Details

Autor(en) / Beteiligte

• Campbell, C.A
• Zentner, R.P
• Basnyat, P
• DeJong, R
• Lemke, R
• Desjardins, R
• Reiter, M

Titel

Nitrogen mineralization under summer fallow and continuous wheat in the semiarid Canadian prairie

Ist Teil von

• Canadian journal of soil science, 2008-11, Vol.88 (5), p.681-696

Erscheinungsjahr

2008

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• The ability of soils to provide a portion of the N required by crops via N mineralization of organic matter is of economic and environmental importance. Over a 40-yr period (1967–2006), soil NO 3 -N and plant-N measurements were made under summer fallow and in systems cropped to spring wheat (Triticum aestivum L.), on a medium-textured Orthic Brown Chernozem (Aridic Haploboroll), at Swift Current, Saskatchewan. These values were used to estimate net N mineralization (N min ). Each year, above-ground plant N was measured at harvest and soil NO 3 -N was measured before seeding, soon after harvest, and just prior to freeze-up in October. Also, in the first 18 yr of this study NO 3 -N and above-ground plant N were measured eight times between spring and fall in selected treatments; these data were used to make a more detailed estimate of N min . In a third experiment, conducted on the same soil at a nearby site in 1975, many small lysimeters were sampled six times between spring and harvest of spring wheat. We used this lysimeter study to assess the effect of N fertilizer rate and soilwater on net N min . Results from the more frequent sampling were more plausible than those from sampling at three different times per year. On average, net N min in the 20-mo summer fallow period was about 118 kg ha -1 (15 kg ha -1 between harvest and the first spring, 93 kg ha -1 between the first spring and second fall, and 10 kg ha -1 between the second fall and seeding). The average net N min under a wheat crop between spring and fall was between 53 and 63kg ha -1 . Net N min increased with water, but excessive water appeared to reduce apparent net N min , probably due to leaching and denitrification losses of N, which were not assessed in our estimation of N min . Regression analysis was used to show a positive association between net N min and precipitation, between spring and fall, for most of the systems examined. There was evidence that tillage promotes N mineralization. At normal rates of N fertilizer (i.e., < 100 kg ha -1 ), fertilizer had no effect on N min . Net N min was directly proportional to fallow frequency, averaging 68, 83, and 90 kg ha -1 yr -1 for continuous wheat, fallow-wheat-wheat, and fallow-wheat rotations, respectively. Although our results may only be applicable to medium-textured soils of similar organic matter content in the Brown and Dark Brown Chernozemic soil zone, they provide data and information against which process-based models can be tested. They also provide useful first approximations of N min measured under field conditions where few long-term data currently exist. Key words: N mineralization, plant-N, fertilizer-N, crop rotation, irrigation, tillage