Soil nitrogen dynamics and nitrogen yield of barley grown on breton loam using nitrogen from biological fixation or fertilizer
Wani, S.P.; Mcgill, W.G.; Robertson, J.A.
Biology and Fertility of Soils 12(1): 10-18
ISSN/ISBN: 0178-2762 Accession: 007801699
Soil N dynamics and barley yields (Hordeum vulgare L.) 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 L.) as green manure, from which two plots were selected, one following fababeans, and the second following 3 years of forage; (2) a continuous grain system, with fertilizer N at 90 kg ha-1 year-1; and (3) a classical Breton 5-year rotation [following oats (Avena sativa L.)] involving forage and cereals, without returning crop residues to the land, selecting one plot with PKS treatment and a second as control. 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. In the first agroecological plot (after fababeans), grain and total plant biomass production were 116% greater than from the continuous grain treatment. Barley plants in the two agroecological plots derived 48.5% and 37.8%, respectively, of their N requirement from non-labelled soil N sources not present in the continuous grain plot. At crop maturity, the recovery of 15N microbial biomass was 1.5 times higher in soil from the first agroecological plot than from the continuous grain plot. The fertilizer N equivalent was 2670 mg pot-1 (485 kg ha-1) for the first and 1850 mg pot-1 for the second agroecological treatment. Fertilizer N equivalent values exceed net amounts of N mineralized by a factor of 4. Recovery by the barley crop of 15N added at 55 mg pot-1 was more efficient in the agroecological treatments (45%-51%) than in the continuous grain or classical Breton treatments (35%-37%). It was concluded (1) 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 (2) 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 fertility.