The Journal of Research ANGRAU

PRASAD and PRASADINI
of bulk density with these two parameters is an oft -
cited phenomenon (Tripathi et al., 2003). Chawla
and Chhabra (1991) also reported that the continuous
application of N fertilizer had no significant influence
on this soil physical parameter. However, the present
study confirmed that the co application of organic
source of nutrients by partly replacing the chemical
fertilizers had a subtle advantage to improve the soil
physical properties. The substitution of 50 % N
fertilizer through FYM, paddy straw or glyricidia in
kharif and the application of recommended dose of
fertilizers in rabi or the substitution of 25 % N fertilizer
with any one of the three organic sources in kharif
and the application of 75 % recommended dose of
fertilizers in the rabi season significantly reduced the
bulk density at transplanting, panicle initiation and
harvesting stage of rice continuously during the four
seasons in the biologically active rooting depth of 0-
15 cm. This reduction in bulk density could probably
be assigned to the reason that the addition of organic
matter increased the volume of the soil per unit
weight. Such benefit of reduction in bulk density of
the soil through the incorporation of organic matter
has been well documented by Vasanthi and
Kumarswamy (1999).
Porosity
The soil was more porous at 0-15 cm soil
depth in all the treatments at transplanting than at
panicle initiation stage both in kharif and rabi seasons
(Table 3). It reduced further at harvest. The porosity
was 42.64 and 41.89 % at transplanting in kharif 2005
and 2006, respectively by growing rice without the
application of manures or fertilizers. The
corresponding values were 42.26 and 41.89 % in rabi
season of 2005 and 2006 respectively. The
continuous application of recommended dose of
fertilizers to rice-rice cropping system had no
significant influence and substitution of 50 % N
through the organics i.e. FYM, paddy straw and
glyricidia in kharif season and the application of
recommended dose of NPK through fertilizers in rabi
season significantly increased the porosity of the soil
during both the seasons. The application of 25 % N
through the organics in the kharif season and 75 %
recommended NPK through fertilizers in the rabi
season also made the soil more porous than the
unfertilised soil.
The porosity was significantly more than in
unfertilized soils due to the carry over effect of
integrated nutrient management treatments. The
trends were persistent at transplanting, panicle
initiation and harvest. The porosity was relatively low
in the lower layer of 15-30 cm soil depth (Table 4).
The porosity increased significantly at transplanting
by the substitution of 50 % recommended level of N
with FYM compared to continuous fertilizer
application at recommended level in the kharif and
rabi season during both the years. This improvement
also persisted at panicle initiation and harvesting
stage in kharif and rabi seasons during the second
year. The trends with the other sources of organic
nutrients substituted with 25 or 50 % of the
recommended level of N were highly irregular.
The porosity of the fertilized soil was similar
to the unfertilized soil. But, a magnificent
improvement in the volume fraction of pores was
evident due to the integrated nutrient management
of rice in kharif followed by fertilizer application in
rabi season during the two year rice-rice cropping
sequence. This trend was obviously due to an
increase in the volume of pore space because of the
addition of organic matter to the total volume of the
soil. But, Katele et al., (1992) observed that the
addition of FYM in an alfisol did not bring a significant
change in this parameter. Bhagat et al. (2003) and
Tripathi et al (2003) also observed that the
incorporation of Lantana camera into the soil reduced
the bulk density and increased the porosity which in
turn improved the retention of water.
Infiltration
There was a distinct response of significant
improvement in infiltration of water at transplanting
due to substitution of 25 or 50 % recommended level
of N with FYM compared to the practice of
recommended level of fertilizer application both in
kharif and rabi season during the two years (Table
5). The substitution of 25 % recommended level of N
with glyricidia also established similar trend. The
response due to the integration of organic nutrients
through paddy straw was irregular. The differences
in infiltration due to fertilizer application and the
integration of organic nutrients were not apparent
during the panicle initiation and harvesting stage of
the crop in either of the two years. Among the organic
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