Boron and Acid Soils

Resistance to Boron and Acid Soils

Acidic soils with low pH, where the soluble aluminum (Al) concentration is very high, are the soils where Boron deficiency occurs most in plants. Today, about 1/3 of the soils under vegetative production have Al toxicity problem. Al damage in plants first begins by inhibiting root growth.  

One of the most common agronomic practices to correct and raise low pH in acidic soils is to apply lime to soils. As expected with lime applications, an increase in soil pH occurs, while free Al ions are converted to Aluminum hydroxide [Al(OH)3]. However, in this process, significant decreases also occur in the availability of Boron, which is soluble in soil. It is reported that boron binds to Al(OH)3 formed in the soil and its uptake by plants decreases. Acidic soils are common in regions with high rainfall. Boron leaching in these soils can be significant and this situation increases the risk of boron deficiency in plants. In other words, in acidic soils, the risk of boron deficiency is very high due to the increase in the leaching potential of Boron and the decrease in chemical usefulness (solubility) caused by lime application.

It is known that the susceptibility of plants to Al damage in acidic soils increases with Boron deficiency in plants. Therefore, it is important to monitor the boron nutrition status of plants in acidic soils through soil and plant analysis. It is reported that there are two mechanisms behind the protection of boron against Al damage to plants. Some studies show that under boron deficiency conditions, negativity (minus charges) increase in the cell walls of the roots and this charge plays an important role in the uptake of Aluminum by the roots. It is stated that boron, in a sense, has a "covering" effect on the points where Aluminum can be attached, reducing the uptake of Aluminum by the root. Another study shows that a good Boron nutrition provides physiological inactivation of Aluminum in the roots. It is thought that a sufficient level of Boron provides the binding and immobilization of aluminum to pectin soluble at alkaline pH in the stem cell walls, thereby reducing Al toxicity.

It is known that root growth is improved when Ascorbic acid (Vitamin C) is applied to the roots of plants under aluminum toxicity and boron deficiency. The improvement of root growth with the application of ascorbic acid indicates that there is probably a deterioration in the metabolism of ascorbic acid in plants under boron deficiency. As a matter of fact, it has been found that there are significant decreases in the amount of Ascorbic acid in plants with boron deficiency problems. As it is known, Ascorbic acid is a strong antioxidant and plays a role in the detoxification (elimination) of oxygen radicals with high toxic effects. There are research articles reporting that Al toxicity in the roots is actually an oxidative stress and causes an increase in oxygen radicals and damages the roots. Based on this information, it can be suggested that the Al damage that occurs under boron deficiency is an oxidative cell damage.