AbstractThis thesis investigated potential effects of two commercial biostimulant products [SOIL-SET™ Aid (SE), IMPRO-GRAIN™ (IG)] on germination rates, natural microbial populations, silage quality (nutritional and hygienic) and aerobic stability of maize (Zea mays) and ryegrass (Lolium spp.) forage during glasshouse and field trials. In addition, biostimulant-treated silage was fed to ruminants (sheep) to assess any effects on dry matter intake (DMI). Biostimulants are commercial products of biological origin with a focus on helping crops to mitigate the effects of biotic and abiotic stress as well as enabling them to increase the nutrient uptake, nutrient efficiency, yield and overall nutrient quality (Caradonia et al., 2018).
Previous work has demonstrated effects of various biostimulants on horticultural or / and arable crops but did not focus on forage nutritional content and subsequent silage quality. The application of SE significantly increased germination of ryegrass by 4.4 % during glasshouse trials and tended to increase germination by 2.3 % during field trials. IG application significantly increased maize chlorophyll by 12 % and ryegrass chlorophyll by 7 %, as predicted by SPAD. IG significantly decreased Enterobacteriaceae spp. (ENB) and yeast counts while significantly increased lactic acid bacteria (LAB) in both maize and ryegrass fresh forage and silage. IG significantly improved nutritional quality of fresh maize and ryegrass forage. More specifically, IG increased dry matter (DM) (maize, 16 g kg -1 FM; ryegrass, 15 g kg -1 FM) and starch (maize, 38 g kg -1 DM) concentrations and decreased fibre [acid detergent fibre (ADF), neutral detergent fibre (NDF)] concentrations by 23 and 29 g kg -1 DM (maize) and 17 and 46 g kg -1 DM (ryegrass), respectively. Similar improvements were observed in the subsequent silage nutritional content where IG significantly increased DM (maize, 17 g kg -1 FM; ryegrass, 21 g kg -1 FM), starch (maize, 32 g kg -1 DM) and water soluble carbohydrates (WSC) (ryegrass, 8.5 g kg -1 DM) while it significantly decreased ADF (maize, 21 g kg -1 DM; ryegrass, 37 g kg -1 DM) and NDF (maize, 14 g kg -1 DM; ryegrass,40 g kg -1 DM) concentrations. Biostimulant products did not affect the fermentation characteristics of maize and ryegrass silage, however, they improved the silage aerobic stability by 125 h (3 ° C above ambient, maize) and by 43 h (2 ° C above ambient, ryegrass). Despite the nutritional quality improvements due to biostimulants, sheep DMI was not improved.
Specific mechanisms were investigated based on the observed significant differences in the parameters mentioned above. Tested products significantly increased micronutrient content of treated soils and crops (maize, ryegrass). Moreover, tested products had a direct effect on isolated natural microbial forage colonies potentially due to their micronutrient content. More specifically, IG enhanced LAB growth while SE decreased yeast growth. Plant hormone content was also increased due to product application with treated crops showing elevated levels of abscisic (ABA) and salicylic (SA) acids. This hormone increase was likely stimulated due to yucca (Yucca spp.) extract that was contained in the products.
In conclusion, application of the tested biostimulant products (SE, IG) affected the nutritional quality and specific natural microbes of both maize and ryegrass forage. In addition, the observed changes were maintained through the ensiling process and were observed on subsequent maize and ryegrass silage. Changes in specific microbial communities resulted in increased LAB and decreased ENB and yeasts counts in subsequent silage. Silage microorganisms created a more desirable ensiling environment, which resulted in improved aerobic stability. Improved nutritional quality and aerobic stability of treated silage did not affect significantly ruminants’ DMI when used as feed. Overall, the observed positive results on forage and silage quality in the present study can serve as a basis for continuous future research to further investigate potential agricultural uses of biostimulants.
|Date of Award||24 Mar 2020|
|Supervisor||Michael Lee (Supervisor) & Tristan A Cogan (Supervisor)|