Investigation into the effect of silicic acid as a biostimulant on fresh horticultural produce

The reliance of modern agricultural production systems on plant protection products, specifically synthetic pesticides and inorganic fertilisers is increasingly being challenged due to environmental, health and sustainability concerns. Increasingly commercial growers are looking to low impact substances to help them in reducing both biotic and abiotic stresses in crops to reduce their reliance on these problematic inputs while also maintaining the high yields and quality that the market expects. Silicon products (containing Silicic acid) are increasingly being utilised by horticultural producers to help manage these stresses, however little data exists on the optimal application rates, application strategies and indeed the actual benefit from utilising these products in protected horticultural crops. The benefits of utilising silicon products in monocot crops like rice and wheat, which are known as high accumulators is well established, however their potential in protected horticultural crops remains unclear. This project seeks to establish agronomic strategies to best utilise silicon containing products in protected horticultural systems and what the potential measurable benefits of the use of silicon products may be. Ultimately, the experiments conducted did not indicate the application of Silicon-containing products resulted in a measurable increase in yield or quality; however this was relatively unlikely given the highly optimised agronomic systems these crops are produced in. Potentially useful observations, such as in a measurable increase in fruit firmness were observed in the later harvests of some strawberry crops. This may be a useful observation as maintaining fruit firmness may improve crop shelf-life, but can also potentially reduce susceptibility to disease or harvesting damage (bruising). Additionally, how the silicon products were applied is significant, as drench applications in some experiments resulting in higher proportions of damaged fruit compared to foliar application. This is an important observation, as the majority of silicon application in protected commercial systems are likely to be made through the irrigation system. While this finding needs to be confirmed, this impact of application is important information for commercial growers if confirmed. In attempting to understand the potential impact of silicon products on plants under abiotic stresses the effect of drought stress in a model crop (spinach) was investigated. Data from the experiments are complex with some measured parameters such as leaf chlorophyll content increasing but it is likely it was the impact of stress conditions causing this increase rather than silicon application. Chlorophyll is increased in drought-stressed spinach but the long-term relevance of this for plant health remains unclear. Better understanding of the impact of experimental methodology on plant parameters under stress conditions from the impact of biostimulant application needs to be addressed in future projects. In order to increase the confidence of commercial growers in adopting more of these types of products, better methodologies to identify the agronomic benefits on individual crops and different production systems needs to be established. This study contributes towards a better understanding of the challenges in demonstrating the benefit of these low impact products,