While we all are aware that the big three, nitrogen (N), phosphorus (P) and potassium (K) are needed for healthy plants, many of us don’t give much thought to the dozen or so trace elements that while needed in tiny quantities are also vital to good plant growth. One of them is chloride (Cl) which is needed for photosynthesis in plants. Cl is an essential anion in maintaining electoral balance in tonoplasts and cell turgor in stomates, which is important in nutrient uptake, storage, relocation, as well as water uptake. It is needed for the synthesis of proteins and growth regulators. Cl is also important in enzyme activities, lodging prevention in wheat, disease suppression, and physiological leaf spot control in cereal crops. Sufficient Cl availability can decrease the incidence of blossom-end rot and reduce injury of gold speck on tomato fruits.
The existence of Cl can impact plant nutrients uptake by interactive effects with other nutrients. There is an antagonism between Cl and nitrate (NO3–) in plants. The uptake of chloride is inhibited by nitrate, and vice versa. There are possible benefits of partial nitrate replacement in the root environment by an equivalent chloride content. For example, increasing the Cl:NO3– ratio in the nutrient solution can decrease the incidence of blossom-end rot in tomatoes.
Unfortunately, it can also increase gold speck injury on tomato fruits. Some research has shown that Cl can enhance calcium uptake by tomatoes, which may explain the reduction of blossom-end rot. However, Cl toxic effects on tomato plants could happen in Cl sensitive varieties and this effect is dependent on accompanying ions, such as sodium (Na), potassium (K), and phosphorus (P). High Cl content in soil or soilless medium can impose a potential risk to negatively affect potato yield and quality.
Another potential benefit from sufficient Cl supply is its interactive effect with nitrogen fertilizer applications on plant nitrogen uptake. Reducing the nitrate content of vegetables is important for human and animal health. Chloride can suppress nitrate accumulation in green leafy crops, such as lettuce without affecting vegetable yield.
Cl deficiency in wheat has been reported in wheat producing regions of the U.S. and in Canada. Physiological leaf spot, the typical Cl deficiency symptom, is commonly observed in many cultivars of winter wheat in this region.
Grain crops yield can benefit from Cl containing fertilizer applications, however, the benefit is dependent on plant cultivars. If Cl deficient, 10-20 lbs/acre Cl should do the job for commercial crops. Home gardeners can select fertilizers that contain chloride. Common fertilizer sources of Cl include potassium chloride (KCl), which is also referred to as Muriate of Potash and ammonium chloride (NH4Cl). Both the potassium (K) and Cl contained in the Muriate of Potash fertilizer are crop essential nutrients. If your soil is K deficient, Muriate of Potash fertilizer is a good choice because your crop can benefit from both Cl and K. Ammonium chloride contains both Cl and N nutrients and may be more economical when your soil is not K deficient. And there could be a positive interactive benefit between NH4+ and Cl making for a more abundant harvest.
Haiying Tao, PhD, UConn Assistant Professor, Soil Fertility & Health
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