Pennisetum purpureum particularly Taiwan Napier or elephant grass is a perennial forage crop with high growth rate, high productivity, good nutritive value and mostly used for cut and carry system over the tropical and sub-tropical area of the world (Cook et al., 2005; Wadi et al., 2004). It have been used widely as fodder grasses, these are the grasses that have been shown to be most adaptable and productive under Malaysian conditions (Wong et al. 1982). It has high forage quality, with low content of dry matter, high contents of crude protein, neutral detergent fiber, acid detergent fiber and acid detergent lignin. Fertilizer application is one of the cultivation method used to realize the potential of dry matter production. High rates of nitrogen application such as urea fertilizer also make significant effects to the Napier grass flexible responsive ability in dry matter production (Ambo et al, 1999). As seen in table 1, nutritional evaluation of the Napier grass at the different cuts frequency and under rate of 200kgN kg/ha fertilizer input. The dry matter contents in elephant grass are around 13.2% -17.7%. Crude protein (CP) concentration decrease from 15.5% to 6.8%, NDF and ADF concentration was increased with advancing maturity (Moran, 2005). Napier grass cut at a 30 cm height was superior to that of the grass cut at 0 cm height.(Wadi et al,2004) However, several other studies showed that the crude protein content of the elephant grass commonly ranges from 3.4-12.9% (Gonçalves et al, 1991, Santos, 1994). The nutritive value is maintained up to harvest intervals of six weeks, after which energy and protein value deterioted rapidly (Moran, 2005)
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Table 1: nutritional evaluation of grasses under different rates of age
Cutting frequency (week)
2.2 Taiwan Napier (Sabah) Unknown Variety
This is a one variety of Napier was shown to be productive grows in Sabah. But, the identity of this variety still not yet to be determine. It needs to compare with Taiwan variety (local) in Peninsular Malaysia which has a similar physical characteristic of it.
2.3 Nitrogen Fertilizer (Urea)
Urea or carbamide is an organic compound with the chemical formula (NH2) 2CO. the molecule has two amine (-NH2) residue joined by carbonyl (-CO-) functional group. Urea is manufactured organic compound containing 46% N that is widely used in solid and liquid fertilizers. It has relatively desirable handling and storage characteristics, making it the most important solid nitrogen-fertilizer material, worldwide. It may contain small concentration of a toxic decomposition product. However, urea manufactured using good quality control practice rarely contains enough to be of agronomic significance. Urea is converted to ammonium carbonate by an enzyme called urease when applied to the soil. Ammonium carbonate is unstable molecule that can break down into ammonia and carbon dioxide. If ammonia is not trapped by soil water, it can escape to the atmosphere. This ammonia volatilization can cause significant losses of N from urea when the fertilizer is applied to the surface of warm, moist soils, particularly those covered with plant residue or those drying rapidly. Relatively high surface pH also aggravates N volatilization from urea. More than 90% of world production of urea is destined for use as nitrogen-release fertilizer. For fertilizer use, granules are preferred over prills because of their narrower particle size distribution which is an advantage for mechanical application. Urea, when properly applied, results in crop yield increases equal to other forms of N. (www.rainbowplatfood.com/agronomics/efu/nitrogen.pdf)
2.4 Function Nitrogen Fertilizer
Fertilizer application is one of the cultivation methods used to realize the potentiality of dry matter production. Napier grass has flexible responsive ability in dry matter productivity to high rates of nitrogen application (Ambo et al, 1999). Napier grass was determined to be tolerant to nitrogen input by, fertilization is carried out by none slowly released chemicals. It has also a flexibility responsive ability to high rates of nitrogen application in yield and forage quality in grasses (Ambo et al, 1999). Plants absorb nitrogen from the soil as both NH4+ and NO3-ions, but because nitrification is so pervasive in agricultural soils, most of the nitrogen is taken up as nitrate. Nitrate moves freely toward plant roots as they absorb water. Once inside the plant NO3- is reduced to an NH2 form and is assimilated to produce more complex compounds. Because plants require very large quantities of nitrogen, an extensive root system is essential to allowing unrestricted uptake. Plants with roots restricted by compaction may show signs of nitrogen deficiency even when adequate nitrogen is present in the soil. Most plants take nitrogen from the soil continuously throughout their lives and nitrogen demand usually increases as plant size increases. A plant supplied with adequate nitrogen grows rapidly and produces large amounts of succulent, green foliage. Providing adequate nitrogen allows an annual crop, such as corn, to grow to full maturity, rather than delaying it. A nitrogen-deficient plant is generally small and develops slowly because it lacks the nitrogen necessary to manufacture adequate structural and genetic materials. It is usually pale green or yellowish, because it lacks adequate chlorophyll. Older leaves often become necrotic and die as the plant moves nitrogen from less important older tissues to more important younger ones. On the other hand, some plants may grow so rapidly when supplied with excessive nitrogen that they develop protoplasm faster than they can build sufficient supporting material in cell walls. Such plants are often rather weak and may be prone to mechanical injury. Development of weak straw and lodging of small grains is an example of such an effect (www.rainbowplantfood.com/agronomics/efu/nitrogen.pdf).
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2.5 Effect of Fertilizer Application on Yield and Quality of Natural Pasture
Both quantity and quality of natural pasturelands can be improved by application of fertilizer. Hence, sufficient response to fertilizer application is one of the desirable characteristics expected of natural pasturelands. The high nitrogen requirement of pastures, coupled with their pervasive root system results in efficient absorption of nitrogen from the soil. Thus, in grass dominated pastures about 50 to 70 percent of applied fertilizer nitrogen is normally taken up, although this decreases at very high nitrogen levels (Miles et al, 2000) due to deficiencies of some micronutrients in the soil and displacement of phosphate concentrations at higher levels of nitrogen (Falade, 1975). Grasses can obtain their nitrogen in a number of ways, but the most important sources are from fertilizers. Hence, the simplest way to achieve maximum production from grass is to apply inorganic fertilizer with high nitrogen content (Skerman et al, 1990). Moreover, fertilizers not only increase yield but also influence species composition of natural pastures.
2.6 Forage Yield
The application of fertilizers on natural pasture has been clearly shown to improve the herbage yields (Adane, 2003). When nitrogen is applied, there is usually an initial linear response. But, there is a phase of diminishing response and a point beyond which nitrogen has little or no effect on yield. The dry matter yield of fertilized plots of natural pasture has been shown to be 9.47 ton/ha as compared to unfertilized plots 5.67 ton/ ha at 90 days of harvest (Adane, 2003).Therefore, the amount of dry matter produced for each kilogram of nitrogen applied depends largely on the species under consideration, frequency of defoliation and growth condition (Miles et al, 2000).
2.7 Forage Quality
Application of nitrogen to pasture usually results in marked increase in the level of crude protein content. However, the great variability in crude protein content due to nitrogen applied exists in early stages of growth. The crude protein content of most grass species is adequate to meet minimum nutritional requirements for livestock in early stages of harvesting but reaches levels below this requirement in later stages of harvesting. Hence, addition of nitrogen and phosphorus results in considerably higher crude protein content (Goetz, 1975). The increase in the crude protein content of grasses through fertilization depends on the availability of soil nitrogen. Nitrogen fertilizer application also increases the level of soil nitrogen. This has increased the crude protein percentage of the grass but has no consistent effect on dry matter digestibility (Minson, 1973). Fertilization at early stages of growth greatly influences the accumulation of non-structural and insoluble carbohydrate levels. Insoluble carbohydrate decreased with increasing nitrogen supply and soluble carbohydrate levels increase with increase in phosphorus supply (Miles et al, 2000). Nitrogen fertilizer also improves the concentrations of neutral detergent fiber (NDF) and acid detergent fiber (ADF) in early cut pennisetum purpureum. However, according to studies of the same author, nitrogen fertilizer could not reverse the adverse effects of maturity on the quality. Similarly, the lignin content (Abade, 2008).
2.8 Yield Analysis
2.8.1 Dry Matter Yields
Moisture content is usually reported on a wet and a dry-matter (DM) basis. Wet basis indicates how much fresh forage would be required to meet DM requirement of the animals. Dry-matter basis is calculated as if the forage had no moisture (Yoana et al, 2000). Napier grass has flexible responsive ability in dry matter productivity to high rates of nitrogen application (Ambo et al, 1999). Table 2 was show are the average dry matter yield (tons / ha / year) of Napier grass compare to other pasture (http://www.dvssel.gov.my/cms/index.php?pt=295).
Table 2: dry matter yields of Napier grass compare to other grasses
DM (t / ha / year)
Napier grass - Local
Napier grass - Uganda
2.9 Nutritive Quality Analysis
Nutritive value refers to aspect a forage quality, which are refers to how well ruminants consume a forage and how efficiently the nutrients in the forage are converted into ruminant products. The right forage tests, accurately conducted, can provide a good estimate of forage quality (Lin et al, 1999). The nutritive quality of forages varies as they grow towards maturity. Consideration of the stage at which both biomass yield and nutrient content are optimal is therefore important. After attainment of maturity, the forages generally depreciate in nutritive value. This is mostly due to increase fibrous material, particularly lignin. For many types of forage, the leaves die off systemically after attainment of maturity, and this reduces photosynthetic activities. As a result, there will be reduced accumulation of nutrients and quality of forages.
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2.9.1 Crude Protein
A protein was a prime source of energy for the most important nutrients for livestock. These nutrients support rumen microbes that consequently degrade forage rue proteins make up 60-80 percent of the total plant nitrogen (N), with soluble protein and a small portion of fiber-bound N making up the remainder (Yoana et al, 2000). The total protein in the sample was including true protein and non-protein nitrogen. Proteins are organic compounds composed of amino acids. They are a major component of vital organs, tissue, muscle, hair, skin, milk and enzymes. Protein is required on a daily basis for maintenance, lactation, growth and reproduction. Proteins can be further fractionated for ruminants according to their rate of breakdown in the rumen. The crude total protein content of a feed sample can be accurately determined by laboratory analysis. The measured amount of nitrogen in the feed is converted to protein by multiplying by 6.25. The basis for this is that protein contains 16 percent nitrogen, or 1 part nitrogen to 6.25 parts protein (J. W. Schroeder 1994). By the high level of chemical fertilizer application crude protein was increased and the dry matter digestibility was lowered (Ambo et al, 1997).
2.9.2 Neutral Detergent Fiber (NDF)
The NDF values represent the total fiber fraction (cellulose, hemicelluloses and lignin) that make up cell walls (structural carbohydrates or sugars) within the forage tissue. Values of NDF for grasses will be higher (60-65 %) (Yoana et al, 2000). A high NDF content indicates high overall fiber in forage, but the lower the measurement of NDF value, was the better quality of forages. Neutral detergent fiber, like CF, uses chemical extraction (with a neutral detergent solution under reflux) followed by gravimetric determination of the fiber residue. Neutral detergent fiber is considered to be the entire fiber fraction of the feed, but it is known to underestimate cell wall concentration because most of the pectin substances in the wall are solubilized (Van Soest 1994).
2.9.3 Acid Detergent Fiber (ADF)
Acid detergent fiber analysis will accurately measure the amount of poorly digestible cell wall components, primarily lignin. Formulas are under development that can be used to estimate net energy content of a feed from an analysis for ADF (Van Soest, 1982). The ADF values are then used in equations to determine total digestibility of nutrient. The ADF values represent cellulose, lignin and silica. The ADF fraction of forages is moderately indigestible. High ADF values are associated with decreased digestibility (J.W. Schroeder 2004). Therefore, a low value of ADF is better for forage quality.
2.9.4 Acid Detergent Lignin (ADL)
ADF residue is subjected to digestion with 72% sulphuric acid to dissolve the cellulose. The remaining residue is ashed to consist of lignocelluloses and acid insoluble ash (mostly silica). Strong acid will dissolve the cellulose component and ashing of this residue will determine the lignin component of the grasses (Hans et al, 1997). Ashing is done by heating a sample in a furnace at high temperature (550-600Ëšc) until all organic material has been burned away. Ash contains essential minerals, non essential minerals and toxic element such as heavy metals. Lignin has a negative impact on cellulose digestibility. As lignin content increases, digestibility of cellulose decreases thereby lowering the amount of energy potentially available to the ruminant.