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Influence of nitrogen sources and cutting interval on the digestility of four (4) grass species in the southern guinea savanna of Nigeria

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AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , ScienceHuβ, Influence of nitrogen sources and cutting interval on the digestility
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AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , ScienceHuβ, Influence of nitrogen sources and cutting interval on the digestility of four (4) grass species in the southern guinea savanna of Nigeria 1 Okwori, A.I. and 2 Magani I.E* 1 Department of Animal Production, University of Agriculture, P.M.B. 2373, Makurdi Nigeria. 2 Department of Crop and Environmental Protection, University of Agriculture, P.M.B. 2373, Makurdi, Nigeria. Corresponding Author ABSTRACT The study on the influence of nitrogen sources and cutting intervals on the digestibility of four (4) grass species was carried out during the 2002/2003 cropping season at the Teaching and Research Farms of the University of Agriculture, Makurdi. The objectives of the study were focused on feed supply as major constraints to ruminant livestock production by evaluating Andropogon gayanus, and three (3) other grass species to identify promising genotypes suitable for exploitation and acceptability to livestock. There were twenty four (24) treatment combinations replicated three times, in a split-split design. The grass genotypes (Andropogon gayanus, Panicum maximum, Cynodon nlemfuensis and Pennisetum purpureum). Nitrogen sources (Mineral fertilizer, legume and zero-nitrogen) and cutting intervals (6 and 9 weeks) constituted the main plot, sub-plot and sub-sub plots, respectively. Among the grass genotypes tested, the highest amount of organic matter (OM) was produced by A. gayanus (899.90g/kg), which was significantly different from other grass genotypes. The highest values of Invitro-organic matter digestibility (IVOMD), Invitro-D and D-values were obtained with P. maximum (64.53, and 59.60% respectively), while the lowest were obtained with C. nlemfuensis (52.7, and 47.75% respectively). The effect of nitrogen source revealed that the legume inter-crop sources produced the highest and significantly values of OM, IVOMD, INVITRO-D and D-Value (881.00g/kg, 60.81, and 55.79% respectively), while lowest values were obtained their zero-n (871.60g/kg, 57.95, and 52.02% respectively). The effect of cutting interval showed that, cutting the grass at 6 weeks produced significantly higher concentrations of OM, IVOMD, INVITRO-D and D-values (878.50g/kg, 60.27, and 55.01% respectively) than the 9 weeks cutting (873.50g/kg, 58.64, and 53.01% respectively). The interaction effects result revealed that A. gayanus recorded similar (non-significant) OM value at all nitrogen sources when compared to other grass genotypes. Keywords: Grass species, nitrogen sources, cutting intervals, digestibility, feed livestock. INTRODUCTION In most tropical countries, inadequate supply of feeds is the bottleneck to livestock production. Basically, is due to the dependence of livestock on naturally available feed resources and little development of forage crops for feeding to animals. One of the alternatives to improve livestock feeding, and thereby productivity could be the cultivation of grass-legume mixtures and offer them to animals during critical periods in their production cycle when other sources of feeds are in short supply. Nitrogen management is important from the stand-point of herbage quality as well as herbage production. The nutritive value of pasture is mainly a function of species composition and its growth stage, which are controlled by climatic factors that affect mineral status, re-growth potential, sward structure, and botanical composition (Whiteman, 1980). Stage of maturity at harvesting or grazing can be considered as crucial management practice that determines nutritional quality of either cultivated or natural pasture. In most of the cases, pasture grasses in the tropics cannot satisfy even the minimum requirement of nutrients of animals due to harvesting at advanced stage of maturity (Beyene et al., 1977). Tropical and sub-tropical grasslands are characterized by rapid growth during periods of heavy rainfall, leading to mature pasture plants containing high levels of cell wall constituents, low sugar (storage polysaccharides) and often very low in true protein. Grazing sheep and cattle have available young green pastures of high nutritive value only for short periods. Pastures rapidly decrease in digestibility with maturity such that during the dry season, the available feed is of poor quality, that is of low digestibility and particularly low in total nitrogen (N). In the tropics, therefore, in order to maintain a high intake of pastures by cattle and ensure that the pasture digestibility is as high as possible, it appears to be necessary to increase the stocking rates to such an extent that pastures are always kept in a young vegetative phase. Legume based pastures give high individual animal performance for growth, fattening, reproduction and wool growth. Cattle live weight gain has been related positively to the proportion of legume in the sward. The consistently high protein content of legumes throughout the year is a considerable advantage over grass alone pastures, which protein content is difficult to maintain unless very frequent nitrogen fertilizer applications are made and grazing pressure adjusted. Including a legume in fodder grasses production would not only provide a nitrogen source to promote grass growth but enhance the quality of feed. Legumes benefit grasses by contributing nitrogen to the soil through atmospheric fixation, decay of dead root nodules or mineralization of shed leaves. The inclusion of a legume in Napier grass based diet has been shown to improve animal performance in terms of milk production because of their high nutrient contents (Mureithi et al., 1995). Herbaceous forage legume have been identified as potential protein supplements for ruminants since they contain high crude protein ( g/kg DM), minerals and vitamins needed for the growth of ruminal microbes (Norton and Poppi, 1995). Protein supplementation of grass diets containing 70gCP/kg DM or less has been reported to increase dry matter intake, dry matter digestibility and animal performance (Osuji et al., 1993; Umuna et al., 1995). An assessment of the performance of goats raised on grass improved by nitrogen fertilization and grass incorporated with forage legumes have been reported (Bamikole et al., 2001). The authors observed that high nitrogen content of N-fertilized grass could not be efficiently utilized in the rumen of goats. Thus leading to high total nitrogen excretion by the animals fed the grass. The use of N-fertilizer to improve grassland is undesirable because it is uneconomical and could increase environmentally related problems (Bamikole et al., 2001) due to excessive release of nitrogenous compounds. The use of herbaceous or tree legumes have been reported (Ezenwa and Aken ova, 1988; Bamikole and Ezenwa, 1999). Dry matter yield generally increases with increasing fertilizer rate and cutting interval (Carvalho et al., 2000). However, there is a penalty in terms of the quality of forage harvested, and the optimum combination of nitrogen fertilizer level and cutting interval will depend on the relative needs for quality and quantity. It is generally considered that a 6-week interval between harvests is the maximum time compatible with high quality in cut for tropical grasses (Singh, 1993). Maturity at harvest has a large impact on hay quality; as forages mature, concentrations of fiber and lignin increases. Highly lignified forages remain in the rumen longer because of their slow rate of digestion, which results in decreased dry matter intake (DMI) and reduced animal performance (Jung and Allen, 1995; Allen, 2000). Crabgrass (Digitaria ciliaris) harvested on seven (7) dates had greater dry matter (DM) and neutral detergent fibre (NDF) digestion rates and less fibre content than Bermuda grass (Cynodon dactylon L.) (Dalrymple et al., 1999; Ogden et al., 2005). Benue State ( N, E) lies in the Southern Guinea Savannah zone of Nigeria The most prevalent vegetation type being of open Savannah woodland vegetation. The open Savannah is characterized by grasses and shrubs with few tall trees. Grass species, that occur in this area include: Panicum phragmitoides, Schizachyrium sanguineaum, Urelytrium muricatum, Cymbopogon giganteus, Beckeropsis uniseta, Brachiaria jubata, Pennisetum pedicellatum, Hypathelis dissoluta, Andropogon gayanus, A. schirensis, A. assinodis, A. tectorum and Hyparrhenia species (Remison, 1978). Hitherto, very little attention has been directed towards developing the vast areas of natural grasslands visa-vis livestock production in this zone. These abundant grassland resources have been wasted annually through bush burning (in search of the so-called bush meat a delicacy in the state) that has caused untold economic hardship in the loss of buildings, agricultural produce and even exposure of the already poor soils to agent of erosion. Therefore, it is imperative to develop a production system that increases availability of livestock feeds and improve fodder quality in this zone. A development of this natural grassland will help to increase livestock and thus help the contribution to the overall economy of Nigeria in general. The aim of the study was to determine the influence of nitrogen source and cutting interval on the digestibility of four (4) grass species in Benue State. MATERIALS AND METHODS i. Experimental Site and Land Preparation 527 The field trial was conducted in 2002/2003 wet season at Teaching and Research Farm of the University of Agriculture Makurdi ( N, E) in the Southern Guinea Savannah of Nigeria. The land was ploughed and harrowed to get rid of grass stubbles. Soil samples were taken from different spots and prepared for initial analysis. A blanket fertilizer application was then applied to supply 20kgN/ha as a starter dosage (application was mainly to the marked out plots to avoid wastage). ii. Planting Materials, Treatment Combinations and Experimental Design Crown splits of the planting materials (grasses) were: a. Andropogon gayanus (local) chosen on the basis of its abundance in Benue State. b. Panicum maximum (Ntchisi) c. Cynodon nlemfuensis (local) and d. Pennisetum purpureum: - chosen on the basis of their performance in previous trials at Makurdi and Yandev experimental station, while the Stylosanthes guinensis (CV.Cook) seeds were obtained from the National Animal Production Institute (NAPRI), Shika in Zaria. There were twenty four (24) treatment combinations replicated three times, arranged in a split split design. The grass genotypes (A. gayanus, P. maximum CV. Ntchisi, C. nlemfuensis (L) and P. purpureum (S.15); Nitrogen Sources (Mineral fertilizer and legume) and cutting dates (6 and 9 weeks) constituted the main plot, sub-plot and sub-sub plots, respectively. iii. Spacing Four (4) rows per plot were used measuring 4.5m length and 4m width. A week after the crown splits and stem cuttings was carried out that scarified S. guinensis seeds were broadcasted in the inter-row spacing of the affected plots. Weeding was routinely done to avoid competition with sown pasture species. iv. Data Collection and Analysis Ten (10) weeks after planting (WAP), all the plots were cut back to a suitable height of 15cm without recording growth and production data. Ten (10) days after cutting, fertilizer N:P:K (20:20:20) was applied at the rate to supply 150gkN/ha. Thereafter, at six weeks and nine weeks after the cut back exercise, the various plots were respectively harvested and production data were recorded. The chemical analysis [Organic matter (OM g/kg), Invitro organic matter digestibility (IVOMD), Invitro-D (%) and D- value (%)] were done at the Biochemical Sciences Laboratory II of the Scottish Agricultural College (SAC) Auchincruive, Ayr, Scotland, United Kingdom. The data were subjected to analysis of variance (ANOVA) based on split split plot design using Genstart 5 Release 3.1 (1993). RESULTS AND DISCUSSION The digestible organic matter (OM), Invitro-organic matter digestibility (IVOMD), Invitro-D and D-value were significantly affected by grass genotype, nitrogen source and cutting interval (Table 1). Among the grass genotypes, A. gayanus produced the highest amount of OM value (899.90g/kg) which was significantly (P 0.05) different from that produced by other grass genotypes. The effect of nitrogen source revealed that the legume inter-crop produced the highest and significantly different amount of OM (881.00g/kg) than those produced by mineral-n and zero-n sources ( and g/kg respectively) which were similar to each other. The effect of cutting interval showed that, cutting the grass at 6 weeks produced a significantly higher concentration of OM (878.50g/kg) than cutting at 9 weeks (873.50g/kg). The high value of OM obtained with the legume intercrop agrees with earlier report (Ezenwa and Aken ova, 1988) that the effect of the legume component in a grass/legume mixture would increase the quality of the mixture. Legumes benefit grasses by contributing nitrogen to the soil through atmospheric fixation, decay of dead root nodules or mineralization of shed leaves. The inclusion of a legume in Napier grass based diet has been shown to improve animal performance in terms of milk production because of their high nutrient contents (Mureithi et al., 1995). The performance of goats raised on grass improved by nitrogen fertilization and grass incorporated with forage legumes have been reported (Bamikole et al., 2001). The authors observed that high nitrogen of N-fertilized grass could not be effectively utilized in the rumen of goats. Thus leading to high total nitrogen excretion by the animals fed the grass. The use of N-fertilizer to improve grassland is undesirable because it is uneconomical and could increase environmentally related problems (Bamikole et al., 2001) due to excessive release of nitrogenous compounds. The higher OM concentration obtained in this trial at 6 weeks than 528 cutting at 9 weeks agrees with the report (Ademosun, 1970) when two varieties of C. nlemfuensis (local and IB8) when harvested at 6 weeks, both varieties yielded about 3 tones/ha and digestibility of dry matter by goats was about 60% for both varieties. In respect to IVOMD, P. maximum produced the highest percentage value (64.53%). This was significantly different from the value produced by A. gayanus (61.38%), while C. nlemfuensis produced the least IVOMD value (52.72%). The effect of nitrogen sources indicated that the legume inter-crop produced the highest IVOMD value (60.81%) which was significantly different from the value produced by the mineral-n source (59.58%). The cutting interval revealed that, the 6 weeks cutting produced a significantly higher IVOMD value (60.27%) than cutting at 9 weeks (58.64%). Among the tested grass genotypes, P. maximum yielded the highest Invitro-D and D-value percentages (56.84 and 59.60% respectively), while the lowest was obtained with C. nlemfuensis (47.00 and 47.75% respectively). Similarly, effect of nitrogen source revealed that the legume inter-crop source produced the highest values of Invitro-D and D-value (53.69 and 55.79% respectively), while the 6 weeks cutting gave higher values of (52.90 and 55.01%) Invitro-D and D-values than the 9 weeks cutting. The higher values of IVOMD, Invitro-D and D-value obtained with legume inter-crop when compared to the other two nitrogen sources is an indicative of nutritive value. This may be due to the fact that more nitrogen is made available through the N-fixation by the legume intercropped and the subsequent increase uptake at a faster rate than the dry matter production as shown by Brockman (1966). Similarly, the 6 weeks cutting gave higher values (IVOMD, Invitro-D and D-value) than cutting at 9 weeks. Herbage cutting management strategies are based mainly on biomass production and forage quality. Optimum field management is aimed at getting the highest biomass production which satisfies the animal s needs, as usually determined by animal performance. Using digestible DM yield as the standard, optimum cutting interval seems to be around 6 weeks, as this is consistent with the general recommendations of Singh (1993). This goes to suggest that most tropical grasses at about 6-7 weeks of age are highly digestible and has an optimum utility after which there is a decline in the level of utilization (Sodeinde et al., 2006). The interactive effects of the grass, nitrogen sources and cutting intervals on OM, IVOMD, Invitro-D and D- value were significant are presented in Tables 2, 3 and 4. The interactive effect of the grasses and nitrogen sources on OM was significant (Table 2). The result indicated A. gayanus recorded significantly (P 0.05) higher OM value at all the nitrogen sources (Mineral-N, zero-n and legume) when compared to other grasses. This may be due to differences in individuals grass genotype s response to N-source. At the three N-sources, the mineral-n, zero-n and legume X A. gayanus, P. maximum and the C. nlemfuensis interactions, yielded similar (P 0.05) OM values. However, the mineral N X P. purpureum and legume X P. purpureum interactions, yielded OM values similar to each other, but significantly higher than the zero-n X P. purpureum interaction. This study is similar that reported by Haggar (1967) that application of increasing quantities of nitrogen as ammonium sulphate to A. gayanus resulted in linear increase in OM production. Previous research of other tropical grasses showed increasing OM as a result of higher growth rates under greater N- application (Thom et al., 1990). Similarly, irrespective of nitrogen sources, the result indicated that IVOMD, Invitro-D and D-value were significantly highest with P. maximum, and the lowest recorded with C. nlemfuensis. Panicum maximum have been reported to respond well to nitrogen fertilizer application like many other tropical grasses (Ayinde, 1998). However, at the three N-sources, the mineral-n X A. gayanus. Legume X A. gayanus interactions yielded higher IVOMD, Invitro-D and D-values than the respective zero-n interactions. The legume X C. nlemfuensis interaction; mineral-n X C. nlemfuensis resulted in significantly higher IVOMD, Invitro-D and D-value respectively than other interactions in this study. The importance of incorporation of legumes into a grass pasture is well known. Legumes have the potential to increase the overall quality and digestibility of forages and also increase the CP content of the grass component of the mixture (Schultz and Stubbendiek, 1983). Table 3 presents the significant interactive effects of the grass species and the cutting interval on OM, IVOMD, Invitro-D and D-value. At both cutting (6 and 9 weeks), cutting interaction with A. gayanus, produced the highest OM value which was significantly different from C. nlemfuensis interaction; while the lowest OM value was produced by P. purpureum. Looking at the two dates, 6 weeks X A. gayanus interaction, yielded higher OM value than the 9 weeks X A. gayanus interaction. All the other grass species yielded similar OM values at the two date s interactions. Interactions between the grass 529 species X cutting dates (6 and 9 weeks) produced IVOMD and Invitro-D values in the following order: - P. maximum A. gayanus P. Purpureum C. nlemfuensis. The 6 weeks X C. nlemfuensis and P. purpureum interactions produced significantly higher IVOMD values than their 9 weeks interactions; while invitro-d value all interactions (except both at 6 and 9 weeks X P. maximum) yielded significantly higher Invitro-D values at 6 weeks than at the 9 weeks. This study agrees with earlier work by Ademosum and Baumgardt (1967) who reported decreased invitro dry matter digestibility with increasing maturity. Generally, under good management with fertilizer, a reasonable number of herbage crops harvested at an early stage of growth have dry matter digestibility figures of over 60% (Ademosum, 1970). The interactive effect
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