Master of Science (MSc)
Faculty of Science
Frédérique C. Guinel
Agricultural productivity is often constrained by nutrient availability; as such, copious amounts of synthetic fertilizers are applied to maintain productivity. However, the intensive use of synthetic fertilizers has reduced the capacity of the soil to carry out crucial roles such as nutrient cycling because of shifts in the microbial community composition and structure. In addition, much of the applied synthetic fertilizers become lost to the environment through run-off, which contributes to soil degradation. With the increasing demand on agricultural systems to provide food and fibre and the adverse impacts of agricultural production on the soil resource, amendments that support soil productivity are required to supply plant nutrients. One way of sustainably improving nutrient acquisition and retention is by improving soil fertility; this can be achieved through integrative farming strategies that increase organic matter levels and stimulate the microbial community. In this greenhouse study, an integrative approach that relied on plant-soil-microbe interactions was used to evaluate the usage of an agromineral as a slow-release fertilizer. This assessment was done by comparing the effects of an agromineral, the Spanish River Carbonatite (SRC), and a synthetic fertilizer (Nitrogen-Phosphorus-Potassium (NPK), 20-20-20) on soil pH, microbial abundance and respiration, as well as on the legume-Rhizobium symbiosis. I hypothesized that the SRC, rich in calcium and other essential plant nutrients, would raise soil pH, stimulate microbial abundance and respiration, and enhance the legume-Rhizobium symbiosis in comparison to the synthetic fertilizer. In addition, the microbial abundance and respiration would differ depending on the plants grown. A mix of leguminous and non-leguminous cover crops was grown for 56 days in soils treated with three soil amendments: SRC, ammonium nitrate, and NPK synthetic fertilizer. The cover crops were grown in the following pairs: 1) alfalfa and chicory and 2) red clover and oilseed radish. At harvest, soil treated with SRC had higher pH values (pH raised by 1.2 units) and exhibited a higher abundance of heterotrophic and symbiotic nitrogen-fixing bacteria than those soils lacking the SRC amendment. This effect of SRC was observed in the rhizosphere of both cover crop combinations. However, the effect of soil amendments on the phosphate-solubilizing bacteria varied between cover crop combinations. The relative abundance of phosphate-solubilizing bacteria was enhanced by the SRC amendment in the rhizosphere of red clover and oilseed radish plants; in contrast, in the rhizosphere of intercropped alfalfa and chicory, the NPK fertilizer was the amendment that stimulated the abundance of the phosphate-solubilizer bacteria. Additionally, microbial respiration was reduced in soils treated with SRC compared to that of ammonia nitrate- and NPK fertilizer-treated soils. The results indicate that soil amendments were the drivers of soil pH and abundance of symbiotic nitrogen-fixing and heterotrophic microorganisms, as well as the drivers of microbial respiration, while the plant combination had more pronounced effects on the abundance of phosphate-solubilizing bacteria. Furthermore, the SRC amendment appeared to have enhanced the legume-Rhizobium symbiosis compared to amendments lacking SRC. These preliminary findings suggest that SRC as a slow-release fertilizer may be useful as part of an integrative strategy to improve soil fertility by stimulating microbial activity.
Christie, Renée V., "Going back to the soil: An integrated approach to farming." (2019). Theses and Dissertations (Comprehensive). 2161.