For Presentation at the Zerotill Association Annual Meeting

January 1992

Maintaining residue cover on the soil surface provides several benefits to efficient crop production. Those are:

1. Reduce soil erosion (both wind and water).
2. Trap snow for soil moisture.
3. Protects winter crops
4. Improves soil tilth.
5. Enhances water intake rate of the soil.

Probably the most important benefit of keeping a residue cover on the soil surface is to reduce erosion. One of this nations most serious conservation problems is soil erosion. No-till planting systems has been shown to reduce soil

erosion by over 95% of that which occurs from clean tilled fields. Figure1 shows that if an 85 to 100% residue cover is maintained on the soil, almost no soil is lost from the field. If water erosion does occur, soil particles are carried along and sedimentation has been identified as a major water quality problem in many parts of North America.

A reduced tillage management system should start with straw and chaff spreading at harvest. Unless straw and chaff

is spread uniformly across the field, it will plug seeding equipment, which makes no-till and reduced tillage seeding

next to impossible. Also, thick mats of chaff and straw are difficult to seed through and are difficult for the young seedling to emerge through. Figure 1.

Fig. 1

High yields coupled with the use f the big headers and large capacity combines mean that large quantities of residue will be deposited behind the machine. Most straw choppers and spreaders commercially available on combines are able to spread straw adequately. Cross harrowing fields immediately after harvest is one method of getting straw spread uniformly. However, this requires an additional field operation and it does little to spread chaff. Chaff pieces are small and a harrow will do little more than move it an inch or two while stirring the soil surface as well.

Harrowing will also break down standing stubble that is necessary to catch snow.

Canadian studies have shown straw choppers and spreaders are capable of spreading residue over a 20 to 24 foot width. If this is not possible on your machine, a modification to the straw chopper is suggested. University of Saskatchewan Agricultural Engineers have a plan available for wide spread fins to replace the standard straw chopper tailplate.

Chaff is usually more troublesome than straw. Chaff dropped directly behind the combine forms a firm mat when it becomes wet. Disc drills have a hard time penetrating heavy chaff and seed placed into the mat may germinate poorly. Hoe drills lift the chaff mat and place the seed beneath it, but seeding emergence can then be a problem with cooler soil temperatures under the mulch. The concentration of chaff ties up nitrogen and provides an excellent place for weeds to germinate and grow. Also, numerous microorganisms are concentrated in the mat that may attack the emerging seedlings as they try to grow through the chaff. Even distribution of crop residue is essential for successful reduced tillage farming.

Several companies offer add-on, mechanically or hydraulically driven chaff spreaders. These usually consist of a horizontally rotating fan or a high velocity stream of air to distribute the chaff. Canadian testing of commercially

available chaff spreaders show that most do a good job of spreading. Chaff is difficult to spread evenly because of

its light weight. From Figures 2 and 3, chaff spreaders are able to spread chaff equal to or beyond the width of spread of straw. The Rem chaff spreader is able to spread chaff 18 to 22 feet to each side of the combine. The John Deere chaff spreader is able to spread chaff up to 14 feet to each side of the machine.

Straw spreaders were included in the trials along with the chaff spreaders. A straw spreader was installed on the Case IH and a straw chopper was installed on the John Deere machine. From Figures 2 and 3, the standard straw spreader on the Case IH spread the straw from 10 to 14 feet to each side of the machine for a total spread of, 24 feet. The John Deere standard straw chopper spread straw up to 12 feet to each side for a total spread of 24 feet, This should be adequate to prevent a major buildup of residue for most no-till operations. If a 40-foot swath is picked up with the combine, the standard straw and chaff spreaders may concentrate the residue in too narrow a strip. Some modifications to equipment may be required to increase the width of spread such as extending straw chopper fins.

Always take safety into consideration when choosing a straw or chaff spreader. They have additional moving parts and should be shielded as much as possible to avoid injury. Ease of access to the combine cleaning sieves should also be considered when looking at the different models. Some spreaders restrict sieve access, making changes of combine settings difficult. Some are driven with hydraulic motors or with belts, and some of the hydraulic models swing to the side for easy access.

Figure 2

Figure 3

**Mention of brand names does not constitute endorsement of one particular product over another.