Interactive effects of chemical fertilizers and biostimulants on yield and fertilizer use efficiency in orange

Ever-increasing need of human for agricultural productions has caused an ever-enhancing trend in use of different chemical fertilizers to achieve more yield production. On the other hand, augmenting the use of chemical fertilizers results in pollution and quality decline in soil and water resources, leading to production of unhealthy food products. Application of plant biostimulants like humic acid, fulvic acid, amino acids, mycorhizal fungi and seaweeds could be a useful approach to reduce using chemical fertilizers. It leads to reduce the use of chemical fertilizers without decline in quantitative and qualitative yield production. Therefore, the present research was accomplished in order to investigate the effects of some biostimulants on fertilzer use efficiency, as well as yield and quality of orange.

This experiment was carried out in a factorial manner based on completely randomized block design (CRBD) with three replications on 63 orange trees var. Washington novel, during two consecutive years in Hormozgan Haji-Abad agricultural research station. There were two factors consisting of 1-Application of chemical fertilzers in three levels (without any chemical fertilizers, %75 of the recommended chemical fertilizers, %100 of the recommended chemical fertilizers), and 2- Application of plant biostimulants in seven levels (control, amino acid foliar spray, seaweed extract foliar spray, soil applied humic acid, fulvic acid foliar spray, soil applied mycorhizal fungi, amino acid and seaweed extract foliar spray accompanied with soil applied humic acid and mycorhizal fungi). The harvesting was done in december, every year. Some plant responses such as yield production, the concentrations of iron, manganese and zinc in leaves, total soluble solids, vitamin C in fruit extract, and fertilizers use efficiency were determined. Finally, the results were interpreted based on the analysis of variances for the data set and comparison of means.

The results showed that application of biostimulants caused an increase in production yield and fertilizer use efficiency, as well as the concentration of iron, manganese and zinc in leaves. Some qualitative properties consisting of total soluble solids and vitamin C content in fruit extract were also improved. Furthermore, use of chemical and organic fertilzers corroborated the positive effects of biostimulants. In other words, interactive effects of biostimulants and fertilzers on quantitative and qualitative properties of orange were significant. The most positive effects were observed in the treatment containing soil applied humic acid and mycorhizal fungi accompanied with amino acids and seaweed extract foliar spray, and %100 of the recommended chemical fertilzers. However, fertilizer use efficiency in trees treated with %75 of the recommended chemical fertilizers was higher, as compared to those supplied with %100 of the recommended fertilizers.

It is recommended that instead of excessive use of chemical fertilizers, a combination of biostimulants including humic acid, amino acids, seaweed extract and mycorhizal fungi be applied along with %75 of the recommended chemical fertilizers in the integrated nutrition management, in order to achieve increased yield, improved fruit quality and reduced environment pollution.