Impact of Leguminous Biomulching on Soil Properties, Leaf Yield and Cocoon Productivity of Tropical Tasarculture under Rain-Fed Conditions
The continuous exploitation of tropical tasar food-plant, Terminalia tomentosa (W and A) rose on wastelands under the rain-fed conditions by rearing its economic insect pest; Antheraea mylitta (D) needs soil management for sustainable yields. To asses the feasibility, legumes like Sun hemp (Crotalaria juncea), Daincha (Sesbania aculeata), Green gram (Vigna radiatus) and Black gram (Vigna mungo) were raised during monsoon (June) season in the inter space of T. tomentosa economic plantation for biomulching. The Sun hemp has yielded highest biomass of 39.0 q ha -1, followed by Daincha, Green gram and Black gram with 26.6, 25.3 and 17.7 q ha -1, respectively after 45 to 50 days of sowing, has been mulched for soil fortification. The water holding capacity, electrical conductivity and organic carbon have been improved with reduced pore space and bulk density of the soil and enhanced leaf yield of tasar food-plant after legume biomulching. The superior Effective Rate of Rearing (ERR), higher cocoon and shell weights, better silk ratio and longer silk filament length of tasar silkworm in biomulch treatments have contributed to increase silk yield. Among the biomulches, Sun hemp has shown improved water holding capacity (56.9%) and moisture (68.5 and 37.9%) at 30 and 45 cm depth with electrical conductivity (0.30 mhos cm -1), bulk density (1.12 g cm -3), pore space (50.4%), organic carbon (0.61%) of soil, leaf yield (24.8 MT ha -1) of food plant and ERR (80.1%), cocoon weight (12.25 g), shell weight (1.90 g), silk ratio (14.03%) and silk filament length (724 m) specify its suitability in making tropical tasarculture sustainable under rain-fed conditions.
The naturally grown and agronomically maintained (economic plantation) tropical
tasar food plants, Terminalia tomentosa and Terminalia arjuna
are mostly available in wasteland and degraded soils under the rain-fed conditions
(Suryanarayana et al., 2005). The soil available
under tasar food plants is primarily deficient in organic matter, nitrogen,
phosphorous, potash and micronutrients. The constant exploitation of these food
plants for rearing tasar silkworm, Antheraea mylitta and soil erosion
due to sloppy fields, the land is getting further depleted in nutrients day
by day affecting the leaf and cocoon yields.
However, the maintenance of soil health to retain the leaf productivity and
quality needs an alternative approach to make tropical sericulture sustainable
(Sinha et al., 2000; Reddy
et al., 2001; Shashidhar et al., 2009),
besides controlling the weed growth (Teasdale and Mohler,
2005) and soil erosion (Chaplot et al., 2009).
In dry areas with inadequate precipitation, annual legumes grown for 6-7 weeks
are incorporated before full bloom not to deplete soil moisture reserves for
the subsequent crop (Mohankumar and Sadanandan, 1988).
Current days inadequacy of bulk organic manure availability can be solved
with the leguminous green mulching as they can be grown within short time, even
under low soil moisture and fertility (Leihner et al.,
1996; Tarfia et al., 2006; Malecka
and Blecharczyk, 2008) and several legume crops like Sun hemp, Daincha,
Berseem and even pulses like Black gram, Green gram, Guar, Labia and Moth bean
are recommended for such green manuring (Becker et al.,
1995; Chakravarti et al., 2005; Muhammad
et al., 2007; Sultani et al., 2007;
Rafael et al., 2009). Further, the application
of green manure supplies nutrients easily to the soil and increases its moisture
retention capacity compared to organic manure (Ossom and
Matsenjwa, 2007; Kone et al., 2008; Pervaiz
et al., 2009). The legumes can generate considerable quantity of
organic matter (up to 80.0 q ha-1) possessing about 40 kg of nitrogen
ha-1, of which about 2/3 is being fixed from atmosphere by the bacteria
(Choudhury et al., 1990; Drinkwater
et al., 1998; Duda et al., 2003).
Hence, an attempt has been made to utilize the interspace available in between
the tasar host plant economic plantation for raising legume crops and mulching
their green biomass into the soil and to study its impact on soil properties,
leaf yield of host plant (T. tomentosa) and cocoon productivity of tropical
tasar silkworm (A. mylitta).
MATERIALS AND METHODS
The present investigation was conducted during the rainy seasons (June to September)
of 2003 to 2005 using tasar food plant economic plantation maintained by the
agronomy section of Central Tasar Research and Training Institute, Ranchi, India
to evaluate the potential of various leguminous mulches on soil fertility status,
leaf yield and bioassay test under rain-fed conditions. The experiment was laid
out in a randomized block design with four replications and five treatments
with legumes viz., Green gram (Vigna radiatus), Black gram (Vigna
mungo), Sun hemp (Crotalaria juncea) and Daincha (Sesbania aculeata)
including the control i.e., without legume mulching for comparison. The other
agronomical practices were carried out uniformly for all the treatments. The
legume crops were sown in between the rows of T. tomentosa plantation
during first week of June of the respective year with onset of monsoon rains.
The raised legume inter-crops were allowed to grow till it reaches flowering
stage for optimal generation of green biomass up to 45 to 50 days. The leguminous
green manuring crops were cut to ground level, weighed and were mulched at 60
to 75 cm depth in to the trenches of the field made in between the rows of T.
tomentosa plants. The season was very ideal for mulching with good soil
moisture and continued rains in the area till end of September of every year.
The samples of soil before initiation of the experiment as well as each year
there on during the investigations were taken to analyze its physical and chemical
properties in addition to moisture levels at 30 and 45 cm depth. The observations
on yield of biomass of different legumes upon their harvest during July, leaf
yield of T. tomentosa and bioassay test as rearing performance of tasar
silkworm, A. mylitta (Narain et al., 2004)
for ERR, single cocoon and shell weights, silk ratio and silk filament length
during commercial crop season (September-December) for three years have been
recorded and the data were subjected to statistical analysis.
Biomass of Legumes, Water Holding of Soil and Leaf Yield of Tasar Food-Plant
The data presented in Table 1 indicates the biomass production
of different legumes, the water holding capacity and average soil moisture at
30 and 45 cm depth, leaf yield of tasar food-plant T. tomentosa in control
and different biomulch applications. Among the four legumes studied, the Sun
hemp has recorded highest average production of 39 quintals of biomass per hectare,
while Daincha, Green gram and Black gram have recorded 26.6, 25.3 and 17.7 quintals
of biomass per hectare. The Water Holding Capacity (WHC) and soil moisture percentage
were also recorded maximum in Sun hemp treatment among the biomulch treatments.
The Sun hemp treatment has recorded 56.4% WHC with an increase of 5.2% over
control, while the soil moisture percentage of 68.5 and 37.9 with an increase
of 22.9 and 20.3% at 30 and 45 cm depth, respectively. However, the WHC of Daincha,
Green gram and Black gram treatments was lesser than Sun hemp, though they are
better over control. The soil moisture has shown same trend in respect of Daincha,
Green gram and Black gram treatments with an increase over the control but less
than Sun hemp. The leaf yield of tasar food-plant was 24.8 MTs per hectare in
Sun hemp treatment was highest among all the treatments with an increase of
34.0% over the control. The leaf yield of 23.0, 22.6 and 21.6 MTs was recorded
in Daincha, Black gram and Green gram treatments were better over the control
but lesser than Sun hemp.
Physical and Chemical Properties of Soil on Biomulching
The data presented in Table 2 indicates the soil physical
and chemical characters like pH, Electrical Conductivity (EC), Bulk Density
(BD), Pore Space (PS) and Organic Carbon (OC) in the control and biomulch treatments.
Though, the pH got tilted slightly towards acidic side in biomulch treatments
over the control but was not significant. The electrical conductivity was increased
in all the biomulch treatments with highest of 42.8% in Sun hemp followed by
Daincha and Black gram treatments with 9.5 and 4.8% over the control, while
it remained unchanged in Black gram. The bulk density of the soils was reduced
in the biomulch treatments over the control with highest of 14.5% in Sun hemp
followed by Daincha, Green gram and Black gram respectively over the control.
of biomass production of different legumes and their mulching impact on
moisture content of soil and leaf yield of tasar food-plant, T. tomentosa
are Mean±SE. Values in brackets i.e., + or are the % change
of leguminous biomulching on the properties of soil
are Mean±SE. Values in brackets i.e., + and are the % change
of leguminous biomulching on the cocoon productivity of A. mylitta
are Mean±SE. Values in brackets i.e., + or are the % change
The pore space recorded decrease in all the biomulch treatments with highest
of 5.6% in Sun hemp followed by Black gram, Green gram and Daincha treatments,
respectively over the control. Though, the organic carbon has been increased
in all biomulch treatments over the control, with highest of 27.1% in Sun hemp
followed by Daincha, Black gram and Green gram.
Bio assay Studies Applying Tasar Insect, Antheraea mylitta
The data presented in Table 3 indicates the bioassay
studies of tasar silkworm, A. mylitta like Effective Rate of Rearing
(ERR), single cocoon weight, single shell weight, silk ratio percentage and
silk filament length among different treatments and control. The highest ERR
of 80.1% with an increase of 30.9% over the control was recorded in Sun hemp
treatment, while it was less in other leguminous biomulches. However, the change
in average single cocoon weight was non significant in spite of improvement
in biomulch treatments over the control with highest of 12.25 g weight and increase
of 6.6% in Sun hemp treatment. The increase in average shell weight was significant
with highest of 1.90 g with 32.9% increase over the control in Sun hemp followed
by Daincha, Black gram and Green gram treatments, respectively. The trends of
silk ratio and silk filament length are similar like shell weights with highest
silk ratio of 14.03% and 724 m of silk filament in Sun hemp treatment with an
increase of 31.9 and 31.6%, respectively over the control. Though, the silk
ratio and silk filament length are better in Daincha, Black gram and Green gram
treatments over control, they were inferior to Sun hemp.
The growing and incorporation of legume crops are recommended as green manure
in rain-fed areas to sustain soil moisture reserves for subsequent crops (Becker
et al., 1995; Chakravarti et al., 2005;
Rafael et al., 2009), as they can be grown within
the short time (Tarfia et al., 2006; Malecka
and Blecharczyk, 2008). The tropical tasarculture being the seasonal rearing
of tasar silk insect, the cultural practices of its economic food-plantation
needs to be attended suitably. The time available to grow and mulch legumes
in the inter-space of food-plants is limited and hence the selection of legume
variety play a key role in generating maximum biomass and to enhance the soil
fertility levels optimally. The better biomass production by Sun hemp (39.0
q ha-1), which is about 2 to 3 fold better production than Daincha
(26.6 q ha-1), Green gram (25.3 q ha-1) and Black gram
(17.7 q ha-1) legumes raised parallel under similar conditions suggests
its suitability as biomulch for rain-fed tasar food-plant economic plantation.
The soil is an important resource and habitat for plant growth and it bears
physical, chemical and biological properties influencing the crop productivity,
quality and returns. Further, the soil being a storehouse of water for land
plants, it influences the rate of evaporation, infiltration and drainage of
water, diffusion of gases, conduction of heat and movement of salts and nutrients.
The optimal application of agricultural inputs such as seed, irrigation and
fertilizer over a given field can not yield uniformly and the soil texture,
organic matter, salinity, subsoil characteristics and water holding capacity
are the factors that can cause changes in yield. The growing of leguminous inter-crop
helps to intercept and break the impact of rain drops preventing from surface
sealing which facilitates better water infiltration (Mohankumar
and Sadanandan, 1998) resulting to higher soil moisture content (Duda
et al., 2003; Muhammad et al., 2007).
The physical capacities of soil are influenced by the size, proportion and arrangement
on mineral composition of the soil particles (Salako et
al., 2006). The soil Electrical Conductivity (EC) is a measure of how
easily an electric current flow through the soil and it responds to the amount
of salt in the soil as well as sand, clay, organic matter and water content
(Corwin and Lesch, 2003; Jung et
al., 2005). The improved EC with legume biomulching in general and with
highest of 42.8% in Sun hemp mulching indicate its role in enhancing the soil
fertility with higher organic matter. This confirmed the suitability of Sun
hemp mulching in attaining the optimal growth of tasar food-plant with higher
leaf productivity and quality over other legumes.
The decrease in bulk density of soil is another desirable feature as it is
an indication of greater pore space within the soil mass. The increase in soil
porosity would be advantageous in the sense, that it would permit more of aeration,
percolation and storage capacity of water. The soil bulk density being the ratio
of mass of dry solids to bulk volume of the soil occupied by those dry solids
and it changes for a given soil with structural condition, mineral make up and
the degree of compaction. The bulk density of quartz is around 2.65 g cm¯3
and the soils high in clay matter with organics is below 1 g cm¯3
indicates the correlation of bulk density of soil with its physical condition,
texture and structure (Assouline, 2006). Though, the
bulk density of soil got reduced on biomulching and the least being with Sun
hemp (1.12 g cm-3), which is nearer to clay and far away from quartz
and with significant decrease of 14.5% over the control indicates its advantage
and better impact among the studied leguminous mulches. Similarly, the empty
space between the soil particles occupied by air and water is termed as pore
space, which is more in sandy soils over clayey soils allowing water to percolate
down so rapidly makes crops suffer due to lesser soil moisture. The reduction
of pore space can be maintained by appropriate cultivation and mulching of legume
biomass as organic matter and makes the crop neither suffers from shortage or
excess of water (Seneviratne et al., 2009). The
reduction in soil pore spacing on biomulching and better with Sun hemp mulch
over other legumes is an added advantage to enhance soil properties and to support
the productivity of tasar food-plant by providing required water and essential
soil nutrients for longer duration under rain-fed conditions.
The organic matter accumulation in the soil is a result of balance between
the loss by decomposition processes and the gain from synthesis of humus from
crop residues. The soils contain carbon (C) in both organic and inorganic forms
and most soils held C as Organic Carbon (OC) and the term organic carbon refers
to the C occurring in the soil in Soil Organic Matter (SOM). The term soil organic
matter is used to describe the organic constituents available in the soil such
as tissues from dead plants and animals, the products produced on their decomposition
and the soil microbial population (Amelung et al.,
2002). The incorporation of Sun hemp biomass has improved the organic carbon
content of soil better over the control, but the improvement was marginal over
Daincha, Green gram and Black gram. Further, the benefit of using a legume as
green manure is to fix atmospheric nitrogen and made it available as biological
source of nitrogen required for the following crop (Chakravarti
et al., 2005; Pervaiz et al., 2009).
The amount of nitrogen fixed by a legume depends on the legume variety, the
effectiveness of the legume-bacteria association in root nodules, soil fertility
and climatic conditions under which the legumes grown and mulched. When, legume
biomass mulching reaches the soil, its immobilization is not fast but the mineralization
gradually increases depending upon temperature, oxygen supply, water content,
hydrogen ion concentration, inorganic nutrients, C/N ratio of the mulched organic
matter. The leguminous plant residues which have high nitrogen encourage the
growth of microorganisms by supplying readily available nitrogen and hence accelerate
the decomposition and soil nutrition. The biomulching of legumes in rain-fed
tasar food-plant field can have such impact of enhancing the soil fertility
with better organic constituents and microbial population to augment the leaf
yield and quality of tasar food-plant.
Though, the application of required organic manure play a vital role in conservation
of soil nutrient status, water retention capacity and building up the micro-flora
population, the tentative returns in rain-fed tropical tasarculture can not
afford such practices. The green manuring in mulberry and tasar food-plant has
reported to enhance soil fertility and leaf yield and quality (Sinha
et al., 2000; Reddy et al., 2001;
Shashidhar et al., 2009), while the mulching
of Sun hemp has shown better mulberry leaf yield over Daincha and Cowpea. The
green mulching can conserve the moisture, builds up organic matter and improves
the properties of soil and activity of microbes supporting the mineralization
rate and release of N, P and K in greater proportion (Sultani
et al., 2007). The enhanced soil fertility with better moisture and
organic matter under Sun hemp mulching are the contributory factors as its biomass
production is higher than other legumes. This might be the reason for better
leaf yield of T. tomentosa in Sun hemp mulch treatment over other legumes
suggesting its application suitability for tropical tasar food-plant economic
plantation under rain-fed conditions.
The economics of tropical tasarculture depends on the yields and quality of
cocoons produced by its economic insect pest, A. mylitta which being
grown on its food-plant, T. tomentosa during particular seasons of the
year. For the sustenance of this forest and agro based industry, an optimal
leaf productivity and quality is essential to grow more tasar insect larvae
and harvest more cocoons with better silk yield (Sinha et
al., 2000). The main commercial parameters of tasar silkworm rearing
like Effective Rate of Rearing (ERR), single cocoon and shell weights, silk
ratio and most importantly the silk filament length decides the crop returns
(Reddy et al., 2008). Among these, the ERR play
an important role as it accounts for the number of cocoons harvested irrespective
of the brushed larvae (Sinha et al., 2001). The
ERR is influenced by several other factors as the tropical tasarculture being
an out-door practice and the manipulation of rearing environment is not under
control. However, the quality feed through its food-plant can enhance the ERR
with robust health and growth of tasar silkworm and better crop yields as the
feed has direct impact on cocoon and shell weights, silk ratio and silk filament
length. Even for other reasons, if the harvested cocoons are less in number,
their healthier quantity and quality of silk can compensate the crop economics.
The ERR though was better in all the biomulch treatments, the highest of 80.1%
with an increase of 30.9% over the control has recorded in Sun hemp mulch treatment.
In support of these results, the highest single cocoon and shell weights were
recorded in Sun hemp compared to other legume mulches indicating the influence
of the quantum of mulched biomass on cocoon quality via leaf quality. The other
commercial factors like silk ratio and silk filament length have shown improvement
in biomulch treatments with highest in Sun hemp over other legumes indicating
the direct correlation among the quality of feed and silk yield. The cocoon
quality of tasar insect during commercial crop season (September-December) records
better as the climate being very congenial for silkworm besides the availability
of quality leaf (Reddy et al., 2009). However,
the improved tasar leaf productivity and silk yields upon legume biomulching
over the respective controls even under rain-fed conditions indicates the application
scope of green manure for tropical tasarculture. The advantage of having better
ERR along with silk quantity and filament length in the Sun hemp treatment among
the studied legumes indicates its better suitability for the better sustenance
of tropical tasarculture under rain-fed conditions.
The incorporation of leguminous biomulches not only conserves the soil moisture and fertility status, but also controls the weed growth and soil erosion under rain-fed conditions. Among the studied legumes, Sun hemp has shown highest biomass production and its mulching has improved soil properties of tasar field, leaf yield of tasar food-plant, T. tomentosa and cocoon and silk productivity of tasar silk insect, A. mylitta to make tasarculture more sustainable.
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