Cobalt Combined with Potassium Humate as Beneficial Applications in Alleviating Water Stress Impacts on Groundnut During Sensitive Growth Stages

Abstract

Enhancing plant nutrition during critical periods of water stress is a paramount objective. As such, this study aims to examine the effects that arise from implementing water stress regimes during the sensitive growth phases of groundnut. Furthermore, we will explore the impact of applying cobalt and potassium humate individually or in combination, either through foliar application (KH-F) or soil amendments (KH-S), to mitigate the adverse effects on nutrient accumulation, yield, and irrigation water use efficiency (Iwue). A field experiment was conducted between 2021 and 2022 using a split-split plot design. In the main plots, an additional control of full irrigation requirement scheme (IR100) was implemented, along with three other schemes: the first involved applying 75% of the irrigation requirement during the development stage (IRD75), the second applied 75% during the flowering till pod stage (IRF75), and the third involved applying 85% from the development stage till the pod stage (IR85). In the subplots, cobalt was applied at rates of 0 and 7.5 mg l−1 to the plants. The sub-sub plots were further divided to investigate the effects of KH-F and KH-S. Plants that experienced water stress during the flowering stage were found to be more vulnerable. However, when treated with KH-S, there were significant improvements in yield compared to KH-F treatment. This effect was particularly pronounced under the IRF75 irrigation scheme. Interestingly, there was an antagonistic relationship observed between cobalt and iron or manganese, in contrast to other nutrients. When KH-S was applied in combination with cobalt, it showed the potential to enhance various characteristics and increase the uptake of iron or manganese. The highest yield, nutrient accumulation, and Iwue were achieved through the combined application of cobalt and KH-S, along with adopting the IR85% irrigation scheme.