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CROP ECOLOGY, PRODUCTION & MANAGEMENT

Row Spacing and Weed Management Systems for Nonirrigated Early Soybean Production System Plantings in the Midsouthern USA

^a USDA-ARS, Crop Genetics and Prod. Res. Unit, P.O. Box 343, Stoneville, MS 38776
^b USDA-ARS Application and Production Technology Research Unit, P.O. Box 36, Stoneville, MS 38776
^c Economist, Dep. of Agric. Econ., P. O. Box 9755, Mississippi State, MS 39762

* Corresponding author (lheatherly{at}ars.usda.gov)

The new paradigm for soybean [Glycine max (L.) Merr.] production in the midsouthern USA is the Early Soybean Production System (ESPS), which involves planting early-maturing cultivars in April. Field studies were conducted for 3 yr at Stoneville, MS, on Sharkey clay (very-fine, smectitic, thermic chromic Epiaquert) with a MG IV soybean cultivar grown in 0.5-m-wide rows (NR) and a MG V cultivar grown in 1-m-wide rows (WR), both with varying weed management inputs, to determine the most profitable system for nonirrigated ESPS plantings. Weed management in NR consisted of broadcast application of herbicides. Weed management in WR included band (0.5-m-wide) application of herbicides plus two to three between-row cultivations. Total weed cover at harvest in all treatments was below 10% in the first 2 yr. In the third year, browntop millet [Brachiaria ramosa (L.) Stapf.] plus pitted morningglory (Ipomoea lacunosa L.) percentages exceeded 10% in 3 of 10 treatments in NR and in 1 of 10 treatments in WR, but these treatments were among those producing the highest yield and net return. Soybean treated for preemergence (PRE) broadleaf management, PRE broadleaf plus PRE grass management, PRE broadleaf plus postemergence (POST) grass management, and PRE and POST broadleaf plus PRE and POST grass management were among the highest yielding treatments, but only the treatment of PRE broadleaf management provided the highest net return across both NR and WR. Soybean with PRE and POST broadleaf plus PRE grass management provided the lowest net returns across both NR and WR. These results indicate that only a broadcast PRE broadleaf herbicide in NR and a PRE banded broadleaf herbicide plus POST cultivation in WR in an ESPS planting that is not irrigated will produce yield and net return that are among the highest, and weed management cost that is among the lowest of $62 ha^-1.

Abbreviations: CSPS, conventional soybean production system • DAP, days after planting • ESPS, early soybean production system • MG, maturity group • NR, narrow-row system • NETRET, net return • PFA, preplant foliar-applied • POST, postemergence • PRE, preemergence • WR, wide-row system • WTRT, weed management treatment