Long term impact of no-till on soil properties and crop productivity on the Canadian prairies

Meeting the needs of an increasing population requires protection of our arable land base and improvements in productivity. The study compared soil quality characteristics and crop yield to nitrogen (N) fertilizer in two adjacent fields; one field managed with no-till for 31 years while the other for 9 years. In 2003, the two fields along with native prairie were sampled for soil quality parameters across two landscape positions. A small plot study involving five rates of urea N (0, 30, 60 90 and 120 kg N ha−1) and two phosphorus fertilizer placement methods (seed-placed vs side-banded) was conducted on the two adjacent fields for the period 2002–2009. The rates of N were superimposed on the same plots each year whereas wheat and canola were normally grown in alternate years. An N balance was conducted after 8 years to account for inputs and outputs of N. Soil bulk density values were 0.98 g cm−3 for native prairie and 1.46 for LTNT and STNT in the 0–15 cm soil layer. The native prairie had 48.2 t ha−1of SOC vs 44.4 and 36.7 for LTNT and STNT, respectively, in the 0–15 cm soil layer and no detectable differences for the 15–30 cm soil layer in 2003. Potentially mineralizable N using the Hot KCl digestion in the 0–15 cm soil layer was 60 kg ha−1 of ammonium nitrogen for native prairie and 30 and 22 kg ha−1 for LTNT and STNT, respectively. For amino sugar-N, native prairie had 558 kg ha−1 vs 462 and 370 kg ha−1 for the LTNT and STNT, respectively. This indicates a positive relationship between SOC levels measured and potentially mineralizable N reflecting differences in land management. Phosphorus fertilizer placed in the side-band with N yielded 3.5% more than seed-placed phosphorus in spring wheat and no difference in canola. Grain yields were 14% and 16% more for LTNT than STNT in spring wheat and canola, respectively. Maximum grain N removal averaged in wheat was 87 kg ha−1 for LTNT and 74 kg ha−1 for STNT and 71 and 65.4 kg ha−1 in canola, respectively. A positive N balance was obtained provided that 60 kg ha−1 of N was applied every year and no accumulation of nitrate-N was noted even with rates that exceeded N removal in the grain. This supports the view that no-till combined with continuous cropping and proper fertility represents a path to sustaining the global soil resource.

► SOC was highest in native prairie followed by long-term and then short-term no-till.
► Higher levels of SOC corresponded with higher rates of N mineralization.
► Higher N mineralization rates corresponded to higher N uptake by crops.
► Long-term no-till out yielded short-term no-till by 14% in wheat and 16% in canola.
► P side-banded with nitrogen yielded more than P seed-placed in spring wheat.