Proximate compositions of some forage grasses and legumes as influenced by season of harvest

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1 Vol. 8(29), pp , 1 August, 2013 DOI: /AJAR ISSN X 2013 Academic Journals African Journal of Agricultural Research Full Length Research Paper Proximate compositions of some forage grasses and legumes as influenced by season of harvest Onyeonagu, C. C.* and Eze, S. M. Department of Crop Science, University of Nigeria, Nsukka, Enugu State, Nigeria. Accepted 15 May, 2013 This study was conducted in Nsukka, Nigeria to evaluate the effect of season of harvest (rainy and dry seasons) on the proximate compositions of 5 legumes (Calapogonium mucunoides, Stylosanthes hamata cv. Verano, Centrosema pubescens, Pueraria phaseoloides and Stylosanthes guyanensis cv. Cook) and 5 grasses (Sorghum almum, Panicum maximum, Cynodon nlemfuensis, Pennisetum purpureum and Andropogon gayanus). The experiment was a 2 5 factorial laid out in completely randomized design (CRD). Among the grasses and the legumes, the concentrations of ash and crude protein (%CP) were significantly higher (P < 0.05) in rainy season than in dry season. The %fat in grass species was significantly (P < 0.05) higher in rainy season than in dry season. C. pubescens significantly produced the highest %CP compared with other legumes, while P. phaseoloides significantly (P < 0.05) had the least %CP value which was similar with that from S. hamata. C. mucunoides harvested in rainy season produced %CP that was significantly (P < 0.05) higher than the values obtained with C. pubescens, S. hamata, or P. phaseoloides in any season. P. maximum harvested in rainy season significantly (P < 0.05) had the highest %CP compared with other grasses in any season. P. purpureum harvested in rainy season significantly (P < 0.05) yielded the highest %ash compared with other grass species in any season, while A. gayanus harvested in rainy season significantly gave higher %fat and %crude fibre than other grasses. Key words: Crude protein, %ash, %fat, crude fibre content, grasses, legumes, seasonal variation. INTRODUCTION Seasonal variations affect the availability of nutrients from the soil to forage species (Ezenwa et al., 1995). The nutritional values of forage species are low in the dry seasons compared to the wet season (Buxton, 1996). This is as a result of the dependence of grass and legume nutrient contents on the amount of moisture found in the soil in which the forage plants grow (McDowell et al., 1983). In addition, concentrations of nutrients according to McDowell et al. (1983) in forage plants are dependent upon the interaction of a number of factors. These factors are plant species, soil type, plant age, pasture management and climate. Differences in forage quality between grasses and legumes can be very large. The protein content of legumes is typically much higher than that of grasses and legume fibre tends to digest faster than that of grasses allowing ruminants to eat more of the legumes (Buckmaster, 1990). Ruminant animals rely more essentially on pasture for their nutrient requirement than on any other feed resources. Grass-legume mixtures provide a balanced diet. Balanced diet is essential for normal physiological functions of ruminant animals (McDonald et al., 1995). It has also been shown that when balanced diet are fed to animals, their performance or productivity is enhanced and they are better equipped to fight diseases as a result of improved immune system (McDonald et al., 1995). In Nigeria, forage species still serve as source of essential elements for grazing animals. However, little *Corresponding author. chike.onyeonagu@unn.edu.ng.

2 4034 Afr. J. Agric. Res. Table 1. Meteorological data for Nsukka in Month September October November December Total annual rain fall (mm) Rain days Maximum air temperature ( C) Minimum air temperature ( C) Relative humidity (%) information is available on the nutrient status of grazing animals and of the forages upon which they subsist. The nutrient status of these forages is a function of multiple factors which interact with one another to produce varied effects (Eze, 2010). It is vital to investigate how seasonal variations influence the nutrient components of different forage grasses and legumes in the tropical environment, especially those in the derived savannah zone of Nigeria. This study was thus planned to investigate the effect of season of harvest on the proximate composition of some grasses and legumes found in Nsukka-derived savannah zone of Nigeria. MATERIALS AND METHODS Location of the study The experiment was conducted on a pasture ground established in 2006 at the Teaching and Research Farm of the Department of Crop Science, Faculty of Agriculture, University of Nigeria, Nsukka. Nsukka is located at latitude N and longitude E and on altitude of m above sea level. It is characterized by the low land humid tropical conditions. The soil is classified as an ultisol (Asiegbu, 1989). Sample collection Ten forages comprising 5 grasses namely: Guinea grass (Panicum maximum), Elephant grass (Pennisetum purpureum), giant star grass (Cynodon nlemfuensis), Northern Gamba grass (Andropogon gayanus) and Columbus grass (Sorghum almum) and 5 legumes namely: Calapo (Calapogonium mucunoides), Centro (Centrosema pubescens), Cook stylo (Stylosanthes guyanensis), Verano stylo (Stylosanthes hamata) and tropical kudzu (Pueraria phaseoloides) were collected on the 25 th of every month from the pasture land and its surroundings. Sampling lasted for 4 months from September to December, Samples collected in September and October were bulked together according to species and considered for rainy season collection, while November and December collections represented dry season collection. Samples were dried to constant weights in a forced air oven at 80 C and grinded using Thomas Wiley laboratory Mill (Mode 4) and stored in air-tight nylon papers. The crude fibre (CF), crude protein (CP) and ash contents were determined using the methods described by Pearson (1976). Fat contents of the samples were obtained using the method described by Association of Official Analytical Chemist (1990). Meteorological data Meteorological data of rainfall, rain days, ambient temperature and relative humidity were collected from Department of Crop Science, University of Nigeria, Nsukka Meteorological Station. Statistical analysis A 5 2 factorial arrangement laid out in completely randomized design (CRD) with two replications was used. The grasses were analyzed separately from the legumes. All data collected were statistically analyzed using the procedure outlined by Steel and Torrie (1980) for factorial experiment in a CRD using GENSTAT (2009) statistical package. Separation of treatment means for statistical significance was done using the least significant difference (LSD) according to Obi (1986). Square root transformation of the form x + 0.5, where x is the observation, was employed whenever there is zero value. RESULTS Rain fell more frequently in September which also had the highest total rainfall compared with the other months (Table 1). The total rainfall was also high in October but decreased in November and December. The maximum air temperature was high in the months of September, November and December. The relative humidity was relatively high in September, followed by October, November and then December. The legumes harvested during the raining season significantly (P < 0.05) had higher ash and CP contents than those harvested during the dry season (Table 2). The rainy season harvests non-significantly (P > 0.05) produced higher concentration of fat in the legumes than the dry season harvests. The CF content of the legume species was significantly (P < 0.05) higher in the dry season than rainy season. Among the legumes, C. pubescens had significantly higher ash content than P. phaseoloides and C. mucunoides but had similar ash values with the other legumes. The CP content also varied significantly among the legumes. The highest %CP was obtained in C. pubescens followed by S. guyanensis which also was significantly higher than other three legumes. S. hamata had similar CP value with P. phaseoloides, while P. phaseoloides produced significantly the least CP content among the legumes. The concentration of fat appeared to be low in Centrosema pascuorum and S. guyanensis compared with other legume species although no significant difference was observed. C. mucunoides produced

3 Onyeonagu and Eze 4035 Table 2. Effect of season of harvest on the proximate components of some forage legumes. Season Legume Rain Dry Mean Rain Dry Mean Rain Dry Mean Rain Dry Mean Species %Ash %CP %Fat %CF C. mucunoides C. pubescens S. guyanensis S. hamata P. phaseoloides Mean comparing 2 season means (S) comparing 2 species means (P) comparing 2 S P means (-) = Non-significant F-test at 5% probability level. significantly the highest %CF compared with the other legumes, followed by P. phaseoloides, C. pascuorum, S. hamata and then S. guyanensis. There was significant (P < 0.05) season species interaction effect on the %ash, %CP and %CF of the legumes. S. guyanensis gave the highest %ash among the legumes during the rainy season harvest, while C. mucunoides harvested during the rainy season produced higher %CP than the other legumes at both season except for Stylosanthes guianensis harvested during the rainy season. P. phaseoloides harvested during the rainy season gave higher %CF compared with other legumes. Season, species and their interaction effects were not statistically significant on fat content. The %ash, %CP, %fat, and %CF of the grass species varied significantly (P < 0.05) in the two seasons (Table 3). Rainy season harvests had significantly higher %ash, %CP and %CF values than dry season harvests. The fat content of grasses was significantly (P < 0.05) higher in the dry season than rainy season. Among the grass species, P. purpureum significantly had the highest ash content compared with other grass species, while A. gayanus produced significantly the least %ash among the grass species. P. maximum significantly produced the highest %CP compared with other grasses, while S. almum had the least %CF among the grasses. A. gayanus produced fat content that was significantly higher than those from other grasses, followed by C. nlemfuensis, P. purpureum, S. almum and P. maximum. A. gayanus and P. purpureum produced similar CF contents which were significantly higher than others. Season species interaction effect was significant (P < 0.05) on the %ash, %CP, %CF and %fat of grasses. P. purpureum had the highest %ash when harvested during the rainy season. P. maximum harvested during rainy season gave the highest %CP compared with other grasses, while A. gayanus harvested during rainy season produced the highest %fat and %CF contents compared with others, but had similar %CF with P. purpureum harvest during dry season.. DISCUSSION Seasonal variations have been shown to influence the nutritional quality as well as chemical compositions of forage species, where appropriate remedial measures were not imposed (George et al., 2005). Hence, this work critically investigated the changes in the proximate composition of various forage legumes and grasses during different seasons of harvest (Rainy and dry seasons). The high proximate (CP, fat, and ash) composition of the forage species observed during the rainy season in the present work, may be due to high concentration of such minerals which are precursors to the proximate formation in the rainy season than in dry season. Minerals activate enzymes and are essential co-factors of metabolic reactions. They also function as carrier of protein (George et al., 2005). For instance, nitrogen is required for protein synthesis, formation of chlorophyll and nucleic acids whereas calcium, potassium and magnesium are components of ash. Underwood (1981) showed that as the dry season sets in, the protein level of

4 4036 Afr. J. Agric. Res. Table 3. Effect of season of harvest on the proximate components of some forage grasses. Season Grass Rain Dry Mean Rain Dry Mean Rain Dry Mean Rain Dry Mean Species %Ash %CP %Fat %CF A. gayanus (1.02) 0.50 (1.00) 0.53 (0.01) C. nlemfuensis (1.00) 0.37 (0.93) 0.44 (0.97) P. maximum (0.81) 0.21 (0.84) 0.18 (0.82) P. purpureum (0.92) 0.15 (0.81) 0.25 (0.86) S. almum (0.71) 0.40 (0.95) 0.20 (0.83) Mean (0.89) 0.33 (0.91) 0.32 (0.90) comparing 2 season means (S) comparing 2 species means (P) comparing 2 S P means Comparison is based on transformed means in parenthesis because of zero data. pasture species drops and the roughage quantity increases. There is also increase in the lignin content with reduction in voluntary intake resulting in weight loss and decreased fertility and milk yield in ruminant animals for up to 4 to 5 months of the year. The to 22.27% and 7.5 to 17.9% ranges for CP in the forage legumes and grasses, respectively, were higher than both the National Research Council (NRC) s 5% recommendation for CP which is the daily protein needs for preservation for ewes that weigh approximately 50 kg (NRC, 1985) and the minimum CP level of 7% required for optimum rumen function (Van Soest, 1994). The higher protein content of legumes observed in the present investigation relative to the grasses was reported by Buckmaster (1990). Buckmaster (1990) indicated that differences in forage quality between grasses and legumes can be very large. He showed that the protein content of legumes is typically much higher than that of grasses and that legume fibre tends to digest faster than that of grasses, allowing ruminants to eat more of the legumes. The high CP in the legumes relative to the grasses indicated the importance of having grass-legume mixtures in the pasture and in the animal diet as observed by Tudsri et al. (2002). The significant differences observed among the grasses in their CP and fibre contents were reported by Durr et al. (2005). The nutrient compositions of forage grass species have been shown to depend among other factors, on their structural compositions which vary among species (Hockensmith et al., 1997). Conclusion This work studied the effect of season of harvest on the proximate components of forage grasses and legumes.

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