Recent data indicate that soil erosion on cropland in most of Iowa is below 5 tons per acre--the allowable or tolerated soil erosion limit assigned to most soils. However, in some areas, soil losses due to water erosion exceed the allowable soil erosion limit. Because the amount of soil lost due to erosion each year is directly proportional to the amount of crop residue remaining on the soil surface, good residue managers intentionally leave as much of the past year's crop residue on the soil surface as possible.
Top 10 Ways to Leave More Residue
Source: Conservation Catalog. USDA Soil Conservation Service, Des Moines, IA (October 1991).
Thinking about crop residue in 2003 yet?
You may already have made substantial changes in your farming operation to reduce erosion, but at the heart of your conservation plan should be some provision for conservation tillage, or tillage that leaves at least 30 percent of the field surface covered with crop residue after planting. Conservation tillage practices are compatible with any cropland and crop practice, and also reduce labor, fuel, and time costs.
How do crop residues work?
Pounding raindrops can quickly dislodge soil particles and splash them up to 3 feet away. The soil splash is only the beginning of the problem. Splashed particles begin clogging soil pores, effectively sealing off the soil's surface, resulting in poor infiltration. Rainwater starts to collect and move down-slope, carrying with it dislodged soil particles. Crop residues retard soil erosion by limiting soil splash and protecting the soil's surface from the direct erosive impact of raindrops. Crop residues are indicators of how well your soil is protected from water erosion, and how you are doing on your conservation plan. Residue also inhibits erosion by slowing runoff and reducing its energy to transport soil.
Planning for 2003 starts now.
Going into 2003, you should be able to answer three questions about your crop residue strategy.
- Do you know how much crop residue is on your field now?
- Do you know how you arrived at that level? and
- What strategy are you are going to use from now until after planting in 2003 to achieve at least 30 percent residue cover?
First, you need to know where you are in the crop residue spectrum and whether you can achieve the 30 percent crop residue target. As the season winds down, go out and check your crop residues. Knowing how to estimate or measure crop residue now will help you estimate what residue will remain as new crops emerge next spring. Did you get an even distribution out of the combine? Was the crop heavy or light? Is the residue from soybean, corn, or another crop? An even distribution of crop residue while harvesting is critical. Leaving residues on top of the soil is even more important.
Second, include the impact of any tillage or fieldwork you've performed since harvest (Table 1) Did you do any fall tillage? Knife in manure? After winter decomposition, where will you be?
Third, consider the strategy that you are you going to use to hit the crop residue target in 2003. Now is a great time to go to conservation tillage. Several tillage management systems preserve significant crop residue. Among them are no-till, a tillage system where no disturbance of the soil occurs before planting with the exception of injection of liquid manure or anhydrous ammonia. It leaves nearly all of the available crop residue on the soil surface at planting time. Strip-tillage requires tilling only in narrow strips (6 to 8 inches in width) where next year's rows will grow (fertilizer such as phosphorus and potassium or anhydrous can be placed in the strips at the same time.)
For resources on tillage strategies, see ISU Extension publication MWPS 45, Conservation Tillage Systems and Management (2nd edition), a 270-page handbook on conservation tillage systems. Also, talk to your county's soil conservation experts and discuss conservation tillage with equipment dealers.
Using crop residue is a simple, powerful strategy for saving that resource. Converting to any conservation tillage practice requires learning and adopting new farming techniques, operating specialized equipment, and handling different products. But many producers find that going to conservation tillage reduces fuel costs, improves water quality by reducing sediment transport to surface water, saves time, and conserves moisture while reducing erosion.
You may already have made some choices for 2003, starting with the amount of residue left on the ground during combining and fall tillage. But as you plan for next spring, keep in mind the important role that crop residues play in your overall conservation plan.
Table 1. Estimating crop residue. Multiply each operation by the existing percentage of residue left to find how much ground cover will be left after each tillage operation.
|Over winter decomposition||0.80-0.90||0.70-0.80|
|Chisel (twisted shank)||0.40-0.50||0.10-0.20|
|Disk (off-set, deep)||0.25-0.40||0.10-0.20|
|Chisel (straight shank)||0.50-0.60||0.30-0.40|
|Disk (tandem, shallow)||0.65-0.75||0.25-0.35|
Two Residue Management Scenarios
|Harvests corn and has 95% residue existing.||95%|
|Over winter, some residue is lost to decomposition; multiply by 0.90||95% x 0.90 =||85%|
|In spring, stalks are run over with the disk (deep); multiply by 0.40||85% x 0.40 =||34%|
|Cultivates field; multiply by 0.9||34% x 0.90 =||31%|
|2003 crop is planted; multiply by 0.9||31% x 0.90 =||28%|
|Therefore, in a best-case scenario, producer A would have approximately 28% residue remaining after planting, which is below the recommended 30%.|
|Harvests corn and has 95% residue existing.||95%|
|Over winter, some residue is lost to decomposition; multiply by 0.9||95% x 0.90 =||85%|
|In spring, 2003 crop is planted in the stalks; multiply by 0.9||85% x 0.90 =||76%|
|Therefore, in a best-case scenario, Producer B would have approximately 76% residue remaining after planting, which is well above the recommended 30%.|
This article originally appeared on pages 193-194 of the IC-488(23) -- November 18, 2002 issue.