The effect of activated carbon on nutrient absorption by tomato, cucumber and eggplant under boron stress of irrigation water

The quality of irrigation water has an important effect on the growth and concentrations of nutrients. The application of boron-rich irrigation water is a global issue and the most important boron pollution source in the environment. Poor water quality unavoidably leads to decreased growth of plants. One of the problems of irrigation in tropical regions is the high concentration of boron element in water and its concentration in irrigation water increases every year. In dry areas where agriculture takes place, boron is often found in high concentrations along with saline soils and salty waters. Boron stress occurs widely and limits plant growth and crop productivity worldwide. Boron is in the form of boric acid in the soil solution and it is washed from the soil in heavy rains, but it is not washed enough when it rains, and by accumulating in the soil, it poisons the plant and prevents its growth. Therefore, in arid and semi-arid areas, irrigation with groundwater that has a high boron content reduces crop growth. Therefore, this experiment aimed to evaluate the effect of activated carbon on nutrient concentrations by tomatoes, cucumbers, and eggplants under the boron stress of irrigation water.

To evaluate the effects of activated carbon on the concentrations and translocation of boron in the plant a factorial experiment with a completely randomized design and three replications was performed in the greenhouse conditions. Treatments included three plants (tomato, cucumber, and eggplant), three levels of boron concentration in irrigation water (0.03, 2.5, and 5 mg l-1) from a boric acid source, and four levels of activated carbon (0, 1, 2, and 3% soil). To prepare seedlings, first, a sufficient number of healthy seeds were selected and for better germination, they were placed in wet napkins for one day and night. Then the seeds were planted in seedling trays with coco peat substrate. In this stage, watering was done once every two days until finally, after 30 days and when the seedlings reached the four-leaf stage and the true leaves appeared, the plants were ready to be transferred to the pots. For cultivation, each of the plastic pots was filled with 3 kg of sampled soil, which was mixed with a proportion of activated carbon according to the type of treatment. Then, in the middle of each pot, several seedlings of the same size were planted. Then the pots were placed in the greenhouse according to the plan. The experiment was conducted with 36 experimental treatments in three replications and a total of 108 experimental units. The soil used was prepared with geographical coordinates (longitude 57˚ 37ʹ and latitude 28˚ 42ʹ) and depth of 0-30 cm and was classified according to the American classification system Sand, mixed, hyperthermic typical Torriorthents. During the growing period, the plants were irrigated daily according to the farm capacity (FC). The day temperature of 25 – 30 °C, the night temperature of 15 – 20 °C, and the relative humidity was 50 – 70%.

The results indicate that the main effects of boron and activated carbon levels had a significant effect (p < 0.01) on the concentration of iron, zinc, manganese, and copper in the aerial parts of the plant. With the amount of boron increased in the treatments, the amount of copper and iron in the aerial parts increased while the amount of manganese and zinc decreased. Regarding the effect of activated carbon, the results showed that by increasing the amount of activated carbon in the treatments, the amount of copper, manganese, and zinc decreased. In contrast, the amount of iron has increased. The highest concentration of iron in the aerial parts (219.6 mg kg-1) belonged to the level of 3% of activated carbon. Also, with the increase in activated carbon in the treatments, concentrations and accumulation of boron in the aerial parts decreased. The highest concentration of boron in the aerial parts (31.77 mg kg-1) was obtained in the cucumber and the level of 0% activated carbon, and the lowest concentration (5.75 mg kg-1) was obtained in eggplant and the level of 3% activated carbon.

It is concluded that the use of activated carbon under boron stress conditions can reduce the concentrations and toxicity of boron in plants.