The narrative below is an overview of the presentations made by Mike Hubbs and Greg Brann at the 2014 Milan No-till Day.

Soil Health: The continued capacity of soil to function as a vital living organism, sustaining and improving soil, plant and animal resources. 

How do you improve soil health?

Less Disturbance: Reducing tillage is essential to protecting benefits of cover and root growth. Disturbances can also be excessive nutrients, pesticides, uncontrolled traffic, grazing without a recovery period or anything else that impacts the soil.

Increase Cover: Cover is essential to increase soil carbon; the start of improving all functions in the soil.  Cover can be increased by good agronomic practices and less disturbance. Crop diversity and living roots  also increases soil carbon.

Increase Diversity: Plant diversity improves soil health by providing different root exudates (sugars) to feed soil life. Different root forms and different rooting depths all improve soil health and soil life.  Diversity in soil life improves resilience of the soil as well as aggregate stability. Aggregate stability is important because the soil maintains a good air and moisture relationship (pore space).

Living Roots throughout the year:  A void in the cropping system is a missed opportunity to capture energy and bank it for future production.  When roots die, they create air space and an avenue for water infiltration. Roots are a major food source for soil biology.

Demonstration

Recently, Tennessee NRCS demonstrated a rainfall simulator on soil samples from eight fields showing the differences in soil health indicators. The indicators observed were erosion, water runoff, infiltration, and slaking test which indicates how stable soil aggregates are.

The old cliché “seeing is believing” is underscored by the observations of the Milan Field Day Rainfall Simulator results from July 24, 2014.

The field samples were collected from five crop fields from the Milan No-till Experiment Station on July 23, 2014. The fields represented will be called treatments for the sake of comparing results. There were three previous fields collected from pasture treatments. Table 1, below, will list the treatments. Care was taken to not disturb the soil samples, taken intact in the pans from the field. Soil clods were taken from each field by shovel, carefully not disturbing the clods and keeping them intact.

Slaking

The slaking test was conducted by placing a soil clod from each of the eight treatments (Table 1). Samples were air-dried for a minimum of 12 hours. A clod from each of the treatments was placed on a mesh screen totally immersed in water from tap source. Rotated pasture treatments, properly rotated and rested, showed excellent resistance to slaking. The resistance to slaking is due to aggregate stability from soil organic matter and proteins and soil-glues from active soil biology. Similar results were observed from treatments with diverse rotations and no-tilled. Overgrazed pasture, although in grass, exhibited some cloudy water (instability) showing the importance of allowing roots to grow through proper rest periods. Continuous cotton with vetch lack diversity and high residue crop in the rotation, thus showed some cloudiness in the water. The vertical tillage treatment showed soil instability, where tillage had broken down the outer portion of the clod. The area deeper in the clod, not affected by tillage, was more stable, thus held together in water. The conventional tillage-clod when placed in water almost immediately disintegrated and turned the water turbid.

Stable soil aggregates are more resistant to erosion, infiltrate more water in less time, and exhibit less runoff.

Rainfall Simulator

The other indicators, erosion, runoff, and infiltration were observed with the application of sprinkle water distributed evenly over the pans of treatments. There were three applications of water amounting to 3 inches of total water during the demonstration. The pans were tilted at an estimated slope on 3-4 percent. All treatments were treated with same amount of water at the same percent slope. One jar per sample was placed below pans to collect water infiltrating through soil profile, which is approximately 2.5 inches in depth within the pan. A second jar was placed below the edge of the pan to collect any water that would exhibit surface run-off.

Erosion

Erosion was qualitatively measured by observation. Most of the time, sheet erosion is an invisible thief and can only be seen by amount of sediment accumulating at bottom edge of pan and of course for bare soil collected as sediment in the run-off jar. As expected, the conventional tillage treatment showed the greatest amount of erosion due to bare soil and aggregates destroyed by tillage. Just as the slaking test showed poor aggregate stability, the erosion test from the rainfall simulator bared that truth as well. The over-grazed pasture and vertical tillage, due to soil disturbance, also showed greater amounts of erosion from other treatments. As seen in the slaking test, the vertical tillage pan showed erosion down to the level of tillage. The rest of the sample resisted erosion due to aggregates being stable that had not been disturbed. All pans with good cover with no disturbance showed slight to none visible sediment at the bottom of the pan. Again, showing correlation to the slaking test, better cover, less disturbance equates to better aggregate stability and less erosion.

Run-off

The amount of run-off had a direct correlation to the erosion indicator described above. Runoff is affected by the aggregates’ ability to infiltrate or not infiltrate water during the intensity of a rainfall event. Poor aggregate stability results in greater amounts of run-off.  Tillage destroys aggregates. Over grazing resulting in areas of bare soil leaves aggregates exposed to being easily broken down. Vertical tillage may seem to be useful to break up compacted surface soil, and distribute residue and leave residue on the surface; however the damage is done by the breaking down soil aggregate resulting in rainfall filling mineral soil in voids. Once the pore space is filled in by the soil, infiltration decreases and run-off increases. Results of run-off are described in Table 1.

Infiltration

The infiltration results had a direct correlation to slaking test. Good aggregate stability equals better infiltration. Conversely as infiltration increases, run-off and erosion decreases. The Milan demonstration held true to this assumption. The treatments with good grazing, good cover, and no-till had high percentage of infiltration. The overgrazed pasture, vertical tillage, and conventional tillage treatments had low infiltration. It was noted that after 3 inches of rainfall simulation that the infiltration-jar under the conventional tillage treatment collected only ¼ inch of water. During a short-term drought, farmers need as much water infiltrated as possible to plants roots. It was also noted that the rested pasture infiltrated an estimated 90+ percent of water. All of the no-tilled treatments with good cover collected substantial water from infiltration jars. Bottom line, infiltration means more water to plants meaning better yields, and better water quality.

Table 1. TREATMENTS for the Rainfall Simulator, July 24, 2014, Milan No-till Field Day.

Treatments	Rotated pasture rested	Rotated pasture grazed	Overgrazed pasture	No-till corn, beans, wheat cover crop	No-till corn, cotton, cover crops	No-till cotton with vetch cover crop	Vertical tillage, corn beans, cover crops	Conventional tillage with corn, beans, wheat
Slaking	none	none	yes	none	none	some	yes	mostly disintegration
Erosion	none	none	some	none to slight	None to slight	slight	Top surface where tilled	Obvious sheet erosion, some small rills
Run-off	Nearly empty	less than ¼ gallon.	¾ gallon from 3” rain simulation	slight- less than 20 percent of jar	slight- less than 20 percent of jar	less than ¼ gallon.	¾ gallon from 3” rain simulation	Nearly a gallon from 3” rain simulation
Infiltration	Gallon	¾ gallon	Less than quart	80 percent gallon	80 percent gallon	65 percent of gallon	½ inch	¼ inch

Conclusion

The rainfall simulator results are qualitative and are meant for observers to visually see the results of soil health concepts and applied conservation practices. The demonstration was not replicated and does not claim to be verified research. However, the results are supported by other research. If farmers reduce disturbances, keep the soil covered, increase diversity, and keep roots growing throughout the year, soil biology will increase along with increasing soil carbon. With soil carbon increases, farmers can expect better aggregate stability, better infiltration, and reduced erosion and run-off. With better soil health indicators, equal healthy soil, healthy plants, and healthy animals.