Effects of multiple agroecological interventions on crop nutrient acquisition and performance

Leah Ritcey-Thorpe Roberta Fulthorpe Marney E Isaac ^*

• University of Toronto, Toronto, Canada

With the growing attention on agroecological interventions in crop production, more work is needed on the effects of multiple strategies to confer soil and plant health. We utilize a functional-trait approach to evaluate resource acquisition strategies of crops to the combined effects of an organic amendment and a growth-promoting endophyte bacterial seed inoculant. Using wheat and soybean as model crops, we evaluated crop performance traits [leaf chlorophyll (μmol m-2), base diameter (mm), biomass (g), nitrogen (N) usage index] and root traits [specific root length (SRL, m g-1), specific root tip density (SRTD, tips g-1), root diameter (root D, mm), root tissue density (root TD, g cm-3), root N (%), root C/N] as well as rhizosphere soil chemical and biological properties at the end of the growing season. We used three soil amendment treatments (organic, inorganic and control) and two seed inoculant treatments (with and without seed inoculation). Soil amendments influenced root trait expression of wheat, expressing acquisitive root traits (higher SRL, SRTD, root N and lower root D) under organic amendments. There was no impact of soil amendments on soybean root trait expression. In contrast, seed inoculation positively affected the performance traits of base diameter and N usage index of wheat. Significant interactive effects of soil amendments and seed inoculation was minimal. In wheat and soybean rhizosphere soil, available phosphorus was significantly lower under organic amendments while active carbon (POxC) was significantly higher under organic amendments for wheat. Well-established significant relationships among soil properties and among root traits were also evident. Furthermore, correlations between root traits and rhizosphere properties were evident, specifically positive correlations between POxC and SRL, and negative correlations with root C/N. Rhizosphere soil fungal community composition was significantly explained by key root traits including root D and root C/N. Broadly, soil amendments over seed inoculants had the strongest impact on crop root response, yet seed inoculants impacted direct measures of crop performance. Importantly, these two agroecological interventions did not significantly interact, indicating opportunities for improved meshing of agroecological strategies.