Drought’s Impact on Nutrient Cycling – Dry Conditions Change the Equation

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Drought has been a major concern for many crop producers throughout 2022, and it remains a concern as planning begins for the 2023 growing season. As of late October, drought across the central and western United States is the most widespread since 2012 and more than 50% of the country is experiencing some level of drought.
Beyond the obvious need for soil moisture to establish and produce a successful 2023 crop, lack of soil moisture in 2022 has impacts on the nutrient profile that should be considered when developing fertility plans for 2023. Crop nutrition experts from The Mosaic Company offer insights and reminders for producers and growers that may change how they approach soil sampling and nutrient planning for the coming year.
Nutrient uptake is reduced, leaving nutrients in the soil 
One of the obvious effects of drought is the reduction of nutrient uptake by crops, as water is the major medium for moving nutrients into plants. Reduced uptake equals reduced nutrient removal at harvest and translates to a residual effect of nutrients. This can be especially true for mobile nutrients like nitrate, sulfate and boron. Nutrient cycling is a complex process involving an interaction between soil minerals and nutrients, soil microbes and the plant’s root system, and it is largely affected by both soil pH and moisture.
“As we explore the rhizosphere and learn more about the activity and role of soil microbes, we’ve come to understand that the lack of soil moisture and increased temperatures typical during drought can decrease microbial activity and nutrient cycling, both of which are important for plant nutrient use for biomass and grain production,” says Curt Woolfolk, agronomist and senior manager of crop nutrition technologies with The Mosaic Company.
“When microbial activity slows during drought, processes like mineralization (conversion from unavailable to available forms) are reduced and don’t fully replenish the nutrients that are found in soil solution under more normal conditions. Nearly every chemical and biological function is reduced during dry conditions. Not only are less nutrients available in soil solution for plant uptake, but many nutrients become trapped in clay layers during extended periods of drought” Woolfolk explains. Drought-inhibited root growth (reduced exploration) and limited availability of water to facilitate nutrient uptake by the root system also cause nutrients to be left in the soil.
Dry conditions and reduced microbial activity slow crop residue decomposition
During drought, growers should consider the role and benefits of crop residue in the crop nutrition and production system. Wetter years lead to increased decomposition rates of crop residues while drier years lead to slowed decomposition that may affect planting conditions. Depending on cropping system, crop rotation and equipment, growers may benefit from sizing and incorporating residue to encourage nutrient cycling by increasing the amount of residue in contact with soil and soil microbes. This returns crop nutrients to the soil more quickly where they can be available for the next crop.
Potassium, for example, is a key nutrient that is easily leached from crop residue into the soil at plant maturity and after harvest. Without moisture, this potassium reserve could stay in the residue. With that said, it is important to remember that these drier situations generally result in lower uptake and lower yields, leaving more potassium in the soil.
Preserve crop residue to recharge soil moisture profile
“When soils are dry, not only are there fewer nutrients in crop residue to release back into the soil, but there is also less microbial activity to break down the residue,” Woolfolk says. “Producers may be better served to consider standing residue to catch snow and reduce wind erosion potential. This is especially true for cereal grain production in western states. Capturing and preserving moisture is a key component to increasing nutrient cycling in these environments; especially during periods of drought.” In no-till systems, keeping residue standing on the soil surface can trap 70% more of the water in rain or snow melt than conventional tillage.
“Along with increased water infiltration and retention, keeping crop residue undisturbed and on the soil surface also can help moderate soil temperature during the growing season to help keep soil microbes actively working if high heat and drought conditions extend into 2023,” Woolfolk explained.
Drought can affect soil sampling technique and soil test results 
Considering all the factors impacting the soil nutrient profile due to drought in 2022, this fall is an ideal time to work with your local retailer, certified crop advisor or certified professional agronomist to conduct thorough soil tests to assess soil nutrient levels, select advanced crop nutrition products that optimize plant nutrient uptake, and prepare a plan that will optimize nutrient use efficiency in 2023.
For more information on nutrient cycling, nutrient use efficiency and soil sampling during drought, visit CropNutrition.com.
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