Fate of Nitrogen-15 in a Perennial Ryegrass Seed Field and Herbaceous Riparian Area

• Published in: Soil Science Society of America journal Vol. 70; no. 3; pp. 909 - 919
• Main Authors: Davis, J.H, Griffith, S.M, Horwath, W.R, Steiner, J.J, Myrold, D.D
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01-05-2006; Soil Science Society of America; American Society of Agronomy
• Subjects: agricultural land; Agronomy. Soil science and plant productions; ammonium compounds; Biological and medical sciences; Cropping systems; Effectiveness studies; Fertilizers; fields; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; grass seed cropping system; Grasses; isotope labeling; Lolium perenne; losses from soil; microbial activity; nitrates; Nitrogen; nitrogen balance; Nitrogen fertilization; nitrogen fertilizers; Nitrogen, phosphorus, potassium fertilizations; nutrient uptake; Overland flow; Plant biomass; planting seed; Retention; riparian areas; Seeds; Soil and water pollution; soil microorganisms; Soil science; Soil sciences; Soil surfaces; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Oregon; United States; North America; America; USA, Oregon, Willamette Valley; Monocotyledones; Cultivated field; Isotope labelling; Riparian vegetation; Inorganic element; Nitrogen Isotopes; Environmental engineering; Seed plant; Herbaceous layer; Gramineae; Agronomy; Angiospermae; Wetland soils; Soil science; Lolium perenne; Wetland; Pollution by agriculture; Macronutrient(mineral); Seed production; N-15; Agricultural soil; Soil biology; Spermatophyta; Herbaceous plant; Fodder crop
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2005.0223

Intensive management of grass seed fields in the poorly drained soils of the Willamette Valley, Oregon, has prompted concern in the capacity of these landscapes and their associated minimally managed riparian areas to process and retain fertilizer N. Our goal was to determine the extent of N losses and effectiveness of a riparian area and an adjacent perennial ryegrass seed field to retain N. The fate of fertilizer ¹⁵NH₄ and ¹⁵NO₃ was determined with a ¹⁵N tracer experiment. During the second year of the study, ¹⁵N recovery in the plant and soil (0-30 cm) from the cropping system was 51% for ¹⁵NH₄ and 43% for ¹⁵NO₃ whereas recovery in the riparian area was only 20% of ¹⁵NH₄ and 31% of ¹⁵NO₃. Greater cropping system retention of ¹⁵N resulted from both greater uptake by the crop and greater retention of ¹⁵N in the soil. Low recovery of ¹⁵N in the riparian area was possibly the result of two significant spring flood events saturating the surface soil of the riparian area but not the cropping system. The prolonged seasonal saturated conditions significantly reduced riparian plant biomass production and N uptake and increased the potential of N loss through overland flow and denitrification. Results indicate that the cropping system had larger available N pools and a larger potential to retain fertilizer N than the riparian zone. However, both areas were prone to substantial loss of applied N.