Leaching in Small Lysimeters of Nitrate Derived from Nitrogen-15-Labeled Field Pea Residues.

Abstract

Field pea (Pisum sativum L.) crop residues labeled with 15 N were incorporated during September in small monolith lysimeters of a sandy loam soil. The leaching of 15 N-labeled and nonlabeled NO3 to below 45 cm was studied during the subsequent 2 to 3 yr comparing (i) planted vs. unplanted soil and (ii) with and without pea residue incorporation. The peak flux of labeled NO3 -N from uncropped soil occurred in December. During the first leaching period (September-April), 15 and 7% of the residue N was recovered as NO3 in the percolate in the two experiments, corresponding to 18 and 13% of total NO3 -N in the percolates, respectively. The difference observed in leaching of labeled N in the two experiments was mainly due to a much higher drainage volume in the first experiment. The different residue particle sizes, 10 mm or <3 mm, used in the two experiments may have influenced the immobilization-mineralization of N in the soil differently and consequently the potential for NO3 leaching. Pea residue N constituted 10 to 15% and 5% of total NO3 -N leached from unplanted soil in the second and third leaching periods, respectively. Incorporating the ground pea residues reduced the total amount of NO3 leached by 15% during the first leaching period, indicating that the pea residue may be an important factor in controlling leaching losses. Ryegrass (Lolium perenne L.) established on lysimeters at the time of residue incorporation reduced the total leaching of N in the first leaching period by 15%, but in the second and third leaching period grass eliminated NO3 leaching completely.