Effect of maturity on the mineral content of Columbus grass (<i>Sorghum almum</i>)

Abstract

This study was conducted in Naivasha, Kenya over a period of 15 weeks to determine the effect of maturity on mineral content in Columbus grass ( Sorghum almum ). Immediately after field preparation, representative soil samples were taken for mineral profiling. Thereafter, 60 plots 2 x 2 sq. m size were demarcated and allotted to 5 similar blocks of 12 plots each in a randomized complete block (RCB) design. Each plot received 25 g of seed evenly drilled to 5 rows (2 m length and 30 cm apart). All the plots were planted on the same day and kept weed free throughout the study. The grass was harvested at 6, 8, 10, 12 and 14 weeks after seed emergence in sequential manner beginning with block 1 to 5, each time leaving a stubble height of 5 cm. From each plot, representative herbage grabs were made, chopped into 2 cm pieces and mixed thoroughly. Two composite samples of about 500 g each were then taken for dry matter determination and mineral analysis using the standard procedures. Results showed that, the plant tissue levels of all mineral elements investigated were significantly affected by advancing grass maturity. Between 6 and 14 weeks, P and K decreased by 35.14 and 46.77% respectively. It was also noted that Na, Ca and Mg decreased by 46.49, 20.41 and 21.74% over the same period. Levels of trace elements also declined as the grass matured. Results showed that Cu, Mn and Zn levels decreased by 36.4, 27.4 and 57.1% respectively, between 6 and 14 weeks. Ca:P ratios however remained consistent over this period. It was generally observed that, although levels of macro-elements declined with advancing maturity of the grass, their overall concentrations remained within the recommended requirements for ruminant production. Trace element levels were generally below those desired for ruminant production. It was therefore concluded that macro-mineral elements might not be a problem in Sorghum almum based diets. Ruminants would however require additional source of trace elements to correct possible deficiencies of the same in their diets. Keywords : Macro–elements; Micro-elements; Ruminants; Diets; Supplementation Animal Production Research Advances Vol. 2 (3) 2006: pp. 134-138