Conservation Agriculture practices reduce the global warming potential of rainfed low N input semi-arid agriculture

Abstract

Conservation tillage and crop rotations improve soil quality. However, the impact of these practices on greenhouse gas (GHG) emissions and crop yields is not well defined, particularly in dry climates. A rainfed 2-year field-experiment was conducted to evaluate the effect of three long-term (17-18 years) tillage systems (Conventional Tillage (CT), Minimum Tillage (MT) and No Tillage (NT)) and two cropping systems (rotational wheat (Triticum aestivum L.) preceded by fallow, and wheat in monoculture), on nitrous oxide (N2 0) and methane (CH4) emissions, during two field campaigns. Soil mineral N, water-filled pore space, dissolved organic carbon (C) and grain yield were measured and yield-scaled N 2 0 emissions, N surplus and Global Warming Potentials (GWP) were calculated. No tillage only decreased cumulative N 2 0 losses (compared to MT/CT) during campaign 1 (the driest campaign with least fertilizer N input), while tillage did not affect CH4 oxidation. The GWP demonstrated that the enhancement of C stocks under NT caused this tillage management to decrease overall CO2 equivalent emissions. Monoculture increased N2O fluxes during campaign 2 (normal year and conventional N input) and decreased CH4 uptake, as opposed to rotational wheat. Conversely, wheat in monoculture tended to increase soil organic C stocks and therefore resulted in a lower GWP, but differences were not statistically significant. Grain yields were strongly influenced by climatic variability. The NT and CT treatments yielded most during the dry and the normal campaign, and the yield-scaled N 2 0 emissions followed the same tendency. Minimum tillage was not an adequate tillage management considering the GWP and the yield-scaled N 2 0 emissions (which were 39% lower in NT with respect to MT). Regarding the crop effect, wheat in rotation resulted in a 32% increase in grain yield and 31% mitigation of yield-scaled N2O emissions. Low cumulative N2O fluxes (<250gN 2 O-Nha _1 campaign -1 ) highlighted the relevance of soil organic C and C0 2 emissions from inputs and operations in rainfed semi-arid cropping systems. This study suggests that NT and crop rotation can be recommended as good agricultural practices in order to establish an optimal balance between GHGs fluxes, GWP, yield-scaled N 2 0 emissions and N surpluses.

Traditional agriculture: a climate-smart approach for sustainable food production

“…Carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) are major GHGs emitted by agricultural activities (Tellez-Rio et al 2017). In year 2005, it was estimated that globally agriculture accounted to 50 and 60% of total anthropogenic CH 4 and N 2 O emissions, respectively (Liu et al 2015).…”

Net Global Warming Potential of Spring Wheat Cropping Systems in a Semiarid Region

“…Sainju (2015) and Sainju et al (2014) found continuously cropped no-tillage systems including barley (Hordeum vulgaris L.) and pea (Pisum sativum L.) mitigated GWP compared to tilled systems including chemical fallow, though evaluated treatments were net GHG sources when emission calculations were based on changes in SOC stocks. Positive net GWP for semiarid cropping systems have also been found outside the northern Great Plains of North America [6,12,13], highlighting a systemic challenge in attaining beneficial climate regulation services from these agroecosystems. While additional GWP evaluations of semiarid cropping systems are sorely needed, novel design features of this important agroecosystem may need to be considered if meaningful GHG mitigation benefits are to be achieved.…”

“…While climatic and edaphic influences on GWP are important, management practices employed by producers are the final determinants on GWP outcomes in semiarid cropping systems. Use of no-tillage has been found effective at reducing net GWP through accrual of SOC [11][12][13]. However, as inferred above, long-term adoption of no-tillage is critical to achieve GHG benefits.…”

“…Nutrient management, particularly practices associated with synthetic N application, have found generally low N 2 O fluxes in semiarid cropping systems (<7 g N 2 O-N ha −1 d −1 ) [14][15][16] but because of its high radiative forcing capacity (298 times more powerful than CO 2 ; Intergovernmental Panel on Climate Change (IPCC);) [17], fluxes of N 2 O can comprise >50% of net GWP [14,18]. Though limited, investigations of crop rotation effects on GWP in semiarid regions have found monocultures to have greater net GWP compared to rotated crops [12,19].…”

Mitigation of greenhouse gas emissions through optimized irrigation and nitrogen fertilization in intensively managed wheat–maize production

“…Many countries including China will have to adopt appropriate intensive production practices to ensure the sustainability of agriculture 2 . Globally, agricultural soil is thought to be one of the major contributors to greenhouse gas (GHG) emissions, accounting for 10%-12% of total anthropogenic GHGs 3 . However, agricultural soil also sequesters 4 × 10 8 − 9 × 10 8 Mg C yr −1 4 .…”