Calculate N and C flows: PN4-biomass to leaching - not reading in code and differences to CENTURY

[kieungocle]

I am comparing C&N flow in CENTURY (Izauralde et al. ,2006 - Simulating soil C dynamics with EPIC: Model description and testing against long-term data) to codes in cbn_zhang2.f90. They are a bit different:

1. PN4 = BMCTP × ABL × NCBM biomass to leaching was EXCLUDED: line 462
   !pn4 = org_tran%bmctp * org_allo%abl * org_ratio%ncbm !biomass to leaching (calculated in ncsed_leach)
2. PN2 = LSLCTP × (1 − ALSLCO2) × NCHS instead of multiply with (1.- a1co2) it was 0.7
   pn2 = .7 * org_tran%lslctp * org_ratio%nchs
3. PN6 = BMCTP × (1 − ABL − ABP − ABCO2) × NCHS, abl : carbon allocation from biomass to leaching was excluded in cbn_zhang
   pn6 = org_tran%bmctp * (1.-org_allo%abp - org_allo%abco2) * org_ratio%nchs !biomass to slow
   The reason I am looking at these is because right now up to version 61.0.2.10, the structural litter is extremely high for corn, starting from the middle of the simulation period. We also still have stepping-stair residue; it only changes when an operation like tillage happens.

Thanks,
Kieu