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Annual Report of Progress
to the
MISSISSIPPI SOYBEAN PROMOTION BOARD
for 1997


Project Title: Soybean Variety Characteristics, Population, Row Spacing, and Influence on Sicklepod Control with Different Weed Management Systems in the Black Belt Prairie
Project Leaders: N. W. Buehring and D. R. Shaw, North Mississippi Research and Extension Center and MSU Plant and Soil Science Department

Objectives

Evaluate selected varieties for seeding rate, row spacing, and herbicide management systems effect on sicklepod control, canopy closure, yield, and foreign matter. 

Significant Accomplishments 

Variety-weather: 
Four soybean varieties: 1) Hartz 5088R - Roundup tolerant MG V variety; 2) Deltapine 3588 - tall determinant MG V variety; 3) Hutcheson - short determinant MG V variety; and 4) Riverside 499 - tall indeterminant MG IV variety in separate studies were eval uated for the effect row spacings (7.5 and 15-inch), seeding rates of recommended [equal to 8 seed/ft row in 30-inch (lx)], medium (2x), and high (3x), and 3 herbicide management systems had on sicklepod control, crop canopy closure, soybean yield, and fo reign matter. The 30-inch row at the recommended seeding rate was also included as a standard in the study. Rainfall in May and June was > 200% of normal followed below normal but adequate rainfall in July, August, and September. The lx, 2x, and 3x seeding rates resulted in soybean populations equal to 100,000, 200,000, and 300,000 plants/ac across all varieties and row spacings. All studies showed moderate to severe levels of sicklepod infestations and soybean yield ranged from 17 to 50 bu/ac. 

7.5 , 15 and 30-inch row spacing comparison at recommended seeding rate: 
All varieties at the lx seeding rate in both 7.5 and 15-inch rows had greater yield and showed higher sicklepod control, lower sicklepod population, and biomass at maturity and foreign matter than in 30-inch rows. 

7.5 and 15-inch row spacing comparisons: 
Management: Under low management (no herbicide), the 2x and 3x seeding rates in 7.5 and 15-inch rows showed fair to good sicklepod control at maturity, had fewer sicklepod plants, and less biomass and foreign matter than at the recommended seeding rates. However, all varieties showed higher yields with higher levels of management. Management with all varieties showed similar effects across both row spacing for foreign matter, sicklepod control, sicklepod biomass, and sicklepod population a t soybean maturity. Except for Hutcheson, management showed similar variety yield effects across all seeding rates and row spacings. Hutcheson (short stature determinant MG V) produced the higher yield in 7.5 inch with the 2x seeding rate (80 lb seed/ac) under high management. 

Row Spacing: 
Row spacing with all varieties had no effect on the control of sicklepod, sicklepod biomass, and sicklepod population at maturity and soybean yield. Row spacing with all varieties showed similar effects across all seeding rates for yield, foreign matter, sicklepod population, sicklepod biomass, and sicklepod control at soybean maturity. Hutcheson was the only variety which showed a row spacing x management interaction for yield. 

Seeding Rate: 
Except for DP3588, all varieties showed a yield response to seeding rate. DP3588 (tall determinant branching MG V) showed no yield increase for rows more narrow than 15-inch and seeding rates no higher than the lx seeding rate of 54 lb seed/ac under hig h management. Both Riverside 499 (tall indeterminant MG IV) and H5088RR (Roundup tolerant MG V variety) showed no added yield from rows more narrow than 15 inches, but showed significantly higher yield for the 2x seeding rate (90 and 64 lb seed/ac, respe ctively) in 15-inch rows under high and medium management, respectively. Hutcheson was the only variety which showed a seeding rate x management and row spacing x management interaction for yield. Hutcheson produced the higher yield with 2x seeding rat e in 7.5-inch rows. 

Publications

Nice, G., N. W. Buehring, D. R. Shaw, and G. Jones. 1997. Sicklepod (Senna obtusifolia) control in response to row spacing, soybean population, and herbicide treatment. 50:20 Proceedings Southern Weed Science Society.
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