Nutrient and weed management in rice- rice cropping Sequence
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Date
2021
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Abstract
A field experiment entitled “Nutrient and weed management in rice-rice crop sequence” was
conducted in ICR Farm of Assam Agricultural University, Jorhat, with autumn and winter rice
varieties, Luit and Ranjit, grown in sequence for two years, 2018 and 2019. The investigation,
laid out in randomized block design (factorial) with three replications, aimed to study the impact
of nutrient and weed management on growth and yield attributes of rice, weed dynamics and
changes in soil microbiota. The treatment consisted of four Nutrient managements viz. T1-100%
N-P2O5-K2O through inorganic fertilizers (recommended dose of 40-20-20 kg/ha)), T2-75% N
through inorganic + 25% N through FYM (P2O5 & K2O recommended doses), T3-75% N
through inorganic + 25% N through vermicompost (P2O5 & K2O recommended doses) and T4-
75% N through inorganic + 25% N through Crop residues and bio-fertilizer (P2O5 & K2O
recommended doses); three weed management treatments viz: W1-Pyrazosulfuron @ 25g/ha +
2,4-D @ 0.5kg/ha in both autumn and winter rice,W2-Pyrazosulfuron @ 25g/ha + 2,4-D @
0.5kg/ha in autumn rice rotated with Pretilachlor @ 0.75 kg/ha + 2,4-D @ 0.5kg/ha in winter
rice and W3-Pyrazosulfuron @ 25g/ha + 2,4 –D @ 0.5kg/ha in autumn rice and only Pretilachlor
@0.750kg/ha in winter rice; and two controls viz: C0- Absolute control and C1- Farmer’s practice
[(0.750 kg/ha pretilachlor + N-P2O5-K2O (20-10-10 kg/ha)]. Soil of the experiment site was
sandy loam in texture, slightly acidic (pH-5.6) in reaction, medium in organic carbon (0.65%),
available N (222.63 kg/ha), available P2O5 (21.18) and available K2O (127.71 kg/ha).
The results of the two years of experiment indicated that among the nutrient management
treatments, significantly higher growth attributes, yield attributes, N-P2O5-K2O content and NPK
uptake by rice was observed with treatment T3 (75% N through inorganic + 25% N through
vermicompost) and the lowest was observed lowest in treatment T1 (100% N-P-K through
inorganic fertilizers) in both the years of autumn and winter rice. Two years of pooled data
showed that yield was significantly highest in treatment combination of T3W2 (75% N through
inorganic+ 25% N through vermicompost along with Pyrazosulfuron @ 25g/ha + 2, 4-D @
0.5kg/ha in autumn rice rotated with Pretilachlor @ 0.750 kg/ha + 2,4-D @ 0.5kg/ha in winter
rice) in both the years for autumn (3627 kg/ha and 3637.44 kg/ha respectively) and winter rice
(3770.7 kg/ha and 3735.2 kg/ha respectively). Significantly lowest weed fresh weight and dry
weight, weed density, weed frequency, and relative dry weed weights, with respect to grasses,sedges and broad leaved weeds were observed in treatment T4 (75% N through inorganic + 25%
N through crop residues and bio-fertilizer) in both the years of autumn and winter rice. Among
the weed management treatments, W2 (Pyrazosulfuron @ 25g/ha + 2,4-D @ 0.5kg/ha in
autumn rice rotated with Pretilachlor @ 0.75 kg/ha + 2,4-D @ 0.5kg/ha in winter rice) was
observed with the lowest weed fresh weight and dry weight, weed density, weed frequency, and
relative dry weed weights, with respect to grasses, sedges and broad leaved weeds.
The results pertaining to metagenomic study of bacterial and fungal population suggested that
there were considerable changes in the population for both the microbes from 0 DAT to
physiological maturity due to the nutrient and weed management treatments. The observed
changes as indicated by their Operational taxonomic units (OTUs) percentage, Alpha diversity
and Beta diversity indices are also indicative of having their direct or indirect impact on soil
fertility status.
In the present investigation, highest value in terms of agronomic efficiency, nitrogen use
efficiency, energy output, energy productivity ratio, energy efficiency index and was highest in
the treatment combination of T3W2 (75% N through inorganic+ 25% N through vermicompost
along with Pyrazosulfuron @ 25g/ha + 2, 4-D @ 0.5kg/ha in autumn rice rotated with
Pretilachlor @ 0.750 kg/ha + 2,4-D @ 0.5kg/ha in winter rice) in both the years for autumn and
winter rice. Also, the same treatment combination, i.e., T3W2 (75% N through inorganic+ 25% N
through vermicompost along with Pyrazosulfuron @ 25g/ha + 2, 4-D @ 0.5kg/ha in autumn rice
rotated with Pretilachlor @ 0.750 kg/ha + 2,4-D @ 0.5kg/ha in winter rice) showed the highest
net return for autumn rice (Rs.42412.99 and Rs. 40972.99 respectively) as well as winter rice
(Rs. 59864 and Rs. 58833.9 respectively) of both the years. B: C ratio was also observed to be
highest in treatment combination of T3W2 (75% N through inorganic+ 25% N through
vermicompost along with Pyrazosulfuron @ 25g/ha + 2, 4-D @ 0.5kg/ha in autumn rice rotated
with Pretilachlor @ 0.750 kg/ha + 2,4-D @ 0.5kg/ha in winter rice) in both the years of autumn
(3.22 and 3.12 respectively) and winter rice(4.63 and 4.56 respectively).
Thus, from the above observations, it can be incurred that application of 75% N through
inorganic+ 25% N through vermicompost along with Pyrazosulfuron @ 25g/ha + 2, 4-D @
0.5kg/ha rotated with Pretilachlor @ 0.750 kg/ha + 2,4-D @ 0.5kg/ha, can be considered as the
best practice of nutrient and weed management for rice-rice cropping sequence in the prevailing conditions of Assam. It is, however, needed to be practiced in multi- locational trials in order to
obtain a much better understanding, conclusion and feasibility before recommending to the
farmers. Further investigations to study the impact of the inorganic herbicides and nutrients on
the soil microbial population is also required so that they are, accordingly, recommended to the
farmers, with the long term motive of maintaining sustainability of soil in addition to focusing
upon increasing productivity and meeting the population demands.