How does flooding and stagnant water affect crops? Flooding can have both negative and positive effects on agricultural land depending on context. Soil nutrients can be either lost or gained depending on the type of flooding and microbial populations can go up or down depending on the type of microbe. In this week’s edition of Growing Possibilities, we will examine the effects of flooding on macro nutrients in the soil and on soil microbial communities. We will also look at effective strategies for remediation of beneficial microbial populations after a flood.

In the ancient world in Mesopotamia, at the confluence of the Tigris and the Euphrates, and along the Nile River in Egypt farmers established on flood plains to benefit from seasonal flooding that would bring nutrients from the river onto the agricultural land (1). Today the practice of obtaining nutrients from riverbeds has mostly been replaced with modern water management and the application of chemical fertilizer.

Flooding of agricultural land still happens but today it is usually not met with the same enthusiasm as it was in the ancient world. This spring we have seen farmers in North America negatively affected by flooding from extreme weather events like extended periods of rain. This type of flooding can affect the macronutrients nitrogen (N) & phosphorus (P) through soil erosion (1). If soil is carried away from the field during periods of flooding, then the nutrients in that soil are lost. However, if the field remains flooded and stagnant for an extended period without significant erosion the nutrient content of the soil can still be affected.

Nitrogen in fields with stagnant water can be lost through leaching below the rooting zone in sandy soils and through nitrification in soils with higher clay content. Nitrification is when N is lost into the atmosphere. The amount of N lost to nitrification is dependant on the amount of time that the field is flooded as well as the ambient temperature with lower temperatures like 5°C experiencing lower losses and higher losses at temperatures around 25°C (2).

Phosphorus can be lost to soil erosion but if the field is stagnant plant available P in the soil can actually be higher during periods of flooding. This is because flooding can mobilize P in the soil and lead to mineralization making it more accessible to plants. Once the field dries out the P can again become unavailable to the plant due to it binding with ions in the soil. This can be compounded by the loss of P-solubilizing microbes during the flood making it harder for the plant to access P through root / microbe interactions in the rhizosphere (root zone) (3, 4).

Farmers can combat nutrient losses through the application of chemical N and P fertilizer to the crop in the aftermath of a flood. In addition, an application of N-fixing inoculants and P-solubilizing ag-biologicals can help to reinvigorate the bacterial activity in the soil after a flood (1). Biological solutions can also help to mitigate costs associated with lost fertilizer and contribute to a more sustainable solution to remediating a flooded field.

Soil microbes are important for promoting plant growth and health. The soil contains a diverse population of microbes that improve plant growth and health. They do this by enhancing the availability of nutrients, the regulation of phytohormones, and increasing plant tolerance against stresses. This symbiotic relationship is beneficial to both microorganism and plant, and ultimately enhances plant growth, health and yield (5).

Flooding and stagnant water depletes oxygen in the soil and creates an anaerobic (oxygen depleted) environment (2). This lack of oxygen is detrimental to the aerobic microorganisms (microorganisms that need oxygen) in the soil, as they require air to survive and perform their functions. Shah et al., 2021, suggests that soil microbiota can be resilient for up to 15 days of flooding in healthy soils with good organic matter. However, despite their resilience the microbiota were disrupted by flooding and stagnant water and needed as much as 3 weeks for their populations to recover (6).

Most of the time farmers cannot wait for 3 weeks after flooding to begin planting. This is where commercial inoculants and ag-biologicals can play a role. Applying N-fixing inoculants powered by AGPT® like XiteBio® SoyRhizo® and XiteBio® PulseRhizo® to soybean and pulse crops can infuse the soil with new bacteria and help the native soil microflora to recover. Using P-solubilizing inoculants like XiteBio® Yield+ can help the populations of P-solubilizing bacteria to recover in crops like oilseeds, cereals and legumes. These two microbial inoculants can help to ensure that your crops have access to the N & P that they need to be healthy in the aftermath of a flood. Flooding and stagnant water can affect every field differently and we always recommend consulting with an agronomist before using any new products. Until next time we wish you healthier plants and better yields.

 

1. https://extension.sdstate.edu/managing-soil-and-soil-fertility-after-flooding
2. https://www.gov.mb.ca/agriculture/crops/crop-management/print,impact-of-flooding-soil-fertility.html
3. https://www.sciencedirect.com/science/article/pii/S258975782300001X#:~:text=Flooding%20also%20increases%20the%20content,of%20all%20forms%20of%20phosphorus.
4. https://www.sciencedirect.com/science/article/pii/S258975782300001X#:~:text=Flooding%20also%20increases%20the%20content,of%20all%20forms%20of%20phosphorus.
5. https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2021.606454/full
6. https://www.sciencedirect.com/science/article/pii/S266701002100113X