Integrating soil carbon cycling with that of nitrogen and phosphorus in the watershed model SWAT: Theory and model testing |
| |
Authors: | Armen R Kemanian Stefan Julich Valipuram S ManoranjanJeffrey R Arnold |
| |
Institution: | a Department of Crop and Soil Sciences, The Pennsylvania State University, 116 ASI Building, University Park, PA 16802-3504, United States b Institute of Landscape Ecology and Resources Management, Justus-Liebig-Universität Gießen, Germany c Department of Mathematics, Washington State University, 208 Morrill Hall, Pullman, WA 99164-3520, United States d Grassland Soil and Water Research Laboratory, United States Department of Agriculture - Agricultural Research Service, 808 E. Blackland Road, Temple, TX 76502, United States |
| |
Abstract: | In this paper we describe and test a sub-model that integrates the cycling of carbon (C), nitrogen (N) and phosphorus (P) in the Soil Water Assessment Tool (SWAT) watershed model. The core of the sub-model is a multi-layer, one-pool soil organic carbon (SC) algorithm, in which the decomposition rate of SC and input rate to SC (through decomposition and humification of residues) depend on the current size of SC. The organic N and P fluxes are coupled to that of C and depend on the available mineral N and P, and the C:N and N:P ratios of the decomposing pools. Tillage explicitly affects the soil organic matter turnover rate through tool-specific coefficients. Unlike most models, the turnover of soil organic matter does not follow first order kinetics. Each soil layer has a specific maximum capacity to accumulate C or C saturation (Sx) that depends on texture and controls the turnover rate. It is shown in an analytical solution that Sx is a parameter with major influence in the model C dynamics. Testing with a 65-yr data set from the dryland wheat growing region in Oregon shows that the model adequately simulates the SC dynamics in the topsoil (top 0.3 m) for three different treatments. Three key model parameters, the optimal decomposition and humification rates and a factor controlling the effect of soil moisture and temperature on the decomposition rate, showed low uncertainty as determined by generalized likelihood uncertainty estimation. Nonetheless, the parameter set that provided accurate simulations in the topsoil tended to overestimate SC in the subsoil, suggesting that a mechanism that expresses at depth might not be represented in the current sub-model structure. The explicit integration of C, N, and P fluxes allows for a more cohesive simulation of nutrient cycling in the SWAT model. The sub-model has to be tested in forestland and rangeland in addition to agricultural land, and in diverse soils with extreme properties such high or low pH, an organic horizon, or volcanic soils. |
| |
Keywords: | C carbon d index of agreement fE combined effect of soil temperature moisture and aeration on soil organic matter residue and manure decomposition fO aeration factor controlling soil organic matter residue and manure decomposition fT temperature factor controlling soil organic matter residue and manure decomposition fW moisture factor controlling soil organic matter residue and manure decomposition fp power factor that affects fE fcm cumulative fmix fmix mixing coefficient associated to different tillage tools ftool tillage factor controlling soil organic matter decomposition rate GLUE generalized likelihood uncertainty estimation h humification hR hM humification coefficient of residue and manure hx maximum humification coefficient for a given soil texture HRU hydrologic response unit IRC IMC input of organic C through residue and manure k maximum apparent soil organic matter decomposition rate multiplied by fE and ftool kM optimum manure decomposition rate kR optimum residue decomposition rate kS apparent soil organic matter decomposition rate kx maximum apparent soil organic matter decomposition rate MC MN MP manure organic C N and P mass MCN MCP manure C:N and C:P ratios MINMN net mineralization rates from decomposing manure MINRN net mineralization rates from decomposing residues N nitrogen Nmin mineral N in the soil layer P phosphorus RC RN RP residue organic C N and P mass RCN RCP residue C:N and C:P ratios SC SN SP soil organic carbon C N and P mass Sx reference or saturation soil organic C mass SCN SCP soil organic C:N and C:P ratios SOM soil organic matter SWAT Soil Water Assessment Tool Zl soil layer thickness |
本文献已被 ScienceDirect 等数据库收录! |
|