Effect of iron impregnated wheat straw and particleboard biochar on the iron uptake and growth of two soybean cultivars in a calcareous soil

Biochar is a carbon-rich product which is produced using pyrolysis of carbon-containing organic residues under anaerobic or oxygen-limited conditions. Due to unique properties such as high organic carbon, specific surface area and cation exchange capacity, application of biochar leads to increase in adsorption and holding capacity of water and nutrients. This, in turn, results in improved soil fertility. The aim of this study was to investigate the effect of iron impregnated biochr on iron uptake and growth of soybean grown in calcareous soil.

An iron deficient calcareous soil (0-30 cm) was collected from east of Golestan province and after air drying, it was passed through a 2 mm sieve. Two types of biochar were produced from wheat straw and particleboard (at 300○C) and impregnated with iron sulfate (Fe2SO4.7H2O). A pot experiment was conducted as a factorial arrangement in a completely randomized design with four replications. Factors were biochars (wheat straw biochar (WB) and particleboard biochars (PB) with 2.5% w/w), iron impregnated biochars (Fe impregnated wheat straw biochar 2.5% w/w (Fe- IWB1) and 5% w/w (Fe-IWB2), 2.5% w/w (Fe-IPB1) and 5% w/w (Fe-IPB2) Fe impregnated particleboards, Fe- Sequestrene (S) and control (C), and two Soybean cultivars (Williams and Saman). The sown pots were maintained in field capacity by weighing method for 12 weeks. Then, height, fresh and dry weights, total iron concentration and uptake of shoot and soil available iron contents were determined after the harvest.

The application of Fe impregnated biochar increased iron availability in the soil. Also, SEM images showed that iron was adsorbed or accumulated on biochars surfaces. Height, fresh and dry weights of both soybean cultivars in Fe impregnated biochars were significantly higher than those of bichars and control treatments (P ≤ 0.01), but there were no significant differences among them with treatment Fe- Sequestrene. Furthermore, with the application of Fe impregnated biochars, the iron concentration and uptake amount of shoots in both soybean cultivars increased significantly compared to control and non-impregnated biochars treatments (P <0.01). Cultivars responses to Fe impregnated biochars showed that shoot dry weight and iron uptake of the Saman variety were significantly higher than those of Williams variety in both levels of Fe impregnated biochars.

The application of Fe impregnated biochar in calcareous soils with iron chlorosis increased iron availability. Therefore, in addition to improving the physical, chemical and biological properties of soil, Fe impregnated biochars like Fe- Sequestrene can effectively remove the iron deficiency of the plant.