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Les traitements étaient disposés en une combinaison factorielle 3 × 3 × 4 comportant 3 méthodes d’élimination [herbicide (H), travail du sol (T) et combinaison des deux (HT)], 3 dates d’élimination (après la première fauche de 2003, après la deuxième fauche de 2003 et au printemps 2004) et 4 taux de fertilisation azotée (0, 40, 80 et 120 kg N ha-1) appliqués à l’ensemencement du blé et du canola cultivés en rotation de 2004 à 2007.
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A field experiment was conducted in a 7-year old alfalfa stand to compare the influence of time and method of terminating alfalfa stands on crop yield, seed quality, N uptake and recovery of applied N for wheat (Triticum aestivum L.) and canola (Brassica napus L.), soil properties (ammonium-N, nitrate-N, bulk density, total and light fraction organic C and N), and N2O emissions on a Gray Luvisol (Typic Cryoboralf) loam near Star City, Saskatchewan, Canada. The treatments were a 3 × 3 × 4 factorial combination of three termination methods [herbicide (H), tillage (T), and herbicide + tillage (HT)], three termination times (after cut 1 and cut 2 in 2003, and in spring 2004) and four rates of N (0, 40, 80 and 120 kg N ha-1) applied at seeding to wheat-canola rotation from 2004 to 2007. In the termination year, soil nitrate-N was considerably higher in T or HT treatments than in the H treatment and decreased with delay in termination. In the first crop year, seed and straw yields of wheat grown on T and HT treatments were significantly greater than H alone (by 1,055-1,071 kg seed ha-1 and by 869-929 kg straw ha-1), due to greater content of soil available N in T treatments. Yields decreased with delay in termination time. In general, yield and N uptake in seed and straw, and protein concentration tended to increase with increasing N rate. A greater yield increase occurred on the H compared to T and HT treatments from the first increments of N applied. Nitrous oxide emissions were generally low and there were no treatment differences evident when cumulative 4-year N2O-N losses were compared. Appropriate N fertilization was able to compensate for yield reductions due to delayed termination timing, but could not do so entirely for yield reductions on the H compared to T or HT termination method. The amounts of TOC, TON, LFOC and LFON after four growing seasons were usually higher or tended to be higher under H treatment than under T treatment in the 0-5 cm soil layer, but the opposite was true in the 5-10 cm or 10-15 cm soil layers.
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