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Subsurface Nitrate–N Leaching Loss as Affected by Drainage Size and Depth in a Shallow Slowly–Permeable Soil

Subsurface drainage discharge nitrate–N (NO3–N) losses were evaluated under corn during a three year period under three replicated drainage systems: i) 100 mm diameter drainage tile at 80 cm depth; ii) 50 mm diameter drainage tile at 80 cm depth and iii) 50 mm diameter drainage tile at 50 cm depth. Each drainage system had 12 m spacings between laterals. The field under investigation possessed shallow, imperfectly–to–poorly drained soils. Throughout the investigation average NO3–N concentrations in the drainage outflow were similar for all three systems ranging from 9.6–11.4 mg L−1. Total drainage discharge was significantly lower for the shallow (50 cm) system compared to the two deeper (80 cm) systems. Therefore, significant differences in total NO3–N loss between the shallow (50 cm) and deep (80 cm) systems were observed with shallow systems providing reduced NO3–N losses. Corn yields were significantly lower in the shallow (50 cm) drainage treatment in only one year. Shallow drainage may have many economical and environmental benefits and require further research to evaluate its potential under various soil types.