Response of nine genotypes of irrigated soybeans to planting pattern and sowing date

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Abstract
A three year study compared the response of promising breeding lines, new cultivars and commercial soybean cultivars to three planting patterns and two sowing dates. The planting patterns were: 25-45 cm rows on 200 cm wide beds, twin 15 cm rows on 100 cm hills, and single rows on 100 cm hills. In all planting patterns, the established plant populations were 20-25 m-2. The sowing dates were December 1 or 5 and January 15 or 22. There was a yield increase of up to 14% (433 kg ha-1) with narrow rows on wide beds and twin rows over 100 cm rows, the extent depending on cultivar and season, with an overall average increase of only 5 to 8%. In the two seasons where narrow rows yielded more than 100 cm rows, cv. Forrest yielded best in twin rows, while the other genotypes yielded best with narrow rows on wide beds. These effects were the same for both sowing dates. January sowings yielded 30% less than December sowings, but this decline in yield was least evident in cvv. Forrest and Ruse. Forrest was the highest yielding cultivar for both sowing dates in every season (3605 and 271 6 kg ha-1 respectively). We conclude that the small increase in yield with narrow rows may be worthwhile economically, as long as no extra costs are involved. The planting pattern and sowing date response of promising lines should be examined as part of a breeding program.