Exploitation of Hybrid Vigour in Rice Hybrid (Oryza sativa L.) Through Green Manure and Leaf Colour Chart (LCC) Based N Application
Field experiments were conducted during Kharif 2000
and 2001 in the wetland research farm of Tamil Nadu Agricultural University,
Coimbatore to study the effects of green manuring and fertilizer N application
based on LCC grades on the yield enhancement, nutrient uptake and economics
of hybrid rice. Treatments consisted of two hybrids in the main plot and
seven levels of N management practices during Kharif 2000 and eight sub-plot
treatments during Kharif 2001. Among the hybrids, PA6201 registered significantly
higher grain yield of 7363 and 7555 kg ha-1 during Kharif 2000
and 2001 respectively with a yield advantage of 9.5% over CoRH2 in both
the seasons. The N, P and K uptake at different growth stages revealed
that rice hybrid PA 6201 was superior than CoRH2 in both the seasons.
Application of green manure @ 6.25 t ha-1 in combination with
N application based on LCC critical value 5 recorded significantly higher
grain yield compared to other treatments in both the seasons. The N, P
and K uptake in green manure @ 6.25 t ha-1 combined with LCC
critical value 5 based N application (N4) was significant at
all the stages, however it was comparable with 200 kg N ha-1
alone (N1) except at tillering stage. In both the years PA6201
hybrid recorded high net returns of 15.05 and 14.60% over CoRH2. Application
of green manure @ 6.25 t ha-1 combined with LCC critical value
5 based N application (N4) recorded higher net returns and
B:C ratio during both the years and it was followed by application of
200 kg N ha-1 alone (N1). Therefore, the rice hybrid
PA6201 with application of green manure 6.25 t ha-1 combined
with LCC critical value 5 based N applications significantly increased
grain yield, nutrient uptake and in turn resulted in higher net return
and B:C ratio.
In view of plateauing trend in yield potential of high yielding varieties
and decreasing natural resource base, hybrid rice technology with a yield
superiority of 15-20% is a viable avocation (Hari et al., 2000).
In hybrid rice cultivation, developing a package of optimum nitrogen management
practices is vital to explore the full hybrid potential. Nitrogen requirement
of hybrid seems to be on the higher magnitude than that of conventional
inbred varieties. The normal practice of timing of N application on specified
growth stages, at times, fails to result in a better match between N supply
from applied fertilizer and crop demand mainly because of variation in
crop N requirement and soil N supply. Therefore, a more reliable method
is needed for better N management. One of the recently introduced N management
approach was estimating the leaf N concentration by the measurement of
leaf greenness. Among the different tools available to measure the leaf
greenness, the non-destructive measurement of leaf green colour intensity
using Leaf Green Colour Charts (LCC) are gaining importance. Nitrogen
management based on LCC cv.4 helped to avoid excess application of N to
rice and reduces N requirement from 12.5 to 25% without causing yield
reduction (Bajpai et al., 2002). Saravanan (2003) registered highest
grain and straw yield of ADT 43 with N applied at LCC cv.3 for inbred
rice varieties. But standardization of leaf colour chart values for Nitrogen
management especially for hybrids has so far not been accomplished. Green
manuring is an inexpensive, eco-friendly alternative to mounting prices
of fertilizer nitrogen and has become an effective technology in economizing
the agricultural production system, ensuring productive capacity of soil
without causing environmental problem (Bana and Pant, 2000). The insight
knowledge about the Integrated Management Practices involving green manure
and N application based on LCC are scanty and hence present study was
made to evolve leaf colour chart values for optimum N application under
green manure supply to exploit the dual advantage of higher grain yield
of hybrids and soil fertility enhancement in India.
MATERIALS AND METHODS
Field experiments were conducted during Kharif (June-September) 2000
and 2001 in wetland research farm of Tamil Nadu Agricultural University,
Coimbatore to study the effect of green manuring and fertilizer N application
and management through LCC grades on rice hybrids. The soil of the experimental
field was moderately drained, deep clay loam, classified taxonomically
as Typic haplustalf having organic carbon 0.64% with pH 7.3, low
in available soil N 244 kg ha-1, medium in available soil P
17.2 kg ha-1 and high in available soil K 505 kg ha-1,
respectively. The experiment was laid out in split plot design with three
replications. The main plot treatments consisted of two hybrids PA6201,
CoRH2 and the sub-plots were allotted with seven levels of N management
practices during Kharif 2000.The rice hybrid PA6201 was released in 2000
by Central Variety Release Committee (CVRC). It is a medium duration (125-130
days) semi dwarf, erect type having long panicle with long slender grain.
The rice hybrid CoRH2 released in 1998 by Paddy Breeding Station, Tamil
Nadu Agricultural University, Coimbatore is also a medium duration (125
days) semi-dwarf type having compact panicle with medium grain type.
The details of the treatments and notations for Kharif 2000 used were:
||Main plot: Hybrid rice
||Sub-Plot: Nitrogen Management
||N1-Basal + 3 splits top dressing of recommended dose
||N2-Green manure 6.25 t ha-1 + N application
as per LCC cv. 3
||N3- Green manure 6.25 t ha-1 + N application
as per LCC cv. 4
||N4- Green manure 6.25 t ha-1 + N application
as per LCC cv. 5
||N5-20 Kg N ha-1 as basal + N as per LCC cv
||N6-20 Kg N ha-1 as basal + N as per LCC cv.
||N7-20 Kg N ha-1 as basal + N as per LCC cv.
During Kharif 2001 one more sub-plot treatment was included with the
treatments imposed during Kharif 2000 i.e., N8 which consisted
of Green manure 6.25 t ha-1 + 3 split top dressing of recommended
dose and it is the existing recommended practice under integrated nitrogen
management approach. An absolute control was maintained separately in
the experimental field to find out the efficiency of applied nitrogen.
Sesbania aculeata was raised in a separate field with a seed rate
of 40 kg ha-1. At the time of incorporation, the age of green
manure was 40 days and 45 days during Kharif 2000 and 2001 respectively.
Above ground biomass was harvested, weighed and applied to the respective
plots as per treatment schedule. The green manure was spread uniformly
and incorporated one week before transplanting. All the recommended agronomic
practices and need based plant protection measures were carried out as
per the crop production guide of Tamil Nadu Agricultural University (TNAU,
2000). The fertilizer nitrogen was applied to the rice crop as per the
treatments. In LCC based N management treatments, the LCC values were
recorded as per the standard procedure (IRRI, 1996) at weekly intervals
starting from 14 DAT to flowering. Whenever the LCC values were found
to be below the fixed critical level, recommended quantity of fertilizer
N was applied (Table 1 and 2). The
amount of N to be applied at different growth stages was as per the schedule
given below (IRR1, 1996).
|| Leaf colour chart based N application at weekly intervals-Kharif
||Leaf colour chart based N application at weekly intervals-Kharif
All the treatments including control received a uniform dose of 50 kg
P2O5 and 50 kg K2O ha-1. The
entire dose of P was applied as basal before transplanting. Potassium
was applied in three equal splits viz., 50% as basal and 25% each at active
tillering and panicle initiation stages. Zinc sulphate @ 25 kg ha-1
was applied to the crop during both the seasons. The moisture content
of the grain was recorded by using moisture meter and adjusted to 14%
moisture. Plant samples were collected at active tillering, panicle initiation,
flowering and harvest stages, finely ground in willey ground mill and
uptake of nutrients at different stage of sampling was analysed. The nutrient
contents of samples was multiplied with the respective dry matter to calculate
the nutrient uptake and expressed as kg ha-1. Gross and net
returns were computed by considering the prevailed market price of inputs
RESULTS AND DISCUSSION
Grain yield: The experimental results revealed that rice hybrid
PA6201 has recorded significantly higher grain yield of 7363 and 7555
kg ha-1 during Kharif 2000 and 2001, respectively. The other
hybrid rice CoRH2 has produced considerably lower yield of 6665 and 6845
kg ha-1. The yield advantage in PA6201 was accounted to around
9.5% over CoRH2 in both the years. Application of green manure @ 6.25
t ha-1 in combination with N application based on LCC critical
value 5(N4) recorded significantly higher grain yield of 8036
and 8239 kg ha-1 in 2000 and 2001, respectively. The straw
yield exhibited the same trend with hybrids whereas N management practices,
of 200 kg N ha-1 application alone produced significantly higher
straw yield over green manure @ 6.25 t ha-1 combined with LCC
critical value 5 based N application (N4) in 2000 whereas it
was comparable with application of green manure @ 6.25 t ha-1
with 150 kg Nha-1 in 2001, respectively (Table
3). The strategy of applying green manure @ 6.25 t ha-1
combined with LCC critical value 5 based N application (150 kg N ha-1)
in seven splits(N4) matched the crop demand at different physiological
stages and reduced the losses through de-nitrification, volatilization
and resulted in the highest grain yield. The increased availability of
nutrient at distinct physiological phases would have supported for better
assimilation of photosynthates towards grain and also due to the favourable
effect of accelerating the yield characters. Similar findings have been
reported by many workers (Vaiyapuri et al., 1998; Stalin et
al., 1999). The significant increase in grain yield due to green manure
application over other sources could be attributed to the enrichment of
soil fertility (Gopalsamy and Vidhyasekaran, 1987) and improved soil physical
property as well as fertility through addition of organic matter. This
in turn might have promoted the yield attributes contributing to the increased
grain yield (Kalpana and Balasubramanian, 2000). The slower and steady
rate of release of nutrients from green manures resulted in nutrient availability
to rice at all the crop stages and thereby favourably influencing the
various yield parameters resulting in higher yield (Budhar, 1994). Though
rice responds to liberal supply of N, it cannot absorb excess quantity
of ammonical N available in soil solution. Excess N application above
the requirement is ultimately lost due to various loss mechanisms. Declining
rate of response with higher level of N application at 200 kg N ha-1
(N1) has been well documented by many workers (Siddeswaran,
1992; Pradeep et al., 1994; Budhar et al., 1994). Application
of higher dose of 200 kg N ha-1 promoted more biomass resulting
in significant increase in straw yield. It may be due to higher number
of tillers and higher level of N uptake at active tillering stage. This
trend of results was also confirmed by Rajarathinam and Balasubramanian
||Effect of hybrids and Nitrogen management strategies
on the grain and straw yield (kg ha-1)
| (ha-1 - per hectare)
Nutrient uptake: One way to achieve better use of the applied
N is to apply the fertilizer in time to meet the demand of rice plant
(De Datta, 1981). Studies on the nitrogen uptake at different growth stages
revealed the rate of nutrient absorption in unit time for the transformation
to different parts of the plant. It was evident from N uptake studies
that the rice hybrid PA6201 was superior than CoRH2 in all the stages
during both the years (Table 4). The N uptake pattern
had showed an uniform trend in all the stages during the Kharif 2000.The
N uptake with application of green manure @ 6.25 t ha-1 combined
with LCC cv.5 based N application (N4) treatment was significantly
higher in all the stages, however it was comparable with 200 kg N ha-1
application alone (N1) all through the growth stages except
active tillering stage. During the crop season of 2001, N4
treatment exhibited significantly higher N uptake and it was on par with
application of green manure @ 6.25 t ha-1 along with 150 kg
N ha-1 (N8) and N1 in all the stages
except active tillering stage. The uptake of both P and K was significantly
higher with PA 6201 than CoRH2 in both the years. With regard to the P
and K uptake as influenced by different N management practices, green
manure @ 6.25 t ha-1 combined with LCC critical value 5 based
N application (N4) produced considerably higher values than
the rest of treatments and it was on par with 200 kg N ha-1
application alone (N1) during Kharif 2000. During the Kharif
2001, though N4 recorded significantly higher P and K uptake
than other treatments it was comparable with (N8) green manure @ 6.25
t ha-1 with 150 kg N ha-1 and 200 kg N ha-1
(N1) alone. Uptake of N associated with the green manuring of Sesbania
aculeata which contains an appreciable quantity of N (2.5-2.6%) favoured
the release of N for growth and uptake of rice. This corroborates the
findings of Somasundaram (1991) who reported that in lowland rice soils,
green manure incorporation undergoes decomposition resulting in the release
of ammonical N into the soil solution, which is readily available to rice
plant. Higher uptake of nutrients by the crop due to organic manure addition
was also reported by Padmavathy (1992).
Higher N uptake of rice in green manuring treatment might be due to better
synchorinisation between green manure N availability and rice N uptake.
This is in line with the results of Clement et al. (1998). Samantary
et al. (1990) observed that N uptake was high between vegetative
and reproductive stages. Studies on N management of hybrid rice at IRRI
also showed a significantly higher response to late season N application
(IRRI, 1993). In addition to the inorganic source of N, the constant supply
of N from green manure mineralization accelerated the uptake of N. The
present finding is supported by Buresh et al. (1993).The results
revealed that economic yield could be better even if the crop was maintained
with a low N status in the early stage of the growth provided a continued
N supply is maintained up to flowering phase. The beneficial effect of
more number of splits, the last one coinciding with flowering on nutrient
uptake has also been suggested by Sanbagavalli et al. (1999). Surekha
et al. (1999) also confirmed higher uptake of nutrient by hybrids
with four splits compared to three splits of N. The increased P availability
due to green manure application might be due to the organic acids produced
during the decomposition of organic material in flooded soils and that
resulted in mineralizing the insoluble iron phosphate into more soluble
phosphorus, which inturn favoured better P uptake (Sreedevi and Thangamuthu,
1991). The increase in K availability and uptake could be also due to
the priming effect of the K besides direct contribution of K by organic
residues (Thomas, 1996).
||Nutrient uptake (kg ha-1) as influenced by
hybrids and nitrogen management strategies
|T-Tillering, PI-Panicle Initiation, F-Flowering, H-Harvest,
ha-1 - per hectare, NS: Not Significant
||Influence of hybrids and nitrogen management strategies
|Data not statistically analyzed (Rs. ha-1
- Rupees per hectare)
Economics: The economics was worked out taking into consideration,
the cost of production for each treatment, the corresponding marketable
yield with prevalent prices per unit output. The mean data of the first
season during 2000 revealed that the treatment H1N4(PA6201
hybrid with application of green manure 6.25 t ha-1 + N as
per LCC cv.5) produced the gross income of Rs. 53,893 ha-1
for a total cost of production of Rs. 17,702 ha-1. This has
resulted in a net income of Rs. 36,171 ha-1 producing a higher
B:C ratio of 3.04 during the Kharif 2000. The treatment H1N4
in both Kharif 2000 and 2001 produced highest benefit per rupee
investment (Table 5). The higher net returns was due
to steady supply of N, which synchronized with the peak period of N requirement
that had produced higher yield. Similar results were obtained by Hiremath
and Patel (1998).
It may be concluded from this experiment that the hybrid PA6201 with
application of green manure @ 6.25 t ha-1 combined with N application
at LCC critical value 5 registered significantly higher grain yield which
resulted in the highest gross return, net income and B:C ratio during
both years of experimentation. Organic manuring coupled with seven split
doses of inorganic N maintaining a LCC value of 5 was highly beneficial
for hybrid rice. Application of N based on LCC value found to be efficient
in economizing N requirement with increased nitrogen use efficiency as
compared to conventional practices under Tamil Nadu condition.
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