Biomass, dry matter yield, proximate and mineral composition of forage legumes grown as early dry season feeds

F C Nworgu and F T Ajayi*

Federal College of Animal Health and Production Technology, Moor Plantation , Ibadan, Nigeria
*Institute of Agricultural Research and Training, Obafemi Awolowo University, Moor Plantation, Ibadan, Nigeria.
ajayiajay@yahoo.com

Abstract

A field trial was carried out at Ibadan, South Western Nigeria in 2001 - 2002 to investigate the biomass, dry matter and mineral composition of Aeschynomene histrix, Centrosema pubescens, Centrosema pascuorum and Lablab purpureus. The experimental design used was completely randomized block design with four replicates for each forage.

Average biomass and dry matter yields at 12 weeks after planting were 71.42 and 46.6 t/ha/year, respectively for Lablab purpureus, while such parameters were least in Aeschynomene histrix (4.21 and 2.43 t/ha/yr). Lablab purpureus grew aggressively and vigorously and had the best green and dry matter yields with best leaf stem ratio. Lablab purpureus withstood dry season better than Centrosema pubescens > Centrosema pascuorum > Aeschynomene histrix. These forage legumes were rich in crude protein which ranged from 16.0 % in Centrosema pubescens to 19.7% in Aeschynomene histrix. The most available mineral was calcium in all the forage legumes (0.83 % in Centrosema pascuorum and 1.28 % in Aeschynomene histrix).

Keyword: Biomass, dry matter, dry season feeds, forage legumes

Introduction

One of the ways of increasing livestock production in Nigeria is to increase the area and quality of legume - based pastures. Most African countries are presently in the midst of food and feed crises. Forage legumes in particular are used as green manure, cover crops, and short term pastures in rotation with cereal crops (Omokanye 2001). They also improve nitrogen content of the soil through nitrogen fixation. Supplementation of feeds with forage legumes encouraged more roughage intake and digestion in sheep (Adu et al 1992). Centrosema (centro) is a vigorous, trailing, twining and climbing perennial herb with trifoliate leaves and is fairly drought tolerant (Skerman et al 1988). The authors revealed that green matter yield of centro varied from 13.5 to 40.0 t/ha/year. Centrosema pubescens is very rich in protein (19.6%) and minerals (Nworgu et al 2001). Muhammad et al (2002) recommended that Centrosema spp. be integrated into the crop - livestock farming system of the low land areas of Northern Nigeria, where livestock rearing forms part of the culture of the inhabitants. Omokanye (2001) observed that Centrosema pubescens seed yields (405 to 776 kg/ha) was favoured more more by June 21^st sowing and the application of 60 kg/ha of P₂O₅. Lin et al (1996) concluded that Lablab purpureus grew normally on soils with pH 5.0 to 7.8 and showed high capacity for nitrogen fixation, although it showed high mortality at ambient temperatures of >50^oC.The authors further noted that green and seed yields of Lablab purpureus were 50.7 and 1.0 to 2.25t/ha/year, respectively with crude protein of 16.6% and that Lablab purpureus is susceptible to aphids at seedling and young pod stages. Sanginga et al (1996) revealed that Centrosema pubescens and Stylosanthes hamata had the highest number of nodules in all sites, while Mucuna pruriens had the least in both pot and field experiments in agro ecological zones in moist savanna in Nigeria. The authors further noted that Mucuna pruriens and Lablab purpureus produced more shoot and nodule biomass than Crotalaria verrucosa, Centrosema pascuorum , Stylosanthes hamata, Centrosema verrucosa, Cajanus cajan andAeschynomene histrix. Lablab purpureus is a promising forage legume for our environment. It is used in feeding pigs in Kenya in form of leaf meal (Beckmann and Clements 2002). The authors further stated that lablab hay improved and increased live weight and milk yield of cattle from 4-6 to 6-7 litres per day. The authors also reported that lablab is suitable for human consumption.

Lablab is a legume that thrives well in the dry season between November and February in the Northern Nigeria. It is drought resistant and is usually sown after the normal cropping season, thereby acting as a buffer crop for ruminant feeding during the period of dry season (Adu et al 1992). Chemical analysis showed that Lablab purpureus contained about 24 % crude protein in its leaf and seed (Ogundipe et al 2003). These authors revealed that when the seeds are properly processed, it could be comparable to many oil-seed cakes presently suitable for feed formulation. Lablab seeds have low human preference for food and unlike soybean and groundnut cake, its value in livestock feeding has not been fully investigated. Like other tropical legume seeds, raw lablab seeds contain some anti-nutritional factors which may limit their use in animal feeding (Chauchifai et al 1991). Heat treatment has been employed to reduce or totally eliminate the anti-nutritional factors (Marty and Chavez 1993). Cooking of lablab seeds for 45 minutes can be done before incorporation into monogastric diets for efficient utilization (Bawa et al 2003).

Materials and methods

The experiment was carried out at the southern farm of the Institute of Agricultural Research and Training, Obafemi Awolowo University Ibadan. The mean annual rainfall in 2001 and 2002 was 1256mm and 695mm respectively with mean monthly temperature of 26.9^oC. Land preparation was done manually. 60kg/ha of phosphorus (P₂O₅) fertilizer was applied immediately after land preparation by broadcasting method. Basal nitrogen fertilizer application of 20kg/ha of urea was done. The legumes studied were Aeschynomene histrix, Centrosema pubescens, Centrosema pascuorum and Lablab purpureus and their seeds were collected from International Institute of Tropical Agriculture (IITA), Ibadan. The seeds were scarified with hot water for 8 minutes for seeds of Aeschynomene histrix, Centrosema pubescens, and Centrosema pascuorum, while the seeds of Lablab purpureus were immersed in hot water for 10 minutes. The seeds were air - dried before planting. The seeds of the forage legumes were planted on the 13^th August each year (One week after the application of P₂O₅₎. Each forage served as a treatment and each treatment was replicated four times. The experimental design employed was completely randomized block design. Size of each small plot was 6m by 3m with a spacing of 60cm x 30cm. The seeds were sown three per hole at a depth of 2.0cm in clay-loam soil. Karate 2.5 EC was applied at the third, sixth, ninth and twelveth weeks after planting at the rate of 500ml per hectare. This was done to prevent the attack of aphids on the lablab seedlings and pods (Lin et al 1996) and on other legumes. Harvesting of the legumes were done 8 and 12 weeks after planting and samples of the legumes were oven - dried at 65^oC for three days for chemical analysis. Representative samples were taken and milled. Mineral composition and the fiber contents of the forages were analysed using AOAC (1990) procedures. Sodium and calcium were analysed with Jenway PFP7 flame photometer, while phosphorus was determined with spectro-photometer (Spetronic 21). Gross energy was determined according to Pauzenga (1985). Data collected were subjected to analyses of variance procedure of SAS (1989). Duncan's Multiple Range Test (Steel and Torrie 1980) was used in assessing the significant differences among the treatments.

Results

Mean monthly rainfall in Ibadan, Nigeria between August and December was 1257 cm for 2001 and 696cm for 2002 (Figure 1)

 The germination percentage varied from 78.1 to 97.0 % and lablab had the highest percent while least was Aeschynomene histrix (Table 1).

Lablab had the highest plant height at 8 and 12 weeks after planting. The least of this parameter was Centrosema pubescens for both years.

Highest biomass yield was with Lablab purpureus with advantages (annual basis) from extending the harvest interval to 12 weeks (Table 2).  However, the leaf: stem ratio favoured the other legumes. DM yields showed the same trends as fresh matter yields (Table 3).

The crude fiber (CF), crude protein (CP), ether extract (EE), ash and gross energy (GE) results at 12WAP are presented in Table 4 and they are significantly (P<0.05) different among the forages.

All the forages were relatively rich in crude protein content with low levels of crude fibre (Table 4). The forages were rich in calcium, phosphorus and potassium but low in sodium  (Table 5).