STUDIES ON FERTILIZER NITROGEN AND CUTTING MANAGEMENT OF SOWN GRASS AND LEGUME PASTURES IN PURE AND MIXED SWARDS

ABSTRACT

Three  field  experiments  were  conducted  at  the  Teaching  and  Research  Farm  of  the Department of Crop Science, Faculty of Agriculture, University of Nigeria, Nsukka. In the first  experiment,  the  effects  of  fertilizer-N  application  and  cutting  management  on establishment, growth and yield of guinea grass (Panicum maximum) were investigated. The experiment was a 4 x 4 factorial laid out in a randomized complete block design with three replications. Treatments comprised four levels of Nitrogen of 0, 150, 300, and 450 kg N ha-1 and four harvesting frequencies of 3-, 6-, 9- and 12-weekly intervals. A second

experiment was conducted using guinea grass/verano stylo (Stylosanthes hamata) mixed swards. The experiment was a 3 x 3 x 2 factorial laid out in a randomized complete block design with three replications. Treatments comprised three swards types (pure grass, pure legume and grass-legume mixed swards), three harvesting frequencies of 4-, 8-, and 12- weekly intervals and two levels of nitrogen at 0, and 300 kg N ha-1. The third experiment was  conducted  to  evaluate  the  effects  of  two  cutting  frequencies  (4-  and  8-weekly intervals)  on  the  growth  and  yield  of  four  legumes  (Lablab  purpureus,  Stylosanthes hamata, Centrosema pascuorum and Stylosanthes guyanensis) and four grasses (Sorghum almum, Panicum maximum, Chloris gayana and Andropogon gayanus). Basal applications

of muriate of potash (75 kg K ha-1) and single superphosphate (44 kg P ha-1) were also made by broadcasting  in all the experiments.  In the first experiment,  tiller  number per square metre, plant height and grass dry matter yield were increased by  44%, 6% and 53%, respectively, during the establishment year when fertilizer-N rate was increased from 0 to 450 kg N ha-1. Grass dry matter yield was increased by 41% and 149% when  the interval between cuts was increased from 3- to 12-weekly intervals at the first and fourth harvest years, respectively. Plots cut at 3- or 6- weeks intervals exhibited much greater weed proportion than those cut 9-, or 12-weekly intervals. Increasing the interval between harvests from 3 to 12 weeks increased the proportion of stem relative to leaf blade in the grass swards. The proportion of inflorescence,  plant height and  dry matter percentages, were generally increased by increasing the interval between cuts. Tiller number decreased with increasing interval of cut. The total annual herbage dry matter yield was increased by 32% and 48% in 2001 and 2004, respectively, when fertilizer-N was increased from 0 to

450 kg N ha-1. Increasing the N rate from 0 to 450 kg N ha-1  increased the proportion of stem relative to the leaf blade in the grass swards. Plant height and tiller number  were increased with increase in N application while the dry matter percentage was  generally decreased with incremental application of nitrogen. A combination of 12-weekly interval

of cut with 300 kg N ha-1 gave a significantly higher forage grass herbage dry matter yield compared with the values got from the 3- or 6-weekly interval combined with any N rate. Fertilizing at 300 or 450 kg N ha-1 when combined with cutting at 9 or 12-weekly interval

between cuts was more effective in suppressing weed growth and weed dry matter as a proportion of the total herbage dry matter. The N % and crude protein contents in the leaf, stem  and  in  total  herbage  dry  matter  decreased  significantly  with  increasing  interval between cuts. Yield of crude protein in the total herbage was  significantly higher when cutting  was done every  6 weeks  compared  with  when  done every  9 weeks.  Nitrogen fertilizer x cutting frequency interaction effects on N %, crude protein contents and crude protein yields in the crop fractions and in total herbage dry matter were not statistically significant. On the average, the crude protein and mineral contents were higher in the leaf fraction than in the stem and inflorescence fractions. In the second experiment, herbage production  was 16% and  69% higher on guinea grass/stylo  swards in 2006 and 2007, respectively, compared with the yields for the pure guinea grass swards. Grass dry matter yield as a proportion of the total herbage dry matter was significantly increased from 45%

to 61% in 2007 with 12-weekly cutting interval compared with 4-weekly interval.  The weed proportion was significantly reduced from 28% to 19% with the infrequent cutting interval  of  8-weeks  compared  with  the  4-weeks  in  2007.  Cutting  frequency  did  not influence  the proportion  of verano  stylo in 2006 and 2007.  However,  the legume  dry matter yield was generally increased with longer intervals  between cuts. The effects of fertilizer-N rates on the proportions of grass, legume and weed in 2006 and 2007, were not statistically  significant.  The  total  herbage  dry  matter yield  was significantly  higher  in guinea grass/stylo swards when cutting was done at 8-weekly interval compared with sole guinea grass or verano stylo at any interval between cuts. Crude protein yield of the guinea grass/stylo sward was higher  than that of pure guinea grass sward by 8 %. In the third experiment,  Stylosanthes  guyanensis  had the highest  dry matter  yield  among  the four legumes in 2007  when  8 weeks interval between cuts was employed. Among the four grasses,  Chloris gayana  produced  significantly  greater  dry matter  yield than Sorghum almum but had a similar yield value with Panicum maximum or with Andropogon gayanus in 2006. Andropogon gayanus yielded more than Chloris gayana but had a similar yield value with Sorghum almum or with Panicum maximum in the first harvest year. Cutting interval did not influence the extent of legume cover. However, the extent of grass cover was increased by 30% when the interval between cuts was increased from 4 to 8 weeks. Weed cover in the legume plots was not influenced by  cutting management.  However, weed cover in the grass plots was significantly depressed by 21% with increased interval of cut from 4 to 8 weeks. The dry matter percentages among the grasses and the legumes were generally increased by  increasing the interval between cuts. In 2006, Stylosanthes hamata  had  significantly  higher  dry  matter  content  among  the  legumes  than  Lablab purpureus and Stylosanthes guyanensis but did not differ with Centrosema pascuorum. In

2007, Lablab purpureum had significantly the least percentage dry matter compared with

the other legumes. Stylosathes hamata had higher percentage dry matter than Centrosema pascuorum but did not differ with Stylosanthes guyanensis. Grass dry matter content did not vary among the grass species in 2006. In 2007, Sorghum almum had higher (P<0.05) dry matter content than Chloris gayana but had similar value with Panicum maximum or with Andropogon gayanus.

INTRODUCTION

In Nigeria, feed deficits and low quality of the available feed, particularly during 5 to 7 months of the dry season are major constraints for optimum livestock production from the  savanna   rangelands   (Omokanye,   Kalla,  Alawa  and  Otchere,   1998).  Livestock production depends closely on the availability of animal feed of high quality. Availability of  high  quality  feed  is  influenced  by  climatic  conditions,  plant  species  and  stage  of maturity,  soil, the level of inputs and by management  (Muhammad,  Hena, Agishi and Olorunju, 2002; Enoh, Kijora, Peters and Yonkeu, 2005).

Smallholder  producers  of  ruminants,  particularly  cattle,  sheep  and  goats,  in Nigeria rely on unimproved natural pasture as the main feed source, backed up with crop residues  after  harvest  (Bamikole,  Akinsoyinu,  Ezenwa,  Babayemi,  Akinlade  and Adewumi,  2004).  The  animals  in consequence  grow  slowly,  produce  little  milk  and reproduce at long intervals. This problem of inadequate feeding stuff is further aggravated particularly in the dry season when grassland productivity is low (Oloyo and IIelaboye,

2002). The present poor production potential of pastures could be attributed to poor soil fertility and to poor management (Dev, 2001).

Most pastures in Nigeria lack proper management  because of poor  defoliation frequency and lack of proper fertilization.  Pastures are often subjected  to  burning and extreme grazing which have been shown to result in serious deterioration of herbage (Dev,

2001).  It has been noticed  that economic  factors  make  a viable  commercial  livestock industry imperative, needing the establishment of suitable sown pasture and feed lots to meet the higher nutritional  needs of more productive  animals  (Bamikole  et al., 2004). Increments in fodder production can be achieved by expansion of land areas under natural pastures or by increasing yields per unit land area. With the present trend of competitive land use, increasing forage production through expansion of land area of natural pasture is hardly feasible as a result of the demographic changes (Muhammad and Abubakar, 2004). In the emerging shift in animal management systems towards confinement because of the pressure  on  land,  a  strategic  forage  harvesting  and  management  system  suitable  for confined ruminant  livestock  and which will guarantee a regular supply of high-quality forages  to  these  livestock  is  required  (Bamikole  et  al.,  2004).  Improvement  of  feed availability for the future requires development of sown pastures that are to be sustained under intensive systems of management. Intensive production system involves the use of

forage species that must prove their superiority in terms of their bulk productivity (dry matter  yield  per  unit  area),  palatability,  chemical  composition,  nutrient  availability, persistence under defoliation regimes and inclement climatic conditions, competition and compatibility  with other forages in the pasture ecosystem  (Muhammad  and Abubakar,

2004).   Improved grasses and legumes have been recommended  for intensive  livestock production in Nigeria due to their high forage production and nutritive value (De Leeuw and Brinckman, 1974; Olubajo, 1974). Various grass species at present exist in Nigeria and the notable ones include Andropogon gayanus, Panicum  maximum, Chloris gayana and   Sorghum   almum   (Agishi,   1979).   The   legumes,   which   include;   Stylosanthes guyanensis,  Lablab  purpureus,  Stylosanthes  hamata  and Centrosema  spp have  proved very valuable (Onifade and Agishi, 1988).

In the tropics, supply of herbage for livestock during the dry months of the year declines substantially (Omaliko, 1983; Oloyo and IIelaboye, 2002). Enough herbage must be produced during the production  period through intensive  management  techniques in order to make possible conservation for the lean season or off-season periods. Intensive management  practices  include  the  use  of fertilizers,  choice  of  forage  species,  cutting management,  control  of bushes and weeds  and  pasture  establishment  (Omaliko,  1983; Dev, 2001). Attempts at enhancing the nutritive quality of the forage, particularly nitrogen component  have been through the  use of nitrogen fertilizer or inclusion of legumes in mixtures  (Bamikole,  2003)  The  use  of  adapted,  improved  and  high  yielding  pasture legumes as sole crop or in mixture with grasses is one of the ways of achieving availability of  good  quality  forage (Omokanye,  Kalla,  Alawa  and Otchere,  1998).  It  is generally accepted that  grasses normally have a competitive  advantage over legumes (Wong and Wilson,   2005);  however,  pasture  management   techniques  such  as  fertilization  and defoliation management, are utilized in order to secure a desirable balance (Rhodes and Stern, 1978; Keftasa, 1996).

Intensive  management  practices  require many inputs, which are not  commonly used in natural grassland livestock production system. To be more readily adoptable and acceptable to the resource poor farmers, the system must not be capital intensive and must not   require   unduly   sophisticated   technology   (Omaliko,   1983).   The   method   of establishment of a pasture should be cost effective and with minimum soil working (Dev,

2001). Some knowledge of the effects of management, such as fertilization and  cutting regimes on aspects of pasture establishment, growth and productivity could help to make many tropical  pastures  more  productive  and efficient  for animal  production  (Wilman,

Droushiotis, Koocheki, Lwoga and Shim, 1976a; Wilman, Koocheki and Lwoga, 1976b; Wilman, Ojuederie and Asare, 1976c).

Some studies have been carried out to test the effects of cutting frequency  and initial cutting date on the production of Panicum maximum pasture sown under Nsukka derived  savanna  zone  of  Nigeria  conditions  (Omaliko  1980;  1983).  In  those  studies, however, the effects of different nitrogen fertilizer application rates in combination with cutting frequencies were not considered. Information is scanty on  the effects of cutting frequency and nitrogen fertilizer application  on dry matter  yield of Panicum maximum sown pastures at different seasons of the year in Nigeria. There is paucity of information on the effects of cutting frequency and fertilizer-N application on the dry matter yield and quality   of  crop  fractions   in  guinea   grass   (Panicum   maximum)   and  verano   stylo (Stylosanthes  hamata)  mixed  swards  grown  in Nigeria.  The proportions  of these crop fractions have important bearing on digestibility (Terry and Tilley, 1964; Duru, Delprat, Fabre and Feuillerac, 2000) and also on voluntary intake (Laredo and Minson, 1975).

Differences  in  habit,  regrowth,  and  physiological  growth  requirements  make management of grass/legume mixtures difficult (Casler, 1988). These differences make it difficult to maintain the proportions of each component in the grass/legume mixture. Many recommendations  for grass/legume  mixtures were based  on monocultures,  which led to errors in developing suitable mixtures (Casler and  Walgenbach, 1990). Species that are highly  productive  in  monocultures  are  often  incompatible  in  mixtures  (Casler  and Drolsom, 1984). The influence of nitrogen fertilization is of interest, since guinea grass has high yield potential and is responsive to nitrogen fertilization (FAO, 2003). However, nitrogen fertilization has been found to reduce the legume content when in mixture with grass  (Guay,  2001),  therefore,  the  influence  of  nitrogen  application  on  the  legume component is of interest.

The maturity stage at cutting has been shown to be a major factor that determines the quality  of grass pastures  (Keftasa,  1996). Optimum  forage  yields  are achieved  by harvesting plants when they reach a height or growth stage corresponding to a high point in the energy reserve cycle (Rayburn, 1993). Benefits  from mixed stands of grass and legume pastures can be efficiently exploited only if proper management strategies such as optimum fertilization and accurate cutting frequencies are followed (Keftasa, 1996).

Some forage legumes and grasses are known to be productive and can complement the low productivity of natural pastures in Nigeria (Njarui and Wandera, 2004). Notable among  the  legumes  are  Stylosanthes  hamata,  Stylosanthes   guyanensis,  Centrosema

pascuorum  and Lablab purpureus  while  the grasses  include  Chloris  gayana,  Panicum maximum Sorghum almun and Andropogon gayanus. However, productivity of some of these species has not been evaluated under varying cutting regimes in  Nsukka derived savannah  area  of  Nigeria.  There  is  a  need  to  develop  an  appropriate  management harvesting strategy for these pasture species to maximize dry matter production.

Objectives

The objectives of the present research therefore are:

1.   to study the effects of fertilizer N and cutting management on the establishment, growth and yield of guinea grass (Panicum maximum) or guinea grass-verano stylo mixed swards.

2.   to evolve the best combination  of fertilizer-N  rate and cutting management  for optimization  of herbage dry matter yield and herbage quality in guinea  grass or guinea grass-verano stylo mixed swards.

3.   to  investigate  the  effect  of  different  cutting  regimes  on  herbage  dry  matter production  of  four  sown  grasses  and  four  legumes  under  Nsukka  ecological conditions.

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