# Residues module (18_residues)¶

## Description¶

This module calculates the production of crop residues (straw etc.) and its subsequent use. Residues can be burned, used for feed, recycled to soils or used for other purposes (construction, fuel etc).
The module also calculates how much additional crops have to be produced in the case that feed requirements for residues exceed the production.
The module is therefore of use for the general model behaviour as well as the nitrogen module. In the future it might be used for a more detailed feed module.

### Input¶

Name Description Unit A B
$vm\_prod\_reg(i,k)$ regional aggreagted production mio. ton DM x
$vm\_dem\_feed(i,kli,kbio)$ regional feed demand including byproducts mio DM x
$vm\_area(j,kcr,w)$ agricultural production area mio. ha x
$fm\_feeding\_convergence(t)$ merging of feed parameters over time 1 x
$fm\_attributes\_residue\_ag(attributes,kve)$ Nutrient content of aboveground crop residues t nutrient per t DM x
$im\_attributes\_harvest(attributes,kve)$ attributes of harvested organs t DM WM Nr P K GJ per ton product x

The last columns of the table indicate the usage in the different realizations (numbered with capital letters)

### Output¶

Name Description Unit
$vm\_prod\_res\_ag\_reg(i,kve)$ production of aboveground residues in each region mio. ton DM
$vm\_prod\_res\_bg\_reg(i,kve)$ production of belowground residues in each region mio. ton DM
$vm\_dem\_res\_substitutes(i,kli,kcr)$ Demand for substitutes of crop residues (when more crop residues are required than would be produced for crop demand) mio. ton DM
$vm\_res\_supply(i,res\_use,kve)$ use of residues for different purposes mio. ton DM
$vm\_res\_use\_feed(i,kli,attributes)$ residues used for feed distinguished by kli Mt attributes

### Interface plot¶

Figure 0: Information exchange among modules

## Realizations¶

### (A) detailed (default)¶

As official global statistics exist only for crop production and not for crop residue production, we obtain the biomass of residues by using crop-type specific plant growth functions based on crop production and area harvested. Plant biomass is divided into three components: the harvested organ as listed in FAO, the aboveground (AG) and the belowground (BG) residues.

Eggleston et al1 (2006) offer one of the few consistent datasets to estimate both AG and BG residues. Also, by providing crop-growth functions (CGF) instead of fixed harvest indices, it can well describe current international differences of harvest indices and also their development into the future. The methodology is thus well eligible for global long-term modelling. Eggleston et al (2006) provide linear CGFs with positive slope and intercept for cereals, leguminous crops, potatoes and grasses. As no values are available for the oilcrops rapeseed, sunflower, oilpalms as well as sugar crops, tropical roots, cotton and others, we use fixed harvest-indices (positive slope without intercept) for these crops based on Wirsenius2 (2000), Lal3 (2005), Feller4 (2007). If different CGFs are available for crops within a crop group, we build a weighted average based on the production in 1995.

The above ground crop residue production is calculated as a function of harvested production (vm_prod_reg) and the physical area (vm_area_reg):

vm\_prod\_res\_ag\_reg(i,kcr) = \\
\sum_{i(j)} \sum_{w} vm\_area(i,kcr,w)) \cdot f18\_cgf("intercept",kcr)
+ vm\_prod\_reg(i,kcr) \cdot f18\_cgf("slope",kcr) \cdot im\_attributes\_harvest("dm",kcr)

Below ground crop production is calculated as a function of total aboveground biomass:

vm\_prod\_res\_bg\_reg(i,kcr) =
(vm\_prod\_reg(i,kcr) + vm\_prod\_res\_ag\_reg(i,kcr)) \cdot f18\_cgf("bg\_to\_ag",kcr)

The production of AG residues (vm_prod_res_ag_reg(i,kcr)) is assigned to four different uses (res_use): feed, on-field burning, recycling and other uses. Trade of AG residues is not considered, so that all produced AG residues have to be assigned to uses within the world region.

vm\_prod\_res\_ag\_reg(i,kcr) = \sum_{res\_use} vm\_res\_supply(i,res\_use,kcr))

The amount of AG residues which is burned or assigned to other uses is a fixed share (ic18_res_use_min_shr) of AG residue production (see q18_res_use_fixed).
Based on Smil5 (1999), residue burning is fixed to 15% of total AG crop residue dry matter in developed and 25% in developing regions for each crop. Other removals are assumed to be only in developing regions of major importance and are set in these regions to 10% of total residue dry matter production. All residues not assigned to feed, food, burning or other removals are assumed to remain in the fields.

vm\_res\_supply(i,res\_use\_fix,kcr) =
ic18\_res\_use\_min\_shr(i,res\_use\_fix) \cdot vm\_prod\_res\_ag\_reg(i,kcr)

While the feed demand in vm_dem_feed is residue-specific (kres), we allow that the demand can be settled by any mix of residues (vm_res_use_feed) or concentrates (vm_dem_res_substitutes) with the same nutritional values in regard to dry matter, energy and protein (dm_ge_nr). As the production of concentrates is costly, they are usually only used when not sufficient crop residues are available; allowing to feed them instead of residues prevents a model behaviour in which crops are produced just for feeding their residues.

vm\_res\_use\_feed(i,kli,dm\_ge\_nr) + \sum_{kcr} vm\_dem\_res\_substitutes(i,kli,kcr) \cdot im\_attributes\_harvest(dm\_ge\_nr,kcr)) \geq \\
\sum_{kres\_kve(kres,kcr)} vm\_dem\_feed(i,kli,kres) \cdot fm\_attributes\_residue\_ag(dm\_ge\_nr,kcr))\\
\\

\sum_{kcr} vm\_res\_supply(i,"feed",kcr)\cdot fm\_attributes\_residue\_ag(attributes,kcr)) =\\
\sum_{kli} vm\_res\_use\_feed(i,kli,attributes))\\

Limitations
no limitations

### (B) off¶

No representation of crop residues in the model.

vm\_dem\_res_substitutes.fx(i,kli,kcr) = 0\\
vm\_res\_use\_feed.fx(i,kli,attributes) = 0\\
vm\_prod\_res\_ag\_reg.fx(i,kve) = 0\\
vm\_prod\_res\_bg\_reg.fx(i,kve) = 0\\
vm\_res\_supply.fx(i,res\_use,kve) = 0

Limitations
underestimates the crop demand in some cases, because the crop residues have to be substituted by harvested crops in future

## Definitions¶

Name Description Unit A B
$ic18\_res\_use\_min\_shr(i,res\_use\_fix)$ minimal use share for residue use - x
$f18\_cgf(cgf,kve)$ crop growth functions for all vegetation types containing slope, intercept and bg_to_ag ratio - x
Set Elements Description
$ghg$ n2o_n, ch4, co2_c Greenhouse gases
$res\_use$ recycle,feed,burn,bioenergy,other use of crop residuess
$res\_use\_fix(res\_use)$ burn,bioenergy,other exogenously fixed use of crop residues
$cgf$ slope, intercept, bg_to_ag crop growth functions

## Developer(s)¶

Benjamin Bodirsky