Effect of stage of growth and frequency of cutting on the yield and chemical composition of some Nigerian fodder grasses—Panicum maximum Jacq

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1. The effects of the stage of growth and frequency of cutting on the yield and chemical composition of Panicum maximum Jacq., under the tropical humid conditions prevailing in Ibadan area were studied in the season 1953 to 1954. The cutting frequencies adopted were seventeen, eight, six and four times harvesting a year which corresponded respectively to a growing period of 3, 6, 8 and 12 weeks before the plants were cut.2. It was shown that Guinea grass gave the highest growth rate and cumulative green fodder yield (approximately 28 tons per acre) per year when allowed a 12-weekly growth cycle. Cutting the grass every 3 weeks gave a total minimum yield of 20 tons per acre. 6-weekly samplings resulted in higher green fodder yield than cutting it every 8 weeks. Such yield differences which exist among the various cutting treatments, however, are not statistically significant. When yields of edible (leafy) green fodder were considered, the order of superiority was 3-weekly > 6-weekly > 12-weekly > 8-weekly.It was shown that the increased yield of green and dry fodder obtained from the 12-weekly cut grass was made up of both fresh regrowth as well as of grasses which had been growing for 12 weeks.3. P. maximum contains a fairly high percentage of dry matter and this increased directly with the length of cutting intervals. Dry-matter yields, like those of green fodder, were highest for the 12-weekly harvested material, followed in order by the 6-weekly cut, the 8-weekly cut and the 3-weekly cut samples. However, the production of leaves and the accumulation of dry matter in them, are inversely related to the length of growing interval up to and including grasses allowed 8-weekly growing periods.4. The stems of P. maximum tend to mature more rapidly than the leaves, particularly at a growing stage of between 3 and 6 weeks of age. At between the 8 and 12 week growth stages, the development of the stem of P. maximum in relation to that of its leaves was not as rapid as observed in the case of either P. purpureum or of Andropogon tectorum.5. The percentage dry matter, nitrogen-free extract, ether extract and calcium are directly related, while those of crude protein, silica-free ash, phosphorus and magnesium, are inversely related to the length of cutting intervals. It was also shown that the mean percentage crude protein of Guinea grass of about 12 at 3 weeks of growth, declined by 45% to 6·4 when the grass was cut every 12 weeks. The grass contains a high amount of magnesium, a reasonably high amount of calcium, but a somewhat low content of phosphorus, a fact which accounts for the wide calcium to phosphorus ratio. This ratio widened with the length of cutting intervals.6. When Panicum maximum was cut at 3 -weekly intervals, it produced 69·3% more protein, 58·5% more silica-free ash, 32·3% more calcium, 49·6% more phosphoric acid, 71% more magnesium and higher amounts of carbohydrate and total nutrient material than when it was allowed to grow for 8 weeks. Similarly when the grass was allowed a 12-weekly growth cycle, it produced 35% more of total nutrient, 36·5% more of carbohydrate material and 62·2% more of calcium than when it was sampled every 8 weeks. It appears totally unprofitable from the point of view of yield of chemical constituents to subject P. maximum to a growth cycle of 8 weeks.7. Yields of green and dry matter and the percentage crude protein, silica-free ash, and nitrogen-free extract are directly related to the degree of precipitation. In general periods of high rainfall were accompanied by higher yields and percentage content of these constituents, while periods of low rainfall gave rise to smaller yields. The percentage content of crude fibre, on the other hand, was inversely related to rainfall.