Agriculture

Flooding Impacts on Soil

How can fields be renovated after a flood?

Erosion, sediment deposition, and crop residue accumulation can leave agricultural fields in need of significant physical repair after a flood. It is extremely important to let soils drain prior to working in fields, since operating equipment in saturated soils can cause severe soil compaction, which has a negative impact on soil water infiltration and crop growth. Large debris should also be removed from fields prior to reworking soil.

Crop residues or sediment deposits which have accumulated to less than 4 inches deep can be incorporated using conventional tillage methods. If sediments or residues have accumulated to a depth of 4 to 8 inches, deep tillage to twice the accumulation depth with a moldboard or chisel plow may be necessary. Formation of minor ditches or gullies from erosion may also be corrected with tillage. However, larger gullies or deeper sediment accumulation may require more extensive repair with earth-moving equipment. Contact your local NRCS office to determine if assistance programs are available to restore damaged farmlands.

Following field renovation, soil samples should be collected to determine fertilizer and lime requirements to restore crop productivity (see section “How are plant-available nutrients affected by flooding?”). If cash crops are not being planted immediately after field renovation, use a cover crop to protect the soil from further erosion.  Since some soil microbial populations may be significantly reduced under flooding conditions, it is important to inoculate legume crops, such as soybean and peanut, following a flood event.

How are plant-available nutrients affected by flooding?

Flooding can result in loss of plant-available nutrients through several pathways: 1) surface-soil erosion can result in loss of valuable plant-available nutrients and organic matter as runoff, 2) nutrients that are prone to leaching, like nitrate and potassium, can be lost to groundwater and 3) gaseous losses of nitrogen can occur in water-saturated soils through denitrification. Agronomic soil testing is recommended following flooding events to assess soil plant-available nutrient contents. After periods of prolonged flooding, phosphorus-deficiencies can occur even if soil-tests indicate adequate plant-available phosphorus concentration, since flooding can reduce populations of soil microorganisms responsible for increasing availability of phosphorus. Supplemental nitrogen applications may be necessary to maintain production in cases where flood waters have not contacted the edible portion of a crop and the producer wishes to salvage the crop. Both public and commercial laboratories can test for plant-available nutrient content.

Contact the Auburn University Soil, Forage and Water Testing Laboratory regarding questions on soil sample collection.

Auburn University Soil, Forage and Water Testing Laboratory

961 S. Donahue Drive

Auburn University, AL 36849-5411

Phone: (334) 844-3958

Email: soillab@auburn.edu

 

Should soil be tested for heavy metal contamination after a flood?

Increased soil metal concentrations of arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn) have been reported in agricultural lands following flooding events[1], [2], [3]. Potential heavy metal contamination is largely dependent on proximity to polluted areas. Heavy metal contamination in soils can be tracked to industry wastes, mine tailings, wastewater treatment, pesticide applications, leaded paints, and many other sources. University extension agents and the county health department may be able to provide information on region-specific contaminants. Heavy metals commonly tested by soil testing laboratories include arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn). Soil samples for metal analysis can be collected in the same manner as agronomic soil test samples. Contact your soil testing laboratory for specific instructions on soil sample collection and shipping.

Should soil be tested for pesticide residue contamination after a flood?

Soil contaminated with pesticide residue is unlikely to pose a long-term threat in flooded fields, since most pesticides degrade relatively quickly in soils. However, pesticide contamination may be a risk if fields are in proximity to areas where large amounts of undiluted pesticides are stored[4]. If pesticide contamination is suspected, contact your state pesticide regulatory agency to evaluate the risk associated with pesticide contamination and determine the best management strategy to reduce risk.

 

 

[1] Ciszewski, D. 2001. Flood-related changes in heavy metal concentrations within sediments of the Biaa Prisma River. Geomorphology. 40:205-218.

[2] Pease, P., S. Lecce, P. Gares, and C, Rigsby. 2007. Heavy metal concentrations in sediment deposits on the Tar River floodplain following Hurricane Floyd. 51:1103-1111.

[3] Adams, C., E.C. Witt, J. Wang, D.K. Shaver, D. Summers, Y. Filali-Meknassi, H. Shi, R. Luna, and N. Anderson. 2007. Chemical quality of depositional sediments and associated soils in New Orleans and the Louisiana Peninsula following Hurricane Katrina. Environ. Sci. Technol. 41:3437-3443.

[4] Provin, T. L., Feagley, S. E., Pitt, J. L., and McFarland, M. L. 2008. Soil Testing Following Flooding, Overland Flow of Waste Waters and other Freshwater Related Disasters. AgriLife Extension Publication SCS-2008-07.

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