ROW SPACING AND SEEDING RATES FOR SOYBEAN IN LOW AND HIGH-YIELDING ENVIRONMENTS

Response of soybean [Glycine max (L.) Merr.] to changes in row spacing and seeding rate have been variable. Some researchers have reported g rain yields to be higher with the use of narrow row spacings. Other in vestigators have found that wide row spacings provided grain yields eq ual to or greater than those obtained with narrow row spacings. This s tudy was designed to determine the influence of environment on the opt imum row spacing and seeding rate for soybean. Eleven field experiment s were established in Kansas from 1991 to 1993. Four seeding rates in 1991 and five seeding rates in 1992 and 1993, ranging from 52 272 to 2 61 360 seeds/acre, were used in 8- and 30-in. rows. At high yielding s ites, maximum grain yields were higher with 8-in. rows than with 30-in . rows. If moisture stress reduced grain yields, maximum yields were g reater with 30-in. rows than with 8-in. rows. Response to changes in s eeding rate varied between row spacings depending upon environmental c onditions. Under high-yielding conditions, grain yields were maximized with 30-in. rows at approximately 115 000 seeds/ acre, whereas seedin g rates of 203 000 to 232 000 seeds/acre were required to maximize gra in yields with 8-in. rows. Under conditions of limited soil moisture, grain yields were not affected by changing seeding rates. At sites wit h adequate soil moisture, mature plant heights increased as seeding ra tes increased. At moisture-deficient sites, plant height was not signi ficantly affected by increased seeding rates.