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Nitrogen fixation potential and residual effects of selected grain legumes in a Kenyan soil

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Abstract

Based on their performance attributes, butter bean (variety Ex-kasuku) and grass pea (Selection 1325) have been identified as potential alternative legumes for the maize-based cropping system in the cold semi-arid region of Laikipia County in Kenya. However, their nitrogen fixation potential and nitrogen residual effects have not been established. A green house experiment was therefore conducted to determine the nitrogen fixation potential and residual effects of the introduced legumes (butter bean and grasspea) relative to the local checks (common bean cv. Katumani 330 and chickpea cv. Desi). The legume seeds were planted in perforated polythene bags, measuring 14 cm diameter and 20 cm high, containing 3.6 kg air dried soil collected from Matanya in Laikipia County, Kenya. Barley, a non-nitrogen fixing reference crop, was also planted in polythene bags and used to determine the amount of nitrogen fixed according the N-difference method. Butter bean and grass pea significantly out-performed chickpea in total nodule number, active nodule number, total nodule dry matter, total plant dry matter, dry matter N yield, amount of N-fixed, percent N derived from the atmosphere and residual N effect, but were comparable to common bean in all these attributes. There was a significant, positive linear relationship between quantity of N-fixed and quantity of total plant biomass accumulated. Butter bean, grass pea and common bean significantly increased soil mineral nitrogen while chickpea had no influence on soil nitrogen. Butter bean and grasspea can therefore provide N to cropping systems in the cold semiarid region through biological N fixation.
RESEARCH PAPER OPEN ACCESS
Nitrogen fixation potential and residual effects of selected
grain legumes in a Kenyan soil
George N. Chemining’wa
1*
, Peter W. Mwangi
2
, Mary W. K. Mburu
3
, Joseph G.
Mureithi
2
1
Department of Plant Science and Crop Protection, University of Nairobi, Kenya
2
Kenya Agricultural Research Institute, Kenya;
3
South East University College (University of
Nairobi), Kenya
Article published on February 28, 2013
Key words: Butter bean, grasspea, N-difference, nodule number, soil nitrogen.
Abstract
Based on their performance attributes, butter bean (variety Ex-kasuku) and grass pea (Selection 1325) have been
identified as potential alternative legumes for the maize-based cropping system in the cold semi-arid region of
Laikipia County in Kenya. However, their nitrogen fixation potential and nitrogen residual effects have not been
established. A green house experiment was therefore conducted to determine the nitrogen fixation potential and
residual effects of the introduced legumes (butter bean and grasspea) relative to the local checks (common bean
cv. Katumani 330 and chickpea cv. Desi). The legume seeds were planted in perforated polythene bags,
measuring 14 cm diameter and 20 cm high, containing 3.6 kg air dried soil collected from Matanya in Laikipia
County, Kenya. Barley, a non-nitrogen fixing reference crop, was also planted in polythene bags and used to
determine the amount of nitrogen fixed according the N-difference method. Butter bean and grass pea
significantly out-performed chickpea in total nodule number, active nodule number, total nodule dry matter,
total plant dry matter, dry matter N yield, amount of N-fixed, percent N derived from the atmosphere and
residual N effect, but were comparable to common bean in all these attributes. There was a significant, positive
linear relationship between quantity of N-fixed and quantity of total plant biomass accumulated. Butter bean,
grass pea and common bean significantly increased soil mineral nitrogen while chickpea had no influence on soil
nitrogen. Butter bean and grasspea can therefore provide N to cropping systems in the cold semiarid region
through biological N fixation.
*
Corresponding Author: Dr. George N. Chemining’wa umchemin@hotmail.com
International Journal of Agronomy and Agricultural Research (IJAAR)
ISSN: 2223-7054 (Print) 2225-3610 (Online)
http://www.innspub.net
Vol. 3, No. 2, p. 14-20, 2013
14
Introduction
The benefit of including legume crops in cropping
systems is mostly associated with their ability to
biologically fix atmospheric N (Cheminig’wa et al.,
2006; Walley et al., 2007). Nitrogen fixation is
reported to be affected by such factors as soil
available N and effectiveness of the rhizobia-host
association (Van Kessel and Hartley, 2000), soil pH,
soil moisture, soil available P and plant management
(Fosu et al., 2004; Muza and Mapfumo, 1998;
Peoples et al., 1995; Thies et al., 1995) and soil
microbial populations (Dogbe et al., 2000). It is
reported to vary with legume species (Chemining’wa
et al., 2004; Mwangi and Wanjekeche, 1997;) and to
be closely correlated with legume dry matter
production (Kumar and Goh, 2000; Lelei et al.,
2009).
Generally soil N can be increased by biological
nitrogen fixation (Mburu and Gitari, 2006). The
amount of nitrogen added to a cropping system
depends on the legume nitrogen yield and the
proportion of N due to biological nitrogen fixation
(Giller, 2001).
Butter bean (variety Ex-kasuku) and grass pea
(Selection 1325) were identified as potential legumes
for the cold semi-arid region of Laikipia district on the
basis of biomass and grain yields, nitrogen yield and
water use efficiency and were comparable to the local
checks (common bean (variety Katumani 3330) and
chickpea (variety Desi)) in most performance
attributes (Mwangi, 2011). Intercrops of these
legumes and maize were also demonstrated to have
land use and monetary advantages over respective
sole cropping (Mwangi, 2011). The nitrogen fixation
potential and nitrogen residual effects of these
legumes have however not been established.
Previous studies have shown that Kenyan soils have
indigenous rhizobia strains that can fix atmospheric
nitrogen in association with commonly grown
legumes such as common bean, cowpea, green gram
and pigeon pea (Chemining’wa et al., 2011; Karanja et
al., 2002).
Presence of indigenous rhizobia that can effectively
nodulate butter bean and grasspea in the cold semi-
arid area of Laikipia has not been established.
Legume species and varieties vary in their capacity to
fix nitrogen and make it available to subsequent
rotation crops (Van Kessel and Hartley, 2000; Giller,
2001; Graham et al., 2004). In previous studies, for
example, chickpea was reported to fix 64-138 kg N ha
-
1
with residual balance of up to 38 Kg N ha
-1
(Fatima et
al., 2008)
Assessment of nitrogen fixation potential and
nitrogen residual effects is critical in the selection of
legumes for integration into the low nitrogen maize-
legume based production systems in the cold semi-
arid area of Laikipia county, Kenya. Therefore, a
green house experiment was conducted to determine
the nitrogen fixation potential and residual effects of
the introduced legumes in a soil from a cold semiarid
area of Laikipia.
Materials and methods
Experimental design, treatments and crop
husbandry
The experiment was conducted in a greenhouse at the
National Agricultural Research Laboratories (Kabete).
The experiment was arranged in a randomized
complete block design and replicated three times.
Treatments were four legumes including: grass pea
Selection 1325, butter bean variety Ex-Kasuku,
common bean variety Katumani 3330 and chickpea
variety Desi.
Perforated polythene bags measuring 14 cm diameter
and 20 cm height were filled with 3.6 kg of air dried
soil collected from the study site (Matanya) at 0-15 cm
depth. Four seeds of each legume and barley (as a
reference crop that cannot fix nitrogen (Soon and
Arshad, 2004)) were planted in each bag. A total of 6
bags per legume were planted. The bags were watered
regularly to maintain field capacity. Butter bean and
grasspea had no history of cultivation in the site
(Matanya in Lakipia county of Kenya) where the soil
for the study was collected.
15
Data collection
Number of nodules per plant and nodule dry matter
At flowering, one bag of each legume (containing four
plants) was flooded with water and the soil carefully
poured out. All nodules from each plant were
counted. Number of fixing nodules was determined
by splitting the nodules and counting those with pink
colouration. Percent of active nodules was calculated
as the ratio of active nodules to total number of
nodules. All nodules were dried to constant weight
and nodule dry matter per plant determined.
Plant total dry matter and nitrogen yield
At physiological maturity, the other bag of each
legume and barley was flooded and soil poured out.
The materials (root and shoot) were carefully washed
and dried at 700C to constant weight and the weight
recorded. A composite sample of each material was
ground to pass through a 2 mm sieve. Percent
nitrogen in each sample was then determined using
the Kjeldahl procedure (Okalebo et al., 1993).
Nitrogen yield for each material was calculated as the
product of percent nitrogen and dry weight.
Amount of fixed nitrogen and percent nitrogen
derived from the atmosphere
The amounts of nitrogen fixed by the legumes were
estimated using the nitrogen difference method
(Brockwell et al., 1982; Soon and Arshad, 2004):
BNF = Nleg - Nref + (Nsoil Nsoilref) where BNF
(biological nitrogen fixation) = amount of nitrogen
fixed, Nleg = legume nitrogen content, Nref =
reference crop nitrogen content, Nsoil = soil mineral
nitrogen before planting and Nsoilref = soil mineral
nitrogen after harvesting the reference crop. Barley
was used as the reference crop. Percent nitrogen
derived from the atmosphere (% Ndfa) was
determined as the ratio of BNF to plant nitrogen
yield.
Soil nitrogen
Soil samples were analysed for soil available N (NO-
3-N + NH+4-N) using the method described by
Okalebo et al. (1993) before planting and at
physiological maturity.
Data analysis
Collected data were subjected to analysis of variance
using SAS statistical package (SAS Institute, 1993).
Where the F values were significant, means were
compared using the least significant difference (LSD)
test, at p = 0.05. Regression analysis was used to
compare the relationship between amounts of fixed
nitrogen and legume total dry matter yield.
Results
As shown in Table 1, the number of nodules were not
significantly different (p=0.05) between introduced
legumes (butter bean and grasspea, with 25.6 and
25.5 nodules per plant respectively) and locally grown
legumes (common bean and chick pea, with 23 and
27.3 nodules per plant respectively). Grass pea, butter
bean and common bean had higher number and
proportion of active nodules, nodule dry matter, total
plant biomass yield and N yield than chickpea (Table
1). They also generally fixed significantly more
atmospheric N, had higher percentage of N derived
from the atmosphere (Table 2) and contributed more
soil residual nitrogen after harvest than chickpea
(Table 3). Linear regression relationship between
amounts of fixed nitrogen and legume dry matter
yield was positive and significant (Figure 1).
Discussion
Grass-pea and butter bean were adequately nodulated
in soil from the cold semiarid site where they had not
been previously grown, indicating the abundance of
indigenous rhizobial strains compatible with these
legumes in the region. Previous studies have
demonstrated the widespread presence in Kenya soils
of rhizobial strains that are compatible with a cross
range of legume crop species (Chemining’wa et al.,
2006; Chemining’wa et al., 2011; Karanja et al.,
2000).
Grass pea, butter bean and common bean fixed more
nitrogen and had higher soil residual nitrogen after
harvest than chickpea. These observations suggest
that the former have greater nitrogen fixation
capacity than the latter.
16
Genetic variation among legumes in nitrogen fixation
potential has been reported in various studies (Giller,
2001; Lelei et al., 2009; Walley et al., 2007; Yusuf et
al., 2008). Graham et al. (2004) reported that
nitrogen fixation in legumes is a quantitively
inherited trait. The results in the current greenhouse
study suggest that grass pea, butter bean and
common bean have the potential to contribute
positively to the overall soil N economy over time.
Table 1. Nodule count, nodule dry matter (g), biomass yield (g/plant), nitrogen yield (g/plant) of butter bean,
grass pea, common bean and chickpea planted in soil collected from Matanya (Laikipia county, Kenya).
Legume
Nodule
Percent
Nodule
Biomass
Nitrogen
number
active
dry matter
yield
Yield
per plant
nodules
(g)
(g/plant)
(g/plant)
Grass pea
25.5a
88.7a
0.5a
108.2a
3.9a
Butter bean
25.6a
86.4a
0.6a
113.8a
3.7a
Common bean
23.0a
86.4a
0.5a
96.3a
3.3ab
Chickpea
27.3a
6.5b
0.2b
66.0b
2.1b
Mean
25.4
67.0
0.4
96.1
3.2
LSD (p=0.05)
Ns
11.4
0.2
23.9
1.2
CV (%)
24.9
8.8
20.2
12.9
18.7
The poor N fixation potential in chickpea could be
attributed to the presence of inefficient but
compatible native rhizobia in the site. This is
supported by the fact that the total number of nodules
per plant was not significantly different among the
legumes while chickpea had significantly fewer active
nodules than the other legumes. The observations
imply the need to inoculate chickpea with commercial
rhizobial strains and screen chickpea genotypes for
capacity to effective nodulatewith native rhizobia.
Currently there are no commercial inoculants strains
for chickpea in Kenya hence there is need to screen
for effective chickpea nodulating rhizobia strains.
Higher N fixation capacities of grass pea, butter bean
and common bean also suggest the presence of
adequate and effective indigenous rhizobia infecting
these legumes. Chemining’wa et al. (2011) reported
that native rhizobia that nodulate common bean and
cowpea were widespread in central Kenyan soils.
According to Dogbe et al. (2000), for effective
nodulation rhizobia population density should not be
less than 50 cells per gram of soil.
The increased soil nitrogen after planting grass pea,
butter bean and common bean could have been due to
enhanced nitrogen supply by the legumes through
nitrogen fixation and decaying nodules and roots.
Several reports have suggested increased soil nitrogen
by some pulse crops (Beckie and Brandt, 1997; Gan et
al., 2003; Soper and Grenier, 1987; Van Kessel and
Hartley, 2000).
Table 2. Biologically fixed nitrogen (g/plant) and
percent nitrogen derived from the atmosphere by
butter bean, grass pea, common bean and chickpea
planted in soil collected from Matanya (Laikipia
county, Kenya).
Legume
Fixed N
(g/plant)
Percent N derived
from atmosphere
Grass pea
2.6a
64.1a
Butter bean
2.4a
61.3a
Common bean
1.8ab
55.7a
Chickpea
0.6b
29.8b
Mean
1.8
52.7
LSD (p=0.05)
1.2
14.8
CV (%)
32.8
14.4
Pulse crops are reported to have high grain protein
content and frequently the net export of nitrogen to
grain often exceeds the total amount of nitrogen fixed
in the biomass (Beck et al., 1991). According to Van
Kessel and Hartley (2000), a positive increment in
soil nitrogen from fixation is only achieved when
nitrogen fixation is relatively high and/or the NHI is
relatively low. Low NHI on the other hand implies
17
low grain yield or quality. The percentage of nitrogen
derived from the atmosphere (%Ndfa) by grass pea,
butter bean and common bean was higher than the
corresponding NHIs (Mwangi, 2011) suggesting that
they are likely to contribute to the soil nitrogen pool.
Table 3. Soil mineral nitrogen content before and
after planting butter bean, grass pea, common bean
and chickpea in soil collected from Matanya (Laikipia
county, Kenya) and percent change in soil nitrogen.
Sampling period
Soil mineral N
(mg/kg)
% change
in soil N
Before planting
0.97c
After grass pea
1.28a
31.6a
After butter bean
1.29a
33.4a
After common bean
1.23ab
27.1a
After chickpea
1.04bc
7.1b
Mean
1.16
24.8
LSD (p=0.05)
0.21
10.0
CV (%)
9.63
20.8
* significant at p=0.05
Fig. 1. Linear regression curve describing the
relationship between amounts of biologically fixed N
and above ground biomass yield of butter bean, grass
pea, common bean and chickpea planted in a green
house at the national agricultural research
laboratories (Kabete) with soils collected from
Matanya.
Legumes with high amounts of nitrogen fixed also
had high biomass yield. The correlation coefficient
(R
2
) between amounts of nitrogen fixed and legume
biomass yield was 0.93. This agrees closely with
findings of Kumar and Goh (2000) who reported
strong correlations between the amounts of fixed
nitrogen for both legume dry matter yield (R2=0.96)
and nitrogen accumulation. Giller (2001) had also
reported that larger amounts of nitrogen fixed in
broad bean (Vicia faba) resulted from better growth
and high biomass accumulation. The positive
correlation between dry matter and amounts of N
fixed indicates that dry matter accumulation of N
fixing legumes may be a good indicator of the amount
of atmospheric N fixed and may be used as a selection
criterion.
Conclusion
Butter bean (variety Ex-kasuku) and grass pea
(Selection 1325) have the potential to contribute
positively to soil N in cropping systems of the cold
semi-arid region through biological N fixation.
Acknowledgements
The authors gratefully acknowledge the financial
assistance received from Kenya Agricultural
Productivity Project and thank the Director, Kenya
Agricultural Research Institute, and staff at the
National Agricultural Research Laboratories where
laboratory analyses were conducted.
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All of the elements needed to significantly enhance N 2 fixation in grain legumes by plant breeding are currently available, but attention to this problem has been limited. This paper considers genetic variation in traits associated with nodulation and N 2 fixation and how they might be utilized. It also considers the role of rhizobia in an effective grain-legume breeding program.
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A field experiment based on the concept of organic nutrient management (ONM) was conducted in Njoro, Kenya to test the effect of improved legume fallows; crotalaria (CR), lablab (LB), garden pea (GP) and natural fallow (NF, as control) on available soil N and P, and maize performance. The experimental layout was a split plot in a randomized complete block design. The main plots were two cropping systems involving the improved legume fallows and NF preceding sole maize and maize bean (M/B) intercrop. The sub-plots were two residue management types; residue incorporation and residue removal with farm yard manure (FYM) incorporated in its place. Incorporation of LB, CR and GP residues resulted in higher concentrations of N and P in soil than NF residue and FYM incorporation in both cropping systems. Under sole maize, grain yield following LB was significantly higher (51, 28.2 and 52%) than after CR, GP and NF, respectively. In the M/B intercrop, maize grain yield following LB was significantly higher (38.5 and 28.5%) than after GP and NF with no significant differences in yields following CR and LB. Maize dry matter (DM) yields followed a similar trend. Overall, maize grain and DM yields were higher in sole maize cropping system than in M/B intercrop with an additional 0.5 - 0.6 kg ha -1 of bean grain yield obtained in the latter cropping system. The improved fallow legumes, with LB being superior, enhanced soil productivity and consequently higher yields of the succeeding crop. The ONM strategy tested is thus a feasible technology that could easily fit into the circumstances of the resource poor farmers within the region.
Article
Previously published data were used to examine the N economy of pulse crops typically grown on the Northern Great Plains with the goal of assessing the potential contribution of field pea (Pisum sativum L.), lentil (Lens culinaris Medik.), chickpea (Cicer arietinum L.), common bean (Phaseolus vulgaris L.), and faba bean (Vicia faba L.) to soil N accretion. Incremental changes in soil N associated with the pulse crops (i.e., the nitrogen increment, Ninc), were strongly correlated to N2 fixation and were highly variable. Data suggest that crops that can achieve relatively high levels of N2 fixation, such as faba bean, field pea, and lentil are more likely to contribute positively to the overall N economy, particularly when a cropping system is evaluated over a long term. In contrast, pulse crops that typically achieve only modest levels of N2 fixation such as desi and kabuli chickpea and common bean are more likely to be either N neutral or contribute to a soil N deficit. Be- cause of extreme variability in levels of N2 fixation achieved, pre- sumably reflecting variability in soil productivity as well as variations in local climate and weather, the Ninc of pulse crops likewise is highly variable. Thus, the N contribution to a subsequent crop is difficult to predict with any certainty, particularly on a yearly or short-term basis.
Article
The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects, but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow. The plots were split into four N fertilizer rates (0, 30, 60 and 90kgNha−1) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer rate. The legume genotypes fixed between 14 and 51kgNha−1 of their total N and had an estimated net N balance ranging from −29.8 to 9.5kgNha−1. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere. The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279kgha−1 while rotation effects ranged between 193 and 513kgha−1. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize, respectively.
Article
Biological nitrogen (N2) fixation is an important aspect of sustainable and environmentally friendly food production and long-term crop productivity. The amount of N2 fixed is primarily controlled by four principal factors: (1) the effectiveness of the rhizobia–host plant symbiosis, (2) the strength of the sink, i.e., the ability of the host plant to accumulate N, (3) the amount of available soil N and (4) environmental constraints to N2 fixation. Much of the N fixed by grain legumes is removed at harvest, the remainder becomes available to subsequent crops following mineralization, may be incorporated into the soil organic matter, or as with fertilizer N, may be lost from the cropping system.This paper reviews some of the agronomic management practices that affect N2 fixation by grain legumes, asking whether grain legumes can provide an overall net N benefit to the soil when grown in rotation with other crops. A survey of long-term trends in N2 fixation by selected grain legumes is included, and some possible explanations for the observed stagnation in efforts to increase N2 fixation under field conditions are presented.
Article
The N accumulation, biological N2 fixation and simple N balance of white clover and field pea grown for seed were determined in field experiments. Both crops accumulated similar amounts of dry matter but pea accumulated more N (427 kg N ha−1) than white clover (387 kg N ha−1). However, white clover fixed 327 kg N ha−1, which was significantly higher than that (286 kg N ha−1) fixed by pea. At final harvest, the per cent N2 derived from the air (%Ndfa) was also significantly higher for white clover (90%) than pea (69%). Amounts of N2 fixed were strongly correlated with dry matter yield in both crops. There was no significant difference in amount of N2 fixed or %Ndfa when N2 fixation was estimated based on 15N enrichment of individual plant component or the whole plant. The N harvest index for both crops (4–28%) was considerable lower than %Ndfa (69–90%), and hence the overall simplified N balances for these crops were positive. The net N gain due to N2 fixation was high (171–313 kg N ha−1) and may play an important role in the N benefits to subsequent crops and/or contribute to increased soil N fertility.
Article
Host legumes can enrich their immediate soil environment with rhizobia through rhizosphere effects. The extent to which this enrichment occurs, the specificity of the process and its interaction with soil management factors remain poorly described. In a series of field trials, we measured changes in the size of indigenous populations of Bradyrhizobium in response to cropping of host and non-host legumes under two N fertilizer regimes. Uninoculated cowpea (Vigna unguiculata) and soybean (Glycine max) were grown with or without applied urea (900 kg N ha−1) at three field sites on the island of Maui, HI, U.S.A., not previously cropped with legumes. Using the most-probable-number plant infection method and Siratro (Macroptilium atropurpureum) as the host, the population density of Bradyrhizobium in the bulk soil at each site was measured at planting and at grain maturity and compared to the population density in adjacent fallow soil. When the size of the initial indigenous population was low (18 and 580 cells g−1 soil), significant increases in the population density compared to fallow soil were observed only in soils cropped with cowpea receiving no applied urea. When the size of the initial indigenous bradyrhizobial population was high (5.8 × 104 cells g−1 soil), no significant increase in the population density was observed. These results suggested that enrichment of soil bradyrhizobial populations was host-specific, that symbiotic legumes can enrich their soil environment with microsymbionts up to a threshold level and that such enrichment can be curtailed by soil management practices that suppress nodulation.