Evaluation of two napier grass cultivars (pennisetun purpureuh) under irrigation at different stages of growth
Two commonly used napier grass (Pennisetum purpureum) cultivars, Bana grass and French Cameroon were grown under irrigation to assess the changes in nutritive value at different stages of growth in Naivasha, Kenya. The experimental design was a split-plot with cutting stage (subplot) nested within variety (main plot). There were three replications per treatment. The response variables were evaluated at 4, 6, 8, 10, 12 and 14 weeks of age. Dry matter yields and grass height at cutting ranged from 1.24 to 10.01 tons/ha and 22.11 to 189.99 cm respectively and significantly (P<0.05) increased with age. The differences between the cultivars for the two parameters were not significant (P)0.05). The leaf:stem ratio declined (P<0.05) with age but the differences between the cultivars were insignificant (P)0.05). The variations for leaf:stem ratio ranged from 5.03 at 4 weeks to 0.53 at 14 weeks of age. Considerable changes (P(0.05) were observed in CP, ash and carbohydrate contents as the napiergrass matured. Crude protein decreased (P<0.05) from 14.84 to 3.98% while CF and NFE ranged from 23.39 to 39.01% and 33.74 to 39.86% respectively. Ash and EE contents decreased (P<0.05) from 26.41 to 15.75% and 3.42 to 1.49 at 4 and 14 weeks respectively. Ash. crude fibre and NFE increased (P<O.OS) as the grass matured but the variation between the cultivars was insignificant (P)O.OS). The dry matter percent varied from 15.81 to 17.70% and significantly (P<O.OS) increased with age. Although French Cameroon had consistently lower DM values. varietal differences were insignificant (P)O.OS). Calcium and phosphorus levels decreased from 0.39 to 0.30% and 0.31 to 0.21% at 4 and 14 weeks of age respectively. The effect of both age and variety for these two components were however statistically insignificant (P>O.OS). Potassium levels were high and ranged from 11.70 to 4.21%. Although these levels decreased significantly (P<O.OS) with age, varietal differences were insignificant (P>O.OS). The detergent fibres NDF and ADF increased (P<O.OS) with age and rose from 54.44 to 72.68% and 25.97 to 42.00% respectively. Lignin (ADL) increased (P<O.OS) with age and ranged from 2.26 to 5.77 from 4 to 14 weeks. Varietal differences in these constituents were not evident Silica levels increased (P<O.OS) with age from 4 to 14 weeks ranging from 4.07 to 6.67% respectively with Sana grass variety showing correspondingly higher (P<O.OS) values. Dry matter and organic matter digestibility in vitro decreased (P<O.OS) with age from 72.04 to 58.30% and 75.72 to 62.22% respectively but the varietal differences were insignificant (P)0.05). The nylon bag dry matter loss in sacco increased (P<0.05) with increase in incubation time and was higher (P<0.05) the younger the napier grass. The ranges were from 71.09 to 27.57% at 72 and 12 hours .of incubation res~edtivelY. Significant (P<0.05) differences were observed in grass height, ash and percent dry matter with changes at cutting age. Silica content increased (P<0.05) with increased maturity and differences between the varieties were significant (P<0.05). However, it was concluded under the conditions of the experiment that dry matter yields, in vitro and in sacco DM digestibility, CP, CF, EE, NFE, detergent fibres, lignin and the minerals studied varied with the stage of cutting although varietal differences were insignificant (P)0.05).