MODELING SOIL HYDROTHERMAL DYNAMICS, ROOT WATER UPTAKE AND RADIATION USE IN PIGEON PEA UNDER CONSERVATION AGRICULTURE
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Date
2017
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DIVISION OF AGRICULTURAL PHYSICS INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
The studies on effect of conservation agricultural practices on moderation of soil
temperature and distribution of soil water in the profile during crop growth need special
attention for understand changes in water and energy balance components, which are
crucial components of crop improvement programmes.
In current study, both water balance and energy balance components of soil under
different conservation agriculture (CA) practices were analyzed using the Hydrus-2D
model during the pigeonpea growth. The treatments were: conventional tillage (CT),
zero tillage (ZT), permanent narrow beds (PNB), permanent broad beds (PBB), ZT with
residue (ZT+R), PNB with residue (PNB+R) and PBB with residue (PBB+R). Results
on soil physical environment changes after 7 years of continuous adoption of different
CA practices showed that both permanent broad bed and narrow bed with and without
residue retention and zero tillage with residue retention reduced bulk density (BD),
increased field saturated hydraulic conductivity (Ksat) and improved soil water retention
significantly over CT.
Ksat values obtained as the output of Rosetta Lite model could not be used as hydraulic
input parameter as they were very low and hence, measured value of Ksat and α and n
parameter obtained as output of Rosetta Lite model were optimized through inverse
modeling and were used as hydraulic inputs of the model which predicted daily
change in SWC of profile with reasonable accuracy (R2= 0.78; RMSE= 0.012). Soil
water balance simulated from the model showed higher cumulative transpiration, lower
cumulative evaporation and higher soil water retention in most of the CA practices as
compared to CT.
Computed values of Thermal conductivity (λ) obtained from observed soil temperature
(ST) data at different soil water contents showed good correlation with the optimized
values of thermal conductivity obtained through inverse modeling. Hydrus 2D
predicted ST variation of 0-20 cm soil profile using optimized values with reasonable
accuracy (R2=0.91) for a simulation period of 10 days, although it slightly over
predicted ST values.
Both observed and simulated results of ST as function of depth and time, revealed that
fluctuation of peak magnitude of temperature wave between 5 and 20 cm was more in
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CT than in PBB+R. Simulated Value of ST at hourly interval for 5 cm depth showed
more variation and occurrence of peak was 2-3 hours earlier than those of ST values at
15 and 20 cm. Among different energy balance components, computed ground heat
flux was lower and Latent heat flux was more in PBB+R as compared to CT.
Hence it was concluded that PBB+R and PNB+R practices should be adopted for
pigeon pea cultivation, as these practices modified soil hydrothermal regimes,
enhanced root growth and improved radiation interception, LAI and biomass
production. The Hydrus-2D can satisfactorily simulate the temporal changes in water
balance components as well as ground heat flux (G) and latent heat flux (LE)
components of energy balance during the crop period; hence it may be adopted for
evaluating different management practices in terms of improvement in water and
radiation use by them.
Description
t-9644
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