Application of zinc and boron fertilizers in field crops: Effectiveness of direct, residual and cumulative doses in an intensively cropped soil of Bangladesh

<h2>Abstract</h2> The application of micronutrients is crucial for maintaining the fertility of soils under intensive cropping particularly in the floodplains of Bangladesh. In the multiple cropping systems, application of micronutrients e.g., zinc (Zn) and boron (B) to one crop leaves beneficial residual effects for the next crops. A field experiment was conducted in a moderately alkaline floodplain soil of Bangladesh over two years with the objectives of studying the immediate and residual effects of Zn and B fertilizers on the growth and yield of crops under wheat-jute-rice cropping pattern. The treatments in wheat, the first crop, included four Zn levels (0, 2.0, 4.0, and 6.0 kg ha⁻¹) combined with three B levels (0, 1.5, and 3.0 kg ha⁻¹). The next crop, jute, received two additional treatments namely, i) 2.0 kg Zn ha⁻¹ and ii) 2.0 kg Zn ha⁻¹ + 1.5 kg B ha⁻¹. Finally, another four treatments containing 2 kg Zn ha⁻¹, were applied to rice, the third crop of the pattern. The yield of jute fiber increased significantly from 2.3 t ha⁻¹ to 2.8 t ha⁻¹, while that of rice grain increased from 3.5 t ha⁻¹ to 4.1 t ha⁻¹, due to the application of Zn and B. However, the yield increases of wheat grain was insignificant, indicating a notable difference in the crops' requirement of the nutrients. Most of the Zn and B applied in wheat remained under-utilized to be consumed by the succeeding crops resulting in improved yield and plant uptake. Statistically similar yields of jute fiber (2.60 t ha⁻¹ vs. 2.59 t ha⁻¹) and rice grain (3.96 t ha⁻¹ vs. 3.83 t ha⁻¹) as well as the system productivity (10.66 t ha⁻¹ vs. 10.50 t ha⁻¹) were observed in the treatments of 4 kg Zn + 1.5 kg ha⁻¹ in wheat and the repeated applications of 2 kg Zn ha⁻¹ to each of wheat and jute. The effect of Zn was dominant over the effect of B in case of their combined application. The application of Zn and B remarkably increased their tissue concentrations in all the tested crops. The findings suggest that the application rates of Zn and B may be reduced, to some extent, considering their residual effects on the field crops in the calcareous floodplain soils. Further research on the utilization of residues of Zn and B fertilizers in soils will lead to development of cost-effective crop management technologies in the intensive cropping environment.