Agronomy

Ontario grain corn is highly valuable, accounting for 60% of Canada's total corn output. Grain producers are increasingly interested in including cover crops (CCs) in their cropping systems, but they have concerns regarding successful CC establishment and potential adverse competitive effects on corn yield and nutrient status. One option to improve the success of CC establishment is the interseeding in corn at the V4 -V6 stages. Interseeding improves the chances of good CC establishment, with potential benefits for soil health, weed control, and plant productivity. This thesis research was conducted to evaluate the short-term effectiveness of interseeding annual ryegrass (AR), red clover (RC), and their mixture (MIX) in grain corn at three locations in central and southwestern Ontario. Cover crop and corn yields, and their nitrogen (N) uptake, residual soil N, soil biological parameters, weed biomass, and residue decomposition rates were measured. CC biomass was highly variable (range: 0 - 1.6 Mg ha-1), influenced by climatic conditions, location, and CC type. Total carbon (C) and N contributions from CCs were similarly influenced by site-year and CC type. Regression analyses showed significant influence of corn biomass on CC establishment. Red clover had a significantly lower C/N ratio (11.8) than AR (18.2) and MIX (15.6). Strikingly, the amount of CC biomass accumulated in early spring reduced weeds by 50%. Moreover, CCs did not reduce corn grain or stover yield, nor N uptake, and soil mineral N in either fall or spring. Soil metabolic activity measured by BIOLOG Ecoplates was significantly greater in plots with AR than RC, MIX or NOCC. Soil biological parameters showed no CC effect. Results of residue decomposition i.e., C and N mineralization showed negligible CC residue effects on corn stover decomposition or N immobilization. The findings from this research suggest the need for assessing a more diverse range of CCs over longer durations to establish more specific CC niches for improving soil health in Ontario corn systems.

Author Keywords: CLPP, cover crops, grain corn, nitrogen uptake, residue decomposition, soil health

Soil mineralizable nitrogen (N) is the main component of soil N supply in humid temperate regions and should be considered in N fertilizer recommendations. The objectives of this study were to determine the potentially mineralizable N parameters, and improve N fertilizer recommendations by evaluating a suite of soil N tests in southwestern Ontario. The study was conducted over the 2013 and 2014 growing seasons using 19 field sites across southwestern Ontario. The average potentially mineralizable N (N0) and readily mineralizable N (Pool I) were 147 mg kg-1 and 42 mg kg-1, respectively. Pool I was the only soil N test that successfully predicted RY in 2013. The PPNT and water soluble N (WSN) concentration (0-30cm depth) at planting were the best predictors of fertilizer N requirement when combing data from 2013 and 2014. When soils were categorized based on soil texture, the relationships also improved. Our findings suggest that N fertilizer recommendations for grain corn can be improved, however, further field validations are required.

Author Keywords: corn, nitrogen, nitrogen mineralization, soil nitrogen supply, soil N test, southwestern Ontario