Over the past few years, one of the primary questions I have been asking is ‘What limits crops from achieving their genetic yield potential?’
We have been looking at this problem for corn, soybean and wheat and found these crops show a common characteristic in that 20% of the difference between the actual and attainable yields occur 80% of the time.
The more important part of this discovery was that this loss of yield was due to short-term stresses related to the inability of the soil to supply the water required for maximum yield.
These short-term stresses account for the yield variation often observed in fields in the Midwest because in production fields we observe that variation in yield occurs during the grain-filling period and directly related to the ability of the soil to provide water to the crop during this critical growth period. These observations have caused me to focus on what limits the soils ability to provide a maximum yield and the effect of tillage systems.
One of the questions I am often asked, is ‘What is the impact of different tillage systems on soil health?’ We have found through our research that a conventional corn-soybean production system loses nearly 1,000 pounds of carbon per acre each year.
In other words, what we consider as a good practice is actually degrading the soil over time through the constant loss of organic matter. Tillage is one of the major causes of soil degradation because it robs the soil of the material needed to protect the soil from the forces of raindrop energy and stable aggregates required to allow for water movement into the soil and oxygen and carbon dioxide exchange between the soil and atmosphere.
“We found that 20% of the difference between the actual and attainable yields occur 80% of the time…”
Any practice that reduces the disturbance of the soil will allow the soil to enhance its function over time. A good, healthy soil will supply plenty of water, have a good gas exchange and show excellent nutrient cycling to supply everything a plant needs to grow.
We build soils by ensuring that the soil biological system has everything it needs to function. These needs are adequate water, plenty of oxygen, lots of nutritious food and shelter. These four basic needs are the same requirements that we humans have to sustain our life.
The first step to improving soil is to provide an environment that allows the soil biology to provide the cycling of carbon and nutrients needed to build stable soil aggregates. Strip-tillage only disturbs the seed zone and leaves the remainder of the soil surface undisturbed and protected with crop residue.
What we have observed with strip-tillage is that the soil is improved, creating a seed zone that provides adequate soil water and oxygen so the plants emerge quickly and uniformly. Plants that emerge in a strip till system are not subjected to stress in the early development, have maximum vigor and are among the most uniform we observe when we compare tillage systems.
Changes in soil are complex and represent a balance among carbon, nutrients and water. All three of these are required to reduce the yield gap. However, in strip-till systems we see that soil carbon increases because an environment is created that allows the soil biology to operate at an optimum.
This in turn enhances the soil so more water is stored in the soil and nutrients are available to growing plant. The more we understand about these processes the greater our ability to help producers enhance their soil and their profits.