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

Abstract

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 CO2e 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 CO2 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 (EI), energy output (EO), energy ratio (ER) and net energy gain were significantly higher for cotton–wheat, compared with other ecosystems.