Fragipan horizon changes using annual ryegrass and other amendments

Authors: MURDOCK, LLOYD - University Of Kentucky; KARATHANASIS, ANASTASIOS - University Of Kentucky; CALL, DOTTIE - University Of Kentucky; Dinnes, Dana; Chatterjee, Amitava

Submitted to: Open Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2024
Publication Date: 6/24/2024
Citation: Murdock, L.W., Karathanasis, A.D., Call, D., Dinnes, D.L., Chatterjee, A. 2024. Fragipan horizon changes using annual ryegrass and other amendments. Open Journal of Soil Science. 14(6). https://doi.org/DOI:10.4236/ojss.2024.146021.
DOI: https://doi.org/10.4236/ojss.2024.146021

Interpretive Summary: Fragipans are hardened soil layers beneath the soil surface that restrict plant root and water movement to deeper soil layers. Fragipans are often glued together by silica and other elements, and they limit crop production on those soils by reducing the soil volume available for root growth. Fragipan soils cover about 12% of the US land area, estimated to be 50 million acres. Therefore, effective methods to break down the fragipan soil layers could improve US crop production. Greenhouse experiments were conducted using pieces of fragipan layers that were covered by materials for incubations lasting 9-17 months. The materials included leaves of grasses that might break down fragipans (annual ryegrass and fescue-ryegrass hybrid mixture), limestone, and humic compounds, which are crop growth-promoting substances created from young coals. We found that decomposition of the ryegrass and fescue-ryegrass leaves weakened the top four inches of the fragipan pieces, especially when used together with humic compounds. These results suggest that the application of these same materials to fields having fragipan layers might help break down those fragipans, and thus potentially lead to increases in crop production on fragipan soils. This knowledge is valuable to American farmers operating on the vast areas of fragipan soils, along with crop production industries and agricultural researchers who seek better management of fragipan soils.

Technical Abstract: Fragipans are solid layers beneath soil surfaces that restrict plant root and water movement to deeper soil layers. These hardened layers often are glued together by silica and other elements, and they limit crop production in those soils by reducing the depth of available soil. Fragipan soils cover about 12% of the US land area, estimated to be 50 million acres. Therefore, effective methods to break down the fragipan soil layers could improve US crop production. A greenhouse experiment was conducted involving intact fragipan soil cores of 50 cm thickness after removing the top soil horizons. The cores were maintained in moist condition throughout the experiment and received several treatments with various amendments for different periods ranging from 9 to 17 months. The amendments included annual ryegrass or Festulolium residues, powder limestone and various humate compounds alone or in combination with the grass residues. The ryegrass and Festulolium residue treatments significantly reduce penetration resistance into the top 10 cm of the fragipan within 9-17 months, particularly when used in combination with humate materials such as leonardite. We hypothesize this fragipan degradation resulted from the release of certain soluble organic compounds from the plant residues or the humate amendments that increased the solubility of Si and Al associated with the fragipan brittleness, thus decreasing the density of the compacted fragipan material.