The Impact of Cool plus Wet plus Compacted Adds to a Different Math in Corn and Soys

What a cool, wet spring on many fields in 2009! Many acres of corn and soybean were planted into soils that were not quite fit for equipment because of frequent and excessive rainfall in May. Some of those acres may have been planted on time according to the calendar, but the resulting destruction of the soil physical condition to support crop growth is now apparent with poor uneven growth. This year, early growth of corn and soybean seems less than satisfactory in some no-till fields compared to conventional-tilled neighboring fields. Should we be drawing some conclusions regarding tillage? Back to conventional? Nope! Even in many conventional fields that have been plowed and worked twice before planting, corn and soybean have stunted growth in areas where wheels once travelled. Sorry folks, but some of these "ugly fields" (see Figure 1) will produce "ugly yields" inspite of the blanket optimism in recent articles that the ugly symptoms will be forgotten at harvest. Allow me to explain. But before I do, let's review some complexities in explaining crop response at the soil interface.

Figure 1. Ugly corn in conventional tillage caused by cool soil + excessive wetness + compaction.

Crop response to tillage is related to four soil physical factors: soil temperature, soil-water potential (the power needed for roots to take water from the soil matrix), mechanical impedance (the ability of a root to penetrate through a soil mass), and oxygen availability. These soil factors are altered by tillage. If one factor is changed, then at least one other factor is affected. For example, during periods of excessive wet weather, crop growth may be affected by the lack of oxygen (not favorable as water consumes air-pore space in the soil matrix). As well, soil temperatures may be cooler (not favorable to the crop), but the mechanical impedance of roots to force their way through the soil matrix is reduced with higher soil moistures (favorable). So what is the resulting crop response? More than one factor needs to be considered when assessing crop response. One factor "yes/no" "with or without" responses are simple to explain, but the plant sees an integration of many factors. Investigating the effect of multiple factors simultaneously continues to be my focus in crop research.

In the past, very little attention has been directed at the effects of excessive soil moisture early in the growing season. Based on my Ph.D. work with Dr. Tony Vyn at the University of Guelph in the 1990s, excessive soil moisture and low air-filled porosity during the month following planting delayed corn and soybean development, reduced dry matter accumulation, and reduced root length. There is a strong correlation for these effects to carry through to grain/seed yield. Other research from Michigan State University supports similar findings on air-filled porosity and early growth in corn and the carry-through impact to harvest (see Lizaso and Ritchie, 1997).

Remember that the growth rate of crop plants is the result of an integration of multiple soil and weather factors. The work in the 90's demonstrated the impact of excessive soil moisture (actually low air-filled porosity) on early crop growth (approx 6 weeks after planting). The spring of 2009 resulted in some soils that were worked too wet which caused compaction in the root zone. This compaction limited air pore space within the soil matrix, and then excessive rainfall reduced the pore space even further. Here is the catch: further work from the 1990s showed that cool temperatures exacerbated the effects of low air-filled porosity on early crop growth (see Figure 2), which produced lower yields compared to environments of higher air-filled porosity and warmer soil temperatures (data not shown). This impact on crop growth and development can occur regardless of tillage, but no-till systems may be more susceptible because of cooler soil temperatures inherent in the system compared with conventional tillage systems (Figure 2).

Figure 2. Corn shoot response to soil moisture contents (from low to high) at three average soil temperatures (19 to 23 C) in conventional tillage and fall zone till systems (dashed line) compared to corn planted using no-till (dotted line).

Soil temperatures and air-filled porosities may be increased in no-till systems with the deployment of fall strip-tillage, no-till coulters, row cleaners, or the use of vertical tillage ahead of no-till planters. For example, our SMART soybean project with Horst Bohner (OMAFRA) shows some good responses to vertical tillage this year (see Figure 3).

Figure 3. Soybean stands with (top photo) and without (bottom photo) vertical tillage ahead of the no-till planter on a SMART soybean trial at Belmont in 2009.

Another excellent example of crop growth effects in unfavorable conditions has been demonstrated this year at the long-term tillage rotation study on the Ridgetown Campus. Figure 4 shows the impact of soil health on corn between two crop "rotations" ("rotations" is in quotes because the rotation on the left is continuous corn and the other on the right is a corn-soybean rotation - it can be argued that neither can be considered a crop rotation). Anyway, which "rotation" produced the greatest early crop response? The difference is obvious. The kicker is that the better looking corn was no-tilled, and the less vigorous, yellow corn was produced using conventional tillage. With the support from all three commodity groups, we are currently using these trials at Ridgetown, along with other long-term experiments in Guelph and those on farm fields, to develop a soil health test for Ontario.

Much of the corn and soybean crops may be looking better now (July 2) than a month ago on many fields, and that yields on those fields may be higher than first expected. However, we cannot become complacent and overlook the impact of management on yield potentials. Crop responses to the environment are complex and not simple, and therefore, the causes of unsatisfactory crop responses must be carefully drawn. There is good evidence that the combination of cool temperatures and wet conditions do not add perfectly like 1 + 1 = 2, but rather 1 + 1 = 3. Is no-till to blame like some are suggesting? Nope! Compaction in conventional tillage and/or poor soil health can have the same impact.

Figure 4. Soil health effects on corn growth in continuous corn under conventional tillage (left) compared to corn-soybean rotation (right) in the long-term rotation tillage project on the Ridgetown Campus in 2009. Rotations we established in 1995.

References

Lizaso, J.I. and J.T. Ritchie. 1997. Maize shoot and root response to root zone saturation during vegetative growth. Agron. J. 89:125-134.

Nielsen, R.L. 2009. Corn and the Ugly Duckling. Purdue University. Available at: http://www.agry.purdue.edu/Ext/corn/news/timeless/UglyDuckling.html

Vyn, T.J. and D.C. Hooker. 2002. Assessment of multiple- and single-factor stress impacts on corn. Field Crops Research 75:123-137.