Annual Report of Progress
to the
MISSISSIPPI SOYBEAN PROMOTION BOARD
for 1995

Objectives

1. Determine economically best set of production and management practices that include planting date, fall tillage, and irrigation for stale seedbed production of soybean monocropped and rotated cropping systems;
2. Determine weed control practices that sustain or increase profits from stale seedbed early-planted soybean grown with and without irrigation;
3. Determine economic benefit from irrigation, fall tillage, and rotation with rice for early-season plantings of soybeans;
4. Determine most profitable weed control options for May-planted MG V soybean varieties grown in 20-in. and 40-in. rows.

Significant Accomplishments

Experiments were conducted at Stoneville, MS in 1992, 1993, 1994, and 1995 on Sharkey clay. Row spacing was 20 in. and seeding rate was 5 seed/ft. of row in all experiments. Estimates of costs and returns were developed for each annual cycle of each ex perimental unit in each experiment. Total specified expenses (direct and fixed costs, excluding costs for land, management, and general farm overhead) were calculated using actual inputs for each treatment in each year of the experiment. Direct expenses w ere costs for herbicides, seed, labor, fuel, repair and maintenance, hauling, and interest on operating capital. Fixed expenses were ownership costs for tractors, self-propelled equipment, implements, and the irrigation system. Costs of variable inputs an d machinery were based on prices paid by Mississippi farmers each year. Irrigation costs included the cost of an engine, well, pump, gearhead, generator, fuel tank and lines, polypipe, and flood irrigation setup. Total fixed costs of the irrigation system consisted of annual depreciation, interest on investment, and insurance. Annual depreciation was calculated using the straight-line method with zero salvage value. Annual interest charges were based on one-half of the original investment times an appropr iate interest rate for each year of the study. Insurance was estimated at 1% of the original investment. Income from each experimental unit was calculated each year using the Mississippi seasonal average soybean prices in 1992 ($5.65/bu), 1993 ($6.60/bu), and 1994 ($5.60/bu), and November price in 1995 ($6.58/bu). The November soybean price was highly correlated (r = 0.983) with the seasonal average price for the 1984-1993 period. From these calculations, net returns above total specified expenses were determined for each experimental unit in each experiment each year. In irrigated studies, irrigation was started soon after beginning bloom of MG V varieties each year, and was applied until near full seed stage whenever l2-in.deep tensiometer readings reached about 70 cb.

WEED CONTROL FOR AND SEED YIELD AND NET RETURNS FROM EARLY-PLANTED, MG IV SOYBEAN

Methods

A furrow-irrigated study was conducted in the summers of 1992 and 1993, and a nonirrigated study was conducted in the summers of 1993, 1994, and 1995. 'RA 452' (MG IV indeterminate) soybean was planted on 4 May 1992, 29 April 1993, 20 April 1994, and 1 7 April 1995.

Weed control treatments (WTRT) were: 1) PRE broadleaf control; 2) POST broadleaf control; 3) PRE and POST broadleaf control; 4) PRE broadleaf and PRE grass control; 5) PRE broadleaf and POST grass control; 6) POST broadleaf and PRE grass control; 7) PO ST broadleaf and POST grass control; 8) PRE and POST broadleaf control and PRE grass control; 9) PRE and POST broadleaf and POST grass control; and 10) PRE and POST broadleaf and grass control. All treatments remained in place for the duration of the expe riment. Each WTRT had herbicides applied that were intended to minimize weed competition for that particular treatment. Herbicides used are shown in Tables 3I-1 and 3NI-1. All PRE herbicides were applied in 20 gal./acre of water. POST broadleaf herbicides were applied in 20 gal./acre of water, and POST grass herbicides were applied in 10 gal./acre of water. Surfactants were used in accordance with herbicide manufacturer's recommendations. POST herbicides were selected and applied to control specific weed problems that were determined on a treatment by treatment basis during the early growing season. The intention was to minimize weed competition as a factor within the constraints of each treatment in the experiment. Weed control costs calculated for each treatment included herbicides, surfactants, and their application. Soybeans were harvested on 28 Sep. 1992, 21 and 22 Sep. 1993, 14 Sep. 1994, and 7 Sep. 1995.

Results-irrigated

Average values from the 1992 and 1993 data were used for all analyses. In these irrigated plantings, POST broadleaf only control (WTRT 2) resulted in lower yield (Table 3I-2). The PRE broadleaf only treatment yield (43.2 bu/acre) was among the highest with one of the lowest costs ($23.38/acre). Evidently, PRE metribuzin + chiorimuron in WTRT 1 provided some early-season grass control. Using PRE and POST broadleaf herbicides (WTRT 3) resulted in yields that were significantly greater than those from using POST broadleaf herbicides (WTRT 2) only. Using PRE and POST broadleaf herbicides (WTRT 3) did not increase yield above that achieved from using PRE broadleaf herbicides (WTRT 1) only. Using PRE or POST grass herbicides in addition to PRE broadleaf herbicides (WTRT's 4 and 5) did not increase yie ld above that obtained from using only PRE broadleaf herbicides (WTRT 1).

Soybeans in Mississippi Mississippi Agricultural and Forestry Experiment Station  Mississippi State University Extension Service Division of Agriculture, Forestry and Veterinary Medicine

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