Modeling impacts of management alternatives on soil carbon storage of farmland in Northwest China

Abstract

Abstract. Long-term losses of soil organic carbon (SOC) have been observed in many agriculture lands in Northwest China, one of the regions with the longest cultivation history in the world. The decline of SOC contents not only impaired the soil fertility but also increased the amount of carbon dioxide (CO 2 ) emitted from terrestrial ecosystems into the atmosphere. However, quantifying the SOC losses at regional scale has long been remaining unsolved. A processbased model, Denitrification-Decomposition or DNDC, was adopted in the study to quantify impacts of farming management practices on SOC dynamics for a selected region, Shaanxi Province. The selected domain, with 3 million hectares of cropland across different climatic and farming management regimes, is representative for the major agricultural areas in Northwest China. The DNDC model was tested against long-term SOC dynamics observed at five agricultural sites in China. The agreement between the observed and modeled results indicate that DNDC was capable of capturing patterns and magnitudes of SOC changes across the climate zones, soil types, and management regimes in China. To quantify SOC dynamics for Shaanxi, we constructed a GIS database to hold all of the DNDC-required input information (e.g., weather, soil properties, crop acreage, and farming practices) for all the farmland in the studied domain. Sensitivity tests indicated the spatial heterogeneity of soil properties, especially initial SOC content, was the major source of uncertainty for the modeled SOC dynamics at regional scale. The Most Sensitive Factor (MSF) method was employed in the study to quantify the uncertainties produced from the upscaling process. The results from the regional simulations for Shaanxi indicated that (1) the overall 3 million hectares of farmland in the province was a source of atmospheric CO 2 with 0.5 Tg C yr −1 lost in 2000 under the current farming management conditions, (2) an increase in the rate of cropCorrespondence to: C. Li (changsheng.li@unh.edu) residue incorporation from 15% to 50% or 90% converted the farmland from the C source to a C sink with 0.7 or 2.1 Tg C yr −1 sequestered, respectively, and (3) applying farmyard manure at a rate of 500 kg C ha −1 also converted the cropland into a weak C sink with 0.2 Tg C sequestered in the farmland in Shaanxi. In the studied domain, crop residue and farmyard manure used to be the major sources of soil nutrients during the centuries-long cultivation history but were gradually abandoned since 1950s when synthetic fertilizers became available. The results from this modeling study suggest that recovery of the traditional farming practices (i.e., residue incorporation and manure amendment) be a feasible approach to substantially improve the soil C status in the farmland of Shaanxi. The values of C gain or loss from this study for Shaanxi could vary if the modeled domain shifts to other provinces in Northwest China although the general conclusion may remain.

Spatial-Temporal Changes of Soil Organic Carbon Content in Wafangdian, China

“…This could be linked to the economic development of Wafangdian City during the 1980s, and the city size and population increased so rapidly that a large area of agricultural land was swallowed by construction areas. Ground vegetation was swapped and the areas were isolated from water recharge and gaseous exchange [11]. Such transformation caused a tremendous decline in SOC content ( Table 2).…”

“…Therefore, studies focusing on the impact of land-use change and environmental variables controlling spatial-temporal dynamics of SOC are important. Especially in China, which is experiencing population expansion, assessment of spatial-temporal changes of soil properties (e.g., SOC) is considered urgent to make policies to regulate actual needs and ecological demand [7,[11][12][13][14]. Moreover, reliable, robust and cost-efficient methods for estimating SOC content and its temporal changes are quite essential.…”

Effect of temporal resolution on N2O emission inventories in Dutch fen meadows

“…[10] The model DNDC was selected because it has been calibrated and validated for many sites around the world [Brown et al, 2002;Butterbach-Bahl et al, 2001;Cai et al, 2003;Grant et al, 2004;Jagadeesh Babu et al, 2006;Kesik et al, 2005;Kiese et al, 2005;Pathak et al, 2005;Saggar et al, 2004;Xu-Ri et al, 2003;Zhang et al, 2006] and can simulate drained organic soils. Version 9.1 of DNDC was used.…”

Climate and land use controls over terrestrial water use efficiency in monsoon Asia

“…LUCC could greatly change the land surface biogeochemical and biophysical processes, leading to dramatic changes in water cycle and ecosystem productivity (Houghton and Hackler, 2003;Tian et al, 2003Tian et al, , 2008Tian et al, , 2010aSakai et al, 2004;Jarosz et al, 2009). Associated with the change in land use and cover, land management practices such as irrigation, fertilizer and/or manure application, residue return, and tillage are recognized as important anthropogenic measures to improve crop yield, and hence, modify the carbon, water, and nitrogen cycles in agricultural land Zhang et al, 2006;Lu et al, 2009), which covers around 20% of the total land area in MA. Although a few studies have assessed the impacts of environmental changes on carbon and water interactions Yu et al, 2008;Wang et al, 2008;Li et al, 2010), none of them has addressed the changes in WUE in response to both natural and human perturbations at a regional scale.…”