lucerne. The soil is finally cultivated and sown after this irrigation. Irrigation immediately after sowing can cause the formation of a crust, which is detrimental to germination. Germination can sometimes be encouraged by a light overhead irrigation if the equipment is available and the irrigation water is of good quality. If the soil does not tend to form a crust the seed can be sown in dry soil and then irrigated. Root development does not take place in dry loose soil.

It is not necessary to irrigate established lucerne frequently. Lucerne can use up to 80 per cent of the available soil moisture without any detrimental effect.

The amount of water that should be applied depends on the length of the growing season, the number of cuts, climatic factors such as temperature, evaporation and rainfall and the degree of infiltration of the water in the soil.

Lucerne is mainly flood irrigated by means of the bed system. The width and length of irrigation beds depend on factors such as the strength of the irrigation stream, the type and depth of the soil and the slope of the land.

Two irrigations of 75 mm each will give better yields on shallow soils or on soils with a poor water holding capacity than one irrigation of 150 mm. Even on deep alluvial soils it has been found that an irrigation of 75 mm immediately after cutting and another irrigation of 75 mm approximately 14 days later produced the most satisfactory yields.

Where irrigation water is limited lucerne can be irrigated by means of a sprinkler system. However, it appears that this method is not always advisable in the Karoo where the brack problem more than often occurs.

 

Lucerne Cultivars

In South Africa seed is at present only produced from South African Standard lucerne. This is a land race cultivar, which originated by natural selection.

 

Weed Control

Weeds not only reduce the yield of lucerne, but also impairs the quality of hay and seed. Weed control should therefore receive attention before establishment.

The following measures should be applied

 

Management and Utilization

The best stage to cut lucerne for hay is influenced by the quality of the hay and effect of cutting on the lifespan of the stand. By cutting lucerne continuously at a stage younger than the 10 per cent flower stage, the plants become weaker and their lifespan is shortened. This is due to a reduction of the root reserves. These reserves are built up in the roots, during flowering and later stages. The detrimental effect of harvesting at a young stage can be offset by letting the lucerne go to flower once or twice in late spring and autumn.

Insignificant differences are found in hay yields from lucerne harvested at the 10, 50 or 100 per cent flowering stage, but a reduction in the percentage leaf and an increase in the fibre content are experienced when lucerne is harvested after the 10 percentage flower. Considerable weed infestation also occurs when lucerne is regularly harvested at a young stage.

As lucerne becomes older, the stand becomes thinner and growth poorer; a result of various factors such as an exhaustion of the soil's fertility and a gradual loss of plant vigour due to regular cutting and perhaps grazing during the active growing season. It then becomes necessary to activate growth again by tilling the lands. A thorough tilling treatment during late winter, i.e. before the active growing season, has various advantages, the most important of which are the improvement of the soil structure and destroying many annual and even perennial weeds. It also gives the opportunity to replenish the nutritional requirements of the soil. A medium application of phosphate before tilling usually stimulates production.

A great advantage of lucerne as a fodder crop lies in the many forms in which it can be utilized. As a hay, it can be utilized as ordinary hay, or leaf meal and stem meal or lucerne cubes. When weather conditions are unfavourable for haymaking, a good quality silage can be made from lucerne.

Although pre-eminently a hay crop lucerne can also be utilized with great success as a grazing crop. As has been previously pointed out however, great care should be taken not to overgraze lucerne lands because this could be detrimental to future production. Such harmful effects can be reduced by cutting two crops at the 10 per cent flowering stage in spring and autumn.

 

Published

Karoo Agric 1 (1)