Growth analysis of soybean under no-tillage and conventional tillage systems

Soybean [Glycine max (L.) Merrill] plants grown with no-tillage (NT) often appear smaller than those grown with conventional tillage (CT), yet they produce similar grain yield. Our objective was to test the hypothesis that the early-season growth depression is offset by compensatory growth and changes in plant development. A 2-yr field study was conducted at Urbana, IL, on a long-term tillage experiment. Grain yield, moisture, protein, and oil content were similar for CT and NT treatments. Total plant, stem, leaf, and pod dry biomass were all initially about 15 to 20% greater under CT, but the difference declined until about R5 or R6; thus, compensatory growth did occur. At the initiation of sampling (V2) crop growth rate was about 20% greater under CT, but the difference declined until about R2. The advantage shifted to NT until about R6. Leaf area index (LAI) was greater for CT until about R4. Net assimilation rate was greater for NT until about R5. Increases in early-season crop growth rate for CT was due to increased LAI. Greater crop growth rate for NT late in the season was due to increased net assimilation rate. Leaf weight ratio was larger for the CT crop until about R6. Specific leaf area was less in CT than NT. This work supports our hypothesis that compensatory growth and alterations in plant development occur when soybean is grown in NT systems and helps to explain why grain yield does not decrease with NT even though early-season growth is affected.