Rhizosphere priming effects of conventional and non conventional organic manures on c and n dynamics
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Date
2018
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Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani
Abstract
A study entitled “Rhizosphere priming effects of conventional and non
conventional organic manures on C and N dynamics” was conducted from August
2017 to January 2018 at the Department of Soil Science and Agricultural Chemistry,
College of Agriculture, Vellayani. The objective of the study was to compare the
priming effects of conventional and non conventional organic manures on
rhizospheric processes with special reference to C and N dynamics. The investigation
consisted of four parts namely preparation of organic manures, characterization of
organic manures, laboratory incubation study and pot culture experiment to find out
the rhizosphere priming effects on C and N dynamics.
Four different types of organic manures - aerobic compost (AC), microbial
compost (MC), vermicompost (VC), and thermo chemical organic fertilizer (TOF)
which were prepared from identical source of organic waste and the popular
conventional manure Farmyard Manure( FYM) were analysed for their physical,
chemical and nutritional properties. Since TOF is recommended for application after
fortification, the fortified treatment TOF-F was also included. The incubation study
was carried out in laboratory by mixing 2 kg of red soil with 0.02 kg of each AC,
MC, VC, TOF, TOF-F and FYM and keeping for 100 days at field capacity. In order
to study the priming effects, fodder maize – var. African tall were sown in pots by
mixing 5 kg of soil with 0.05 kg of each AC, MC, VC, TOF, TOF-F and FYM and
grown for 90D. A no manure control was also kept under both situations and
sampling of soil and plants were done at 0, 15, 30, 60 and 90 D. The studies on
characterization revealed that all manures had acidic pH range and safe electrical
conductivity (EC) .The highest Total organic carbon (TOC) was recorded by TOF.
Dissolved organic carbon (DOC) was not detected in any manures. Regarding the
nutritional properties TOF-F had the highest content of N, K, Ca, S, Mn, Zn and B
whereas P, Cu and Fe content were the highest in VC.
In the laboratory incubation study, soil pH in all the treatments, irrespective of
the type, recorded a decreasing trend upto 60 days. EC of the soil also increased upto
30 days in case of all treatments and a slight decrease was observed at 90 days. An
increase was recorded in the DOC content until the 30th day in all the treatments. A
general increase in the TOC content was observed on 15 D in all the treatments
except VC and control(C). At the end of experiment the highest TOC was recorded
by TOF-F and TOF. A general decrease in N content was observed in all the
treatments with time and at the end of experiment TOF-F maintained the highest
value but was on par with MC, VC and TOF and significantly different from the rest
of the treatments. The effect of treatments on soil mineralisable nitrogen (Nmin)
remained significant from 0 to 30 D only where the highest value was recorded by
TOF-F at 0 D. A high status of P was observed in all the treatments at all sampling
intervals and the highest P content in the experiment was reported by FYM at 90 D.
The K content in soil decreased in all the treatments with time except FYM where an
increase in status was observed at the end of the experiment. The content of Ca, Mg,
Cu and B in soil remained deficient in the different treatments. Significant difference
could not be observed for Fe content at 30 D and 60 D and for Cl at any of the stages
of sampling. Analysis of microbial population revealed that bacterial number
exceeded both fungus and actinomycetes.
In the pot culture experiment also soil pH showed a decreasing trend upto 60
D followed by a slight increase at 90 D. The TOC content ranged from 0.29% (C at
90 D) to 4.73% (TOF at 30 D) and the DOC content in the experiment ranged from
0.04 mg kg-1 (C at 90 D) to 20.28 mg kg -1 (FYM at 30 D). The N content in pot
ranged from 75.26 kg ha-1(C at 90 D) to 326.14 kg ha-1(TOF – F at 90 D). Significant
difference was observed between treatments for soil Nmin at all stages of sampling.
The soil P content in the different treatments were high at all the stages. Even after
the crop, the status remained high in all the treatments including the control (C). A
general decrease in K content was observed in all the pots after experiment. The
secondary nutrients except S were found to be deficient irrespective of treatment.
Significant difference between treatments was observed in the case of micronutrients
with the exception of Cl. Plant C ranged from 40% (C at 30 D) to 85% (TOF – F at
90 D).The highest N content was recorded by the treatment TOF-F and highest P
content was registered by the treatment VC at all levels of sampling. The treatment
TOF-F recorded the highest K content in plant at 15 and 30D while TOF was found
to be superior at 60 and 90 D. Regarding the Ca level in plant, TOF-F had the highest
values followed by MC at all levels of sampling. The plants treated with MC were
found to be superior in terms of Mg and S content. The effect of treatments on
micronutrient levels remained significant in pot culture experiment. The plants
treated with TOF-F recorded the highest shoot mass, root mass and dry matter yield
followed by plants treated with MC. A significant positive rhizosphere priming effect
was evident in the case of C and other plant nutrients. The microbial population was
found to be higher in planted soil than non planted soil.
It can be concluded that the conventional and nonconventional organic
manures behaved similarly in soil, however fortified TOF (TOF-F) and MC were
superior in terms of physical, chemical and nutritional properties. A significant
positive rhizosphere priming effect was observed in C and N dynamics, irrespective
of the method of preparation of organic manures.
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