Herbicidal weed management practices: History and future prospects of nanotechnology in an eco-friendly crop production system.

Weed management is an important aspect of crop production, as weeds cause significant losses in terms of yield and quality. Various approaches to weed management are commonly practiced by crop growers. Due to limitations in other control methods, farmers often choose herbicides as a cost-effective, rapid and highly efficient weed control strategy. Although herbicides are highly effective on most weeds, they are not a complete solution for weed management because of the genetic diversity and evolving flexibility of weed communities. The excessive and indiscriminate use of herbicides and their dominance in weed control have triggered the rapid generation of herbicide-resistant weed species. Moreover, environmental losses of active ingredients in the herbicides cause serious damage to the environment and pose a serious threat to living organisms. Scientific advances have enabled nanotechnology to emerge as an innovation with real potential in modern agriculture, adding a new dimension in the preparation of controlled release formulations (CRF) of herbicides. Here the required amount of active ingredients is released over longer periods of time to obtain the desired biological efficacy whilst reducing the harmful effects of these chemicals. Various organic and inorganic carrier materials have been utilised in CRF and researchers have a wide range of options for the synthesis of eco-friendly carrier materials, especially those with less or no toxicity to living organisms. This manuscript addresses the history, progress, and consequences of herbicide application, and discusses potential ways to reduce eco-toxicity due to herbicide application, along with directions for future research areas using the benefits of nanotechnology.

Controlled release herbicide formulation for effective weed control efficacy.

Controlled release formulation (CRF) of herbicide is an effective weed management technique with less eco-toxicity than other available commercial formulations. To maximise the effectiveness of CRFs however, it is crucial to understand the herbicide-releasing behaviour at play, which predominately depends on the interaction mechanisms between active ingredients and carrier materials during adsorption. In this study, we investigated and modelled the adsorption characteristics of model herbicide 2,4-D onto two organo-montmorillonites (octadecylamine- and aminopropyltriethoxysilane-modified) to synthesise polymer-based CRFs. Herbicide-releasing behaviour of the synthesised CRF microbeads was then analysed under various experimental conditions, and weed control efficacy determined under glasshouse conditions. Results revealed that adsorption of 2,4-D onto both organo-montmorillonites follows the pseudo-second-order kinetics model and is predominately controlled by the chemisorption process. However, multi-step mechanisms were detected in the adsorption on both organoclays, hence intra-particle diffusion is not the sole rate-limiting step for the adsorption process. Both organoclays followed the Elovich model, suggesting they have energetically heterogeneous surfaces. Herbicide-releasing behaviours of synthesised beads were investigated at various pH temperatures and ionic strengths under laboratory and glasshouse conditions. Furthermore, weed control efficacy of synthesised beads were investigated using pot studies under glasshouse condition. Desorption studies revealed that both synthesised microbeads have slow releasing behaviour at a wide range of pHs (5-9), temperatures (25-45 °C), and ionic strengths. The results also revealed that synthesised microbeads have excellent weed control efficacy on different broad-leaf weed species under glasshouse conditions.

Investigation of herbicide sorption-desorption using pristine and organoclays to explore the potential carriers for controlled release formulation.

Injudicious application of available commercial herbicide formulations leads to water, air and soil contamination, which adversely affect the environment, ecosystems and living organisms. Controlled release formulation (CRFs) could be an effective way to reduce the problems associated with commercially available herbicides. Organo-montmorillonites are prominent carrier materials for synthesising CRFs of commercial herbicides. Quaternary amine and organosilane functionalised organo-montmorillonite and pristine montmorillonite were used to investigate their potential as suitable carriers for CRFs in herbicide delivery systems. The experiment involved a batch adsorption process with successive dilution method. Results revealed that pristine montmorillonite is not a suitable carrier for CRFs of 2,4-D due to its low adsorption capacity and hydrophilic nature. Conversely, octadecylamine (ODA) and ODA-aminopropyltriethoxysilane (APTES) functionalised montmorillonite has better adsorption capacities. Adsorption of 2,4-D onto both organoclays is higher at pH.3 (232.58% for MMT1 and 161.29% for MMT2) compared to higher pH until pH.7 (49.75% for MMT1 and 68.49% for MMT2). Integrated structural characterisation studies confirmed the presence of 2,4-D on the layered organoclays. The Freundlich adsorption isotherm model fitted best to the experimental data, which revealed an energetically heterogeneous surface of the experimental organoclays, and adsorption which specifically involved chemisorption. The cumulative desorption percentages of adsorbed 2,4-D from MMT1(2,4-D loaded) and MMT2(2,4-D loaded) after seven desorption cycles were 65.53% and 51.45%, respectively. This outcome indicates: firstly, both organoclays are potential carrier materials for CRFs of 2,4-D; secondly, they have the ability to reduce the instantaneous release of 2,4-D immediately after application; and thirdly, eco-toxicity is greatly diminished.