EFFECT OF VARIETY, HARVEST DATE AND FRACTION ON THE HERBAGE YIELD, CHEMICAL COMPOSITION AND IN VITRO GAS PRODUCTION (AN KOMRFGAS PRODUCTION SYSTEM) OF NAPIER GRASS (PENNISETUM P(IEPUREUM) IN THE HUMID ZONE OF GHANA

Abstract

Two Experiments were conducted to assess the effect of variety, harvest date and fraction on the herbage yield, chemical composition and In vitro gas production of Napier grass . The varieties were Local , 16798, 16786 and 16840. Except for the Local variety, all other varieties were improved varieties from the International Livestock research Institute (lLRI) . The harvest dates were 60, 90 and 120 and the fractions were leaf and stem. In Experiment 1, a 4X3 factorial in a randomized design was used for the herbage yield evaluation. The main factors were varieties (4) and fraction (3). A simple randomized design was used for the evaluation of the chemical composition with plant material from Experiment I. The chemical composition parameters measured were crude protein (CP), neutral detergent fiber (NDF) , acid detergent fibre (ADF), acid detergent lignin (ADL), organic matter (OM), ash, cellulose , hemicellulose and dry matter . In Experiment II, a 4X3X2 factorial in a randomized design was used to evaluate the in vitro gas production . The main factors were varieties (4), harvest date (3) and fraction (2). The Napier grass varieties harvested in Experiment I was used in Experiment II. The Ankorn/" gas production system was used for In vitro gas studies. Measurement from the herbage yield for the four varieties indicated that, dry matter herbage yield was significantly (P.<05) 0 higher for variety 16798 (44,994 kg/ha) with variety 16840 giving the lowest dry matter herbage yield (24,863 kg/ha). Measurement from the herbage yield for the three harvesting dates indicated that harvesting at 120 days gave a significantly (P<0.05) higher dry matter herbage yield (46,013 kg/ha) with the 60 days giving the lowest (22,489 kg/ha). Measurement from the chemical composition for the four varieties indicated that the Local variety gave the highest CP (96.77g 1kg) with variety 16786 giving the lowest (8S.3Sg/kg). The cellulose content was high for the Local variety (420.8g/kg) with variety 16840 producing the lowest (360.3). The AOL content was higher for variety 16840 (138.2g/kg OM) and lower for variety 16798 (89.0g/kg OM) Measurements from the chemical composition for the three harvesting dates indicated that the 60 days harvest gave the highest CP (l09.88g/kg), lowest NOF (686g/kg) lowest AOF (488.63gkg OM) and lowest AOL (84.13g 1kg OM), and the lowest OM (478.Sglkg). The cellulose fraction was highest for the 60 days harvest (427.6g/kg OM) with 120 days harvest recording the lowest (3S4.6g/kg OM). • Measurements from the chemical composition for the two fractions indicates that leaf fraction had a higher CP (l22.24g/kg OM), 10werNOF (708.61g1kg), lower AOF (468.S3g 1kg OM) and a lower AOL (10S.83g/kg OM). The stem fraction however recorded a higher cellulose fraction (406.9g/kg OM) compared to the leaf fraction. The results from the in vitro gas production evaluation showed multi-phasic curves . In view of this, the results were separated into three phases based on the mean rate of gas production for the statistical analysis. In phase I and II, there was no significant difference (P>O.OS) among the 4 varieties for the mean gas and mean rate of gas production. However, there was significant difference (P<O.OS) among the 4 varieties for mean gas and mean rate of gas production in phase III. The Local variety yielded the lowest mean gas and the slowest mean rate of gas production whilst variety 16798 yielded the highest mean gas and the fastest mean rate of gas production.There was no significant difference (P>0.05) among the 3 harvest dates in phases I and II for the mean gas production . There was however a significant difference (P<0.05) among the 3 harvest date for mean gas production in phase III. The 60 days harvest yielded the highest mean gas with the 120 days harvest yielding the lowest. The mean rate of gas production for the 3 harvest dates was significantly different (P.<05) 0 for phases I, II and III. In phase I, the 120 days harvest produced gas at most fastest rate with the 60 days harvest producing gas at the slowest ra. te However in phases II and III, the 60 days harvest yielded a higher mean rate of gas with 120 days harvest yielding the low. est There was a significant difference (P<0.05) between the 2 fractions for mean gas production in phases I and II. The stem fraction yielded a higher mean gas compared to the lea f fra. ction The mean rate of gas production was significantly different (P<0.05) for fractions in phases I, II and III. In phases I and II, the stem fraction produced gas at a faster rate compared to the leaf t fract. ion Howev, er in phase III, the leaf fraction produced gas at a faster rate compared to the leaf fraction. There was an interaction between the variety and harvest date in phases II and III, variety by fraction in phase III and fraction by harvest date in phases I and II. Variety 16786 harvested at 90 days produced a significantly higher gas than the 60 and 120 days harvest in phase II, however in phase III there was no significant difference among the 3 harvest dates. The stem fraction of variety 16798 produced more gas in phase II but in phase III, the leaf fraction produced a significantly higher gas. The lea f fraction of the 3 harvest date did not show any significant dif ference in phase II, however in phase III, the leaf fraction of the 90 days harvest produced a significantly higher gas than the other 3 harvest dates . In conclusion , variety 16798 produced the highest herbage yield and gas at 48 hours of incubation. The 120 days harvest produced the most herbage yield but produced the lowest gas at 48 hours of incubation . The leaf fraction produced the highest gas compared to the stem fraction at 48 hours but was not significantly different. Based on the results of this study, variety 16798 is recommended for cultivation and use for livestock feeding. It is also recommended that Napier grass be harvested at 90 days even though the herbage yield was not as high as the 120 days and the gas production lower than the 60 days . harvest. This is because harvesting at 60 days will give a very low herbage yield with high moisture content and harvesting at 120 days will give only one time harvest within the 8 month major rainy season in the humid zone where as with the 90 days, harvesting can be done twice . The whole plant is recommended for feeding livestock without separating into leaves and stem fractions since there was no significant difference between them after 48 hours of incubation.