The potential of pasture legumes and their role in improving farming practices under extensive livestock production systems in Zambia

J. Kulich

Nanga National Irrigation Research Station
P/Bag S 3, Mazabuka, Zambia

Introduction
Past and present situation
Results and discussion
Conclusions
References

Abstract

The development of improved pastures in Zambia is reviewed on the basis of research and farmer experiences. Pasture research programmes have provided much basic information about development of pasture systems for both dairy and beef cattle. There is need to know much more about how to maintain stable pastures, the persistence of legumes, establishment of improved species, maintenance fertilizer requirements and pasture management; more information is needed on the economic aspects of these systems. To increase production with minimal increase in costs seems possible only with an integrated usage of improved and native pastures.

Introduction

The most important constraints to improving livestock production in Zambia are related to animal nutrition. The feed resources mainly based on the natural pastures, are poorly managed throughout the country. Due to the long dry season, there are feed shortages so that animals lose weight, suffer high death losses and exhibit low fertility. When animals are under so much stress, they are also more susceptible to diseases. Overstocking and overgrazing, which are very common in many grazing areas in Zambia, have resulted in serious land degradation, the disappearance of valuable pasture species and the spread of unpalatable species. When natural veld pastures are developed with a legume-base and fertilized mainly with superphosphate, most of them can yield large quantities of low-cost animal products. Legumes supply nitrogen cheaply for the associate grasses and grazing ruminants, and their large scale use in the future will ensure that adequate quantities of beef and milk will be within the financial reach of the rapidly expanding population of Zambia.

In many areas of Central, Southern and Lusaka provinces in Zambia, inorganic nitrogen-grass systems are used for dairying and intensive beef production, but with increasing costs and the removal of subsidy and possible shortages of energy, there has been created a potential instability in price/supply of fertilizer N. thus making this practice uneconomical. There is, therefore, a swing in these areas to legume-grass systems.

One of the most important facets of tropical pasture research is to find legumes suitable to the Zambian environment. Pastures based on these legumes have the potential for both higher stocking rates and faster cattle growth rates which can result in a significant increase in animal production.

Past and present situation

The volume of pasture research, and hence of literature, on the improvement of pasture production in Zambia, is very great, and no attempt is made here to review it fully. There have been other reviews by Prins (1970), Craufurd (1979), Kulich and Kaluba (1985), Kulich (1985), Kulich and Nambayo (1985), and Kulich (1986). During the past 30 years there have been significant contributions on pasture legume research notably by Smith (1962, 1963), van Rensburg (1967, 1969a, 1969b), Potter (1972), Verdoom (1965), Prins (1972, 1975), Peterson (1975), Shalwindi (1978), Craufurd (1978), J. and S. Kulich (1973, 1976) and by Kulich (1977, 1981). Despite the efforts of these people to stimulate commercial interest, farmers have not responded in any significant way.

During the '50s and early '60s beef production was not particularly profitable; the beef enterprise played second fiddle to tobacco and maize. Although farmers were planting pasture grasses, they were not prepared to spend money on the more expensive legumes. In the '70s, the situation started to change with an increase in consumer demand coupled with the banning of beef imports. When beef became more profitable there was increasing interest in pasture development. This interest, however, was not matched with a corresponding interest by most farmers with pasture legumes. The farmers relied on inorganic nitrogen which was heavily subsidised. As costs of N fertilizer increased with removal of subsidy in the '80s interest in pasture legumes was renewed and a high research priority was given aimed at finding stable legume-grass systems. There was an increased emphasis on pasture seed production as a result.

Locations

The investigations were carried out at two locations:

1. Mount Makulu Research Station, situated 16 km south of Lusaka at an altitude of 1,206 m. The average annual rainfall at this site is about 803 mm, falling during the rainy season that spans the November-March period. The mean annual temperature is 20.7°C with the coldest months, June and July, experiencing occasional ground frosts.

2. Chimyamauni Farm, Mkushi, situated 300 km north of Lusaka at an altitude of 1,300 m. This site has an average annual rainfall of 900 mm and a mean annual temperature of 19.8°C.

Results and discussion

Excellent results have been obtained from three pasture legumes: Siratro, Stylo and Glycine at Mount Makulu. They have been grown in pure stands and in pasture mixtures for a number of years, and their suitability has been well established. For instance, two-year-old Chloris gayana (Giant Rhodes grass) was oversown with Macroptilium atropurpureum (cv Siratro), Stylosanthes guianensis (Stylo) and Neonotonia wightii (Glycine). The pasture received a fertilizer application of 400 kg/ha of single superphosphate and 200 kg/ha of muriate of potash. All three legumes developed satisfactorily and formed a considerable proportion of the total herbage as demonstrated in Table 1.

Table 1. Herbage yield from Rhodes grass/legume pastures.

Pastures mixtures	July		January		Legume as percent of total
	kg DM/ha	kg DM/ha grass	kg DM/ha legume	kg DM/ha total
Rhodes grass/Glycine	1,307	771	144	915	15.7
Rhodes grass/Siratro	1,840	1,442	260	1,702	15.3
Rhodes grass/Stylo	1,743	1,504	96	1,600	6.0

Glycine and Siratro recovered rapidly on a section that was burnt accidentally in May. Stylo suffered most from the burning and the plants were subsequently damaged by termites. Siratro spread evenly in a very striking manner throughout the plots producing the most satisfactory and vigorous growth.

All three species were compatible in Rhodes grass/legume pastures and were observed even to grow well with Star grass and in natural pasture swards. In the latter case, establishment and development were relatively small. The legumes were capable of producing well over 6,000 kg/DM/ha and over 1,000 kg CP/ha (16.6% CP). They produced high-quality herbage throughout the season with crude protein values ranging from approximately 10 to 20% generally two to three times higher than the value for grasses. Glycine and Siratro also produced a considerable amount of dry-season growth and yielded 500 to over 1,000 kg DM/ha between June and October when good-quality forage is generally very scarce. These legumes stood up very well to heavy intensive stocking when they were allowed adequate rest between grazing cycles.

Rhodes grass and native grass oversown to legume and stocked at 0.50 to 0.75 ha/steer supported steers for about seven to nine months. The steers gained 90 to 100 kg during the dry period. Glycine and Siratro are fire-tolerant and produce new growth soon after burning. Where they were completely burnt in June, the two species produced vigorous dry-season growth, yielding about 1,160 kg DM/ha. Stylo which is more drought-resistant is not fire-tolerant. The roots are readily killed by burning. It will, however, grow and re-establish itself during the rainy season following the fire from fallen seed.

The above-ground herbage of all three species is killed by frost, but their root-stock is frost-tolerant. Both Glycine and Siratro produced vigorous new growth soon after severe frost which occurred in July, and they continued to produce excellent growth throughout the rest of the dry season. Regrowth of Stylo on the other hand seemed slower.

On loamy soils of medium and heavy texture the most suitable species are Glycine and Siratro, while on the light-textured sandy soils Siratro and Stylo seem to be more suitable. Other cultivated and indigenous species such as Silverleaf desmodium, Macrotyloma and Rhynchosia, can also play an important role in pasture and forage improvement.

Prior to 1974, large areas in the Mkushi District had been sown to both Rhodes grass and Star grass and some farmers had experimented with Torpedo grass (Panicum repens) in their 'dambos'. As a result of the increased profitability of beef, one farmer between 1979 and 1982 was able to clear 600 hectares of land along Mkushi River. The whole area was cleanly wind rowed and ploughed. Grass seed (Rhodes grass, Signal grass and Green panic) was sown with the legumes (Silverleaf desmodium, Greenleaf desmodium, Stylo cvs. Cook, Endeavour, Graham, and Seca, Lotononis and Siratro) into a rough seedbed and lightly harrowed.

In the 'dambos' the area was disced during the dry season. Torpedo grass was planted vegetatively on a metre square spacing and Lotononis oversown into the rough seedbed. Since establishment, paddocks have been grazed at an overall average stocking rate of about 1.6 LU/ha. The pastures were heavily grazed during the December to February period and then either rested or lightly grazed for the next three to four months. In the latter part of the dry season they were again subjected to heavy grazing. Results of this exercise are presented in Table 2.

In all cases the legumes were slow to establish although the companion grasses did well. Greenleaf desmodium started well but was quickly grazed out. The Silverleaf desmodium was the most encouraging, quickly establishing itself after the first year and maintaining or even increasing its share of the sward over the following four to five year period.

Of the Stylosanthes spp. both Cook and Endeavour did well, but they suffered from termite attack during the last two years. In the rainy season of 1984/85 for the first time in Zambia the incidence of Anthracnose was confirmed. Worst affected were the cvs Endeavour and Cook in Rhodes grass. The one stand of cv Graham looked most promising having increased steadily over four years. It seemed less affected by termites and devoid of Anthracnose.

The one plot of cv Seca (Stylosanthes scabra) started very slowly but had increased steadily despite being heavily frosted in 1981 and 1982. Seca plants spread into adjacent pastures, presumably through dung of grazing animals. The Lotononis had done exceptionally well in conjunction with Torpedo grass in the 'dambo'. Because of its palatability, it tended to be very heavily grazed in the dry months, but despite this it still managed to maintain itself.

Conclusions

It has been proved during the last decade that many of the common pasture legumes will grow in Lusaka, Central and Southern provinces in Zambia. A good balanced pasture should contain both twining and bush-type legumes. The former group is represented by Silverleaf desmodium and Siratro while Seca and Graham Stylos are the most promising of the latter group. Lotononis continues to be the main hope for 'dambo' improvement. There is no point in growing grass and legume pastures unless they can be properly utilised. It is likely that they would grow and thrive well if they are adequately managed. If pastures are allowed to grow unchecked during the entire growing season, the herbage becomes mature and coarse, and it rapidly deteriorates in feeding value. Pastures which are subjected to intensive rotational grazing remain relatively green and leafy and improve in basal cover. The major constraint to the expansion of legume/grass pastures is availability of seed. The seed production programme is being carried out under the auspices of the Government of Zambia and the Swedish International Development Authority, Agriculture Sector Support Programme. This programme has demonstrated the potential that there is for local seed production of different kinds of pasture species if a good management and good permanent maintenance breeding programme is introduced.

Table 2. Pasture legume establishment at Chimyamauni Farm, Mkushi, Zambia in 1979-1982.

Legume	Area ha	Year of establishment	Companion grass	Estimate of % legume in sward
				1980	1981	1982	1983	1984	1985
Greenleaf desmodium	80	2/1979	Rhodes grass	7	15	8	5	3	2
Silverleaf	8p	2/1979	Rhodes grass	2	10	12	14	15	16
Cook Stylo	80	2/1979	Rhodes grass	3	15	25	20	18	15
Endeavour Stylo	80	2/1979	Rhodes grass	3	13	18	12	10	7
Lotononis	80	2/1979	Rhodes grass	-	1	2	3	4	5
Silverleaf desmodium	20	1/1980	Rhodes grass	-	5	11	20	25	23
Siratro	20	1/1980	Rhodes grass	-	4	12	15	15	15
Cook Stylo	20	1/1980	Rhodes grass	-	4	10	37	30	25
Seca Stylo	10	1/1980	Rhodes grass	-	18	35	48	50
Lotononis	4	1/1980	Torpedo grass	-	15	30	40	45	45
Silverleaf desmodium	10	2/1980	Signal grass	-	5	12	18	25	40
Lotononis	6	1/1981	Torpedo grass	-	-	20	35	45	40
Greenleaf desmodium	60	2/1981	Rhodes grass	-	7	18	20	10	8
Graham Stylo	20	1/1982	Signal grass	-	-	10	14	20	25

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