SOIL NUTRIENT ASSESSMENT AND GHG EMISSIONS OF PUDDLE RICE SOILS UNDER INTEGRATED NUTRIENT MANAGEMENT PRACTICES
Loading...
Date
2020-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AAU, Jorhat
Abstract
The present work was carried out during 2016-2018which forms a part of
the long-term Permanent Plot Experiment on Integrated Nutrient Supply System in Cereal
Based Cropping Sequence laid out during 1987-1988 under All India Coordinated
Research Project on Integrated Farming System at Assam Agricultural University (AAU),
Jorhat. The experiment was laid out in a randomized block design at Instructional-cum-
Research Farm, Assam Agricultural University, Jorhat replicating 3 times with 8 treatment
combinations viz.,T
1
: no fertilizer, no organic manure (control), T
2
: 100% RDF (chemical),
T
3
: 50% RDF (chemical) + FYM @ 2.5 t/ha for winter rice and 100% RDF (chemical) for
autumn rice, T4
: 75% RDF (chemical) + FYM @ 1.25 t/ha for winter rice and 75% RDF
(chemical) for autumn rice, T
5
: 50% RDF (chemical) + rice stubble @3.0 t/ha for winter
rice and 100% RDF (chemical) for autumn rice, T
6
: 75% RDF (chemical) + rice stubble
@1.5 t/ha for winter rice and 75% RDF (chemical) for autumn rice, T
7
: 50% RDF
(chemical) + Azolla @ 0.5 t/ha for winter rice and 100% RDF (chemical) for autumn rice,
T
8
:75% RDF (chemical) + Azolla @ 0.25 t/ha for winter rice and 75% RDF (chemical) for
autumn rice.
Results revealed that the application of 50% RDF (chemical) + Azolla @
0.5 t ha-1 in case of winter rice and 100% RDF (chemical) in case of autumn rice (i.e. T7)
showed the highest NH4-N, NO3-N and available N content in soil followed by the
application of 50% RDF (chemical) + FYM @ 2.5 t ha-1 in winter rice and 100% RDF
(chemical) in autumn rice (i.e. T3) in case of the rice-rice sequence after 32 cycles of the
cropping. On the other hand, different fractions of P (viz., available P, Occluded P, Saloid
P, Ca-bonded P and total P) and K (viz., water soluble K, available K, exchangeable K,
non-exchangeable K, lattice K and total K) were found maximum in case of T3 followed by
T5.
Different fractions of C in rice soil were increased and varied significantly
due to INM practices over unfertilized control (T1). The total organic carbon (TOC), total
inorganic carbon (TIC) and total C was found to be highest in case of T3; whereas, the
highest content of Walkley & Black C, less labile C and non-labile C in soils were
recorded in case of T5. Yet again, T7 [50% RDF (chemical) + Azolla @0.5 t ha-1 in winter
rice and 100% RDF (chemical) in autumn rice] was registered with the maximum content
of water soluble C, microbial biomass C, very labile C and labile C in the soils underricerice
system. In this study, all the fractions of NPK and C were found to be lowest in T1
(unfertilized control) treatment. The sensitivity index revealed that the microbial biomass
C and water soluble C fractions were the most sensitive ones for different nutrient
management practices as compared to other C fractions under study; whereas, the lowest
sensitive fractions included non-labile C, less labile C, total inorganic C, total organic C
andtotal C.
Data on SOC stock due to INM practices varied significantly from 39.11
Mg ha-1 under T1 (unfertilized control) to 67.14 Mg ha-1 under T3(receiving FYM @2.5 t
ha-1 + chemical fertilizers).The soil C sequestration ranged between (-)2.77 Mg ha-1 under
T1 and 24.07 Mg ha-1 under T3. Over the control treatment (T1), 41.81 to 71.67% build up
of C in the soils were recorded due to various INM treatments after 32 years of rice-rice
cropping sequence.
In this study, the highest bacterial population was recorded in case of
T7(receiving Azolla @0.5 t ha-1 + chemical fertilizers); whereas, fungal population was
found maximum in case of T3 (receiving FYM @2.5 t ha-1 + chemical fertilizers). Various
6
soil enzymes viz. dehydrogenase (DHD), phosphomonoeaterase (PMEase), fluorescein
diacetate (FDA) and urease, involved in energy flow and nutrient cycling showed
significantly higher activities under INM treatments. Significantly highest activity of DHD
and urease was found in T7, while PMEase and FDA hydrolysis activities were found to be
maximum in T3.There was a decrease in all the enzymatic activities over initial in the
unfertilized control treatment (T1) after 32 years of rice-rice cropping.
The pattern of CO2, CH4 and N2O emissions under rice-rice cropping
system varied significantly with the stages of rice growth as well as by the different INM
treatments under study. The CO2 and CH4 emissions peaked at 60 days after transplanting
(DAT) of winter rice (cv. Ranjit) and 45 DAT of autumn rice (cv. Disang). On the other
hand, N2O emission peaked first at 30 DAT and secondly at 60 DAT of winter rice (cv.
Ranjit) in case of all the treatments except unfertilized control. However, only one N2O
emission peak was observed at 45 DAT in case of autumn rice (cv. Disang) under study.
The highest emissions of CO2 and CH4 during winter crop (cv. Ranjit) were observed in
case of T5 receiving rice stubbles @3.0 t ha-1 + chemical fertilizers. In contrast, N2O
emission during winter crop cv. Ranjit initially (up to 45 DAT) was found to be highest in
case of the T2 (100% RDF, chemical); and afterwards, highest N2O emission was observed
in case of T7 receiving Azolla @ 0.5 t ha-1 + chemical fertilizers. In case of autumn rice
(cv. Disang), the maximum emissions of CO2, CH4 and N2O were recorded in T5(receiving
rice stubbles@3.0 t ha-1 + chemical fertilizers). The lowest CO2, CH4 and N2O emissions
were recorded in T1. It was evident in this study that the GHG emissions for the control
(T1) and for Azolla cover + chemical fertilizer treatments (i.e. T7 and T8) were relatively
low and similar during the initial stages of winter rice cv. Ranjit (up to 60 DAT) and
autumn rice cv. Disang (up to 30 DAT). Among all the organic sources, supplementation
of Azolla along chemical fertilizers resulted maximum reductionin GHG emissions from
rice-rice system over FYM and ricestubbles.
Pearson correlation matrix between the GHGs indicated that the emission of
CO2 had a positive and significant correlation with CH4 (r=0.874**)and N2O
(r=0.748*)emissions from the rice-rice cropping system. However, the correlation between
the CH4 and N2O emission was positive and non-significant (r=0.623NS)in this study.
Significant and positive correlation of CO2 and CH4 emissions from rice-rice cropping
system were recorded with different fractions of C viz., WSC, WBC, MBC, VLC, LLC,
LC, NLC, TOC and TC. The correlations of N2O emission with NH4-N, NO3-N and
available N were found to be significant and positive; whereas, it was positive but nonsignificant
with total N in soil. Likewise, microbial activities, enzymatic activities in soil
and yield and yield attributing characteristic of rice crop were positively correlated with the
emissions of CO2, CH4 and N2O from the rice-rice system of cropping. Yet again, in this
study, GHGs were found to have not significant correlation with the plant height of rice
crop.
Overall, the findings of the present study lead to the conclusion that
application of 50% RDF (chemical) + rice stubbles @ 3.0 t ha-1 in winter rice (cv. Ranjit)
followed by 100% RDF (chemical) in autumn rice (cv. Disang) i.e. T5 could be considered
as the best nutrient management practice for the rice-rice sequence in terms of highest yield
(7.27 Mg ha-1), gross return (67.72 ×103 Rs. ha-1) andnet return(39.79 ×103 Rs. ha-1)with a
B:C ratio of 2.42 in one way, enhancing the soil health under long run condition, in other.
However, so far as the issue of GHG emission and global warming is concerned, application
of 50% RDF (chemical) + FYM @ 2.5 t ha-1 in winter rice and 100% RDF (chemical) in
autumn rice (2nd best treatment in terms of soil properties and yield with the B:C ratio 2.41)
may be considered as better option for rice-rice cropping system under the prevailing
climatic condition of Assam.