There has been recent interest in producing ethanol from crop residues to reduce U.S. reliance on imported fossil fuels. In the Midwest, corn residue remaining after grain harvest is one of the most abundant sources of crop residue. If corn residue removal for ethanol production will occur, we believe that it will preferentially occur in fields where corn is grown continuously and not in rotation with soybean, since corn residue is a source of inoculum for many corn diseases. Furthermore, corn residue has a high carbon to nitrogen ratio, thereby favoring immobilization (the process by which soil microorganisms convert plant available nitrogen to a form that they tie up in their bodies, rendering it unavailable to plants). We therefore hypothesize that when corn is grown continuously, removal of corn residue will reduce the economic optimum nitrogen rate.
While removal of corn residue may reduce the amount of nitrogen fertilizer required for a subsequent corn crop and suppress diseases, we have to consider other roles of crop residue on subsequent crops, and on soils. Residue removal can affect water content, temperature, and strength of soil, thereby affecting corn emergence and growth. Crop residue on the soil surface also reduces water erosion by intercepting raindrops and protecting against soil detachment, hence its removal will tend to reverse these effects.
Maintenance of soil organic matter requires a continuous supply of plant residue to the soil. Previous research with continuous corn in Iowa showed that maintenance of soil organic matter levels required 2 tons/acre of corn residue left on the soil surface prior to plowing each fall (Larson et al., 1972). Similarly removal of corn residues for 10-12 consecutive years in Indiana and Iowa reduced soil organic matter levels by 10 to 13% under conventional tillage (Barber, 1979; Larson et al., 1972). More recently, differences in soil physical properties and organic matter in the upper four inches of the soil were identified after only two seasons of residue removal in no-tillage continuous corn in Ohio (Blanco-Canqui et al., 2006). The effects of residue management on corn response to nitrogen fertilizer and soil quality, however, will likely be influenced by tillage due to complex associations between residue and soil near the soil surface. Furthermore, different levels of nitrogen fertilization may influence soil response to residue removal. Such information is vital to decisions about future cropping systems.
While there is some published research on the effects of residue removal on continuous corn yield, there is little published research on how residue removal affects continuous corn response to nitrogen fertilizer or other management practices under various tillage systems. When we have completed this work, we will better know the effects of corn residue removal on the response to nitrogen fertilizer, and on soil quality. With recent instability in the cost of energy and subsequent explorations into alternative energy sources, removal of corn residue for ethanol production is likely in the future. Understanding corn response to nitrogen fertilizer rate and tillage in fields will be key to our ability to manage corn for maximum economic and environmental outcomes. Illinois producers also need to know how residue removal will affect soils and yields before they can confidently remove some of it, and before they can know what price they will need for the residue. Our objective with this research is to answer these questions.
This study was initiated following corn harvest in the fall of 2005 at four University of Illinois Crop Sciences Research and Education Centers: DeKalb, on an Elpaso silt loam soil; at Monmouth, on a Muscatune sil; at Perry, on a Clarksdale sil; and at Urbana, on a Drummer sicl. Main plots are assigned on of three levels of residue removal—full, partial, and none—with full removal accomplished by chopping stalks and raking them off the plots and partial removal done by raking without chopping stalks. Partial removal thus approximated the effect of baling off some stalks without chopping them: it removed bout 50 to 60% of the residue and left in the field portions of mostly lower stalk and fine material. Full removal left a considerable amount of fine material, but less than 10% of the residue dry weight.
Two tillage systems—chisel plow and none—were assigned to subplots within residue removal main plots, with chiseling done soon after residue removal. No-till plots were undisturbed in the fall, and were planted using a planter equipped with trash movers. Four N fertilizer rates—60, 120, 180, and 240 lb N per acre—were assigned to sub-subplots, and were applied as 28% urea-ammonium nitrate solution, either just before planting or as a sidedress application. Sub-subplots were 6 or 8 rows (15 or 20 ft.) wide by 50 to 60 ft. long. Treatments have remained in the same place each year in each field.
A plot combine was used to harvest the center two or four rows from each sub-subplot. Yields were adjusted to 15% moisture.
Results of the first two years of this experiment showed that removal of residue tended to increase yield and to reduce the optimum N rate under no-till in the three locations (DeKalb, Monmouth, Urbana) with deep, higher-organic matter soils (Mollisols), while in the transitional soil (Alfisol) at Perry, where both 2006 and 2007 were dry growing seasons, residue removal and tillage both tended to decrease yields (Coulter and Nafziger, 2008).
The 2008 growing season was quite favorable at all four locations. Data from DeKalb, Monmouth, and Urbana were combined with that from the previous two years at these locations in order to form response curves over 8 environments (Figure 1.) As we saw in the first two years, removing residue increased yields in no-till, but had little effect on yield under tillage. The response to rates of fertilizer N was also affected by the amount of residue under no-till; the presence of full residue
The results from Perry in 2008 (Figure 2) were unlike those from the first two years at that location, in that the presence of residue in 2008 reduced yield and increased the amount of N required to maximize (or optimize) yield, similar to the response at the three sites with Mollisols. This suggests that the increased yields from no-till during the two previous years at this location were more related to seasonal weather effects than to soil type or productivity.
This study will continue for at least two more years, after which an attempt will be made to measure changes in soil that might result from intermediate-term (five years) of removal of residue and from tillage. It is clear that in the short term, removing at least some of the residue has the potential to increase yields and to lower N rates needed for continuous corn.
Barber, S.A. 1979. Corn residue management and soil organic matter. Agron. J. 71: 625-627.
Blanco-Canqui, H., R. Lal, W.M. Post, and L.B. Owens. 2006. Changes in long-term no-till corn growth and yield under different rates of stover mulch. Agron. J. 98: 1128-1136.
Coulter, Jeffrey A. and Emerson D. Nafziger. 2008. Continuous Corn Response to Residue Management and Nitrogen Fertilization. Agron J 100:1774-1780.
Larson, W.E., C.E. Clapp, W.H. Pierre, and Y.B. Morachan. 1972. Effects of increasing amounts of organic residues on continuous corn: II. Organic carbon, nitrogen, phosphorus, and sulfur. Agron. J. 64: 204-208.