Evaluating the Spatial Variation in Soil Nitrogen Supply of Potato Fields in Prince Edward Island.

The PEI Potato Board would like to advise their members on the potential for "right rate" soil N testing-based site-specific N fertilizer rates, to improve the profitability and reduce the environmental impact of potato production in PEI. Currently there is no data quantifying the magnitude and variability of soil N supply as a function of climate, soil type or agricultural management. In the fall of 2014, 26 fields scheduled to be planted to potato in 2015 from across the province were surveyed. In each field 4 replicate samples were collected from two depths (0-15 cm, 15, 30cm). Soil N supply was surveyed by measuring soil mineral N content, N mineralization using a two-week aerobic incubation and soil total N as a proxy for N mineralization potential.

The average soil mineral nitrogen (SMN) content was 5.2 mg N kg^-1 ( 0 to 16 mg N kg^-1 soil). The amount of nitrogen mineralized during a two-week aerobic incubation, averaged 8.2 mg N kg^-1 soil (0 to 16.3 mg N kg^-1 soil). The total nitrogen content of the soil averaged 1.36 g N/kg soil (0.79 to 2.33 g N/kg soil). There was greater variation in soil mineral nitrogen (SMN) content (CV=68%) relative to nitrogen mineralized during a two-week aerobic incubation (CV=41%) or total N (CV=19%).

The value for the estimated nitrogen that would be mineralized over a 130-day period averaged 33.3 mg N kg^-1 (70 kg N ha^-1) soil with a range of 12.0 to 60.2 mg N kg^-1 soil (25 to 125 kg N ha^-1).

The magnitude of N mineralization and the variability in N mineralization between locations suggests that the measurement of N mineralization would be a useful input into the determination of the "right rate" of N fertilizer addition in potato fields in Prince Edward Island.