Conservation Systems for Positive Net Ecosystem Carbon Balance in Semiarid Drylands

Abstract

Core Ideas The soil organic C dynamics and net ecosystem C balance of five dryland cropping systems were compared. Conservation systems stored up to 15% more soil organic C than conventional system. Net ecosystem C balance was positive with cover cropping. Cover crops and conservation tillage are crucial for soil C storage in drylands. Biomass C inputs often limit agroecosystem C dynamics, nutrient cycling, and soil organic carbon (SOC) storage in semiarid drylands. This study evaluated SOC and net ecosystem carbon balance (NECB) of five cropping systems in the drylands of the Southern Great Plains. Cropping systems evaluated included corn (Zea mays)–sorghum [Sorghum bicolor (L.) Moench] rotation with conventional tillage without cover cropping (CTNC), strip tillage with and without cover cropping (STCC and STNC, respectively), and no tillage with and without cover cropping (NTCC and NTNC, respectively). After 4 yr of experimental tillage, we measured CO2 emissions, soil and soil surface air temperatures, soil moisture content, potentially mineralizable carbon (PMC), total SOC, total nitrogen (TN), and net primary productivity (NPP). Conservation systems (any treatments including no‐till, strip till, or cover crops) had 5 to 6°C lower soil temperature and 2.8 to 4.9°C lower soil surface air temperature and stored 2.3 to 3.9% more soil moisture content than CTNC. Conservation systems also stored 15.2% more SOC than CTNC. Cropping systems that integrated cover crops in the rotation (STCC and NTCC) had greater NPP and positive NECB. Regardless of tillage management, cover cropping had a greater NECB, including SOC (NECBSOC) than CTNC. Reducing tillage and diversifying cropping systems through cover cropping can benefit semiarid dryland agroecosystems by increasing SOC storage and maintaining positive NECB.

Cover crop effects on soil carbon dioxide emissions in a semiarid cropping system

“…Gas emissions were calculated by using a linear procedure of flux calculation using a formula described in Thapa et al. (2019). Gas samples were collected between 0900 and 1100 h during each observation to reduce variability in CO 2 –C flux due to diurnal fluctuations in temperature.…”

“…During each measurement, a SRC-2 chamber was placed into a PVC ring for 5 min, and gas accumulated in the chamber headspace was measured directly into the EGM-5 analyzer connected to the chamber. Gas emissions were calculated by using a linear procedure of flux calculation using a formula described in Thapa et al (2019). Gas samples were collected between 0900 and 1100 h during each observation to reduce variability in CO 2 -C flux due to diurnal fluctuations in temperature.…”

“…In recent years, cover cropping is increasingly considered in semiarid regions to increase SOM sequestration and improve soil health because of their biomass C contribution, soil temperature moderation, moisture conservation, soil aggregation, and aggregate stability (Blanco-Canqui, Holman, Schlegel, Tatarko, & Shaver, 2013;Ghimire, Ghimire, Mesbah., Sainju, & Idowu, 2019;Thapa, Ghimire, Duval, & Marsalis, 2019). Cover crops can enhance nutrient cycling and water productivity and thereby sustain crop production compared with fields without cover crops (Holman et al, 2012;Reese et al, 2014).…”

Soil organic matter dynamics in semiarid agroecosystems transitioning to dryland

“…Three years of no-tillage after 11 years of dryland cropping and conventional tillage was not enough to detect increase in SOC in this hot, dry semiarid agroecosystem. Management systems that reduce soil disturbance along with cropping system intensification could increase SOC and maintain net positive ecosystem carbon balance compared to no-tillage alone in hot, dry environments of the Southern High Plains ( Rosenzweig, Stromberger & Schipanski, 2018 ; Thapa et al, 2019 ). Cropping system intensification increases SOC through greater C inputs to soil, as well as through increased fungal biomass and soil aggregation ( Rosenzweig, Stromberger & Schipanski, 2018 ).…”

“…The glass jars had an aluminum lid with a rubber septum for gas extractions. The CO 2 and N 2 O gas produced during incubation was measured with a portable EGM-5 CO 2 analyzer (PP systems Inc. Amesbury, MA, USA) and MIRA PICO N 2 O analyzer (AERIS Technologies Inc. Redwood City, CA, USA) using method described by Thapa et al (2019) for CO 2 emissions with modifications to conform to the laboratory conditions. In brief, a syringe connected to the analyzers through a rubber tubing was inserted into a septum on the lid of each jar was connected to the CO 2 analyzer and the gas-out port from the CO 2 analyzer was connected to the N 2 O analyzer.…”