Cereal Straw Raking: Wheat, Barley and Oat Windrow Guide

Cereal Straw Raking: Wheat, Barley and Oat Windrow Techniques

Straw raking after grain harvest operates under engineering constraints that are fundamentally different from forage hay raking. The primary objective is not leaf retention — straw has no significant leaf fraction — but soil contamination control, windrow positional accuracy for baler pickup, and stubble clearance management to prevent tine-to-ground contact that drives soil into the windrow. The two variables that control straw raking quality are tine ground clearance above the stubble surface and forward speed relative to the combine straw spreading width. These two parameters — not ground pressure or moisture content — are the primary calibration targets for straw raking operations.

Why Straw Raking Is a Different Engineering Problem from Forage Raking

Forage hay raking optimizes for dry matter recovery from a crop that has a leaf fraction carrying most of its nutritional value. Straw raking optimizes for bulk collection of a material that has virtually no leaf fraction, minimal nutritional value, and is valued primarily for bedding and mulch volume rather than nutritional composition. The quality criteria for straw bales are cleanliness (low soil contamination), dry bale density (for transport and storage volume efficiency), and uniform moisture distribution within the bale (to prevent mold during storage). None of these criteria requires the low-impact, low-speed, low-ground-pressure approach that dominates forage raking management.

Straw is harvested by a combine that cuts the grain heads and deposits the straw chaff through the rear of the machine in a spread pattern. Combine straw spreading width varies from 3.5 m to 8.0 m depending on the combine model and chopper/spreader configuration. The deposited straw layer is typically 60-150 mm thick and lies directly on the stubble surface — there is no intermediate field-drying phase as with forage crops, because the straw has already been field-cured through the grain maturation process and arrives at the rake with a moisture content of 10-18%.

At these low moisture levels, straw is rigid and brittle. The brittle failure mode of dry straw under tine contact is fundamentally different from the petiole detachment failure of legume leaves: broken straw creates fine chaff that is lost to wind dispersal rather than remaining in the windrow, reducing the recoverable yield per hectare. However, because straw has no nutritional value in its leaf fraction, the chaff loss rate that would be commercially unacceptable in alfalfa raking (above 3% dry matter) is operationally acceptable in straw raking if it does not exceed approximately 8-12% of the total straw yield. The quality concern in straw raking is soil contamination, not material loss.

Wheat, Barley and Oat Straw: Physical Property Comparison

Stubble Height, Tine Ground Clearance and Soil Contamination

The Soil Contamination Mechanism in Straw Raking

Soil contamination in straw bales enters through one primary mechanism: the tine tip contacts the soil surface and physically displaces soil material into the straw mat as the tine lifts and sweeps the windrow. A tine operating at ground contact drives a small wedge of soil in front of the tine tip during each contact event — the displaced soil is then swept into the windrow with the straw material and enclosed in the bale. At the density of tine contact events in a 9-wheel rake operating at 10 km/h (over 10,000 contact cycles per hour across the machine width), a consistent tine-to-soil contact produces meaningful soil contamination of the windrow within a single field pass.

The critical control parameter is the vertical gap between the lowest point of the tine arc and the soil surface — the effective ground clearance. This gap must be large enough to prevent tine-to-soil contact throughout the full wheel rotation arc, including the point of maximum ground pressure spring deflection on undulating terrain. On flat stubble fields with a consistent stubble height of 20-25 cm, maintaining 50-80 mm of clearance between the tine tip at its lowest arc point and the soil surface is achievable with the ground pressure set to 15-22 kg per wheel — the tine lifts the straw from the stubble surface without driving into the soil below the stubble root zone.

On lodged barley fields — where barley stems have fallen horizontally before harvest and the combine cuts at near-ground level, leaving stubble of only 8-15 cm — maintaining clearance becomes the primary engineering challenge. Short stubble and soil-level crop deposition require the rake to operate with the tine arc contacting close to the soil surface to recover the fallen material. In these conditions, soil contamination is an accepted operational cost that must be managed by limiting ground pressure to the absolute minimum that achieves adequate pickup and by avoiding raking in wet soil conditions where the tine wedge effect is amplified by soil cohesion.

Stubble Height x Tine Ground Clearance x Contamination Risk Matrix

Raking Speed and Windrow Width for Straw Baling Efficiency

Straw raking forward speed can be higher than forage hay raking because the primary quality constraint — soil contamination — is controlled by ground clearance and soil conditions rather than by forward speed. At 13-16 km/h, a well-clearanced finger wheel rake in a tall wheat stubble field produces a clean windrow with recovery rates above 90% — a forward speed that would be unacceptable in alfalfa or clover hay raking but is within the normal operating range for straw.

The upper speed limit for straw raking is set by windrow integrity rather than contamination or leaf loss. At very high speeds (above 16 km/h), the centrifugal tine action at the outer wheel positions throws straw material beyond the windrow boundary rather than depositing it cleanly into the windrow. This reduces windrow density and creates scattered straw residue that the baler pickup cannot cleanly recover. The practical speed ceiling for straw raking is 14-16 km/h on flat fields with tall stubble, reduced to 12-13 km/h on fields with shorter stubble, variable topography, or in humid conditions where the straw mat has reabsorbed surface moisture from overnight dew.

Windrow width for straw baling should be matched to the baler pickup width at 90-95% of rated pickup width — the same baler-matching principle that applies to forage raking, but with wider tolerance because straw windrows are structurally rigid and do not spread laterally between raking and baling as forage windrows do. A straw windrow raked at 1.6 m width will remain at approximately 1.5-1.6 m width 4 hours after raking; an alfalfa windrow raked at 1.6 m may spread to 1.9 m in the same period under warm, windy conditions. This structural stability allows straw windrows to be raked to closer to 100% of baler pickup width without edge spillage risk.

Combine Straw Spread Width and Rake Working Width Matching

The working width of the straw rake should be matched to the combine straw spreading width, not to the combine header width. A combine with a 9.0 m header and a straw chopper/spreader system that delivers a 5.5 m spread pattern requires a rake working width of 5.5-6.5 m to consolidate the spread straw into a windrow in a single pass without leaving residue at the spread edges.

When the rake working width is less than the combine spread width, the outer edges of the spread straw are not reached on the first pass and require a second raking pass — adding machine hours and increasing the risk of soil contamination from the second pass over material that was not fully recovered in the first. When the rake working width exceeds the combine spread width, the outer wheel positions operate on clean stubble without straw material, producing unnecessary drawbar load and tine wear with no yield benefit.

For combines spreading at 5.0-6.0 m, the mower-rake combination configuration is a highly efficient option for straw raking operations, particularly on farms that also cut forage crops in the same season. The 9GL-5.0/5.6 trailed mower-rake covers 5.0-5.6 m working width in a trailed configuration that requires no front-mounted toolbar — the trailed geometry suits farm fleets where the tractor front hitch is used for other attachments during the cereal harvest period.

Straw Raking After Rain: Timing and Recovery Protocol

Harvested straw exposed to rain reabsorbs surface moisture rapidly — the hollow culm and large surface area of cereal straw produces a surface wetting event within 1-2 hours of rain onset. After a 10 mm rain event, surface straw moisture can rise from 12% to 28-35% within 4-6 hours. This moisture reabsorption does not uniformly penetrate the straw mat — the upper straw layer wets first, while the lower layers in contact with the stubble surface may remain closer to the pre-rain moisture level.

Post-rain straw raking protocol: allow a minimum of 4 hours of sun and wind drying after the rain ends before beginning raking. The windrow formed immediately after rain will have a moisture stratification — wet upper surface, drier lower layers — that will not equilibrate uniformly in the bale without extended field-drying time post-rake. At 6-8 hours post-rain under moderate drying conditions, the surface moisture has typically returned to within 5 percentage points of the pre-rain level, which is the practical raking-ready threshold for straw.

Soil contamination risk after rain is elevated regardless of stubble height. Wet soil has higher cohesion and adheres to tine surfaces more readily than dry soil, which transfers more soil material per contact event into the windrow. Reduce forward speed to 10-12 km/h post-rain and verify tine cleanliness by hand inspection after the first 200 m — soil buildup on the tine surface changes the contact geometry and increases contamination disproportionately once a soil layer begins to accumulate.