Corn Stover Yields

Corn stover is harvested from the main plots and subplots of the BCSE shortly after grain harvest in October or November. To measure corn stover yield, the mowed stover is either fail chopped directly into a wagon and weighed or is windrowed, baled, then weighed. Subsamples of harvested corn stover are taken, weighed, oven dried at 60°C to a constant weight, and weighed again to determine percent moisture and express stover yields as megagram dry matter per hectare. KBS and ARL use/used slightly different equipment and methods, as described below.

KBS Protocol: From 2008-2014, corn stover from the main plot was mowed, flail chopped directly into a forage wagon, removed from the field, and weighed. From 2015-onward, corn stover is mowed, windrowed, and baled. The bales are weighed and stover percent moisture is determined as given above.

ARL Protocol: From 2008 until retirement at the end of 2017, corn stover from the main plot was mowed, flail chopped directly into a forage wagon using a Case IH 684 Tractor and pull type flail chopper (10 – 13 cm cut height) and weighed at field moisture in the chopper wagon using 4 – 4,500 kg x 2.25 kg wheel scales (one for each wheel of the wagon). Stover percent moisture was determined as above.

Subplot Grain Yields

Corn is harvested in the subplots to examine the effect of stover removal on grain yield . KBS and ARL use/used slightly different equipment and methods to harvest subplots, as described below.

KBS Protocol: Since 2010, the middle 5 ft of the 15 ft wide subplot (equal to 2 corn rows) is harvested from both the stover non-removal and the stover removal subplots. For 2008-2009, however, there were no stover removal subplots established so yields must be compared to main plot yields.

Arlington Protocol: From 2010-2017, the western 15 ft subplot (6 corn rows in stover non-emoval subplots) was harvested and compared to the eastern 15 ft subplot (6 corn rows in stover removal subplots). The same equipment was used as is in the main plot which allowed for same day harvest and the larger area harvested minimized yield variability. In 2008, a 5 ft wide area (2 corn rows in stover non-removal subplots) was hand harvested and in 2009 a small plot combine was used to harvest the same areas. Like KBS, there were no separate harvests from the stover removal (same as main plot) subplots in 2008 and 2009.

Stover Harvest Efficiency

To determine the efficiency of the stover harvest machinery and process, the amount of stover left on the ground after machine harvesting (residual stover) was measured by placing a quadrat on the ground and hand-collecting the residue within the frame.

For the BCSE:
KBS Protocol:From 2009-2014, three random samples in a 0.5×0.5m quadrat were collected per plot, weighed, dried at 60C for a minimum of 48 hours, and the dry weights recorded. From 2015-present, with the initiation of windrowing of corn stover in 2015, sampling was altered to accommodate the unequal distribution of stover across the field. To collect representative samples, walk a transect from the southwest corner of the plot to the northeast corner of the plot and use a 0.5 × 0.5 m quadrat to hand collect the residue from within each of the windrowed strips as well as between the windrowed strips as encountered in the transect. Then measure the width of each of the windrowed (W) strips and between windrow (B) strips and determine an average width for W and B. Record wet weight, then oven dry samples as above and determine the dry weight of stover biomass within (SW) and between (SB) strips in g/m2. Calculate the biomass of residual corn stover on the field (g/m2) as:

ARL Protocol: Same as KBS in 2009-2014.

For the Scale-up Experiment:
Stover removal from fields started in 2015. The stover is windrowed, baled and weighed in the same manner as for the BCSE. The efficiency of the stover harvest was examined in 2015-2017. At each station flag, a 1 m2 quadrat (dimensions: 1.52m x 0.66 m) was placed entirely within the nearest windrowed area and the residue collected. Another sample was taken in the nearest area between the windrows. Within-windrow (W) and between-windrow (B) samples were kept separate. The average width of the between-(B) and within- (W) windrow areas was measured and recorded. Samples were processed as above to determine biomass (in g/m2) of within windrow (WS) and between windrow (BS) areas. The residual stover at the field scale can be determined by the above equation.

Calculations:
Determine the efficiency of stover harvest as: