No abstract

Soybean [Glycine max. (L.) Merr‐.] double‐cropped with small grain accounted for 16% of the total U.S. soybean acreage in 1982. Projections indicate that double‐cropped acreage will increase in areas where adequate growing seasons and irrigation capabilities exist. Field experiments were conducted from 1982 to 1985 to determine the effect of continuous wheat (Triticum aestivum L.)‐soybean double‐cropping on yields, costs of production, and net returns for both irrigated and nonirrigated conditions. Treatments included monocrop soybean and three wheat‐soybean double‐crop systems planted either in standing stubble or burned residue with either conventional, minimum, or no‐till land preparation. Total returns for each irrigated production system in the stubble environment indicated monocrop soybean was more profitable than any of the double‐crop systems. However, for the nonirrigated production systems, total returns were higher from the double‐crop systems, mainly due to returns generated by wheat. In the burned stubble environment, the double‐crop production systems with minimum tillage provided maximum profits in both the irrigated and nonirrigated experiments. Returns from nonirrigated monocrop soybean were not sufficient to cover land rental charges.

Field studies were conducted for three consecutive years to determine if PRE and/or POST herbicides were needed in addition to preplant foliar-applied glyphosate and POST cultivation for maximum seed yield of irrigated and nonirrigated soybean planted in stale and undisturbed seedbeds on clay soil. Soybean seed yields following the use of PRE and POST herbicides alone or in combination were similar in all years, and exceeded seed yield following the use of glyphosate plus POST cultivation only. Plantings made in no-till and fall-till seedbeds produced similar seed yields when both PRE and POST herbicides were used. These results indicate that glyphosate plus cultivation was not adequate for soybean in stale seedbed plantings, and that either PRE or POST herbicides, but not both, were required for maximum seed yield.

An area of a shrink-swell clay soil (Tunica clay, Vertic Haplaquept) with an established population of redvine, trumpetcreeper, honeyvine milkweed, redberry moonseed, and maypop passionflower was treated with dicamba once in the fall of 1983. The effect on perennial vines was determined for the following 4 yr in three rotational cropping systems involving winter wheat, soybean, corn, and sorghum, all with and without irrigation. Dicamba reduced the population of perennial vines 80% over 4 yr. Redvine and trumpetcreeper, the first and second most abundant species, were reduced by over 83 and 76%, respectively. Yield of soybean increased 17% in 1985 and 1987 while corn yield increased 9% in 1986 with dicamba use. In 1984 no effects on crop yield were measured. This inconsistent crop yield reponse after dicamba treatment, even though perennial vines were suppressed, must be considered in evaluating the economics of using dicamba for perennial vine control.

1994a, 1994b, 1995). Cotton, grain sorghum, and rice (Oryza sativa L.) are also adapted to these soils, butDeep tillage (subsoiling) of clayey soils in the fall when the profile they're planted on fewer hectares. is dry is a new concept that results in increased yields and net returns from soybean [Glycine max (L). Merr.] grown without irrigation.The use of large, heavy field equipment early in the Crop rotation may also result in increased crop yields. Field studies season when the soil is wet may compact soil or reduce were conducted on Tunica clay (clayey over loamy, smectitic, nonacid, its productivity (Phillips and Kirkham, 1962; Gameda thermic, Vertic Haplaquept) near Stoneville, MS (33؇26 N lat) to et al., 1987; Voorhees, 1985). When soil is compacted, determine the individual and combined effects of fall deep tillage and its particles are rearranged such that the total pore space crop rotations on crop yields and net returns. Treatments included is decreased, whereas bulk density is increased (Singer monocrop cotton [Gossypium hirsutum (L.)], soybean, and grain sorand Munns, 1987). In most cases, the larger soil pores ghum [Sorghum bicolor (L.) Moench], and biennial rotations of cotton (macropores) are destroyed by the compactive force with grain sorghum and soybean with grain sorghum grown without exerted on the soil, which results in reduced content irrigation and in either a conventional-till (CT) or deep-till (DT) and movement of air, water, heat and nutrients in the production system. Yields from all cotton and soybean crop sequences grown in the DT respectively averaged 541 kg ha Ϫ1 and 525 kg ha Ϫ1 soil. Compaction also increases soil strength, thereby greater than comparable cotton (2184 kg ha Ϫ1 ) and soybean (2983 kg increasing the resistance to root penetration. When ha Ϫ1 ) crop sequences grown in the CT. Net returns from monocrop plant roots cannot explore the entire soil structure, plant cotton ($552 ha Ϫ1 ) and soybean ($462 ha Ϫ1 ) in the DT respectively nutrients become positionally unavailable. averaged $392 ha Ϫ1 and $121 ha Ϫ1 more than similar crop sequences Studies conducted by Akram and Kemper (1979) indiin the CT. Rotations increased cotton and soybean yields but not net cated that soil water content determined the degree of returns because of the low value of the grain sorghum component. R.A. Wesley and C.D. Elmore, USDA-ARS Application and Produciness, 1977). Soybean yields from DTs averaged 2892 tion Technical Res. Unit, Stoneville, MS 38776; and S.R. Spurlock, Dep. of Agric. Economics, Mississippi State Univ., Mississippi State, kg ha Ϫ1 and were significantly higher than the 1950 kg MS 39762.