Pasture Aeration to Improve Production

PROJECT BACKGROUND
My operation has three hundred acres of mixed grass of which one hundred forty acres have been interseeded with clover and grazing alfalfa. I graze eighty five registered Angus cow/calf pairs. I also graze thirty six breeding heifers. I have a small feedlot. Two hundred sixty acres are now rotationally grazed. Drinking water is primarily from developed springs and tanks below ponds. I have aerated my pastures for over then years.

PROJECT DESCRIPTION AND RESULTS
The main objective of this project was to investigate how aeration influences the soil and grass growth. Three different pastures were used for this study. One pasture (plot Diss) had been aerated for six years and contained a test strip that has never been aerated. The other two pastures (plot DH and plot RW) were aerated for the first time the fall of 1999 leaving test strips not aerated. All plots were soil sampled for complete analysis in the fall of 1999 and again one year later. Infiltration time was measured on plot Diss October of 1999 and all plots were measured the fall of 2000. Infiltration was measured using six inch diameter metal tubing six inches long. The tubing was driven into the ground to a depth of two inches and lined with thin plastic wrap. Four hundred fifty five ml distilled water was poured into each tube equivalent to one inch of rain. The stopwatch was started as the plastic wrap was pulled out of cylinders. June 15th 2000 grazing cages were erected in four aerated and four non aerated areas of plots Diss and RW. Plot DH was large enough to accommodate five cages in each area. Cages were made of sixteen foot wire cattle panels bent in a circle and wired to steel post. September of 2000 grass was harvested from two one foot square areas from each cage and weighed on a gram scale. Forage samples were submitted for complete analysis to determine if there was a variation in nutrient density. Biological activity was measured with Woods End Solvita test kit that measured CO2 production by soil organisms. Soil for this test was taken at the time of soil sampling. Soil was placed in a test container with a paddle that would change color to indicate the level of CO2. Aerated soil was compared to non aerated soil plots for biological activity. Root mass was measured on plot Diss because it was a longer established test plot. Two inches by six inch bulb planters were used to collect soil samples. The two inch cores were transferred to six inch long sections of three inch diameter PVC that had been cut in half and a slot cut nearly through to divide the core in three equal cores two inches long. A heavy knife was used to cut the samples at each slot to obtain two inch long samples. The grass was first cut form the top of the sample to remove grass and other debris. Five cores were taken from each of the four aerated and four non aerated sub plots. The top thirds were pooled, as were the other thirds for aerated as well as non aerated. Each group of samples were then placed in plastic cloth mesh and soaked in water for twenty four hours. The samples were transferred to a strainer and sprayed with water until all soil was removed. The rock and other non root material was carefully removed. Roots were then oven dried and weighed.

People:
- Greg Shepard as a West Central of Stuart Student was very helpful in collecting data and establishing the new test plots the fall of 1999.
- Justin Wilhelm and Floyd Faust were very helpful in erecting all the grazing cages that were necessary for this project. They also assisted in sampling soil and forage.
- Hope Wilhelm I thank for her help in performing the infiltration study
- Doug Karlen, Federal Soil Tilth Laboratory, Ames Iowa. Soil Consultant and assisted with protocol for project.
- Steve Barnhart, ISU Extension Agronomist, ISU, Ames Iowa. Forage Consultant and assisted with protocol for project.
- Don Owings, Soil Service, Carthage, Illinois. Soil and Forage Consultant and provided the soil analysis for this project.
- Jean Dissinger, Dexter, IA provided pasture
- Rod Williams, Stuart IA, provided pasture
- Dwight Hawley, Stuart IA, provided pasture

Results:
Soil sample results for fall of 1999 and fall of 2000 are included with report. I was unable to detect any significant differences in the two reports. I was unable to detect any significant difference in quality although the aeration did improve yield. Also included in report is a summary of results of infiltration rate, (that was measured fall of 2000 one year post aeration), production data, and root mass on plot A, and biological activity. I have presented summary of results at a pasture management tour in Guthrie County, Iowa, July 2001, and also a field day in Wayne County, Iowa, September 2001.

Summary of Results of Aerway SARE Grant: 1999-2000
Test plots: 3 separate
Infiltration time = the time it takes for the equivalent of 1 inch of rain to soak into the soil.

Plot A: long term, 1999
Aerated: 2.7 minutes (average of 4 subplot runs)
Non aerated: 25 minutes (average of 4 subplot runs)

Plot A: 2000
Aerated: 6 minutes (average of 4 subplot runs)
Non aerated: 25 minutes (average of 4 subplot runs)

Plot DH: 2000
Aerated: 22 minutes (average of 5 subplot runs)
Non aerated: 46 minutes (average of 5 subplot runs)

Plot RW: 2000
Aerated: 5.5 minutes (average of 4 subplot runs)
Non aerated: 9.4 minutes (average of 4 subplot runs)

Production: even in a dry year (2000) the aerated plots averaged 53% more than the non aerated. Range 6% on plot RW, 80% on plot DH, 74% on plot A.

Root mass: harvested, dried and weighed in grams on a 2 inch core with 6 inch depth (long term A plot only)

Aerated, non aerated
Top third, 2.75, 1.99
Middle third, 0.49, 0.16
Bottom third, 0.31, 0.07

Biological activity (CO2 production): scale 0-5 activity, with 0=low and 5=very high
Aerated: 4.2 (average of 9 samples)
Non aerated: 2.4 (average of 9 samples)

Summary: aeration allows for penetration and retention if water and oxygen. Dead grass and dry manure can infiltrate 6-8 inches of soil and add humus. Humus enhances water retention, bacterial activity, and deepens root penetration and thus results in higher yields.

Discussion:
I expected the infiltration time, root mass, and production results. The results support what I have noticed in my pastures. The summer of this study was very dry for our area. I did not have a cumulative rain gage out but I should have used one. Pasture production was very poor. Water is still my main nutrient for producing grass. I think the infiltration rate and root mass results are the most important details for my production unit. I think over time the results would become accumulative. As aeration continues infiltration rates should improve, humus and root mass should improve allowing grass to be more drought tolerant and more responsive as rainfall resumes. This type of study should be funded for three to five years to determine if any of the results are cumulative and if they are when do they occur. It is a labor intensive study and should be a group project.

Project Impact: pasture land is becoming more valuable. The new owners think in the rent should equal a CRP payment. Land has to become more productive as pasture or it will not be pasture. Much of the pasture in my area in hilly, highly erodible clay soil vulnerable to compaction. With the infiltration rates that I demonstrated in this trial not much of the water is available for forage production. Aeration was the simplest test cost procedure I could find to try on my unit. It is difficult to give hard economic data because I have adapted other practices such as rotational grazing and inner seeding. My stocking rate is up forty percent. It is evident that I have a more vigorous stand of forage, especially on the side hills. I have an opportunity to evaluate side hill production because one eighty acre pasture has fifty one percent > eighteen percent slope.

OUTREACH
I have presented my summary data at one pasture tour in Guthrie County, Iowa (75 people attended) and another field day in Wayne County, Iowa (65 people attended). Also numerous one on one conversations and many phone calls and emails.