Nutrient management impacts on net ecosystem carbon budget and energy flow nexus in intensively cultivated cropland ecosystems of north-western India

摘要

Nutrient management has led to unprecedented increase in crop production, but with significant carbon (C) trade-off that has close nexus with energy flow. We quantified the impacts of nutrient management on emission of greenhouse gases, net ecosystem C budget (NECB) and energy flow in three cropland ecosystems (rice-wheat, maize-wheat and cotton-wheat). Carbon dioxide (CO2) and nitrous oxide (N2O) emissions were significantly (p < 0.05) higher in rice than cotton, while maize ecosystem was in-between. The greenhouse gas intensity was significantly higher for rice-wheat (by 0.2 kg CO2e kg(-1)grain) and maize-wheat (by 0.1 kg CO(2e)kg(-1)grain), compared with cotton-wheat. The higher carbon emission ratio for maize-wheat (9.59) and rice-wheat (8.07) suggested their higher potential to fix C per unit loss, compared with cotton-wheat (7.03). Atmospheric CO(2)assimilated into net primary production (NPP) totalled 14.1 +/- 0.18, 11.5 +/- 0.13 and 9.7 +/- 0.13 Mg C ha(-1)for rice-wheat, maize-wheat and cotton-wheat ecosystems, respectively. With an estimated net ecosystem exchange of 9.5 +/- 0.29, 5.8 +/- 0.19 and 2.7 +/- 0.23 Mg C ha(-1), respectively, for three ecosystems, rice-wheat (2427 kg C ha(-1) year(-1)) had significantly higher NECB, compared with maize-wheat (27.1 kg C ha(-1) year(-1)) and cotton-wheat (- 3834 kg C ha(-1) year(-1)). Rice-wheat had significantly higher C addition in soil organic carbon (SOC) pool, compared with other two ecosystems. Conversely, cotton-wheat had depletion of SOC pool (- 817 kg C ha(-1)). Although the three ecosystems did not differ significantly for fertilizer-related energy input (E-I), energy output (E-O), energy ratio (E-R) and net energy gain were significantly higher for cotton-wheat, compared with other ecosystems.