Drought and Heat Stress Effects on Soil Fertility
Besides the immediate concerns for crop health and yield in the current growing season, the effects of the drought may linger into following years and growing seasons; especially if drought conditions persist through harvest.
Soil moisture affects the soil fertility aspects of crop management, but soil testing is still a valuable tool in determining the fertilizer needs on each farm. Properly interpreting the results given the dry season, however, is crucial to making economical management decisions. With reduced grain removal from many fields across the nation, producers should benefit from understanding how the dry conditions impact soil fertility and fertilizer efficacy.
- Water pH.
- Producers can expect pH to drop slightly following drought years. Due to lower exchange capacity in the soils, greater pH drops may be noticed in low cation exchange capacity (CEC) soils than in higher CEC soils.
- Lime applications to dry soils will remain nonresponsive until rain events come to help break down the particles and disperse them into the soil.
- Phosphorus (P).
- Phosphorus has no significant change in soil fertility due to moisture variance in soils. Due to the relatively immobile characteristic of phosphorus, slight drops in test results may occur, but not consistently or significantly.
- Moisture is essential in mitigating dry phosphate fertilizers (18-46-0, 11-52-0, etc.) across the soil profile. Therefore, dry fertilizer applications will give minimal benefit until a rain event occurs to dissolve and distribute the fertilizer particles into the soil.
- Potassium (K).
- Potassium is certainly impacted by droughty soil conditions. Low CEC soils are impacted to a greater extent than higher CEC soils. Soil analyses test the exchangeable portion of the soil solution. As the solution of the soil decreases with the drought, the potassium ions bind into the soil layers. Soil analysis will then not report the bound potassium ions, and potassium results will read lower than might be expected. With ample rains, the soil conditions rejuvenate and potassium is again released into the soil solution for analysis; but it may take longer than a year of normal rainfall before potassium results move back to pre-drought conditions.
- Moisture is again essential in mitigating dry potash (0-0-60) throughout the soil profile. Therefore, potash will give minimal benefit until a rain event occurs to dissolve and distribute the fertilizer particles into the soil.
- If yields are reduced and fertilizer adjustments are made due to lower grain removal rates, apply a minimum of 100 lbs. potash following the droughty year to boost production for the following season. Economic return is significant when at least 100 lbs. fertilizer is applied.
- Nitrogen (N).
- Nitrogen may or may not carry over fertilizer to the following year. Producers should not bank on significant nitrogen carryover, however, and should fertilize as they normally would for the following crop year. Be aware that knife tracks must properly close following fall-applied fertilizer to minimize nitrogen loss from the field, and dry soils will often not properly close.
Testing soil following the drought year gives producers the basic knowledge of where the soil fertility lies in each field. It is important to understand how reduced removal rates and dry soil conditions impact soil fertility so that proper fertilizer applications and savings can be made. Normal fertilizer recommendations should be followed during a drought year, but with considerations for reduced yields and financial constraints.
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