What do plants need during a dry spell?

The current dry conditions across many parts of the Prairies have farmers keeping one eye on the sky and the other on their crop. Although it is heartwarming to know that dry soils in spring are not a sure sign of crop failure, it is important to be aware of a few things that happen under dry conditions: There is slow movement of soil nutrients towards plant roots so plants are unable to take up nutrients in adequate amounts; soil microorganisms involved in nutrient cycling are inhibited; plants reduce or close stomatal opening, thereby reducing transpiration; this reduction in transpiration limits nutrient transport from the roots to the shoot and results in a low absorption power in the roots. In short, dry conditions cause reduced uptake of nutrients from the soil, and poor nutrient transport within the plant.

What do water-stressed plants look like?

Even before they show any visual signs, the leaf temperature of water-stressed plants will rise. This is because when stomata are closed, energy transfer between plant and surrounding air is limited. Depending on the type of crop, visual symptoms may include dull green colour, curled leaves, droopy appearance, yellowing or browning of leaves, and wilting. By the time visual signs of water stress appear, a reduction in final yield may already have occurred.

So, what can we do?

Growers may be tempted to cut back on input such as fertilizers in a dry spell so as to reduce economic risk. However, research shows that good nutrition is even more important in dry periods. Crops need an adequate supply of macro and micronutrients early in the growing season to develop a strong root system and ameliorate the effects of drought. Some elements have been found to be particularly beneficial in dry conditions. For example, in 1999, south-central Ohio suffered severe drought, and corn yields ranged from 40 to 70 bushels per acre. Certain farmers in the area, however, produced more than 150 bushels per acre. Soil test results showed that these high-yield farmers also had high soil test levels of potassium (K).¹ Potassium is critical in dry conditions because the element governs the stomatal opening mechanism and can help plants tolerate water stress. The ability of plants to cope with water stress has also been shown to be enhanced by adequate phosphorus nutrition². Furthermore, trace elements such as zinc (Zn), copper (Cu) and manganese (Mn) play a role in the structure of many antioxidant enzymes; therefore, a deficiency of these elements makes the plant more susceptible to environmental stresses³.

When the soil is dry, roots are unable to take up adequate amounts of nutrients from the soil, so foliar application of nutrients will be more effective than application of fertilizers to soil. Using a fertilizer with a low salt index becomes even more important in this situation so as to avoid damage to shoots and roots. Furthermore, water-stressed plants have a reduced defence mechanism against pests and diseases, and can easily be outcompeted by weeds. Detecting and dealing with these problems early will give crops a better chance of recovery when moisture becomes adequate. Talk to your SynergyAG rep for product and agronomic advice.

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

References

1. Mosaic Crop Nutrition. Potassium and drought (https://www.cropnutrition.com/potassium-and-drought) Assessed May 30, 2019.
2. da Silva, E. C., Nogueira, R. J. M. C., da Silva, M. A., & de Albuquerque, M. B. (2011). Drought stress and plant nutrition. Plant Stress, 5(Special Issue 1), 32-41.
3. da Silva Folli‐Pereira, M., Ramos, A. C., Canton, G. C., da Conceição, J. M., de Souza, S. B., Cogo, A. J. D., … & Rasool, N. (2016). Foliar application of trace elements in alleviating drought stress. Water Stress and Crop Plants: A Sustainable Approach, 2, 669-681.