PRODUCTION UPDATE
U. S. soybean production in 1997 totaled a record high 2.727 billion bushels, up 14 percent from 1996 and up 8 percent from the previous record set in 1994. Harvested area totaled 69.9 million acres up 10 percent from 1996 and the highest since 1979. Indicated planting for this year's crop are 72 million acres. This on top of a record South American harvest has resulted in a large supply of soybean on the market, therefore I would not expect prices to be going up. Usually, we could count on a preharvest rally due to dwindling supplies of South American soybeans in late-July through August, but this year it is predicted that Brazil will still have soybeans left once the U. S. harvest begins. Brazil has actually been a major importer of U. S. soybeans, but they will not likely import significant amounts this year. Of course, weather-related problems can easily change this. With all this said, its still rather remarkable that November futures are above the $6 level. The high world demand for soybean is the reason. Therefore, I remain optimistic about the future of soybean.
Return to the Index.
ESTIMATING STAND / REPLANT DECISIONS
Full-season soybeans should have emerged by now and evaluation of the stand is needed. Poor stands will likely occur at one time or another and producers need to be aware of the potential yield loss from those deficit stands and the cost of replanting. Soybeans have a high capacity to compensate for low plant populations and gaps in the row. Use the following guidelines when evaluating the stand.
- Determine the cause of the poor stand. Was the poor stand the result of poor seed quality, cold wet soils, hot dry soils, planting too deep or shallow, soil crusting, herbicide injury, insect feeding, poor soil to seed contact, or disease infection? Determine if the cause can be corrected to avoid a similar situation.
- Estimate the stand and percent stand loss due to gaps. Pace off the sections of row 20 paces long in at least 6 areas of the field. Determine (in number of paces) the total length of row lost to gaps. Then determine the percent of row lost to gaps. In addition, count and determine average number of plants per foot in sections of row not reduced by gaps. Use Table 1 to determine remaining plant population. Or use "hula hoop" method to determine population if rows cannot be distinguished. This involves placing a circular measuring device such as a hula hoop on the ground and counting the plants contained within. To determine the plant population per acre, use Table 2.
- Estimate the yield of the poor stand. Use Table 3 to determine percent of full yield potential. Multiply this percentage by the expected yield. This is the yield to expect from the deficient stand.
- Estimate the yield from replanting. Up until mid-June, decrease the expected yield 1 bu/A per week from the original planting date. After mid-June, decrease the expected yield an additional 1/2 bu/A per day. This is the yield to expect from delayed planting.
- Determine the gain or loss from replanting. Subtract the expected yield of the poor stand (step 3) from the yield expected from delayed planting. This is the gain or loss in bu/A from replanting. Multiply this number by the expected price ($/bu) to obtain gain or loss in $/A.
- Estimate the cost of replanting. Include per acre cost of tillage, herbicide, seed and labor.
- Determine profitability of replanting. Subtract your cost of replanting from your estimated gain from replanting.
Table 1. Plant populations of different row spacing with different plant counts/foot.
| | Row Spacings |
|---|
| Plants/foot | 36 | 30 | 24 | 15 | 7.5 |
|---|
| | Plant Population (1,000's/A) |
|---|
| 1 | 15 | 17 | 22 | 35 | 75 |
| 2 | 29 | 34 | 44 | 70 | 149 |
| 3 | 44 | 52 | 65 | 105 | 224 |
| 4 | 58 | 70 | 87 | 139 | 298 |
| 5 | 73 | 87 | 109 | 174 | -- |
| 6 | 87 | 105 | 131 | 209 | -- |
| 7 | 102 | 122 | 152 | 244 | -- |
| 8 | 116 | 139 | 174 | -- | -- |
Table 2. Hula hoop method for determining drilled soybean populations.
| | Inside Diameter of Hula Hoop |
|---|
| No. of plants | 30" | 32" | 34" | 36" | 38" |
|---|
| | Plants (1,000's)/acre |
|---|
| 6 | 53 | 47 | 41 | 37 | 33 |
| 10 | 89 | 78 | 69 | 62 | 55 |
| 14 | 124 | 109 | 97 | 86 | 77 |
| 18 | 160 | 140 | 124 | 111 | 100 |
| 22 | 196 | 172 | 152 | 136 | 122 |
| 26 | 231 | 203 | 179 | 160 | 144 |
Table 3. Yield response of full season soybeans to deficit stands.
| | Remaining Plant Populations (1,000's/A) |
|---|
| % Stand lost to gaps | 140 | 105 | 70 |
|---|
| | % Full Yield Potential |
|---|
| 0 | 100 | 97 | 95 |
| 10 | 98 | 96 | 93 |
| 20 | 96 | 93 | 91 |
| 30 | 93 | 90 | 88 |
| 40 | 89 | 86 | 83 |
| 50 | 84 | 81 | 78 |
| 60 | 78 | 75 | 73 |
Source: Illinois Agronomy Handbook (Anonymous, 1986), University of Illinois
Return to the Index.
ROW SPACING AND SEEDING RATE FOR DOUBLE-CROP SOYBEANS
Planting soybean after small grain harvest (double-crop) is the most common method of growing soybean in Virginia. While a double-crop system is usually more profitable than full-season soybeans, yield of the soybean crop will suffer due to planting later that the optimum time for Virginia (mid-May to early-June). This is because the crop does not have the time to produce the needed leaf area and dry matter in order to maximize yields. On average, yields will decrease about one bushel per week up to early June and three bushel per week thereafter. However, this relationship is not very consistent. Sometimes a late June planting will yield as much as a May planting; in contrast a late-May planting may yield much less than a mid-May planting. The key is to obtain approximately 3.5 to 4 square feet of leaf area for ever square foot of land by flowering. If this can be done, maximum yields for that year and location are attainable. Research in North Carolina has resulted in the below relationship between planting date and yield. Note that the graph does not contain dates, but weeks before or after the last planting date that would result in plants about 3 feet tall that completely lap the middles (about 4 ft2 of leaf area) by flowering. In a good year or on a productive soil, we could theoretically plant late, develop enough leaf area, and obtain maximum potential yield. Still, we really do not know the optimum planting date for a given year or site until after we know the productivity potential for that year. Therefore, the predictive capability of this graph is limited. But it contains the primary principle for planting date to yield relationships, a principle that we can utilize to make management decisions.
Soybean Yields and Planting Dates
How do you use this information? Narrow rows, higher seeding rates, later maturity group varieties, and higher-yielding environments will minimize the effect of late planting (see figure below). Narrow rows and higher plant populations will result in more leaf area. Later-maturing varieties give the crop more time to produce the needed leaf area. And of course, the better the year, the more leaf area.
Soybean Yields and Planting Dates
*Data courtesy of Jim Dunphy, Corn and Soybean Specialist, North Carolina State University
Most producers are planting narrow rows in double-crop settings, so I won't dwell on that. Recommended final plant populations for double-crop soybeans should be 180,000 to 220,000 plants/acre. Seeding rate would be proportionally higher after adjusting for % emergence. In early to mid-June, the lower end of this range would be appropriate. As the season progresses, gradually increase the seeding rate. Also, as the season progresses, select a later-maturing variety (be mindful of not selecting too late of a variety as it may be affected by frost). If planting on a productive soil, the lower seeding rates and earlier varieties may be adequate. In summary, narrow rows (down to 7 inches), higher seeding rates, and later-maturing varieties will result in the higher yields for double-crop soybeans.
Return to the Index.
POSTEMERGENCE HERBICIDE APPLICATIONS
Listed on the following pages are tables with the appropriate rate and weed stage for most postemergence herbicide applications. In order to obtain control, it is recommended that these stages not be exceeded. Weeds can literally double in size in just a few days during the summer, therefore watch their development closely.
Return to the Index.
SOYBEAN THRIPS: ARE THEY A PROBLEM?
D. Ames Herbert, Jr. - Extension Entomologist
General Description - Thrips are tiny, slender insects that feed by rasping off the outer layer of leaves and sucking out the juices. This insect is normally not a problem, however, during dry weather thrips populations are often high and feeding, along with drought effects, can severely stunt plant growth or occasionally kill plants.
Thrips are very small insects and the yellow immatures and/or the black and white (or straw colored) adults are not easily seen. On seedling plants thrips may be found on the upper and lower leaf surfaces as well as in unfolded leaves. Thrips problems are always accompanied by crinkled, deformed leaves which often have a silvery appearance. Leaf drop is also common.
Scouting Procedure - Sample only if damage is readily noticeable. At each sample site randomly pick 10 leaves (a leaf consists of 3 leaflets) and examine them for thrips damage (substantial silvery scaring and/or deformed leaves). Record the number of leaves damaged. Sample a minimum of three sites (small fields) or maximum of 10 sites (large fields). After sampling the field calculate the percentage of leaves damaged. If the plants are stressed for any reason (e.g., chemical injury or drought) take special notice of thrips activity since thrips damage and other plant stress factors are additive. Thrips numbers can be checked by careful leaf examination or by picking leaves and slapping them over a horizontally held white card.
Action Threshold - Thrips rarely require treatment; however, early season injury to drought-stressed plants may occasionally reduce yields. Treatment can be considered if 75% of the leaflets are damaged, the plants are under stress, and numerous thrips are present (more than 8 per leaflet). All three conditions should be met before treatment is applied. If the plants are growing vigorously, it is likely they will outgrow the damage. Most states refer to data indicating no effects on yield unless thrips damage is combined with drought stress.
Last year the cool, dry weather early in the season and continued drought stress did allow for some possible yield losses and maturity delays. This year conditions are quite different. Moisture is adequate and temperatures are warming so we should not expect problems even though some thrips are present in fields.
Sincerely,
David L. Holshouser
Extension Soybean Specialist
Return to the Index.
Return to David Holshouser
