Soil type and grazing management practices : effect on vegetation composition and distribution in selected Communal Property Associations (CPAs) of Bela-Bela Municipality

Abstract

The objective of this study was to investigate the effect of grazing management on soil properties, vegetation composition and nutritive value of species found in selected CPAs of Bela-Bela Municipality. The CPAs were as follows: Mawela (Hutton- clay loam: HCL), Bela- Bela (Hutton-clay: HL), Moretele (Hutton-loamy sand: HLS) and Ramorula (Ecca sand-clay loam: ESCL). Three 200 m line transects served as replicates and were laid 50 m apart from each other in each of the three camps per CPA. In each of the three line transects, sub-transects were marked at 50 m intervals (50, 100,150 and 200 m) to create four 10 m x10 m homogenous vegetative units (HVU) making a total of 12 HVUs per camp. For physical and chemical properties, the soil samples (top and sub-soil) were analysed for particle size distribution, acidity, resistance, pH, organic carbon, macro and micro minerals. The abundance, height and nutritive value were determined for both types of grass and woody species. For chemical composition and in vitro dry matter degradability of both types of grass and browse leaves were bulked, respectively. All data for soil properties were subjected to a two-way factorial analysis of variance (SAS 2010) while data for species composition were subjected to a one-way analysis of variance (SAS, 2010). The highest (P < 0.05) pH (7.1) recorded on the sub-soil was in HLS. The topsoil had the highest (P <0.05) nitrate-nitrogen (N-NO3) concentration (2.4 mg/kg) and ammonium nitrogen (N-NH4) concentration (4.5 mg/kg) in the HC soil type. Soil organic carbon for both topsoil (0.66 %) and subsoil (0.41%) was significantly low (P <0.05) in the HLS soil type and ESCL soil type, respectively. The ESCL and HCL had the highest (P <0.05) chlorine (Cl) concentration (42.2 and 66mg/kg, respectively) in the top and sub-soil respectively. Phosphorus (P) and iron (Fe) concentrations were significantly high (P <0.05) in ESCL soil type for both topsoil and sub-soil. Sub-soil, manganese (Mn) concentration was found to be higher (P <0.05) in ESCL soil type (7.6 mg/kg). Copper (Cu) and zinc (Zn) concentrations were high (P < 0.05) in the HC soil type for both the topsoil and sub-soil. The

HLS soil type had the lowest (P <0.05) acidity (0.01) in topsoil while HC had the lowest (P <0.05) acidity (0.02) in sub-soil. The HCL soil type had the highest (P <0.05) soil resistance (2880 Ω) in topsoil, while ESCL had the highest (P <0.05) soil resistance (3640 Ω) in sub-soil. Across all soil types, Aristida congesta and E. rigidor were the two dominant (P <0.05) grass species. Hutton-clay (HC) soil type had the highest (P < 0.05) biomass (823.3 kg/ha) and also had higher (P <0.05) basal cover (55.8%). The HCL had taller (P <0.05) Digitaria eriantha and Aristida congesta. For the tuft diameter, Setaria sphacelata in the ESCL soil type had the largest (P <0.05) diameter (21.3 cm) when compared to the one found in the HC soil type (4.3cm). Bothriochloa insculpta diameter was significantly larger (P <0.05) in ESCL soil type (19.7 cm). The crude protein (CP) content (45.4 g/kg DM) was significantly higher (P <0.05) in ESCL soil type. Bulked grasses in all soil types had similar (P >0.05) neutral detergent fibre (NDF), acid detergent fibre (ADF), digestible energy (DE) and metabolizable energy content. Grasses in the Hutton clay (HC) soil type had the lowest (P <0.05) acid detergent lignin (ADL) content when compared to those from other soil types. The bulked grass species in the HLS soil type had the lowest (P <0.05) ether extract (EE) content (20.8 g/kg DM). The in vitro dry matter degradability (DMD) of bulked grasses at 24 (366.1 g/kg), 36 (478.4 g/kg) and 48 (629.8 g/kg) hours was highest (P <0.05) HC soil type. Hutton-loamy sand (HLS) soil type had high (P<0.05) total plant density (TPD) (4300 plants/ha), canopy cover (CC) (55.8%) and total tree equivalent (TTE) (5068.9 plant/ha) compared to other soil types. Bulked browse leaves from all soil types had similar (P >0.05) CP, ash and NDF content. In all soil types, the condensed tannins (CT) concentrations in browse leaves was similar (P >0.05). Browse leaves from the HC soil type had the lowest (P <0.05) soluble phenols concentration (289.8 g TAE/ kg DM). Browse leaves from all soil types had similar (P >0.05) DMD at 36 and 48 h. For most of the soil types, mineral concentration is more in the topsoil than in the sub-soil. This trend explains that the uptake of these minerals by plants took place due to the inconsistencies of grazing

management employed in these selected CPA farms. With HC soil type outcompeting others in terms of both basal cover and biomass, which suggests that improved grazing management would improve the productivity of other soil types. The CP content of bulked grasses was low, and which suggests that animals should be supplemented with high protein sources such as the current bulked browse leaves due to their high CP and DMD for optimum livestock productivity. In order to encourage the growth of the herbaceous layer, the principal feed source for ruminants, it is crucial to manage the matured tree population prevalent in some of these CPAs as shown by the highest number of woody species (seedlings and adult trees). The observed high CP and DMD in bulked browse leaves from all soil types shows their potential as a solid, affordable source of protein for livestock.