Foliar Application of Humic Acid on Nutrition Accumulation in Leaf and Fruit of Strawberry cv. Selva under Different Cultivation Beds

The use of biofertilizers instead of chemical fertilizers has an effective role in increasing the health of plants, animals and humans and reducing environmental pollution. Biofertilizers are gradually being replaced by chemical fertilizers. Strawberry is a fruit with high nutritional value. Choosing the right nutritional conditions such as fertilizers and suitable cultivation beds to achieve high quantitative and qualitative yield in this plant is inevitable. In recent years, the use of humic acid has been common in enhancing the vegetative and generative characteristics of crops. Humic acid is a rich source of potassium, phosphorus and nitrogen. The method of application of humic acid has an effective role in improving the quantitative and qualitative characteristics of plants. The leaf application of humic acid was effective in increasing the amount of phosphorus, potassium and nitrogen. The amount of potassium and phosphorus in strawberry fruit is more than other elements. Combining some cultivation beds (perlite and composts) and fertilizers such as agricultural waste (rice bran and tea wastes) into soil cultivation beds have an effective role in improving the quantity and quality of plants.

A pot experiment was conducted to evaluate the effect of foliar application of humic acid and different cultivation beds on nutrition uptake of strawberry. Different concentrations of humic acid (0, 300, 600, and 1000 mg.l−1) were applied as foliar application in two steps (late March and late April) on strawberry cultivated in different beds (usual soil, usual soil + rice bran, perlite, or tea wastes). This study was carried out as two factorial experiment in completely randomized design. Soil nitrogen, phosphorus and potassium, soil pH and electrical conductivity and leaf and fruit nitrogen, phosphorus and potassium content were measured. Measurement of nitrogen, phosphorus and potassium was carried out by Kjehldal, spectrophotometry and flame photometry, respectively.

The interaction effect of humic acid ×cultivation beds on nitrogen and phosphorus content of leaves and fruits was significant at 1% of probability level and on fruit potassium at 5% of probability level. The interaction of these two factors on leaf potassium was non-significant. The results of comparing the mean comparison of humic acid and cultivation beds on soil elements showed that the highest amount of nitrogen was obtained in the treatment of 600 mg.l−1 humic acid and in the cultivation bed of usual soil+rice bran. The highest amount of phosphorus was obtained in the treatment of 1000 mg.l−1 humic acid and the cultivation bed of usual soil + tea wastes. The highest amount of potassium was obtained in the treatment of 600 mg.l−1 humic acid and in the cultivation bed of usual soil + tea wastes and the lowest one was obtained in the same bed without humic acid. Results showed that the highest potassium content (518 mg.l−1), and phosphorus (4.84 mg.l−1) of fruit were obtained in plants treated with 1000 mg.l−1 humic acid cultivated in usual soil + rice bran. The highest nitrogen content of fruit was obtained in plants cultivated in usual soil +tea wastes. The plants grown in this cultivation bed with humic acid application at 1000 mg.l−1 had maximum content of leaf nitrogen (5.47%). The highest content of leaf potassium (4.50 mg.l−1) and phosphorus (6.32 mg.l−1) were obtained in plants treated with 600 mg.l−1 humic acid in the cultivation beds of usual soil and usual soil + rice bran, respectively. The application of humic acid at 1000 mg.l−1 and using usual soil+rice bran as bed is recommended for strawberries production as potassium, phosphorus and nitrogen are the most important elements for increasing the quality of strawberry fruits , respectively. A positive association has been reported between the use of humic acid and the increase in growth, yield and product quality in strawberries and other plants. Humic acid can improve quantitative and qualitative production of crops by providing more available essential elements and increasing plant resistance to various biological and non-biological stresses.

Strawberries are widely cultivated worldwide due to their high nutritional value. Chemical fertilizers have been used as a way to increase crop yields, but have led to problems such as nitrate accumulation, short pot life, and poor quality and environmental pollution. Therefore, organic fertilizers have been recommended. A stimulating effect of humic acid on biomass production and plant growth is to increase the uptake of nitrogen, phosphorus and potassium. Proper cultivation bed plays an important role in the optimal growth and development of plants. According the result of this study, the use of beds containing agricultural waste and foliar application of humic acid increased the growth, yield and quality of strawberry fruit.