Italian ryegrass and nitrogen source fertilization in western Oregon in two contrasting climatic years. II. Plant nitrogen accumulation and soil nitrogen status

To develop optimum nitrogen (N) fertilization practices with the least impact on environmental quality and with the greatest economic return, it is imperative that a greater understanding of crop and soil N dynamics be sought. This paper reports on research conducted with these objectives: (i) to determine the relationship between plant N and dry matter accumulation and soil N status as affected by N‐source fertilization as a function of accumulated growing degree days (GDD), and (ii) to determine if western Oregon soil conditions favor ammonium (NH4) over nitrate (NO3) nutrition during the period of grass seed crop growth. In a companion paper, plant growth and seed yield component data were discussed in relation to N‐source treatments and climatic year effects. Western Oregon field plots of Italian ryegrass (Lolium multiflorum Lam.) were fertilized with calcium nitrate, ammonium nitrate, ammonium sulfate, ammonium chloride, and urea‐dicyandiamide (DCD) to manipulate soil NH4 and NO3 ratios. Ita...