Solutions for high-salinity irrigation water or soils — II
How to Mitigate Salinity
When cultivating plants in increasingly saline conditions, adopting irrigation and soil management techniques becomes necessary. Application of these will even allow you to grow a big range of plants, as long as they are not considered too sensitive. Check this database to know more about salt tolerance of fruit trees.
A — Irrigation Techniques
Drip irrigation is the most efficient option because it delivers water directly to the plant roots, which helps prevent salt build-up on the soil surface.
When you water your plants, some of the salt in that water naturally stays in the soil. Over time, this salt can build up and harm your plants. To prevent this, you need to flush extra water (non-saline) through the soil to wash away the salt — a process called leaching. The FAO suggests using 15-20% more water than usual for leaching. Try leaching once or twice a week and monitor your soil’s salt levels; if conductivity increases significantly, you may need to leach more often because that means that salts are accumulating too much; if it remains stable, you can reduce the frequency.
Leaching process, https://thealevelbiologist.co.uk/nitrogen/
Research and studies recommend using leaching with good quality water to prevent salt accumulation. However, this assumes you have access to such water. Below, we share some practical cases you can consider, depending on your specific situation.
Leaching : practical cases
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You have both saline and good quality water in large amounts. For example, if you have access to dam water but have quotas about it
Your borehole water is not too saline
→ Mix water from both sources
Let’s say that your dam water is 200 µS/cm and your borehole 1500 µS/cm. If you blend them 50-50, you will have a final product of water with a conductivity of 850 µS/cm, which is still safe for most crops.
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You have access to a very limited amount of good quality water
→ Use it for leaching
To prevent salt accumulation, the best way is to leach. If it is possible to use clean water, then go for it!
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You only have access to borehole water
→ Use it for leaching, but in greater amounts
Leaching can also be done with your saline water but it will require greater amounts. Be careful! If it is not done properly, it can lead to salt accumulation in the soil instead of preventing it.
We recommend checking the website of Utah University that gives more detailed information about leaching requirements: https://extension.usu.edu/irrigation/research/managing-saline-and-sodic-soils
Finally, when flushing salts from the soil, a good drainage system is crucial to prevent waterlogging, which is also harmful for plants. Drainage refers to the soil's ability to allow water to flow through it, which depends on soil texture. Simply put, the larger the soil particles, the better the drainage.
To determine your soil texture — whether it's sandy, loamy, or clay — you can check regional soil websites, consult a local farmer, or test it yourself. Take some soil, moisten it, and try forming a ball. If it falls apart, it's sandy soil with good drainage. If you can form a ring without breaking, it's clay soil with poor drainage. Loamy soil, which falls in between, has moderate drainage.
In any case, you should improve your soil texture to make sure the leaching will work, you can do this by following our soil management techniques provided in the section below. But keep in mind that the heavier in clay your soil is, the more you have to put care into improving its texture and drainage.
B — Soil Management Techniques
(a) Tillage: it helps to improve the soil structure, loosen the soil particles and create a better drainage.
(b) Sanding: mixing the soil particles with sand also helps improving the soil drainage.
(c) Chemical amendments: they replace the excess sodium with calcium ions. The amendments can be gypsum, calcium chloride, lime combined with organic manure and sulfur-containing products.
The most used amendment is gypsum because it is less costly, not harmful against the environment, contributes with calcium but also sulfur (another essential nutrient for the plants), it dissolves more easily in water than other products and it doesn’t affect significantly the soil’s pH, contrary to lime that will increase it. To use this amendment, you just need to apply it on the soil surface or with the tillage and it will dissolve with irrigation. The FAO even states : “In gypsiferous soils, plants will tolerate (soil) EC about 2,000 µS/cm higher than indicated”
A very complete study about gypsum suggests the application of 1kg/m² (10T/Ha). Suggested application time is a few months prior to planting.
(d) Organic matter: it improves soil structure, increases water retention, boosts microbial activity and enhances nutrient availability. At the Orchard of Flavours, 20% of soil composition is made of compost.
(e) Mulching: when water evaporates from the soil, the salt concentration increases. Mulching helps to prevent evaporation.
(f) Phytoremediation: use of very salt-tolerant plants, known as halophytes, to lower soil salinity (these plants are much more salt-tolerant than our fruit tree champions). You can plant them around your crops — along borders, between rows, or near irrigation areas — or as intercrops (before planting your main crop). Common halophytes are Saltbush, Kallar Grass, Sea Lavender, and Bermuda Grass. At our orchard, we use Vetiver grass for several purposes, and it is also great for absorbing salts.
(g) Mycorrhizal fungi: We typically use mycorrhizal fungi for their symbiotic benefits to plants, such as improved nutrient and water uptake. However, some strains have proven to be particularly effective in mitigating the harmful effects of salinity on plants such as Glomus intraradices and Glomus mosseae.
In high-salinity conditions, the use of appropriate soil management and irrigation techniques can make a big difference in the health and productivity of your soil and plants. But there are other approaches that farmers and gardeners in those challenging situations can rely on. Keep scrolling to find more content in this Research series.
This article was compiled by Miguel COTTON & Angela DUZAN. If you have any questions or suggestions, do not hesitate to contact us. Please write us anytime at miguel@orchardofflavours.com
Interested in more content relating to the growing issue of soil salinity and its effects on plants and soils, as well as solutions? This article is part of our Research series "Salinity and Edible Plants":
