THE floods of 2021 have inundated hundreds of farms and hundreds of thousands of acres of croplands in Guyana. Fortunately for some farmers, the floodwaters drained off fairly quickly and they were able to return to the fields, assess the damage, and begin to think about planting a crop.

Repairing farm fields after floods is possible, but it can be time-consuming and labour-intensive. Farmers are eager to get into their fields and do something, but this can result in compaction, ruts, and further damage to fields. Patience is a virtue when bringing flood-damaged croplands back into production. To avoid compaction of these soils, it is crucial to let soils drain and dry out sufficiently before removing any large debris from fields or working the soil. Inventorying what needs to be done and planning your course of action is critical for flood recovery.

The most noticeable damage from floods is (1) where the land erodes, (2) where floodwater transported materials such as sand or gravel are deposits of into fields; and (3) loss of beneficial soil microbes and the function. The question now becomes, ‘what to do to bring fields affected by flooding back into production?’

Field Temporarily Flooded with strong water currents.
This may result in damage from deposits and erosion. Where sand and other materials are deposited (<10cm), farmers will have to move in with ploughs to level out the piles and blend them in with the original soil. Earthmovers will have to be employed for larger piles, which may be used to fill ditches,levelling the field and making it easier to plant. In cases of sandy deposits, sand makes the soil more drainable and of smaller water-holding capacity. Thus, the irrigation cycle will be shortened for most soils necessitating frequent irrigation. Also, the deposited materials may be of poor fertility, requiring higher fertiliser inputs for production. Alternatively, the deposits may be fertile requiring fewer fertilisers. In all cases of deposits, a determination should be made about the suitability of the material for ploughing into the soil.

On the other hand, when flooding causes erosion, it may strip soils to their compacted plough pan layer 15 – 20 cm below its original surface. In this case, ploughing is needed to fix these fields by loosening this subsoil. In other cases, floodwaters may remove the fertile topsoil, requiring inputs of fertilisers for optimum production. In all cases, gullies and gaps should be assessed to determine the cost of corrective ploughing, and the quality of topsoil on these surfaces before a decision is made on the way forward.

Field flooded with standing water for long periods
This may result in damage from the loss of beneficial soil microbes (mycorrhizae fungus and rhizobia bacteria) and their function. When there was standing water for several weeks on the field, soil oxygen is reduced (as water holds less oxygen than air) which causes part of the soil phosphorus (P) to be present but unavailable to the plant. Thus, phosphorus application is required to avoid purple-stunted plants – a sign of P deficiency. Alternatively, it is recommended to plant a cover crop (legumes or small grains) as soon as possible. This will re-establish the population of mycorrhizae fungi needed to release the unavailability in the soil.

Nodulation in legumes may be a problem after a flood. The condition of less soil oxygen results in a loss of soil nitrogen, because of enhanced denitrification. Thus, it is recommended that seed inoculation be done with a rhizobia-bacteria to ensure nitrogen fixation in the first crop after a flood.

Weeds may be another factor that may affect crops after flooding. Farmers may need to use additional weed control (chemical or mechanical) and this may increase costs. Also, floodwaters can bring in new weed seeds that increase control costs and reduce yields in future years.

Steps to Optimize Your Soil Fertility After a Flood
Floods bring with them a lot of potential for nutrient additions and losses to agricultural fields and the only way to know the nutrient status of your field is through a soil-fertility test.
* After the soil surface is dry, the soil should be tested to determine fertilizer requirements to optimize crop yields.
* It is recommended that the soil surface be allowed to dry before starting fieldwork (especially the use of machinery) to prevent compaction. Wet soils are more prone to compaction. Compacted soils lack pore space and restrict root growth and movement of air and water in the soil.
* When planting legumes (including soybean) after flooding, the seed should be inoculated with rhizobia to help ensure nodulation and nitrogen fixation, as flooding can reduce some of the microbial populations responsible for this process.

* Phosphorus deficiencies (evident by slow, early growth and purple colouration) may still occur, even if soil tests indicate an adequate amount of phosphorus, as flooding can decrease the populations of soil microorganisms responsible for increasing phosphorus availability.
* If cash crops are not being planted after flooding, consider planting a cover crop to protect the soil from further erosion and to promote the growth of micro-organisms that are essential for nutrient cycling. The fungi mycorrhizae require live plant roots to grow; thus, fields lacking growing plants tend to have low amounts of arbuscular mycorrhizae.