DAYCENT Model Overview, Testing and Application to Agroecosystems S.J. DEL GROSSO, W.J. PARTON, D.S. OJIMA, A.R. MOSIER and C. KEOUGH

Improved NPP Submodel P G = G pot *F(light)*F(LAI)*F(Temp)*F(H 2 O) Potential Growth (CO 2,T,H 2 O) SHOOT C,N,P,S ROOT C,N,P,S GRAIN C,N,P,S NPP Nutrients Shading Phenology Nutrient/H 2 O stress SURFACE LITTER SOIL LITTER Tillage Temp H 2 O Temp H 2 O Crop H 2 O Del Grosso et al. in prep.

Parton et al. 2001

Del Grosso et al coarse fine

Variable effective plant rooting depth PET = F(Lat, DOY, T avg, T max – T min ) Weekly scheduling of management events Germination = F(T surface ) Harvest/Senescence = F(GDD, T surface ) Canopy absorption of NOx emitted from soil Recent Model Improvements

IPCC Emission Factor Calculations N cult = 0.1 gN m -2 yr -1 N om = N sludge + N manure N 2 O direct = 1.25%*(N stuble + N fert + N om ) + N cult NH 3 + NOx = 0.1N fert N leach = 0.3N fert N 2 O indirect = 0.01(NH 3 + NO x ) N leach Direct N 2 O emissions Indirect N 2 O emissions

Fig4 a) b)

National GHG Inventory Bruce McCarl’s 63 regions EPIC soils and daily climate data Simulated dominant rotations for each region Rain fed and irrigated N fertilizer but no manure additions Converted model output in gN 2 O-N m -2 to regional totals for the dominant crop rotations using state level planted acres reported by NASS

Regional Level Validations

Simulated Regional N 2 O Emissions

N 2 O by Crop

National N 2 O and GHG net

Area normalized N 2 O

Area normalized GHGnet EPA vs. DAYCENT N Inputs