Agro Ecosystem Soil Organic Matter Decomposition Modeling A Remote Sensing and GIS Based Integrated Approach
S. K. Saha and L. M. Pandi
Agriculture & Soils Division
Indian Institute of Remote Sensing
Dehradun - 248 001 (U.P.), India
Abstract
Agro-ecosystem soil organic matter decomposition modeling is important for assessing the problems of sustained productivity matter status, and regional climatic change. A GIS based integrated methodology was developed for execution of CENTURY model ecosystem using satellite (IRS-LISS-I) derived soil map and soil characteristics; agro-meterological and ancillary soil data as inputs. The study area was Doon Valley (Dehradun district, Uttar Pradesh). This study demonstrates that agro-ecosystem soil organic matter decomposition can be adequately modeled following GIS based integrated approach using remote sensing inputs and other ancillary data of agro-meteorological and soils.
1. Introduction
The study of agro-ecosystem soil organic matter decomposition is important for assessing the problems of organic matter depletion in soil, long term soil fertility, sustained productivity of agro-ecosystems and regional climatic change.
A variety of soil parameters based models have been used by several researchers to represent short and long-term changes in single state variable model form to represent the decline of organic Cin cultivated sols. Van Veen and Paul (1981); Pastor and Post (1986); Parton et al. (1988) improved upon the approach different components. These models were mostly utilized for studying soil carbon dynamics of eco-systems of smaller areas based on ground collected soil data from various sites (point observations). At regional scale, the only appropriate instrument for monitoring carbon dynamics are satellite or aircraft based sensors. Remote sensing provides the needed dynamic temporal view of agro-ecosystems and large area coverage that eliminates the need for regional extrapolations based on small data sets.
The objective of this study was to develop an integrated methodology for execution of CENTURY model (Parton et. Ala., 1988) for assessment of agro-ecosystem soil organic matter decomposition using remote sensing derived soil; soil characteristics and agro-meteorological data as inputs.
2. The Century Model
In the original CENTRUY model (Parton et al., 1987) the soil organic matter (SOM) consists of three fractions. They constitute (i) an active fraction (active SOM) of soil C consisting of live microbes and microbial products, alongwith soil organic matter (SOM) with a short turnover time (1-5 years); (ii) a pool of C (slow SOM) that is physically protected and/or in chemical forms with more biological resistance to decomposition, with an intermediate turnover time (20-40 years), and (ii) a fraction that is protected with the longest turnover time (200-1500 years) (Parton et al. 1988).
In our soil organic matter decomposition modeling approach, we have consider only "active SOM" fraction of soil organic matter with a short turnover time. In soil system, a continuing loss of soil humus carbon (decomposition loss) taken place by microbial oxidization.
According to CENTRUY model, the rate of decomposition of soil organic matter depends on soil types; soil texture (silt + clay content); rainfall (R): soil temperature (Ts); Potential evapotranspiration (PET); initial soil organic carbon content (Ci) and the maximum decomposition rate parameter (Ki).
Decomposition (oxidation) loss (DL) of soil humus carbon is computed using the following expression (Parton et al., 1988)
dDL/dt = Ki (1 - 0.75 . T). Md. Td. Ci…………………… (1)
where
T = (Sil + C1)
Md = f (PET, R)
Td = f (Ta)
Where, DL/dt is the rate of decomposition of soil hums carbon in time 't' (her, 1 years); T is soil silt (Sil) plus clay (C1) content; Md is the effect of moisture condition on decomposition rate (Md is the function of PET an dR); Td is the effect of average soil temperature on decomposition rate (Td is the funcorganic carbon content.
3. The Study Area
The study are comprises of Doon Valley (Dehradun district) of Uttar Pradesh and lies between 770 35' E to 780 19' E longitude and 29' 57' 30" N to 30' 30' 30" N latitude approximately. The climate of the region is sub-tropical (annual mean air temperature ranges between 130C to 230 C). The average rainfall of the area is ranged between 1130 mm to 2025 mm. The study area have variety of agro-ecosystems comprising mountain (Himalaya), hills (Siwalik), Piedmont plains, river terraces and flood plains as major physiographic units; various cultivated crops viz., paddy, wheat and sugarcane; ad Inceptisols, Entisols, Alfisols and Mollisols as dominant soils, in addition to climatic variability.
4. Data Used
The variety of data used in this study are IRS-1B LISS-I, FCCs of October, 1992 and March, 1993, of path-row 29-46; agro-climatic data of monthly rainfall, mean air temperature, relative humidity, sunshine hours etc. Survey of India topographical maps; field soil survey data and laboratory analyzed ples collected form sample sites of the area.
