With drought conditions taking hold in much of the US, it is important to understand the challenges that arise when water supply is limited. There are a lot of factors that influence water retention and nutrient uptake in the soil, and one such factor is the electrical conductivity (EC) which can become a problem when drought conditions persist.

Electrical conductivity is a reading that measures the soluble salts in your soil. This includes table salt (NaCl) which is the salt that comes to everyone’s mind, but it also includes nitrate and ammonium salts, calcium salts, zinc salts, really any ion that carries a charge can form a salt with an ion of the opposite charge (Na+ and Cl-, for example). So, an elevated EC in water or soil could indicate a high level of fertility if the salts are nitrogen, phosphorus, potassium, and other micronutrients, however, a high salt environment encourages competition between ions of a like charge and can lead to nutrient deficiencies in plants. This is especially true with sodium and chlorine (Na and Cl) which tend to compete with critical nutrients for plant uptake and can interfere with photosynthesis wreaking all sorts of havoc on your crops.

Salts in soil are always a concern, but with an abundance of water the salts tend to wash deeper into the soil profile keeping them in lower concentrations near the root zone of the plants. In fact, the easiest way to deal with residual salts in the soil is to water heavily and push the salts out of the system. While this can work as a short-term solution, you are either pushing the salts downstream which is ecologically not ideal, or the salts will sit in the lower portion of the soil often forming hardened blocks or lying in wait for a prolonged dry spell. Drought can become problematic for the EC of the soil, because evaporation at the soil’s surface pulls water from deeper in the soil upwards, and pulls the salt up with it. Once evaporated, the water is gone, but the salt is left behind. This means that salts accumulate on the surface of the soil, typically near the most absorptive roots of the plant, leading to increased sodium and chlorine uptake.

Often this kind of salt concentration can be missed in a soil test which typically takes a 0”-6” or 0”-12” soil core. Since the EC is an average over that depth, the high concentration of salt within the first 1”-2” of soil gets diluted across the sample. Plants will also uptake salts over time, and sodium and chloride have low usages within the plant, so as nitrogen and phosphorus are used by the plant, the Na and Cl builds up in leaf tissues. This means that the accumulation of sodium and chlorine are most easily detected not in the soil, but in the sap of the plant and leaf tissues. It is always recommended to evaluate both the soil and the sap of the plant to get a more complete picture of nutrient usage.

The presence of elevated Na and Cl in a plant will cause ion imbalances that make nutrient uptake very difficult, it will also interfere with water uptake and will even cause damage to chloroplast structures (photosynthetic engine of plants). This leads to reduced photosynthesis, meaning less carbohydrate and sugar production. With a lower sugar concentration, plants become more susceptible to pests and diseases, release fewer exudates, and struggle to produce high yields.

If soil is calcareous (high levels of calcium carbonate) then adding sodium salt can lead to increased pH as sodium ions bind to the calcium and release hydroxide ions (OH-). This adds to nutrient uptake issues, as soils begin to creep above pH of 7.0 it becomes more difficult to release phosphorus and other micronutrients. Remember to evaluate your specific context to better understand how salt and drought might impact your fields.

To help reduce salt exposure, it is important to limit raw manure usage. Raw manure will typically have high salt levels exacerbating the issues, especially when in drought conditions. It is better to use a well processed compost, one that has more than just manure as a base recipe. Adding humic acids is another beneficial practice. Humic acid has charged binding sites that help to buffer salts that are in soil solution, by chelating (or binding temporarily to an ion) salts in the soil, humic acid can lower the relative impact of soluble salts on the plant. Improving the soil microbiome will also help to remove salt from solution and lower the pH at localized sites to improve solubilization of critical nutrients. Using salt accumulating cover plants is another option to remove some excess salt from the soil without washing it downstream.

As we all fight more volatile environmental conditions, it is important to adapt to the risks those conditions create in our fields. It is not possible to control the weather, so we must make changes to protect our crops to the best of our ability.