Nodulation, Nitrogen Fixation and Biomass Yield of Selected Forage Legume Species in Coastal Savannah Zone of Ghana
Abstract
Two field experiments were carried out in the major and minor rainy seasons at the
BNARI research farm at Kwabenya, Accra, Ghana from July – November, 2016 to
investigate nodulation, biomass yield and nitrogen fixation potential of ten forage legumes
(Macroptilium atropurpureum, Stylosanthes guianensis, Crotalaria
ochroleuca, Pueraria phaseoloides, Centrosema pubescens, Calopogonuim
mucunoides, Cajanus cajan, Flemingia macrophylla, Lablab purpurus and Desmodium
distortum). Completely randomized block design (RCBD) with four replications of each of
the above named forage legumes was used. Sampling was done at eight weeks after
planting for all the legume plants for both major and minor rainy seasons. Sub – samples
of both maize and legume species for both major and minor rainy seasons were oven dried
at 65oc for 72hrs, milled to fine powder and per cent total N analyzed using Kjeldahl
Digestion Method at ECO LAB, University of Ghana, Legon. Nitrogen content for each
sample was calculated using the per cent N analyzed and nitrogen difference method used
in determining the N-fixed by the legume species. Nodules harvested from sampled plants
were washed, moped, weighed for both fresh and dry nodule weight, counted for nodule
number and sliced for nodule effectiveness for both major and minor rainy seasons. Data
collected was subjected to analysis of variance (ANOVA) of RCBD using GENSTAT
statistical package version 16 edition and Duncan’s Multiple Range Test (DMRT) used to
separate means where significant differences were observed. On the whole, Crotalaria
ochroleuca, C. cajan, L. purpureus, D. distortum and M. atropurpureum produced high
dry matter yields. However, the highest (6817kg ha-1) and lowest (1747 kg ha-1) mean
shoot dry matter yield for the major rainy season was produced by L. purpureus and S.
guianensis respectively. The highest mean dry matter yield for the minor rainy season was
255.30 kg ha-1 for C. ochroleuca while the lowest was 110.30 kg ha-1 for C. pubescens.
The highest mean total N yield being 144.50 kg N ha-1 was produced by L. purpureus and
47.70 kg N ha-1 being the lowest value was obtained by S. guianensis during the major
rainy season. Crotalaria ochroleuca produced the highest N yield with the value 77.96 kg
N ha-1 while the lowest N yield of 38.37 kg N ha-1 was produced by C. pubescens during
the minor rainy season. The highest and lowest mean number of nodules produced per
plant for the major rainy season were 266.50 for C. cajan and 16.5 for C. mucunoides
respectively while the highest and lowest mean number of nodules for the minor season
were produced by L. purpureus (153.5) and C. pubescens (3.75) respectively. However,
the highest and lowest mean effective number of nodules for the major rainy season were
produced by C. cajan (238) and C. mucunoides (10) respectively while the highest and
lowest values for the minor season were 139 and 2 for L. purpureus and C. pubescens
respectively. Cajanus cajan had the highest mean effective nodules (237.75) and F.
macrophylla produced the lowest (10.25) effective nodules (EN) for the major season
while in the minor season, L. purpureus had the highest EN (139) with C. pubescens
having the lowest EN (3.75). The highest total nitrogen derived from atmosphere (Ndfa)
for major rainy season was 112.45 kg N ha-1 for L. purpureus and the lowest total Ndfa of
15.64 kg N ha-1 was produced by S. guianensis. The legume species, C. ochroleuca had
the highest Ndfa of 52.93 kg N ha-1 whiles C. pubescens produced the lowest Ndfa of
13.35 kg N ha-1 for the minor rainy season. Statistical analysis indicated highly significant
(p ≤ 0.001) seasonal effect on most of the parameters measured for the forage legume
species except root dry matter and N yields that had non- significant (p ≥ 0.05) seasonal
effect. In conclusion, the linear regression between dry weight of effective nodules and
Ndfa for each season, showed positive relationship with R2 values of 0.5807 and 0.4513
respectively, implying that increasing dry weight of effective nodules results in increasing
Ndfa
Description
Keywords
Nitrogen Fixation, Biomass, Legume