Soil Microbial Response to Seven Different Organic Transition Strategies
The three year transitional period from conventional to organic row cropping can be the most challenging time for an organic farmer. Maintaining or improving soil health is never more vital than during this time, but it is also the period in which a new organic farmer is likely to have the least experience with organic practices. In this experiment we are examining seven transitional cropping systems to gain information on best management practices for soil building during the transition into organic row cropping. The overall goal of this research project is to improve the competitiveness of transitional organic grain crop producers by documenting critical information on cropping systems that will help maintain or increase productivity, suppress weeds and build soil health.
In Missouri, many farmers transition into organic production by stopping chemical herbicide and fertilizer use while increasing tillage. Increased tillage has been implicated in soil degradation and erosion and is of major concern in a state with 5.3 tons of topsoil loss per acre per year. In organic row cropping, reduced tillage must be accompanied by increased ground cover to reduce weeds. Organic no-till has been found to be successful in some areas of the U.S. and can improve soil carbon retention, water holding capacity and soil structure. In this experiment we compare organic no-till to conventional tillage and modified tillage/cover crop production systems.
Rationale for each rotation
Cover crop only: This rotation uses the transition years as a time for intense soil building and weed control. Sorghum-sudangrass increases organic matter build-up, and along with buckwheat, is an excellent weed smother crop. The terminal rotation crop is high nitrogen-fixing Sunn hemp, providing N for the next year’s cash crop. The other six treatments are being compared to this system as a strategy for maximum soil building and weed control vs. practices that provide a cash crop during the transition years. Cover crop modified: This system provides two years of good soil building and weed control before a cash corn crop. The sorghum-sudangrass will be mowed once during the season to force greater root development, which produces more soil organic matter than aboveground vegetation. Residue will be removed from one cutting to simulate a hay crop. A corn cash crop is grown the third year. No-till: Uses covers crops with a soybean/corn/wheat rotation, which is a typical grain crop rotation once organic certification is achieved. Many MO farmers want to see the feasibility of organic no-till demonstrated before adopting it. No-till reduces the carbon footprint of organic farmers by using cover crops flattened and killed by a roller/crimper as a weed blocking mulch instead of relying on multiple tillage for weed control. Conventional: This is the most widely used organic grain crop system in Missouri and includes a soybean/corn/wheat rotation with cover crops exploited for nitrogen, weed control and soil building. Tillage prior to planting and during the growing season will follow conventional practices and be used as needed to control weeds. Sorghum-soybean rotations: Both no-till and conventional rotations will be replicated using grain sorghum as the 2nd year cash crop rather than corn. Grain sorghum has a history of success in MO, has better weed control and yields more organic matter than corn. Modified conventional: This transition begins with one year of soil building and weed suppression, using a winter cover crop mix and sorghum-sudangrass in the summer. This is followed by winter wheat and soybeans in year two and the cover crop mix and corn in year three, with tillage as needed to control weeds
This research is being conducted at the Bradford Research and Extension Center (BREC), located 5 miles east of Columbia, MO. Soils at this site are primarily Mexico silt loam (fine, smectitic, mesic Vertic Epiaqualfs) and are on the central glacial till claypan plain. The experiment is a randomized complete block design with 5 replications of 7 different cropping system treatments for 35 plots total. Plots are 30 ft long and 20 ft wide. Additional non-replicated plots are grown on three participating organic farms.
A cover crop mix of cereal rye, spring oats, tillage radish, hairy vetch, Austrian winter pea and crimson clover was planted on October 8, 2011 in 15-inch rows with a Kinzie planter. Sixteen soil cores were taken from each plot in a grid pattern in April, 2012 and divided into three depths (0-5 cm, 5-15 cm and 15-25 cm). Bulk density for each plot was calculated gravimetrically and soil macronutrient levels were determined at the time of sampling. Soil samples were frozen for later testing for weed seed analysis, enzyme activity, phospholipid fatty acid analysis, total carbon, active carbon, aggregate stability and nitrogen levels.
On April 6, composted turkey litter was applied to each plot at a rate of 3,552 pounds dry weight/acre. On May 18, dry matter samples were taken then cover crops were rolled in no-till plots with an I&J roller/crimper and were chopped using a flail mower in plots with tillage treatments. Sorghum sudangrass was planted in 15-inch rows in no-till plots. Conventional tillage plots were disked twice and planted with soybean in 30-inch rows. There was no rain until June 11. Due to lack of emergence, sorghum-sudangrass plots were replanted on June 12. On June 13 we began a bi-weekly irrigation schedule with an application rate of one inch per irrigation.
Conventional-till soybean plots were cultivated on June 21 and July 16. Due to lack of crop growth, soil macronutrient levels were retested on July 16 and an additional 2,525 pounds dry weight/acre of composted turkey litter was applied to each plot. On August 21, sorghum-sudangrass plots were mowed in the modified cover crop plots. The remaining sorghum-sudangrass plots were mowed on September 21 and the middle two rows of soybean plots were harvested on October 22. Wheat was drilled (7.5 in rows) in the modified conventional plots on October 19 and the winter cover crop mix was drilled in the remaining plots on October 22. Soil cores were collected in a grid pattern from each plot and stored in late October.
Soil Analyses: Soil samples taken at the onset of the study and after season one were stored for testing for soil nitrogen content, active carbon, total organic carbon, nutrients, enzyme assay and phospholipid fatty acid analysis. Soil nitrogen and active carbon tests have been completed and the remaining soil tests will be completed in the upcoming months. Soil NH4-N and NO3-N content at three soil depths were determined using a 2M KCl soil extraction procedure and flow injection analysis (QuikChem Method 12-107-04-1-B ) with the Lachat Quik Chem 8000 automated ion analyzer. Active carbon levels were determined for the top 15 cm of soil using 2M potassium permanganate and a True-Spec spectrometer to measure color changes caused by chemical oxidation.
Preliminary analysis of active carbon data shows little change from spring to fall and little difference in experimental treatments. This is not unexpected because the major difference between treatments in year one was three tillages, which probably did not cause enough of a change in carbon to register in one year. Active carbon effects have been shown to differ after cultivation over a several year period.
Impacts and Contributions/Outcomes
We held a cover crop field day on May 14, 2012 at the Bradford Research Center that was attended by approximately 25 NRCS and Extension staff and several farmers. The roller/crimper was demonstrated and various cover crops mixes were discussed and evaluated. Presentations were made on organic cover crops and cover crop/no-till effects on water runoff at the Crop Injury and Diagnostic Clinic on July 24-25, 2012 (75 Extension and Industry personnel) and the Integrated Pest Management Field Day on July 12, 2012 (200 farmers, Extension staff), both held at the Bradford Research Center.
Organic no-till cropping presentations were made at the Graves Farm field day in Corning, MO on August 28, 2012 (attendance 130) and the Hundley-Whaley Research Center field day in Albany, MO on August 29 (attendance 200). A talk on soil microbes was given to approximately 200 high school students at the September 11 FFA field day at Bradford.
In December, 2012, a 10 page website on organic research at the University of Missouri was activated at the following web address: http://aes.missouri.edu/bradford/. Several articles on organic research at MU were produced by our communications office and can be accessed at the following addresses: http://cafnrnews.com/2012/02/seeds-of-change/ and http://cafnrnews.com/2011/11/gases-and-grasses/.
Drought was probably the most significant factor in this research in year one. Although we were able to irrigate, the heat and dryness were so severe that moisture from irrigation was hard to detect within a few days of application. Irrigation had no effect on subsoil moisture. Poor germination and slow crop growth can be attributed to extremely dry conditions. Mowing sorghum-sudangrass is effective weed control and even in dry conditions, regrowth of the sorghum-sudangrass was good. Non-mowed plots had a large number of weeds that went to seed.
The use of rolled cover crops and no-till for soybeans was not an effective treatment in year one. Reduced yields might have been avoided if we had broken the experiment protocol and tilled the plots, then replanted soybeans after it was apparent that the weeds were going to outcompete the soybeans. Tillage would likely have been difficult in the thick, rolled cover crop mulch. Our experience shows that farmers wishing to use no-till organic should start with small areas to protect against economic loss from reduced yields.
University of Missouri Dept of Soil, Environmental and Atmospheric Science
Columbia, MO 65211
Office Phone: 5738826607