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4/16/2012 - 4/22/2012

How Much Crop Residue to Remove

By Mahdi Al-Kaisi, Department of Agronomy

Crop residue removal—what effect does it have on corn yield and soil quality? That’s a question quite often asked these days.

The adoption of no-till and other conservation tillage systems help keep significant amounts of crop residue on the soil surface, which can create management challenges, especially in areas with wet and cold soil conditions. Also, more acres of continuous corn are being grown, which leads to a greater amount of crop residue on fields compared to corn-soybean rotation. These higher levels of crop residue bring more challenges for farmers.

Increased use of no-till and other conservation systems helps sustain the soil quality and improve environmental quality by reducing soil erosion. However, in the near future corn residue could be removed from fields for cellulosic ethanol production in addition to current animal uses. This trend may encourage the switch to continuous corn, which can lead to high N application and more conventional tillage. The increase in conventional tillage coupled with high use of nitrogen fertilizer in continuous corn will present a significant soil and water quality challenge. The trend to more continuous corn, more crop residue removal, higher rates of nitrogen applied and potentially more tillage will present economic and environmental challenges that we need to consider.

The use of corn stover for cellulosic ethanol production or any other use should be weighed against the potential impact on soil productivity, environmental consequences and food availability. That’s why researchers are looking at the potential for crops like miscanthus and switchgrass for making cellulosic ethanol. To strike a balance between environmental sustainability and economic viability, alternative perennial biomass sources for cellulosic ethanol production are being explored to combine with corn grain ethanol.

The value of crop residue is obvious.

How much residue to harvest?

The main crop Iowa grows is corn and the crop residue corn produces each year is the most readily available feedstock for making cellulosic ethanol and for animal use. But that residue plays a very important role in sustaining soil quality which must be kept in mind when deciding how much corn stover to harvest and how much to leave on a field.

Leaving crop residue on the soil surface will improve the cycling of nutrients and ultimately soil quality, both of which increase and sustain soil productivity. Corn residue left on the field after harvest is a critical source of soil organic matter; it provides protection for the soil against water and wind erosion; and it contributes to the improvement of soil and water quality.

Alternative uses of corn residue for various purposes, such as baling the residue for livestock use or for cellulosic ethanol production, needs to be approached carefully. Removal of too much crop residue potentially can have adverse effects on soil and water quality.

How much corn residue can be safely removed from a field? Sustainable stover removal rates depend on several factors such as soil erodibility, surface slope, cultural practices and climate conditions. Recent studies suggest that only 20 to 30 percent of the total stover production could be removed for biofuel, based on ground cover requirements to control soil erosion. However, other studies suggest that residue removal should be lower than 20 percent, especially with conventional tillage, in order to maintain soil quality and nutrient cycling for long-term soil productivity.

Consider long-term effects of residue removal

The impact of crop residue removal on soil productivity and environmental quality is not a short-term outcome, particularly in the Midwest, where high organic matter, high soil productivity and good agriculture production conditions mask the short-term effect of residue removal.

Possible short-term impacts of corn stover removal may include an increase in amount of nitrogen, phosphorus, potassium, calcium, magnesium and other nutrients that need to be applied to replace these nutrients lost due to crop residue removal. Potential deficiencies of nutrients and decline of organic matter in the soil are both the long-term impacts. It was estimated that nutrients replacement cost due to corn residue removal was approximately $20 per ton of removed corn residue. These nutrients will be permanently lost from the soil system nutrients pool due to lack of replenishment from crop residue and they have to be added to maintain soil productivity.

Keep in mind that when you harvest corn crop residue from a field, a significant amount of carbon, nitrogen, phosphorus and potassium is removed. Using no-till and above agronomic nitrogen fertilizer rate may help in reducing soil organic matter loss in the short-term due to crop residue removal.

Key Points:
• What else do you remove when you harvest corn crop residue from a field?
• A significant amount of carbon, nitrogen, phosphorus and potassium is removed.
• Using no-till and adequate N application rates may minimize soil organic matter loss due to residue removal in the short-term.


Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or (515) 294-8304.

Pay Attention to Soil Crusting After Heavy Rain Events

By Mahdi Al-Kaisi, Department of Agronomy and Mark Hanna, Department of Agriculture and Biosystems Engineering

Recent rain brings another challenge for farmers, especially in fields conventionally tilled last fall or early this spring. In addition to potential soil erosion and damages to soil structure rainfall can cause, there are after effects of the rain when the soil surface starts to dry. The potential problem is soil crust.  Soil crust is a product of a weak soil structure and the absence of residue or cover crop to protect soil surface from the intensity of rainfall.  
This could occur especially in intensively tilled fields where residue cover is not adequate, as well as with fine texture soils and soils with low organic matter content. These conditions could increase the potential for soil crust formation. Residue cover plays a significant role in reducing soil crust by absorbing the impact of rain drops that destroy soil surface structure.  The destruction of soil structure impacts plant germination and seedling emergence for both corn and soybean. 

Soil crusting can also result in poor growing conditions and reduced water infiltration. Soybean seedling emergence can be a problem if a dense surface crust forms. In this situation, hypocotyl is broken when pushing up against a solid crust. Monitor high-risk fields for soil crusting, especially where plant emergence has not yet occurred, in order to avoid damage to seedlings.

Rotary Hoe
The quick-relief solution to such a problem is the use of a rotary hoe. This tool is commonly used in treating soil crusting to improve seedling emergence. However, the timing is critical in order to achieve the intended results and prevent seedling damage.  The rotary hoe is a potentially good tool to use to break up soil crust, but make sure you've got a crust that is actually sealing the soil surface before using it. 

To minimize the damages to the seedlings and to increase success, rotary hoe at a time when the soil surface is at the right moisture conditions. This will require frequent field scouting to ensure that soil surface moisture is just above field capacity. Field capacity is the point when a handful of soil will crumple easily in your hand under minimum pressure, leaving a trace of moisture on your palm. This moisture condition will ensure less damage to emerging seedlings and less soil compaction during the hoeing process. 

Rotary hoe at high field speeds (8 to 10 miles per hour) unless safety is a concern. However, if soybeans are the crop emerging, make sure both cotyledons aren't broken off by the hoe. Corn will likely be the crop emerging from rains this past weekend. Expect a minor stand loss (approximately 1 to 2 percent) from hoeing, but this should be insignificant if corn is truly having difficulty breaking through a crust.  Getting off the tractor and checking for stand loss is a good idea when starting a field. If loss seems excessive (greater than 3 to 5 percent), you may want to slow your travel speed to be less aggressive with the tool.  

It is very important to check early-planted fields periodically, especially those conventionally tilled with fine soil texture and low organic matter. Timing is important to manage soil crust at the proper moisture conditions.


Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or (515) 294-8304. Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at or (515) 294-0468.

How Long Will it Take Corn to Emerge?

By Elwynn Taylor and Roger Elmore, Department of Agronomy

It’s an understatement to say that March in Iowa was much warmer than normal (Figure 1). Although only a few record high daily temperatures were set, the average monthly temperature set a new record by a substantial margin. The consistent warm weather encouraged a few to plant corn as early as mid-March. Soil temperatures state-wide reached 50 F by March 15. Although not a first historically, it was a full month before soils normally warm to 50 F at the 4 inch depth.

The warm soil temperatures encouraged rapid germination and seedling emergence – by the third week of March. With April came a “hard” freeze (low air temperatures below 28 F) and a cooling of the soils to levels that did not sustain rapid seedling development.

Planting corn into cool soils increases variability not only of emergence, but also of plant to plant sizes and development stages. In addition the freeze likely destroyed some or all of the leaves of emerged plants; but, since seedlings’ growing points were still well below ground, plants likely recovered and stands (plant populations) were unaffected. Frosted plants typically recover at different rates resulting in variable growth and development. Variability in plant size – whether from cool soil temperatures or from frost - will affect plant-to-plant competition and reduce yield.

Corn typically requires 90 to 120 Growing Degree Days (GDD) from planting to emergence. Of course this GDD range assumes adequate soil moisture and varies with planting depth, tillage system and residue cover. As a rule of thumb, if 120 GDD have accumulated since planting and seedlings haven’t emerged, check the condition of planted seed.

You may track GDD accumulations for the Corn Belt location of your choice by clicking on ‘single site graphs’ on the Mesonet website. Your specific planting date information is easily selected from the drop-down windows. Choose the weather station near your farm from the list or select by clicking the “dot on the map” near your farm. Track the GDD accumulation at your location (a blue line is produced) and compare it to the normal GDD accumulation for your location (a red line is displayed). It is helpful to also make a graph of last year to give you an idea of average GDD accumulation to help visualize the similarities and differences between this year and the past year.

You need to remember that GDD’s are calculated based on air temperatures using the 86/50 method typical for corn production. Using that method, if air temperatures remain at or below 50 F, emergence will not occur. 

Since GDD calculations are based on air temperatures, four-inch soil temperatures may actually better predict seedling emergence than accumulated GDD’s. The Mesonet provides a daily update of both the Iowa soil temperature and GDD. Laboratory studies have shown that for most corn hybrids grown in the Midwest, seedling emergence is about three weeks if the soil temperature is 51 F and is about one week if the daily soil temperature holds near 70 F (Figure 2). 

After emergence, evaluate the surviving plant stand carefully whether or not you expect good emergence and seedling survival. Both poor stands and plant-to- plant variability lower yield potential. Depending on the potential date of replant though, keeping the surviving stand – albeit of variable plant heights and development – may still be the best option. (See: Replanting Information)

Figure 1. Most Iowa locations enjoyed at least one March day of temperatures reaching 80 F.   At Ames the average daily high was 64 F, eclipsing the old record of 58 F set in 1968.
 Climodat information from


Figure 2. If the soil temperature is averaging 50 to 55 F (10-12.8 C) at the time of planting, corn may take three weeks to emerge. Temperatures averaging 60 F (15.6 C), may have emergence in 10 days to 12 days. Soybean emergence usually requires that soils be about 10 degrees warmer than for corn although soybean does begin to respond at 50 F.
  Data from Elwynn Taylor, Iowa State University.


 Elwynn Taylor is extension climatologist and can be reached at or by calling (515) 294-1923. Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or (515) 294-6655.

This article was published originally on 4/23/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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