Ecosystem Economic Benefits Research Articles

Successive straw biochar amendments reduce nitrous oxide emissions but do not improve the net ecosystem economic benefit in an alkaline sandy loam under a wheat–maize cropping system

AbstractCrop straw is converted to biochar with subsequent applications to soils as a multi‐benefit strategy for greenhouse gas (GHG) emission mitigation, carbon sequestration, and straw disposal and utilization in intensive agriculture. However, tradeoffs between agronomic, economic, and environmental performance of long‐term agricultural biochar use remain unclear. Using a case study of biochar‐amended alkaline sandy loamy soil, we investigated the effects of field application of straw biochar at 0, 2.25, 6.75, and 11.25 Mg ha−1 to 10 successive wheat and maize crop seasons over five rotation years on crop yield, nitrous oxide (N2O) emissions, soil total organic carbon (TOC), and soil carbon pool (SCP). The net global warming potential (net GWP) and net ecosystem economic benefit (NEEB) were assessed to examine the tension between balancing economic returns and environmental benefits. Results indicated that biochar treatments slightly increased total crop grain yields and greatly reduced the total N2O emissions over five rotation years. The soil total organic carbon content was enhanced while the CO2 emissions during biochar production almost offset the increase in the soil carbon pool. Economic assessment showed that the net ecosystem economic benefit was lowered with enhanced costs of the increasing biochar use under the current low C trade market. These results highlight the promotion of the use of straw biochar in successive applications as a strategy to effectively offset greenhouse gas emissions from agriculture requires optimization of the straw pyrolysis system to reduce the energy consumption and overall biochar costs, and price enhancement of C trade.

Assessing the viability of soil successive straw biochar amendment based on a five-year column trial with six different soils: Views from crop production, carbon sequestration and net ecosystem economic benefits

Converting straw to biochar (BC) followed by successive application to soil has been increasingly suggested as a multi-win approach for soil fertility improvement, carbon (C) sequestration and efficient disposal of straw residues in intensive cropping agroecosystems. However, different soil types response differently in terms of crop growth and non-CO2 greenhouse gas (GHG) emissions after BC application. Furthermore, few studies have comprehensively evaluated the net global warming potential (GWP) and net ecosystem economic benefits (NEEB) after long-term BC incorporation across representative soil types in China. A five-year outdoor column experiment was conducted using three rice-wheat rotated paddy soils and three millet-wheat rotated upland soils developed from different parent materials. Rice straw BC application rates of 0, 2.25 and 11.3 Mg ha−1 were used in each crop season with identical doses of NPK fertilizers. Compared with the no BC controls, BC significantly boosted crop growth, enhanced C sequestration, and decreased cumulative N2O and CH4 emissions in all six soils over five rotation cycles. The response of the upland soils to BC was better in terms of crop growth and N2O mitigation, whereas the soil organic carbon (SOC) increment and CH4 mitigation were less effective compared with the paddy soils. Net GWP decreased 0.6–19 fold after BC application; however, given the low trade price of CO2 (0.21 × 103 CNY Mg−1), only a small contribution was made in terms of C costs to the NEEB. The BC-induced NEEB was mainly dependent on grain yield gains and BC costs. These findings highlight that widespread adoption of successive straw BC application to farmland requires an increase in crop yield and substantial lowering of the BC cost regardless of the soil type. From the standpoints of agronomics, environment and economics, acid upland soil shows most potential in terms of BC application.

Organic-substitute strategies reduced carbon and reactive nitrogen footprints and gained net ecosystem economic benefit for intensive vegetable production

Partially substituting inorganic fertilizer with organic fertilizer is widely adopted to improve intensive vegetable production as well as potentially reduce carbon (C) and reactive nitrogen (Nr) footprints, but the associated comprehensive evaluations with life-cycle assessment (LCA) from environmental and economic perspectives have rarely been executed. Covering one-year consecutive vegetable crops rotation, five fertilization strategies were established at an equal N level (SN: single inorganic fertilization; SM: single organic fertilization; mixing organic and inorganic N fertilizer at the ratio of 1:2 (M1N2), 1:1 (M1N1) and 2:1 (M2N1)) and a CK as control. Compared with the SN strategy, the M1N2, M1N1 and M2N1 strategies significantly decreased N2O emission (32.2–50.0%), NO emission (41.8–52.5%), NH3 volatilization (17.8–22.2%), N runoff (29.7–35.3%) and N leaching (34.2–44.8%) as well as significantly increased vegetable yield (4.3–7.4%) and annual SOC sequestration (244.5–463.1 kg C ha−1 yr−1). Consequently, the three organic-substitute strategies significantly reduced C footprint (17.0–21.8%) and the field interface Nr footprint (34.1–43.0%). The production of both organic and inorganic N fertilizer (31.1–51.5%) and N2O emissions (19.9–35.1%) were the hotspots of GHG emissions. The production of organic fertilizer dominated their foreground interface Nr footprint (86.6–97.9%) and environmental damage costs (EDC, 48.6–71.0%), while N leaching dominated the field interface Nr footprint (45.1–50.0%). Therefore, the substitute strategies improved the net ecosystem economic benefits (NEEB, which integrated net economic benefit and EDC) by CNY 2,799−12,151 ha−1 yr−1 and the M2N1and M1N1 strategies produced better NEEB, highlighting that appropriate substitute fertilization strategies are recommended for simultaneously environmental and economic benefits in intensive vegetable production in China.

Winter legume-rice rotations can reduce nitrogen pollution and carbon footprint while maintaining net ecosystem economic benefits

Abstract Achieving reductions in nitrogen (N) losses and carbon (C) emissions without enduring a yield penalty is an environmental and economic challenge in sustainable rice production. The use of legumes as a winter crop in rice rotations may provide environmental benefits by reducing synthetic N inputs, yet few studies have integrated long-term field measurements of cropping system N and C dynamics with life cycle assessment (LCA) and net ecosystem economic benefits (NEEB) to determine whether legumes can improve environmental performance while minimizing tradeoffs related to yields and economic returns. We evaluated four contrasting rice cropping rotations (Rice-wheat (R-W); rice-rape (R-Ra); rice-fava bean (R-F); and, rice-milk vetch (R-M)) over six years to determine N input and output balances, methane (CH4) emissions, and soil C changes. These field observations were then incorporated into LCA and NEEB to estimate C footprint, economic and environmental benefits. Results showed that R-F and R-M maintained rice yield but reduced annual synthetic N inputs by 50–63% compared with the conventional R-W and R-Ra rotations, leading to consistent reductions in reactive N losses (ammonia (NH3) volatilization: 39–48%; N runoff: 66–82%; N leaching: 14–34%; and nitrous oxide (N2O) emissions: 40–64%). The estimated C footprint was 37–50% lower in R-F and R-M than R-W and R-Ra, largely owing to reduced fertilizer use which decreased direct soil N2O emissions as well as indirect emissions relating to reactive N losses. In contrast to N losses, there were no significant differences in CH4 emissions or soil C changes among rotations. When changes in N pollution and C footprint were accounted for in the economic assessment, R-F resulted in NEEB values similar to R-W, while substituting milk vetch as a winter crop reduced NEEB by 6–37%. In the first two study years before grain legume yields declined, NEEB for R-F was 38% greater than R-W, highlighting the potential for simultaneous environmental and economic benefits. This study demonstrated the potential of mixed winter grain/forage legumes-rice crop rotations to consistently reduce N pollution and C footprint while maintaining NEEB based on economic and environmental benefits.