Evaluation of Nitrate-Nitrogen Leaching From Lysimeter-Grown Bearing Apple Trees

A 2-year investigation was conducted on eight replicate plots located 30 miles east of Lake Michigan on sand to sandy-clay-loam soil, using 1.8-m-deep lysimeters (4.8 m3 of volume), consisting of an undisturbed monolith excavated from the soil and containing a bearing (2- to 3-year-old) apple tree each. The aims of this research were to study the leaching rate and migration time of nitrate-N (NO3−-N) through the soil profile and to assess the suitability of soil suction tube (SST) water samples to predict the NO3−-N leaching rate. The NO3−-N concentration in the water collected by the lysimeters ranged from less than 10 mg L−1 (in late summer) to more than 40 mg L−1 (in winter). We calculated that NO3−-N lost via leaching in a year amounts up to 141 kg ha−1, with the most potential for groundwater pollution occurring during the cold and wet season. The application of labeled N ammonium nitrate as fertilizer increased the concentration of NO3−-N in the solution collected by SST. Labeled N was found at the bottom of lysimeters 3 months after its application, leaching through the soil profile at a speed of 2 cm day−1, so that the NO3−-N concentration of SST was correlated significantly with NO3−-N concentration of lysimeters only when the time of movement was considered. The application of fertilizer did not increase the amount of NO3−-N collected by lysimeters, meaning that the NO3−-N leaching rate is mostly the result of the breakdown of soil organic matter.