Can strip tillage with deep fertilizer banding improve agronomic nitrogen use efficiency?

Background/Question/Methods

In strip tillage (ST), tillage is limited to crop rows while the rest of the soil remains undisturbed.  Improved agronomic nitrogen use efficiency—increased crop uptake with less loss to the environment—may be possible with ST and deep-banded nitrogen fertilizer.  We conducted field experiments to determine the impacts of relative strip placement and deep fertilizer banding on sweet corn (2011) and cabbage (2012) yield and two measures of nitrogen loss—residual soil nitrate (NO₃^-) that may be leached and nitrous oxide (N₂O) flux.  Three treatments were examined in a field that was in ST the previous year: 1) conventional (full-width) tillage (CT); 2) ST with the strips located in the same position as the previous year (STsame); and 3) ST with the strips offset from their previous year’s position (SToffset).  In all ST treatments the initial N fertilizer application was banded 9-15 cm deep in rows (IR); it was surface broadcast and incorporated in the CT treatment.  Deep soil cores (1 m) were collected after harvest and the following spring, cut into 20 cm sections, and analyzed for NO₃^-.  Trace gas flux was measured approximately weekly using static chambers located IR and between crop rows (BR).

Results/Conclusions

Sweet corn yield was highest in SToffset, lowest in CT, and intermediate in STsame.  Cabbage yield was similar in all treatments.  Following sweet corn, both ST treatments had less residual surface (0-20 cm) and deep (20-100 cm) soil nitrate than CT.  Following cabbage, however, ST surface soils had more residual nitrate than CT.  Residual soil nitrate in the spring following sweet corn was low and did not vary between treatments.  In sweet corn, cumulative N₂O flux was higher IR compared to BR.  Within BR, N₂O flux was higher in CT compared to both ST treatments but there were no differences within IR.  Residual soil nitrate to 1 m and cumulative N₂O flux were summed to estimate the potential N losses on a field scale.  Following sweet corn, CT had the highest potential N loss; variability in these estimates precluded detection of treatment differences.  Results from these experiments demonstrate that yields can be maintained or improved with ST.  However, more research is needed to confirm whether reductions in N losses can be achieved through ST with deep N placement.  Our results also demonstrate that N₂O flux varies with location relative to the crop row in both CT and ST systems.