Tillage and Fertilization in Soybean: Are They Always Necessary to Increase Grain Yield?

TRIAL OBJECTIVE

• Reduced tillage might benefit soybean production by helping with soil preparation and water management. Furthermore, adequate and balanced plant nutrition is a key factor in maximizing plant growth and grain yield. However, it is unclear if either tillage or fertilization is always needed to achieve higher soybean yields.
• This study aimed to evaluate the effect of tillage and fertilization on soybean grain yield.

RESEARCH SITE DETAILS

• The trial design was a randomized complete block with four replications and three treatment factors:
  • Tillage:
    • Strip-till
    • No-till
  • Fertilization:
    • Not fertilized
    • Fertilized with nitrogen (N), phosphorus (P), sulfur (S), and zinc (Zn)
    • Seed treated with cobalt and molybdenum (CoMo) + inoculant (I)
  • Maturity Group:
    • Each block had a different XtendFlex^® soybean product with a maturity group rating of either 2.8 or 3.2.
• Soybean plants were fully irrigated throughout the growing season.
• One 0- to 8-inch depth composite soil sample per block was taken prior to fertilization on 5/4/2023 (Table 1).
• The trial was strip-tilled on 5/4/2023 according to treatments.
• Fertilized plots received 29 lb/acre N, 60 lb/acre P2O5, 25 lb/acre S, and 0.25 lb/acre Zn on 5/4/2023. Fertilizer was deep banded (9-inch depth) with a strip-till machine for strip-till plots and surface banded for no-till plots.
• Weeds were controlled uniformly across the study area.
• Plots were combine harvested and grain moisture content, test weight, and total weight data were collected. A Fisher’s Least Significant Difference statistical analysis was performed

UNDERSTANDING THE RESULTS

Tillage – Figure 2

• The average soybean yield was 4.3 bu/acre higher under strip-till compared to no-till, regardless of fertilization.
• Soil compaction might be responsible for lower yields in no-till plots. Previous soybean experiments at this location have shown no tillage effect, or even higher yields under no-till when soil structure is not an issue.

Fertilization – Figure 3

• Fertilization with NPS + Zn did not result in any significant difference in soybean yield. Based on state fertilization guidelines, nutrient concentrations for all reps (Table 1) were well above critical levels for soybean. No yield response is expected when additional fertilization is provided at these starting nutrient levels, and this outcome was seen in this trial.
• Soybean seed treated with CoMo + inoculant resulted in lower yields on average. Although the yield difference was relatively small compared to unfertilized plots (2.9 bu/acre), it was significant. Molybdenum toxicity might be responsible for the yield drop, but further research is needed.

KEY LEARNINGS

• Reduced tillage, like strip-till, could be helpful in situations where soil structure is an issue. However, it is still important to consider the difference in costs when choosing strip-till over no-till.
• Soybean yields did not respond to combined nitrogen, phosphorus, sulfur, and zinc fertilization in this trial, regardless of tillage. The lack of yield difference was likely due to soil nutrient levels being well above critical levels for soybean production.
• Fertilization with cobalt and molybdenum + inoculant resulted in slightly lower soybean yields. Previous studies suggest this could be the result of molybdenum toxicity, but further investigation is needed.¹

Sources

¹Campo, R.J., Araujo, R.S., and Hungria, M. 2009. Molybdenum-enriched soybean seeds enhance N accumulation, seed yield, and seed protein content in Brazil. Field Crops Research. 110(3): 219–224. https://doi.org/10.1016/j.fcr.2008.09.001

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