2019 Fragipan Remediation Report
The fragipan is a naturally occurring soil horizon that virtually stops water movement and root growth through the soil. Its’ depth averages about 20-24 inches in the soil types in which it occurs. The layer is due to the cementation of the soil particles with a silicate rich amorphous aluminosilicate binding agent. The fragipan is present in about 2.7 million acres of Kentucky soils and about 50 million acres in the U.S. Fragipan soils reduce yields of crops for 2 reasons: 1) limited water holding capacity due to limited soil depth 2) water saturated soil conditions during wet periods.
The fragipan itself is a silt loam soil that has been cemented. If the cementation is dissolved, the released soil particles can begin functioning as a productive soil again. The goal of this project is to try to dissolve the cementation and make a deeper soil that will hold more water for summer growing crops and reduce waterlogging in the winter which would make the soil better suited for winter crops and better support trafficking at this time of the year.
The approach to investigation of a remedy to the fragipan has three phases.
· Laboratory research and evaluation
· Greenhouse research and evaluation
· Field research and evaluation
The research on the fragipan by the research team is having excellent success. Of the many plants, compounds and combinations tested, there is two plants, 4 compounds and another material that have been found to be effective in breaking apart the fragipan. They are annual ryegrass, potassium chloride, potassium sulfate, sodium fluoride, sodium nitrate and possibly leonardite humate and festulolium.
Annual ryegrass has been chosen as the central focus of the greenhouse and field research due its notable advantages and the compelling proof of its effectiveness. Annual ryegrass roots contain exudates that have a degrading effect on the cement of the fragipan. The deep root penetration also increases soil porosity and may facilitate the leaching of the 4 or 5 other effective compounds down to the fragipan. We are presently looking for varieties of annual ryegrass that are more effective in breaking down the fragipan.
Through research findings in the laboratory, greenhouse and the field, we have gained enough confidence in the ryegrass treatment as a fragipan remedy and its yield increase potential, that we are cooperating with a few farmers across the state to establish on-farm trials. When annual ryegrass was grown 6 times in a rotation with soybeans in the greenhouse, the depth of the newly formed productive soil increased about 7 inches. We have also found 3 fields in Kentucky, 2 in Indiana and 1 in Illinois that had a history of at least 5 years of annual ryegrass over a 10 year period. The annual ryegrass increased soil depth by as much as 14 inches and as little as 3 inches. The average depth increase for growing annual ryegrass across all of these fields is about one inch for each year annual ryegrass is grown. However there is a wide range.
We are finding lower bulk density and increased porosity as well as an enrichment in some organic compounds in the fragipan horizons undergoing degradation in the greenhouse where ryegrass is present when compared to the control. We are also finding compounds which are suspected to be the compounds which are exudates released from the ryegrass roots which induce the fragipan degradation. At present time, we are trying to scientifically verify and identify the exudates. It will greatly aid in this effort and may lead us to a quicker and more effective method to remediate the fragipan.
Yield Responses to Changing the Fragipan
As the cementing agent in the fragipan is dissolved, the freed soil particles begin to act as a productive soil making the soil deeper. This should increase the yields of these soils as the depth increases.
Six years of research completed in the 1970’s and 80’s in Kentucky and Tennessee, indicate that for each inch of soil above the fragipan, corn yields are increased an average of 2 to 2.3 bushels/ac (2 to 2.5%) and soybean 1:1 bushels/ac (4%). The yield increase varied greatly from year to year as the many things that affect yield, changed from year to year. The yield change ranged from a plus 5 bu/ac for each added inch to a one-year negative of 2 bu/ac.
The yield comparisons that we presently have from field trials with and without annual ryegrass on fragipan soils are of rather short duration (3 to 6 years). It appears that little or no yield gain is common in the first two years. Yield gains after this become more consistent and significant. In 2018, yield comparisons from seven field trials are seen in Table 1.
The only long-term data demonstrating the ability of annual ryegrass to degrade fragipans was collected from a field owned by Ralph (Junior) Upton in Hamilton County Illinois. Annual ryegrass was grown as a cover crop alone or in a mixture for 15 years on a fragipan soil type (Hickory silt loam). Corn yields in the field with the ryegrass cover crop were compared to the yearly average corn yields for Hamilton County (Figure below). The trend line indicates that yields on his fragipan soil with ryegrass cover crops begin 15 to 20 bu/ac below the county average and after 15 years was 40 plus bu/ac. above the county average. This sloping, somewhat eroded field was compared to all the soils and different management practices in that county. This data demonstrates that the long-term use of an annual ryegrass cover crop positively influences fragipan soils and can increase yields over a long period of time. This is the only long-term data we are aware of at this time. This data is encouraging and suggests the extra effort for this practice is justified.
Degrading the Fragipan in Greenhouse Experiments
Complete intact soil profiles in transparent plastic tubes were used in the greenhouse experiments (Figure below). Different plants were grown in them and the most promising treatments were applied to the surface soil as they would be in the field.
Complete soil profiles in transparent tubes allow for visual verification of different treatments added to break apart the fragipan.
The top of the fragipan was marked on the tube when the core was taken. Rooting patterns and any changes to the fragipan from those roots or applied treatments were observed. Annual ryegrass roots reached the fragipan (18 to 24 inches) about 5 to 6 weeks after planting. Top growth of the annual ryegrass was about 4 to 5 inches tall at this time. Extensive rooting reached the fragipan in about 2 to 2.5 months.
The more often annual ryegrass was grown the more the fragipan was degraded and the degradation became more extensive and deeper. Some chemicals proven in the laboratory to degrade the fragipan were added to the soil in the ARG/soybean rotation. Some appear to accelerate the degradation of the fragipan when added to the soil surface during each cycle (Table 2). These combinations are now being tested in field trials.
With these limited results, it appears that it might be possible to increase yields of corn and soybeans by 25% on the fragipan soils by using an annual ryegrass cover crop. We also expect to improve the yields of wheat. A 25% increase would result in $500,000,000 in increased returns to Kentucky producers per year or $5,000,000,000 over a 10 year period on the 1.5 million acres of cropable fragipan soils in Kentucky. There is 2.7 million acres of total fragipan soils in Kentucky. Kentucky has only a small portion of the fragipan soils in the U.S. There is about 50 million acres of fragipan soils in the U.S.
The altered fragipan (lower profile) after annual ryegrass is grown 6 times in an annual ryegrass/soybean rotation. The upper profile is the control.
