Effectiveness of Organically-Complexed Bioaugmented Boron Coated DAP on Growth, Yield and Oil Content of Brassica

Abstract

The application of boron (B) and phosphorus (P) is a major issue worldwide. In addition, most of the Pakistani soils fail to supply sufficient B and P to growing plants because of calcareous nature of soils. Conversely, a few bacteria have been reported as B tolerant but their characteristics for enhancing nutrients supply to plants have not been studied yet. Likewise, bioaugmentation along with mineral fertilizer is attracting worldwide scientific community. In this scenario, the application of controlled-release fertilizers reduces nutrient losses and improves nutrient use efficiency (NUE). A reduction of about 20-30% of the recommended dose of commercial fertilizer can be obtained by the use of controlledrelease fertilizers while maintaining same crop yield. The current research work is therefore aimed to develop a coated fertilizer for simultaneous application of B, P and bacteria to achieve maximum benefits by reducing fertilizer losses. For this purpose, first of all, six pre-isolated bacterial strains (S-5, MN-34, MN-42, MN-17, MN-54 and MN-13) were screened however, the Bacillus sp. strain MN-54 was found to be the most tolerant to higher levels of B. In the next step, effect of molasses and B concentrations was determined on P solubilization and auxin production by the strain MN-54. It was found that P solubilization was improved by increasing molasses concentration from control to 1% in NBRIP medium, whereas B did not significantly change P solublization by the strain MN-54 at tested concentrations (0-180 mM B). The bacterium was also capable of auxin, siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production. Moreover, temporal release of B and P in soil was improved up to 37 and 30%, respectively, in native soil in the presence of strain MN-54, which further resulted in improved growth of canola. These findings led to the development of 0.5, 1 and 1.5% organically-complexed bioaugmented boron coated DAP fertilizer formerly named as DAP-B. The experiment conducted to investigate the temporal release of DAP-B formulations elucidated that the availability of B was improved by increasing the amount of B on coated product. It was also noted that 50 and 75% application of 1.5% DAP-B showed slower but higher release of P compared to conventional fertilizer, while B was readily available. After that, a pot experiment followed by a field experiment were conducted to investigate the effectiveness of different formulations of DAP-B over conventional fertilizers (DAP and boric acid) by analyzing the growth, physiology, yield, quality and oil content of Brassica napus (canola) and Brassica juncea (mustard). For this purpose, three formulations of 0.5, 1 and 1.5% DAPB were investigated at four different levels i.e. 25, 50, 75 and 100% compared to recommended level of DAP. Considerable increase in growth, physiology, yield, quality, B and P concentration in grains and oil content of aforementioned crops was observed in treatments where any of the three formulations of DAP-B were applied at recommended rates compared to conventional DAP. However, 1.5% DAP-B applied at 75% of the recommended dose of DAP was found most effective for both crops under observation compared to other treatments. In inference, the present approach not only enhances plant growth, yield and oil content but also brings environmental and economic benefits as, a complex fertilizer becomes available to plants by reducing fertilizer losses. Furthermore, availability of mechanical fertilizer minimizes the labor cost due to single application of aforementioned nutrients (B, P) at once.