ABSTRACT
Soybean is a legume and has a
great potential to fix atmospheric nitrogen and improve soil fertility in
addition to providing edible grains. Nitrogen fixation, however, is constrained
by environmental factors which include soil nutrient inadequacy. A field
experiment was carried out at Nkorang, Nkawie, which fall under the moist
semi-deciduous forest vegetation zone in Ghana, to investigate the effects of
different rates of NPK and poultry manure on growth, N fixation and grain yield
of soybean under zero tillage cultivation.The experimental design used was a 3x3
factorial arranged in a randomized complete block design. The factors studied
were poultry manure rates and NPK rates. NPK rates were 0, 45 and 90 kg/ha and
poultry manure rates were 0, 2, and 4 tons/ha. Each treatment was replicated
four times and there were nine plots per block.The field was slashed and
glyphosate 360 (isopropylamine salt) was applied as a pre-plant herbicide at 2
L per hectare of water two weeks after slashing. Plots were then laid with each
plot measuring 2.5 m x 4 m and planting was done at a spacing of 10cm x 5 cm.
Data taken on plants included plant height, number of leaves, number of
branches, crop growth rate, shoot biomass, leaf area, nodule number, number of
effective nodules, number of pods per plant, number of seeds per pod, hundred
seed weight, grain yield and amount of N fixed.The results of the experiment
showed that application of NPK or poultry manure significantly affected the
growth of soybean. Higher rates of NPK and poultry manure caused significantly
higher growth in some parameters.Generally, yield components were not affected
by NPK or poultry manure rates. This observation was mainly due to low rainfall
at the onset of pod formation. In contrast, poultry manure rate at 2 tons/ha
had a significanteffect (p<0 .05="" a="" and="" apparently="" because="" effectiveness="" fixation.="" further="" generally="" grain="" ha="" in="" increase="" increased="" manure="" n="" name="page8" nodulation="" nodule="" observed="" of="" on="" poultry="" studies="" there="" tons="" treatments.="" were="" yield="">
can be executed to verify the
results, but such must be sited where irrigation can be done when rainfall
fails.
CHAPTER ONE
INTRODUCTION
Soybean [Glycine max (L.)Merrill] is an annual legume that
belongs to the family Leguminosae and subfamily Papilionoidae (Berk, 1992).It
produces pods on an erect stem and has opposite and ovate unifoliate primary
leaves, alternate and trifoliolate secondary leaves and compound leaves with
four or more leaflets occasionally present(SheafferandMoncada, 2012). It is a
self pollinating diploid plant with 40 chromosomes (2n=40 chromosomes)(Chang
andQiu, 2010).
In Ghana, average yield of soybeanis 1.5Mt/ha, however,
achievable grain yield of soybean under rain-fed conditions is estimated at
2.5Mt/ha (40% more than average yield) (MOFA, 2011). According to Mbanya
(2011), low yield of soybean in Ghana can be attributed to low level of
adoption of technology such as soil fertility management strategies that would
improve soybean production.
The poor soil fertility problem is well recognized as the
main obstacle to maximizing crop yield (Hilhorst et al., 2000). Recent research
works have brought to light some approaches to curb the poor soil fertility
challenge which include the supply of organic and/or mineral nutrients to the
soil. Nevertheless, the use of mineral fertilizers by smallholder farmers in
sub-Saharan Africa is not properly adhered to owing to high costs,
unavailability and at times lack of technical knowledge(Bationo et al., 2006).
Adequate sources of organic fertilizers are also difficult to acquire as larger
quantities are required as well as competitive alternative uses of organic
sources; farmers prefer to give stovers to farm animals rather than use them as
farm manure and consequently add nutrients to the soil. Again, organic
fertilizers are also bulky and difficult to transport (Alimi et al., 2006).
The challenges arising out of the use of organic and
inorganic fertilizers have led to exploration of other economical and
environmentally friendly means of supplying nutrients to crops. One of
suchmeans is biological nitrogen fixation. For a very long period, biological
nitrogen fixation (BNF) in legumes has been a key constituent of many cropping
systems throughout the world. Gregory (2006) stated thatglobal nitrogen
fixation in the soil before extensive human activity was
90-140 million ton N ha- 1. Soybean has the capacity to acquire its total
Ndemands from symbiotic nitrogen fixation and leaves excess nitrogen reserves
in the soil for subsequent crops (Salvagiotti et al., 2008). Biological
nitrogen fixation (BNF), therefore is an inexpensive and environmentally
friendly means of improving crop yield, reducing N application and enhancing
the soil quality. BNF consequently reduces the dependence on mineral
fertilizers that could be costly and unavailable to smallholder farmers.
Even though rhizobia seem to be widely distributed in the
soil (Herridge et al., 2002), N fixation is closely linked to the physiological
condition of the host plant. Crop stress factors such as, nutrient deficiency,
insufficientassimilates and crop disease occurrence can impair the growth and
development of the crop, and subsequently, adversely affect the symbiotic
relation of plants and rhizobia. As a result, the rhizobia strain existing in
the soil will not be able to successfully infect plant roots and consequently
aid N fixation to their maximum potential (Zahran, 1999).Eventually, little
biomass is produced and amount of N fixed is reduced. The ability of the plant
to ameliorate the soil, as well as improve yield will consequently be greatly
hampered.
Biological nitrogen fixation (BNF) is largely influenced by
four main factors namely, the effectiveness of the symbiotic relationship
between the host plant and the rhizobia strain, capacity of the plant to store
N, the amount of N in the soil available to crops and environmental limitations
(Van Kessel and Hartley, 2000). Soil as a medium through which crops grow and
develop, therefore, has greater effect on N fixation, growth and yield of
crops. Hence, the control of the soil environment plays a very prominent role
in securing crop productivity. In soil management, recent research has
indicated that supplying starter soil nutrient at early stages of crop
vegetative growth can increase pod yield and crop biomass (Yinbo et al., 1997).
According to Omondi et al. (2014), cultivation of crops under
no tillage system enhances biological nitrogen fixation and when it is
practiced for a long period is able to improve most soil properties and
consequently leads to yield increases. This is because no tillage contributes
to increased soil fertility and soil organic carbon content, improved moisture
conservation and other soil benefits.
It is therefore hypothesized that growing soybean under no
tillage cultivation with the application of minimal NPK or poultry manure can
enhance biological nitrogen fixation and produce yields equivalent to yields
obtained by applying higher amount of mineral or organic fertilizers.
The general objective of the research
was therefore to assess productivity of soybean by enhancing BNF through
inorganic and organic fertilizer applications under no tillage cultivation.
The specific objectives were to:
determine the effects of NPK and poultry manure on growth and
yield of soybean.
determine the effects of NPK and poultry manure on nodulation
and N-fixation.
determine the combined effect of NPK and poultry manure on
growth, N-fixation and yield of soybean.
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