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Long-term experiments provide the best possible platform for studying the
changes in soil properties and processes, identifying emerging trends in nutrient
imbalances and deficiencies and help to formulate future strategies for maintaining soil
health and quality.
The present study entitled “Soil quality index and nutrient balance in rice-rice
cropping system under Long Term Fertilizer Experiment” was undertaken at RARS,
Pattambi and College of Agriculture, Vellanikkara. The objectives were set out to
estimate soil quality index and NPK balance in rice-rice cropping system as affected by
nutrient management practices under Long Term Fertilizer Experiment.
The Long Term Fertilizer Experiment (LTFE) in rice-rice cropping system
maintained (since 1997) at RARS Pattambi has been laid out in RBD consists of 12
treatments viz.,T1 : 50 per cent NPK, T2 : 100 per cent NPK, T3 : 150 per cent NPK, T4 :
100 per cent NPK + 600 kg ha -1 CaCO3 , T5 : 100 per cent NPK, T6 : 100 per cent NP, T7
: 100 per cent N, T8 : 100 per cent NPK + Farm Yard Manure (FYM) @ 5 t ha -1
, T9 : 50
per cent NPK + FYM @ 5 t ha -1
, T10 : 100 per cent NPK + in situ growing of Sesbania
aculeata, T11 : 50 per cent NPK + in situ growing of Sesbania aculeata and T12 :
Absolute control (No fertilizer or manures). The soil samples from 0-15 cm depth were
collected from the different treatments of LTFE after the harvest of Virippu crop, 2020
and were analysed for various physical, chemical and biological properties. Principal
Component Analysis (PCA) was performed to arrive at the Minimum Data Set (MDS)
and Soil Quality Index (SQI) was formulated for different nutrient management practices.
Integrated nutrient management with FYM and in situ green manuring with
daincha recorded higher grain and straw yields of rice. The increase in fertilizer load into
the soil resulted in increase in yields while the omission of primary nutrients resulted as
decline in yields. Integrated Nutrient Management practice (INM) of application of FYM
along with 100 percent NPK had lower bulk density (1.17 Mg m-3
) and higher water
holding capacity (43.65 %), higher levels of available nutrients and enzyme activities in
the soil. However, dehydrogenase activity did not follow the same trend as that of
microbial biomass carbon in treatments wherein fertilizers alone were applied indicating
the chances of shift in the microbial populations as a result of the long term application of
nutrient management practices.
Principal Component Analysis (PCA) was performed for 28 soil attributes to
develop the MDS and SQI was formulated using non linear scoring method. The MDS
included bulk density, porosity, soil pH, permanganate oxidizable carbon, available N,
total N, available sulphur, microbial biomass carbon, acid phosphatase and aryl sulfatase
activities. The SQI ranged from 1.82 to 3.01. The SQI declined in the order of: T8> T10
>T9> T11> T4> T3> T2= T1> T5> T6 >T7> T12. The highest SQI was observed in T8 where
100 per cent NPK and FYM were applied. When the dosage of fertilizers was increased
from 50% to 100% NPK on integration with FYM, the SQI increased. The soil quality
index of the INM treatments (55.50 to 62.11%) and lime incorporation (52.98%) were
categorized under medium category as per the computed Relative SQI (RSQI) values.
The virippu crop (2020) under LTFE maintained at RARS Pattambi was
monitored and various inputs and outputs regarding primary nutrients were assessed for
balance predictions using NUTMON toolbox. The NUTMON toolbox includes five
inflows, viz., mineral fertilizers (IN1), manure (IN2), atmospheric deposition (IN3),
biological N fixation (IN4), and sedimentation (IN5), and five outflows, viz., harvested
product (OUT1), crop residues (OUT2), leaching (OUT3), gaseous losses (OUT4), and
erosion (OUT5). Nutrient flows like fertilizers, manures, crop residues and harvested
outputs were monitored and measured during the experiment. Other flows like nitrogen
fixation, leaching, and erosion were estimated by means of regression models from the
data related to climate and crop parameters. Available NPK content of soils, rice grain,
straw, stubbles, weeds and all inputs were analysed and stored in background database.
The data were fed into the data processing module of the NUTMON toolbox to arrive at
the partial and total balance of N, P and K in the experimental soil.
The total balance of N, P and K were found to decline in order of:
T3>T7>T8>T6>T5>T2>T4>T10>T9>T1>T11>T12 for N,
T3>T8>T6>T10>T2>T5>T4>T9>T1>T11>T12>T7 for P and
T3>T2>T5>T8>T9>T10>T4>T11>T1>T12>T7>T6 for K
Summarizing the results, integrated nutrient management with FYM and in situ
green manuring with daincha recorded higher yield and available nutrients in the soil.
The incorporation inorganic fertilizers with FYM, daincha and lime maintain the soil
quality index in the long run while, SQI was poor in control, imbalanced nutrition as well
as in treatments where only fertilizers were incorporated. The balance sheet of P
establishes the need for maintenance dose of P fertilizers in rice-rice cropping system.
The negative balance of N and K indicate the need for supplementing the nitrogen pool
and the possibility of mining of K on long term intensive cropping, respectively.
Further study should be focused on monitoring the soil quality index at regular
intervals and analyzing the effect of nutrient management practices on microbial diversity
in rhizosphere and phyllosphere.