By Bruce Barker
The evidence keeps piling up: No-till combined with retaining crop residue on the field improves soil properties and may also be better for the environment. The most recent finding comes from Agriculture and Agri-Food Canada at Melfort, Saskatchewan, where research scientist Dr. Sukhedv Malhi conducted an eight-year field experiment with two, four-year rotations near Star City in northeastern Saskatchewan.
|No-till researchers continue to show the agronomic and environmental benefits of no-till. Photo by Bruce Barker.
The evidence keeps piling up: No-till combined with retaining crop residue on the field improves soil properties and may also be better for the environment. The most recent finding comes from Agriculture and Agri-Food Canada at Melfort, Saskatchewan, where research scientist Dr. Sukhedv Malhi conducted an eight-year field experiment with two, four-year rotations near Star City in northeastern Saskatchewan. “The changes in soil properties due to tillage and crop residue management practices and their impact on crop yield and nutrient uptake is a slow process, so we required a longer term study to measure those changes,” explains Malhi.
The objective of Malhi’s study was to determine the influence of tillage, crop residue management and N rate on crop yield, soil properties and nitrous oxide emissions. The factors compared included no-tillage versus conventional tillage; straw retained versus straw removed; and four levels of fertilizer N: 0, 40, 80, and 120 kg of N per hectare (0, 36, 72 and 108 lbs of N per acre). No N was applied to the pea phase of the rotation. The four-year rotation was barley-pea-wheat-canola.
Data collected included seed, straw and chaff yield, root mass measurements, the mass of nitrogen (N) and carbon (C) in-crop, soil organic C and N, inorganic N and aggregation. Nitrous oxide (N2O) emissions were also measured in the second four-year rotation cycle in collaboration with Dr. Reynald Lemke, a research scientist, Agriculture and Agri-Food Canada, Saskatoon, Saskatchewan.
In the trials, no-till produced greater seed (by 51 percent), straw (23 percent) and chaff yield (13 percent) of barley than conventional till in 2002, but seed yield for wheat in 2004, and seed and straw yield for canola in 2005 were greater under conventional till than no-till. Malhi explains that the beneficial effect of no-till and straw return on crop yield is accomplished mainly through conservation of soil moisture in a dry year or in a dry region, and improvement in soil properties. The greater yield of barley under no-till compared to conventional till, particularly where straw was retained in 2002, a year with below-average precipitation in the early and peak growing season (May, June and July), was most likely associated with greater soil moisture conservation in the no-till and straw-retained plots says Malhi.
After eight crop seasons, tillage and straw management had no effect on total organic C and N in the zero to 15 centimetre (zero to six inch) soil depth, but light fraction organic C and N were greater with retained straw than when straw was removed, and also greater under no-till than conventional till, indicating a slow improvement in soil organic matter and carbon sequestration.
Lower greenhouse gas emissions
At the end of the second four-year rotation cycle, the increase in NO3-N concentration from applied N was significant but small. Malhi says this was most likely due to increased uptake of applied N due to improved soil moisture conditions in 2004 and 2005. The NO3-N concentration in the zero- to 15-centimetre (zero- to six-inch), 15- to 30-centimetre (six- to 12-inch) and 30- to 60-centimetre (12- to 24-inch) soil layers increased (though small) with increasing N rate.
Cumulative N2O loss was not influenced by tillage system in 2002, 2003 or 2005, but emissions were significantly lower from no-till than conventional till treatments in 2004. Lemke says similar or lower emissions from no-till are contrary to the results from many other regions, but are in agreement with previous work in the Canadian Parkland region. “In a general way, the magnitude of cumulative N2O loss reflected precipitation levels,” explains Lemke. “During 2002 and 2003 when precipitation was at or below long-term average, the mean cumulative N2O loss did not exceed 300 g of N per hectare (about 0.3 lbs of N per acre). During 2004 and 2005 when precipitation was considerably higher than the long-term average, losses ranged as high as 1300 g of N per ha (about 1.2 lbs of N per acre).”
Malhi also found that the retained straw plots had better soil aggregation with a greater proportion of large, dry aggregates and large mean weigh diameter. He says this suggests a lower potential for soil erosion when crop residues are retained.
The researchers summarize by saying “the findings suggest that returning crop residue and no tillage would improve soil quality and productivity, and may also be better for the environment. However, N fertilization, although improving crop production, may increase the potential for NO3-N leaching and N2O-N emissions if N fertility isn’t matched to crop needs.”