Abstract
Abstract. Earth observation driven ecosystem modeling have played a major role in estimation of carbon budget components such as gross primary productivity (GPP) and net primary production (NPP) over terrestrial ecosystems, including agriculture. The present study therefore evaluate satellite-driven vegetation photosynthesis (VPM) model for GPP estimation over agro-ecosystems in India by using time series of the Normalized Difference Vegetation Index (NDVI) from SPOT-VEGETATION, cloud cover observation from MODIS, coarse-grid C3/C4 crop fraction and decadal grided databases of maximum and minimum temperatures. Parameterization of VPM parameters e.g. maximum light use efficiency (ε*) and Tscalar was done based on eddy-covariance measurements and literature survey. Incorporation of C3/C4 crop fraction is a modification to commonly used constant maximum LUE. Modeling results from VPM captured very well the geographical pattern of GPP and NPP over cropland in India. Well managed agro-ecosystems in Trans-Gangetic and upper Indo-Gangetic plains had the highest magnitude of GPP with peak GPP during kharif occurs in sugarcane-wheat system (western UP) and it occurs in rice-wheat system (Punjab) during Rabi season. Overall, croplands in these plains had more annual GPP (> 1000 g C m-2) and NPP (> 600 g C m-2) due to input-intensive cultivation. Desertic tracts of western Rajasthan showed the least GPP and NPP values. Country-level contribution of croplands to national GPP and NPP amounts to1.34 Pg C year-1 and 0.859 Pg C year-1, respectively. Modeled estimates of cropland NPP agrees well with ground-based estimates for north-western India (R2 = 0.63 and RMSE = 108 g C m-2). Future research will focus on evaluating the VPM model with medium resolution sensors such as AWiFS and MODIS for rice-wheat system and validating with eddy-covariance measurements.
Highlights
Global land ecosystems in recent time appeared as major sink of global carbon cycle and curtailing the increasing CO2 concentration in the atmosphere (Zhao and Running, 2009)
net primary production (NPP) databases from crop statistics are area-based and lacking spatial detail required for agro-ecosystem management and ecosystem related services
The VPM model is based on contribution of photosynthetically active vegetation (PAV) and non-photosynthetic vegetation (NPV) to fraction of PAR absorbed by canopy
Summary
Global land ecosystems in recent time appeared as major sink of global carbon cycle and curtailing the increasing CO2 concentration in the atmosphere (Zhao and Running, 2009). As of most studies related to primary productivity and carbon budget in India and abroad have focused on forest ecosystem due to their potential to sequester high magnitude of atmospheric CO2. Few studies based on crop yield and area statistics yielded a varying estimates of total cropland NPP in India ( i.e., 0.407 Pg C in 1989 (Dadhwal et al, 1996; Dadhwal and Chabra, 2002), 0.63 Pg C in 1980 (Hingane, 1991). NPP databases from crop statistics are area-based and lacking spatial detail required for agro-ecosystem management and ecosystem related services
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