This variable will force the ratio of yield to total above-ground biomass to the specified value. If biomass is cut and removed (e.g., in hay cuttings), harv_idx must be used to specify the amount of biomass cut. For grain harvest, the harvest index in the plant growth database (plants.plt) is used instead of harv_idx, which assumes that only the seed is being harvested.

If the biomass is below harv_bm_min, the harvest operation will not be performed.

There are several SWAT+ files that contain pre-defined management operations:

• Harvest: harv.ops

• Grazing: graze.ops

• Irrigation: irr.ops

• Application of fertilizers, manure, and pesticides: chem_app.ops

• Burning/fire operations: fire.ops

• Street sweeping in urban areas: sweep.ops

The default harv.ops file includes the following harvest types:

The fertilizer name for manure deposited during grazing is a foreign key referencing name in fertilizer.frt.

This operation harvests the portion of the plant designated as yield and removes the yield from the HRU but allows the plant to continue growing.

The name of the harvest operation is a primary key referenced when harvest operations are scheduled in management.sch or lum.dtl. All names in the harv.ops file must be unique.

For grain harvest, the harvest efficiency defines the fraction of yield biomass removed by the harvesting equipment, with the remaining yield lost. For biomass harvest, if harv_eff is close to zero, the cutting or clipping are left on the ground and if harv_eff is 1.0, all cut biomass (yield) is removed. If the harvest efficiency is not set or 0.00 is entered, the model assumes the user wants to ignore harvest efficiency and sets the fraction to 1.00 so that the entire yield is removed from the HRU.

This operation removes plant biomass at a specified rate and allows simultaneous application of manure.

The name of the grazing operation is a primary key referenced when grazing operations are scheduled in or . All names in the graze.ops file must be unique.

The name of the irrigation operation is a primary key referenced when irrigation operations are scheduled in management.sch or lum.dtl. All names in the irr.ops file must be unique.

Trampling becomes significant as the number of animals grazing per hectare increases. This is a very subjective value which is typically set equal to bm_eat, i.e., the animals trample as much as they eat.

The irrigation efficiency is the fraction of water used for irrigation that is available for crop uptake from the soil.

The name of the chemical application is a primary key referenced when the application of fertilizers, manure, or pesticides is scheduled in or . All names in the chem_app.ops file must be unique.

Amount of the chemical applied to the upper 10 mm of the soil.

The name of the fire operation is a primary key referenced when burning/fire operations are scheduled in management.sch or lum.dtl. All names in the fire.ops file must be unique.

The name of the street sweeping operation is a primary key referenced when street sweeping operations are scheduled in management.sch or lum.dtl. All names in the sweep.ops file must be unique.

The entire curb length is often not available for sweeping due to the presence of cars and other obstacles.

The removal efficiency of street sweeping is a function of the type of sweeper, whether flushing is a part of the street cleaning process, the quantity of total solids, the frequency of rainfall events and the constituents considered. Removal efficiency can vary depending on the constituent being considered, with efficiencies being greater for particulate constituents. The removal efficiencies for nitrogen and phosphorus are typically less than the solid removal efficiency (Pitt, 1979).

Because SWAT+ assumes a set concentration of nutrient constituents in the solids, the same removal efficiency is in effect used for all constituents.

References

Pitt (1979)