long term estimation of carbon dynamic and sequestration for iranian agro-ecosystem: i- net primary productivity and annual carbon input for common agricultural crops

evaluation of carbon input is one of the most important factors for estimating soil carbon changes and potential for carbon sequestration. to evaluate the net primary productivity (npp) and soil carbon input in agricultural eco-systems of iran, data for yield, cultivated area, harvest index (hi) and shoot /root ratio in different crops including: wheat, barley, maize, cotton, rice, alfalfa and chickpea were obtained for different provinces. then, allocated carbon to different organs of plant were calculated based on carbon allocation coefficients and finally, the net primary productivity based on carbon (nppc) was calculated. the ratio of nppc that was annually returned to soil was considered as carbon annual input. the results showed that the maximum amount of nppc for wheat, barely and alfalfa were obtained in khazari climate for rice, chickpea and cotton was achieved in warm-wet climate and for maize was gained in warm-dry climate. in all regions of iran, chickpea had the lowest effect on nppc and consequently on carbon sequestration. the highest amount of carbon input per unit area among studied crops and different regions were observed in khazari region for alfalfa whereas, the lowest carbon input per unit area was relation to chickpea in cold region. the lowest gap between actual and potential of carbon sequestration was observed in alfalfa whereas wheat, rice and cotton showed the most gap by 0.4, 0.38 and 0.37, respectively.