Crude protein and mineral status of forages grown on Pellic Vertisol of Ginchi, Central Highlands of Ethiopia
S/gebreal, Lemma Gizachew
MetadataShow full item record
The study was conducted at Ginchi, which is situated in the western Shoa zone of the central Ethiopian highlands. The main aim of the study was to assess the crude protein (CP) and mineral status of feeds produced in the Vertisol area of Ginchi by relating them to pasture management, seasonal and/or soil factors. Aspects of the farming systems that relate to feed resource management, utilization, constraints and opportunities were also investigated. The N and mineral element status of the soil and the feeds were evaluated during the dry and wet seasons of 2001 by analysing samples collected from adjacent 18 year round grazed grassland (YRG) plots, 12 seasonally stock excluded grassland (SSE) plots, 10 tef (Eragrostis tef) and 9 grass pea (Lathyrus sativus) plots, and noug (Guizotia abyssinica) seedcake samples obtained from oil extracting plants. The results of the farming systems study demonstrated a strong inter-dependence between crop and livestock subsystems. Livestock rely on crops for their diets as much as the latter do on livestock for traction power and manure. Stored feed supplies are preferentially fed to working oxen, milking cows and animals intended for sale. The period extending from the late dry season (March-May) up until the mid wet season (July) appeared to be the time when feed shortages were most critical. Smallholders try to cope with the problem through efficient use of SSE, grassland, crop residues and crop weeds. Occasionally they also provide domestic herbivores with locally produced supplemental feeds, common salt, mineral rich soil or mineral water. Soil samples were analysed for particle size class, pH, organic matter (OM), cation exchange capacity (CEC), N, P, Ca, Mg, K, Na, Fe, Mn, Cu and Zn. Most of these soil parameters differ markedly (P<0.05) between the different land use systems. Parameters such as OM and total N in particular were very high in grassland soil in comparison to soil under cropping systems (P<0.01). The results also revealed a substantial across site variation of these soil parameters. For native pastures, the type of pasture management had a considerable influence on floristic composition, herbage CP and mineral concentration. Compared to the YRG grassland the SSE grassland contained a higher proportion of herbaceous species with superior CP and mineral concentrations. The CP and mineral contents of YRG grassland exhibited marked changes with the advance of the season (P<O.05). For the majority of the elements, the across site variation of herbage mineral concentrations were substantial. Appreciable mineral concentration differences (P<0.05)were noted between residues of tef and grass pea. These residues were also characterized by substantial CP and mineral concentration variations across sites. Noug seedcake and grass pea grain were rich in CP. The level of Pin noug seedcake was also exceptionally high. The observed high variations in soil and feed N and mineral element contents, and the lack of strong and consistent correlations between soil and feed suggest that soil analyses are not reliable in determining the N and most mineral elements status of feeds produced in the Vertisol area of Ginchi. The only soil mineral elements with any degree of reliable predictive ability were exchangeable Na and available P. The findings of this study clearly demonstrated that the CP and mineral element concentrations differed among the different feed classes produced in the Vertisol area of Ginchi. For most of the examined feeds, concentrations of P, Na, Cu and Zn were below the recommended dietary requirements of cattle.