Reports of high yield potential and the advantages of an earlier harvest have created interest in planting soybeans early in Louisiana.
Acreage devoted to early maturing soybeans, such as maturity group IV varieties, has increased in recent years. Although new to Louisiana, group III soybeans have been planted by some producers because of their potential for even earlier maturity.
In plot trials at Louisiana State University AgCenter's Northeast Research Station, group III varieties did not yield as well as group IV varieties. When these maturity groups were planted in early April, narrow row spacings improved performance.
In 2005, separate, non-irrigated tests were conducted for narrow rows (20-in. average row spacing, planted flat) and wide rows (40-in. row spacing on raised beds). The studies included six group IV and two group III varieties. The earliest planting date was April 15 for narrow rows and March 31 for wide rows.
In 2006, the two row spacings were established on wide seedbeds (80-in. centers) in a single, irrigated study. One group V, four group IV and three group III varieties were included. Planting dates ranged from March 15 to June 2.
In the 2005 narrow-row study, yields were generally high when planted April 15, April 29 and May 16. Some group IV varieties produced their highest yields when planted on April 15, while others produced the greatest yield when planted on April 29.
The highest yield for each of the group III varieties was planted on April 29. Group IV varieties yielded higher than group III varieties in most cases. This was especially true when planted on April 15.
In the conventional row study in 2005, all varieties — regardless of maturity group — produced the greatest yield when planted on April 21. Group III varieties tended to yield less than group IV varieties, especially at the earlier planting dates. Low yields of group III varieties at the earliest planting dates may have been caused, to some degree, by delayed harvest, which led to preharvest seed losses through shattering.
In 2006, narrow rows generally yielded more than wide rows for all maturity groups in March and early April plantings. For group III and IV varieties, the earliest planting date for near-optimal yield was April 7 in narrow rows and April 18 in wide rows.
The group V variety yielded highest when planted between March 27 and April 18. This may indicate a major change in group V adaptation, because in earlier research in the 1980s and 1990s, optimal planting dates for group V varieties were in May.
Group III varieties were generally lower yielding than those of other maturity groups at all planting dates.
What are the implications for Louisiana soybean producers?
Group III varieties did not yield as well as group IV varieties and probably should not be planted unless early maturity is a production objective.
Producers may experience yield reductions from planting group III or IV soybeans before mid-April in wide-row spacings.
Although more years of data are needed, the results from 2006 suggest that these maturity groups may be planted for high yield in early April if narrow row spacings are used.