Biostimulants are one tool in the regenerative grower’s toolbox
By Ida Wilson, Chantel Ndhlovu, Okamelang Shao and Janneman Cornelius
Crop production faces a number of simultaneous challenges today. Climate used to be a stable and predictable component of the crop production system; it has now become unpredictable, with extreme weather events occurring more frequently, precipitation patterns changing from what was known in the past and droughts and floods becoming more troublesome in many agricultural production regions.
Due to the changed climate, plants are more often faced with abiotic and biotic stresses. Abiotic, or “non-living,” stressors include high temperatures, salinity, and wind or hail damage. Biotic, or “living,” stressors include attacks by pests and pathogens. Warmer climates support faster generation times in pests and pathogens, while also breaking down the inherent resistance that plants may have. Under high temperatures, pesticides may evaporate with application, and efficacy also declines. Moreover, various stresses may occur in the same production system concurrently, making the management of risk challenging.
Along with the changing climate, our growing human and domesticated animal populations require continued advances in crop productivity. This is while our natural resources are declining through soil degradation and pollution of air and water. Moreover, the available land for growing crops is restricted and cannot merely expand to hold up with the growing demands. Highly intensified agriculture, along with lower rainfall, is driving the salinization of both soil and water, with billions of hectares of agricultural land already impacted by high levels of salinity.
Conventional agriculture relies on pesticides to reduce risks and optimise yields. Yet long-term use of agrochemicals causes a decline in crop productivity since the non-target organisms, like pollinators and beneficial soil microbes, also decline in these systems over time. Although useful when used accurately, in some cases there is an over-reliance on agrochemicals. These tools should be used sparingly and only when needed.
Benefits of Biostimulants
Biostimulants are commercially available products of various origins that are applied to plant tissues or soil. These products benefit plants in multiple ways. Biostimulants have scientifically been proven to boost germination and root growth, to build symbiotic relationships among soil microbes, and to improve plants’ resistance to biotic and abiotic stress. The greater root surface area from enhanced root growth also helps plants to optimize the uptake of water and nutrients.
Biostimulants boost the plant’s primary metabolism and, as a secondary benefit, higher yields of better quality are often obtained when biostimulants are applied. The type of biostimulant, as well as timing and number of applications, will influence the effect the biostimulant will have on the plant. Moreover, the response to the biostimulant will vary between species of plants and will also be different under varied environmental conditions.
The application of biostimulants to crops often enhances their tolerance of biotic and abiotic stressors. This is because the biostimulant activates the natural processes in the plant that support plant stress tolerance. As the pressure of stressors lowers, plants become more resilient; the use of biostimulants may thus be useful in lowering the use of pesticides, since the plant’s inherent health and resilience is boosted.
Types of Biostimulants
Here are six different types of commonly used biostimulants:
- Flavonoids
Flavonoids are polyphenolic compounds that are naturally synthesized by plants and play a role in multiple plant functions. There are six main subgroups of flavonoids: chalcones, flavones, flavanols, flavandiols, anthocyanins, and proanthocyanins.
The structure of the flavonoid will determine the function. Functions of flavonoids include providing plants with greater stress tolerance, inhibiting insect herbivory and supporting beneficial microbe colonization. Furthermore, flavonoids benefit seedling germination and function as detoxifying agents.
- Humic and fulvic acids
Humic and fulvic acids are naturally found in soil organic matter as the products of the decomposition of organic matter.
Humic acids have a positive impact on soil fertility by impacting the chemical and biological properties of the soil, which in turn affects root growth and productivity. This enables the roots to absorb more macronutrients and micronutrients and therefore increase yield. Humic substances may aid plants in resistance to stress by enhancing the production of phenolic compounds that are responsible for stress responses.
Fulvic acids are naturally occurring organic acids and are oxidized fragments of larger humic substances. They constitute an important part of naturally formed soil organic matter. The chemical composition is also influenced by the geographical location and depth of soil layers from which they are extracted. Fulvic acids improve the absorption of nutrients from the soil and function as carriers of substances from the surface of plant organs to plant cells. They have a low molecular weight and can penetrate the pores of plant membranes, while also transporting chelated nutrients and remains in soil solutions, even at high salinity and over a wide pH.
Fulvic acids have been found to enhance the uptake of nutrients including nitrogen, phosphorus, potassium, calcium, magnesium, copper, iron and zinc. They also promote the growth of lateral roots and shoots, which in turn benefit crop yield and quality. Fulvic acids may also contribute to abiotic stress tolerance — particularly drought tolerance.
- Beneficial microbes
Beneficial microbes including, mycorrhizal fungi and bacteria, stimulate plant growth, improve crop quality and yield, and induce resistance to abiotic stresses. Priming seeds with bacteria may also enhance their tolerance to salinity and increase the germination rate and speed of germination.
- Chitosan
Chitosan is a form of chitin involved in plant defense mechanisms. It has been found to increase the tolerance of plants to abiotic stresses and support water holding capacity in plants. Another benefit is support in drought tolerance via an abscisic acid pathway.
- Seaweed extract
Seaweed extract-based biostimulants, which often include alginate, fucoidan and laminarin, are widely known to improve crop quality and increase yields. These biostimulants may also contain polysaccharides, including alginates, carrageenan, sterols and betaines, which enhance plant nutrient utilization. They are also known to promote plant-growth-promoting soil bacteria via both the regulation of plant hormone genes and the hormones naturally present in seaweed. The ample presence of antioxidants in seaweed extracts also alleviates stress in growing plants.
- Plant extracts
Plant extracts, although a far smaller component of the compounds used for producing biostimulants, also improve the development and growth of crops and may increase the amount of chlorophyll produced in plants, aiding in photosynthesis.
Benefits to Production Systems
Although the support biostimulants can give is not always as immediately apparent as synthetic products, biostimulants have been proven to be effective and can benefit crop production system in various ways. These include the following:
Water-use efficiency
Biostimulants can support the water-use efficiency of plants. They enable the optimal use of water in the production system and also help plants produce a high yield of quality produce.
More effective use of applied nutrients
With the cost of fertilizer skyrocketing recently, biostimulants play an important role in ensuring the effective uptake and transport of nutrients in plants. It is important to know that the greatest benefit is obtained from the specific input — biostimulants will give the producer peace of mind that the nutrient uptake in the plant, with the help of beneficial microbes, is optimal.
Greater stress tolerance
Farming under uncertain and unpredictable climate conditions is nerve wracking. It is more important than ever to proactively enable plants to resist the multiple stressors that they may encounter. Biostimulants support stress tolerance by allowing plants to direct energy and metabolites toward the production capacity of the plant. Biostimulants hold great potential to support future plant production systems under uncertain climates.
Thriving microbiome
Since biostimulants activate and enhance microbial life in the production system, they put the “machinery” responsible for nutrient cycling and nutrient uptake in plants to work. The value of the activation of soil microbes, which are also the main indicator of soil health, cannot be stressed enough. The microbiome is the most important component of the production system, and a thriving, healthy microbiome will result in a thriving, healthy farm.
Long-term sustainability
Supporting the vitality and resilience of the plant production system over years, with the support of biostimulants, will support the longevity of your operation. Biostimulants are “pro-life” — they enhance the growth of plants as well as that of so many other living creatures in the production system. Nature thrives for a reason. Shifting the production system to a “pro-life” system will also support the long-term sustainability of your operation.
The timely and accurate use of a biostimulant products can therefore be a useful tool in the toolbox of growers — both today and in the future.
Ida Wilson is a professor in the department of agronomy at Stellenbosch University in South Africa. She is assisted in her research, and this article, by her students Chantel Ndhlovu, Okamelang Shao and Janneman Cornelius. To get in touch with any of the authors, contact ida@biorevolution.co.za.
