Q. We are small farmers owning 2 acres of land in India, We have just seen your opinion on RO water for horticulture crops. We are growing roses and colour capsicum under poly greenhouse cultivation. Our ground water electrical conductivity level (salinity) is too bad that it comes to 1.8. So our plants came to death condition. We heard about reverse osmosis system and fixed it to our farm. By this system leaves shrinkage and nutrient deficiency had risen. So we are pleasing to suggest your idea about it. We are looking for your grateful suggestion.
A. Pepper plants are very tolerant of this level of salinity. It only becomes a problem if we let the soil becomes excessively dry or if the drainage of the soil is very poor and the water drains slowly. Improve the drainage of the soil and irrigate so that the soil never dries to less than 60% of its water content. With a little bit of experience, you can determine this just using your hands and feeling the moisture content by squeezing it and using your fingers.
The kind of salts that you have in the soil will dictate if you were to use soil additives such as gypsum or not to help flush the salts from the soil. Sending a soil sample to a soils laboratory to determine which salts are present would be very helpful.
Generally speaking we start to see yield reduction in pepper at about 1.5 dS/m (mmhos/cm). You are close to that threshold at 1.8. I think you would only need to dilute your irrigation water maybe 20% with RO water to get below this threshold.
New Mexico's advice on salt damage to peppers
Another option is to water with your irrigation water and then flush salts using an irrigation cycle using water with lower salts. Use these in an irrigation cycle of salts/low salts/salts/low salts/etc.
Monitor your drainage water for salt content. Monitoring your drainage water and recording it regularly will help you with managing salts (flushing, etc.)
Two types of salt damage occurs to plants; one is due to total salts (EC) and the other is due to the type of salts (specific ion effect). Particularly damaging are sodium, chloride and boron. If these salts are involved then this might mean a very different problem than just salts in general.
What to do?
- If it is possible, determine which salts are present and not just the level of salinity (1.8).
- When irrigating never let the soil or substrate dry out too much.
- With high salts you should be irrigating frequently with a smaller volume of water. This prevents the salts from becoming too concentrated.
- If you can over irrigate and flush salts from your soils make sure you over irrigate by about 20% to keep salts moving through your soil profile and maintain a steady state of salts and prevent the buildup of salts.
Depending on the type of salts in your irrigation water you will see different nutrient deficiencies.
Note: This question was from farmers in India. Potable water, water in the Las Vegas Valley coming from the tap, is close to this level of salinity or salts. This is because a large percentage of this water comes from the Colorado River unless you are on well water. Salt levels of our native soils here in the Las Vegas Valley are 25 times this level. Water management is very important to control salinity.