Soil N dynamics and yield of barley grown on breton loam using N from biological fixation or fertilizer

Soil N dynamics and barley yields were compared in pot experiments using surface samples from a Gray Luvisol under three cropping systems at Breton, Alberta: (1) an agroecological 8-year rotation including cereals, forage, and fababeans (Vicia faba) as green manure; (2) a continuous grain system, with fertilizer N at 90 kg/ha per year; and (3) a classical Breton 5-year rotation involving forage and cereals, without returning crop residues to the land. The fertilizer N equivalent for the cropping system, 'AN' value and 'A' value (analogous to AN, but in fertilizer 15N units), soil biomass, and C and N mineralization were monitored. It was concluded that past soil history may be associated more with the ability of barley plants to compete for available N, and hence the use of N, than with net soil N mineralization; and that an increased supply of N to crops following the incorporation of fababean residues, manure application, and the soil N-conserving effect of growing legumes were all partly responsible for the observed differences in soil fertilit