Is strip-till a useful soil management tool for Wisconsin corn and soybean production?

Materials and Methods

Small-plot trials were conducted in Arlington, WI during the 2016, 2017, and 2018 growing seasons. The site included a corn–soybean rotation in all phases and a corn-on-corn sequence present since 2001. Management practices for this study consisted of 12 combinations of spring strip-till or no-till, deep-banded or broadcast fertilizer, and soybean 15- or 30-inch row spacings and in-furrow fungicide (Priaxor at 6.0 fl oz per acre) or a non-treated control. Soybean was planted at 140,000 seeds/ac into all plots in either 15- or 30-inch row spacing. For strip-till plots in soybean, 30-inch row spacings were planted directly over strip-till rows whereas every other row of the 15-inch row spacings was planted directly over strip-till rows. To avoid planting over corn stalks from the previous year, 30-inch plots were offset from the center of the previous-year corn row by 15 inches whereas 15-inch plots were offset by 7.5 inches. Strip-till was applied using a four-row, 76-cm spacing Remlinger unit with two Grandy fertilizer boxes, which allowed for deep-banded 15–38-131 lb/ac NPK fertilizer application. The same fertilizer rate was also applied as the broadcast treatment. Nitrogen was sidedressed at 190 and 160 lb/ac in the continuous corn and corn–soybean rotation, respectively. All corn plots were planted in 30-inch row spacing directly over 30-inch strip-till rows or in no-till. Soil temperature and penetration resistance were collected as well as plant population, canopy coverage, and yield. Soil penetration resistance was collected using a cone penetrometer in crop rows and between crop rows. Soybean seed yield was corrected to 13% moisture, and corn grain yield was corrected to 15.5% moisture.

Soil Temperature

No differences in soil temperature were observed between strip-till and no-till plots for any date during the 2016, 2017, or 2018 growing seasons; therefore, data for this measurement are not shown.

Soil Penetration Resistance

In soybean, the three-way interaction between tillage × row location × row spacing significantly affected soil penetration resistance (Figure 1). Across row spacings and in the in-row location, a reduction in penetration resistance was observed in the upper 12.5 cm (Figure 1A, B, D). In between-row locations, there were no differences in penetration resistance by depth in 30-inch row spacings, and one significant difference was observed at the 5-cm depth in the 15-inch row spacing (Figure 1C). This suggests that penetration resistance in between-row location in strip-till 15-inch row spacing was comparable to no-till. The only difference in strip-till 15-inch row spacing between in-row and between-row locations was observed at a 10-cm depth (Figure 1E). Planter disturbance likely contributed to similar penetration resistance values in in-row and between-row locations in the upper 7.5 cm. Overall, penetration resistance was decreased in strip-till rows, resulting in a more favorable seedbed for soybean production.

In corn, within the corn–soybean rotation, a significant interaction between tillage × row location was observed (Figure 2). Within no-till plots, between-row locations had greater penetration resistance than in-row locations at the 0- to 2.5-cm depths, possibly due to disturbance from planting in the upper 5 cm (Figure 2A). Within strip-till locations, in-row location had significantly less penetration resistance from 0 to 10 cm—a reduction likely caused by the strip-till row unit (Figure 2B). A similar resistance difference was observed when comparing no-till and strip-till within the in-row location between 5 and 10 cm (Figure 2C). Again, planter disturbance in the no-till row likely decreased disturbance in the top 2.5 cm, resulting in no response. These results agree with similar studies on penetration resistance in strip-till and no-till systems that also found a reduction in penetration resistance from strip-till in the upper 10 to 20 cm of soil (Licht & Al-Kaisi, 2005).

Plant Population

In soybean, the main effect of row spacing was significant. Plant population was 9,100 plants/ac (8.0%) greater in 30-inch row spacing than in 15-inch row spacing. Plants in 30-inch rows likely benefited more from intra-plant assistance during emergence due to their reduced intra-row spacing.

In corn, crop rotation and fertilizer were found to be significant factors (Table 1). Banded fertilizer had 900 plants/ac (2.5%) greater plant population than surface-applied fertilizer (Table 1). Compared with continuously planted corn, CS-rotated corn had 1,300 plants/ac (3.8%) greater plant population (Table 1). Few studies have included the interaction of in-furrow fungicide with crop rotation; however, studies have found little response of plant population with crop rotation (Pedersen & Lauer, 2003). Improving stand viability is important as plant populations and corn grain yield are positively correlated (Pedersen & Lauer, 2002).

Canopy Coverage in Soybean

Canopy reached 50% coverage earlier in 2018 than in 2017, likely due to an earlier planting date in 2018 (Figure 3). In 2017, 50% canopy coverage was reached ∼5 days earlier in 30-inch row spacing than in 15-inch row spacing. This result contradicts most research in soybean canopy coverage, which suggests earlier canopy coverage and greater light interception in narrow row spacings (i.e., 15 inches) (Wells, 1991). Increased plant population in 30-inch row spacings could have contributed to this result. Strip-till and fertilizer placement response to canopy coverage varied by year, and no response was observed from in-furrow fungicide use.

Yield

In soybean, banded fertilizer resulted in 4.4 bu/ac (6.5%) greater yield than surface-applied fertilizer; however, without a deep-banded no-till treatment, it is not possible to compare results to similar studies (Farmaha et al., 2011) (Table 2). The greatest soybean seed yield within the crop row spacing × tillage × in-furrow fungicide interaction was obtained by combining strip-till, in-furrow fungicide, and 15-inch row spacing. However, this combination resulted in similar yield to no-till, non-treated control, and 15-inch row spacing and to strip-till, non-treated control, and 15-inch row spacing (Table 2).

In corn, strip-till yielded 13.1 bu/ac (5.7%) greater than no-till, and banded fertilizer yielded 11.4 bu/ac (4.9%) higher than surface-applied fertilizer (Table 3). Corn–soybean × in-furrow fungicide had greater grain yield than corn–soybean × non-treated control, corn–corn × non-treated control, and corn–corn × in-furrow fungicide (Table 3). The effect of in-furrow fungicide depended on crop rotation and likely was a result of a differing pathogen load between rotations (Peters et al., 2003). In general, CS-rotated corn yielded greater than corn–corn. A 9.3% yield increase was attributed to the CS-rotated corn compared with continuous corn.