Effect of Tillage on Soybean Growth and Seed Production1

Abstract Soybean [Glycine max (L.) Merr.] grown without tillage often produces less grain on silty clay loam soils than soybean produced under conventional tillage. A 3‐yr (1982, 1983, and 1984) study was conducted to gain a better understanding of the factors affecting yield differences between conventional and no‐till soybean production systems on silty clay loam soils. The study was conducted near Columbia, MO, on a Mexico silt loam soil (Udollic and Mollic Ochraqualf). Conventional tillage consisted of spring moldboard plowing and secondary tillage. The no‐till treatment received a foliar application of glyphosate [N‐(phosphonomethyl) glycine] at the time of planting. Soybean grain yields were less for no‐till in 1982 (1890 kg/ha vs. 2260 kg/ha) and greater in 1983 (2310 kg/ha vs. 1510 kg/ha) and 1984 (1870 kg/ha vs. 1670 kg/ha). Seasonal rainfall was above average in 1982 and below average in 1983 and 1984. In 1983 and 1984, soybean in the no‐till plots depleted greater soil moisture at soil depths of 840 and 990 mm and had less plant water stress during podfilling, with afternoon leaf water potential measurements averaging 0.11 MPa greater in 1983 and 0.34 MPa greater in 1984, than soybean grown under conventional tillage. Conventionally tilled soybean had a greater yield potential due to greater vegetative growth, but with less than adequate rainfall the soybean in no‐till had less plant water stress, resulting in greater yields.