Saline soil and water damage many citrus groves in Florida. The major citrus plants’ reaction to excessive salt in the soil or water is a decline in growth. In general, when the dissolved salt concentration in soil or water increases, we call that soil or water “saline” soil or water. But how much increase in salt concentration make soil or water saline?
The electrical conductivity (EC) of a solution, expressed as deci-Siemens per meter (dS/m), is measured as part of the usual technique for salinity testing. Another method to report salinity is milligrams per liter (mg/L), or parts per million (ppm) of total dissolved solids (TDS). A saline soil, according to the U.S. Salinity Laboratory Staff (1954), has an EC of more than 4 dS/m, or around 40 mmol salts per liter. Florida waters typically have an EC of 0 to 5 dS/m.
The major citrus plants’ reactions to excessive salt in the soil or water are reduced root growth, decreased flowering, smaller leaf size, and impaired shoot growth. Injury symptoms resulting from saline irrigation water are not typically permanent, but if trees are young, injured trees may show restricted growth compared with trees not receiving salty water. The reason is that a solution with more salts inhibits roots’ ability to draw out as much water as a solution with fewer salts. Therefore, the energy required by the trees to carry water through them increases, which affects root growth and therefore decreases shoot growth and production.
Different citrus rootstocks show different tolerance to soil salinity. The most tolerant citrus rootstocks to salinity are: 1. Cleopatra mandarin; 2. sour orange; 3. sweet orange; 4. Swingle citrumelo; 5. Carrizo citrange; 6. rough lemon. Grapefruit trees tend to be less salt-tolerant than orange trees.
Tips to manage soil and water salinity in citrus groves:
- Use an EC meter to regularly assess the salinity of irrigation water. If TDS surpasses 2000 ppm, a salt problem is very likely. A salt problem may become apparent when TDS rises from 1000 to 2000 ppm.
- To remove excess salts from the root zone, special treatment may be required in locations with fine-textured soil, compacted soil, or inadequate drainage.
- To reduce evaporation and salt deposition, irrigate during the night whenever possible.
- The lowest salt index per unit of plant nutrients should be used when selecting fertilizer formulations.
- Increasing the frequency of fertilization will lower the salt content of each application and assist prevent the buildup of extra salt in the root zone.
- Reduce the amount of fertilizer used on trees that are irrigated with salty water compared to plants that are irrigated with high-quality water because the yield is likely to be lower.
- To find deficits of other elements brought on by salt-induced nutritional imbalance, analyze leaf tissue for high Na or Cl levels.
- To drop the EC of the soil solution below the critical threshold for the crop, excess salts should be leached below the root zone. As a general guideline, 6 inches of water will dissolve around half of the salt, 12 inches will dissolve 4/5 of the salt, and 24 inches will dissolve 9/10 of the salt.
- It is advised to break root-restrictive hardpans or clay pans by heavy tillage for soils with poor drainage in order to allow water to permeate and flush the salts.
- When soil contains excess sodium, it is sodic soil. Too much sodium limits the development of soil aggregates, leading to soil dispersion, which can seal or crust the surface. To reduce sodium, the soil needs to be treated with calcium. Gypsum is one of the most common calcium sources for treating sodium-contaminated soil.