DISTRIBUTION OF NITROGEN SPECIES IN CANADIAN MARGINAL LAND SOILS THROUGH SORGHUM GROWING SEASON

Candidate: Zhongwei Shi
Supervisor: Dr. Julia Lu

ABSTRACT

Nitrogen is one of the essential elements in soil quality and plant growth. Fertilizer application is a common practice in agriculture to input nitrogen for higher yield. This research studies the distribution of nitrogen species, including total Kjeldahl nitrogen (TKN soil ) and leachable nitrogen species (LN, including NO 3 - , NO 2 - , and NH 4 + ) in soils, and total Kjeldahl nitrogen in sorghums (TKN sorghum ). The purpose is to evaluate factors affecting the distribution of these species: depth and temporal changes; N-fertilizer application; sorghum hybrid. Soil samples were collected from three marginal lands and one agricultural land (as comparison) in Canada, at three different times: Before Planting (BP); After Fertilizer Application (AFA); At Harvest (AH), in 2021 and 2022. Sorghum samples were collected at harvest from one marginal land and one agricultural land in Ontario in the same period. Total Kjeldahl Nitrogen (TKN) measurements utilized Kjeldahl digestion method combined with Devarda’s Alloy reduction; LN measurements used colorimetric methods (Griess-IIsovay reaction and Berthelot reaction). The experimental results indicated that both TKN soil and LN from the agricultural land and marginal lands were comparable. N-fertilizer significantly increased the LN availability after its application; the increase, however, was not proportional to the rate of the N-fertilizer applied. TKN soil in the soil samples collected from BP and AH within each year, showed no difference, which suggested that sorghum growth was not reducing the soil fertility.