Abstract
The use of biostimulants has become a common practice in agriculture. However, there is little peer-reviewed research on this topic. In this study we tested, under controlled and replicated conditions, the effect of one biostimulant derived from seaweed extraction (Bio-1) and another biostimulant derived from microbial fermentation (Bio-2). This experiment utilized 2-years-old almond plants over two growing seasons in a randomized complete design with a full 2 × 4 factorial structure with two soil potassium treatments (125 μg g-1 of K vs. 5 μg g-1) and four foliar treatments (No spray, Foliar-K, Bio-1, Bio-2). Rubidium was utilized as a surrogate for short-term potassium uptake and plant growth, nutrient concentration, and final plant biomass were evaluated. There was a substantial positive effect of both biostimulant treatments on total shoot leaf area, and significant increases in shoot length and biomass under adequate soil potassium supply with a positive effect of Bio-1 only under low K supply. Rubidium uptake was increased by Bio-1 application an effect that was greater under the low soil K treatment. Though significant beneficial effects of the biostimulants used on plant growth were observed, it is not possible to determine the mode of action of these materials. The results presented here illustrate the promise and complexity of research involving biostimulants.
Highlights
The use of biostimulants, defined here as ‘a substance or material, with the exception of nutrients and pesticides, which has the capacity to beneficially modify plant growth’ has grown dramatically over the past decade and it is predicted that the market for biostimulants will exceed US$2 billion by the year 2018 (SaaSilva et al, 2013; Calvo et al, 2014)
Shoot leaf area was significantly increased by the application of Biostimulant 2 (Bio-2) in contrast to control or Foliar K treated plants at all sample dates under the adequate K regime (125 μg g−1 K), but there was no a significant effect under 5 μg g−1 (Figures 1A,B)
By the last sample date shoot leaf area on the Bio-2 plants was 195% greater than in control plants
Summary
The use of biostimulants, defined here as ‘a substance or material, with the exception of nutrients and pesticides, which has the capacity to beneficially modify plant growth’ has grown dramatically over the past decade and it is predicted that the market for biostimulants will exceed US$2 billion by the year 2018 (SaaSilva et al, 2013; Calvo et al, 2014). The mode of action of the majority of biostimulants is poorly or not understood and has been variously ascribed to hormone composition, the presence of plant signaling molecules or the presence of molecules that facilitate the transport and efficacy of mineral nutrients (SaaSilva et al, 2013; Calvo et al, 2014). In a majority of cases the specific metabolic components of the biostimulant have not been characterized and the function is unknown. Determining the function of biostimulants is made more difficult since many of these products contain naturally occurring or commercially added micronutrients, sugars, amino acids and other compounds that may have synergistic, complementary or no effects or may have been added merely for marketing or commercial registration purposes. Separating the effect of the one or more active ingredients from the host of additional components is often very difficult
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