Glycine max L.

Common names
Soybean, soyabean

Author: Jason Koivisto

Rapid-growing annual with branching habit, stems being mostly primary tissue. Leaves are alternate, pinately trifoliate with pulvini, stipels and stipules. The plants are tap-rooted, up to 2 m in depth, with numerous lateral roots. On each plant, inflorescence comprises one or two self-fertile flowers that are borne in the axils of the leaves. Flower colour differs according to cultivar with white and purple represented. Flowers also have pubescence that are either tawny or grey in appearance. Pods typically contain two or three seeds. Seeds are flattened when young but becoming roundish later with two cotyledons and little endosperm. Seeds normally yellow with either a dull or a shiny seed coat and a hilum colour ranging from yellow to black, with black being most common.

*Each specific V or R stage is defined only when 50 percent or more of the plants in the field are in or beyond that stage.
Adapted from Ritchie et al., 1997.

Distribution

Soybeans originated in Asia and were first introduced to Europe and North America as a forage crop (Caldwell, 1973). It is now only used as a forage crop if there is a need for extra forage, or if the soybean crop had been damaged too severely for use as a grain crop (University of Wisconsin-Extension, 1999; Johnston and Bowman, 2000). Koivisto et al., (2003) found that some of the recently developed cultivars were able to produce up to 12 t ha^-1 DM in southern England, although the average was 9.2 t ha^-1 DM across the eight cultivars tested.

Characteristics

Initial growth of forage soybeans appears to be determinate in nature forming a bush habit, but some cultivars will have an indeterminate habit as the photoperiod shortens. Growth period of 16-20 weeks, depending upon cultivar. Lodging can occur with increasing maturity, particularly under wet conditions. Since the soybean is a subtropical plant it generally grows best between 25 ēC and 30 ēC.

Place in rotation

To prevent the build up of soil-borne diseases, soybeans should not be grown on the same site for more than two years. Grows best in the rotation after cereal crops such as maize or small grains. They should not follow edible beans, canola (oilseed rape), or sunflowers, because diseases like white mould (Sclerotinia sclerotium) can carry over and reduce soybean yields (Upfold and Olechowski, 1994).

Season of growth

In temperate areas, the crop should be sown once soil temperatures have reached 10 ēC, and grown until the plant reaches a maximum growth stage R7. This may take up four months depending on climate, photoperiod and the cultivar sown. If the climate allows it may is possible to grow the crop as a short-term catch crop after harvesting a winter-sown cereal in mid-summer. Grown in winter when grown as a cool-season crop in warm, subtropical areas. Due to the variety of cultivars it is possible to find a suitable cultivar for a range of environmental conditions from the sub-tropics to latitudes greater than 50° , such as southern England or northern Ontario.

Drought tolerance

Soybeans are intolerant of drought. Drought can have a particularly adverse effect on production if it occurs at flowering.

Soil requirements

Free-draining, sandy or medium-loam soils are best. Moderately fertile soils are particularly suitable. Soil pH 6.0 and above are required.

Rhizobial relationships

Rhizobial inoculation of seed with Bradyrhizobium japonicum is beneficial to nodulation, plant growth and nitrogen fixation on soils where soybeans have not been previously grown. Soil applied granular inoculants, up to 10 kg ha^-1, can provide more consistent nodulation and higher yields than seed applied inoculum (Upfold and Olechowski, 1994). If sown at soil temperatures below 10 ēC, it may be necessary to apply fertilizer N to the field to insure good crop growth until the Rhizobium-plant relationship is initiated. Soybeans require root zone temperatures between 25 and 30 ēC for optimal establishment of symbiotic activity.

Land preparation for sowing

Well prepared firm seedbed with good surface tilth allows rapid even germination without risk of crusting.

Sowing depth and soil cover

Ideal sowing depth for soybeans is between 2.5 and 4 cm; shallow sowing is recommended for cool soils. Deeper sowing exposes the seedling to greater risk of damage from soil-borne pathogens (Upfold and Olechowski, 1994) and poor emergence of those cultivars with short hypocotyls.

Sowing time and rate

Generally, spring sown, soybeans germinate in soils at temperatures above 10 ēC. They can also tolerate exposure for a short duration to temperatures as low – 2.8 ēC, but prolonged exposure to low temperatures will result in permanent damage because the growing point is at the top of the plant. Sowing rates are highly variable for two reasons, variation in seed size and row width. In order to obtain a population of 500,000 plants ha^-1 it is necessary to vary sowing rate depending on the seed size used and the row spacing which can vary between 18 to 76 cm.

Number of seeds per kg

4000 to 8000.

Seed treatment before sowing

There are no fungicides recommended for use on soybeans for forage production.

Nutrient requirements

The main requirement is for phosphate and potash application at rates dependent on the soil P and K status; typically soybeans require 60 to 70 kg ha^-1 of P₂O₅ and up to 300 kg ha^-1 K₂O. In cooler soils, a ‘starter’ dressing of 50 kg N ha^-1 is sometimes applied to encourage rapid initial growth. Soybeans are highly susceptible to fertilizer burn so care should be taken to avoid sowing the seed with the fertilizer. Soybeans can be susceptible to manganese deficiency; this can be corrected by applying up to 8 kg ha^-1 manganese sulphate.

Ability to compete with weeds

Initially poor especially in cold springs, but competitive once full canopy achieved.

Tolerance of herbicides

Currently no herbicides are registered for use on soybeans for forage production.

Seedling vigour

Strong.

Vigour of growth

Vigorous growth towards maturity particularly when sown in early season.

Nitrogen-fixing ability

Estimates of N₂ fixation by soybeans range from 200 (Smith and Hume 1987) to 617 kg N ha^-1 (Lindemann and Glover 1999). Work in North Dakota found that grain soybeans had a residual N yield of 100 kg N ha^-1 for subsequent crops (Peel, 1998). This may be higher for forage soybeans as it has not transferred much N from the nodules to grain by the time of harvest.

Cultivars

Most cultivars can be used for forage, including those intended for oil production, if emergency forage is required. However in recent years the USDA Agricultural Research Service has developed three new cultivars; Derry, Donegal, and Tyrone (Devine and Hatley 1998; Devine et al., 1998a, b). These cultivars have been specifically bred for forage production. Of the two cultivars being used in trials, Donegal is the cultivar that is most promising for UK conditions, being a maturity group V. Derry is a maturity group VI.

Diseases

Derry and Donegal are resistant to bacterial leaf blight (Pseudomonas syringgae pv. glycineqa), and all three cultivars are resistant to bacterial pustule (Xanthomonas campestris pv. glycines). Donegal and Tyrone are resistant to phytophthora root rot (PRR) (Phytophthora sojae). Derry has also expressed tolerance to PRR. All three cultivars are susceptible to soybean cyst nematodes (Heterodera glycines), but Donegal has expressed resistance to race 5 and 14. Donegal has also expressed moderate resistance to downy mildew (Peronospora manshurica), but the other cultivars are susceptible to this disease. All the cultivars were found to be susceptible to southern stem canker (Diaporthe phaseolorum) (Devine and Hatley, 1998; Devine et al., 1998a, b).

Pests

The most significant pests are pigeons and rooks, which may be particularly troublesome at sowing or seedling emergence. Some damage has been found as a result of rabbit grazing on early plants. Slugs can also be a pest for soybeans.

Dry matter yields

Table 2 outlines the potential of several purpose bred cultivars and experimental lines of forage soybeans. The forage cultivars have been reported to yield up to 66% higher than adapted grain cultivars (Devine and Hatley, 1998a).

Suitability for silage

Soybeans are suitable for ensiling, which is the main use for pure-sown forage stands. To avoid soil contamination when cutting, the stubble height has to be 10 cm above ground level and the cut swath left unturned. In North America, intercropping maize and soybeans has been found to improve total forage yield and forage quality marginally (Martin et al., 1990; Putman et al., 1985). There was an increase of 11 to 51% in the CP concentration for maize-soybean intercrops relative to pure sowings of maize (Putman et al., 1986). Martin et al., 1990, concluded that this increase in the CP concentration of the intercrop significantly reduced the need for concentration supplementation of the ration. Soybeans also improved the land equivalent ratios (LER) relative to corn monocrops (Martin et al., 1990). In Italy, there was an 89% higher yield for the mixture relative to pure crops of soybeans, but only a 4% higher yield when compared to pure crops of maize (Marchiol et al., 1992). The spatial distribution of the maize and soybeans is important, as the maize can out-compete the soybean mitigating the improvement in forage quality that adding soybeans was intended. Anil et al., (1998) concluded that mixing maize and soybeans could result in a potentially valuable option for farming systems that can grow both crops Coffey et al. (1995a) found that silages produced from forages harvested at the R6 growth stage (Table 1, Full Seed) had the highest lactic acid and lowest ammonia concentrations and in one of the years also produced the lowest total volatile fatty acids. Coffey et al. (1995a) concluded that, based on the changes in quality and yield, farmers should wait until R6 to harvest and ensile soybeans.

Nutritive value

In vitro dry matter digestibility (IVDMD) of whole plant soybeans remains relatively constant at approximately 60% DM digestibility across various reproductive growth stages (R1, R3, R5, R6 and R7). Leaves and pods were much more digestible (circa 68 to 72% IVDMD) than stems (circa 40 to 46% IVDMD). Stem digestibility decreased drastically beginning with pod development. (Munoz et al., 1983). In contrast to other forage crops, the nutrient content and forage quality of whole plant soybeans does not change as drastically with advancing maturity because the seed is much higher in protein and energy (fat). In contrast, silage harvested at the R4 stage had lower digestibility than silages harvested at the R2 or R6 stages. This seems reasonable since most of the structural carbohydrates are formed by the R4 stage, but the yield of pod material increases substantially through the R7 stage. At R6 the digestibility of pods exceeds that of stems by as much as 25 percentage units and contributes significantly to the overall nutritive value of the whole plant (Coffey et al., 1995b). Direct cut soybeans make very wet silage. Average DM content of soybean silage (averaged across two varieties and two years) harvested at R2, R4, and R6 growth stages were 22.1%, 25.7%, and 30.1%, respectively (Coffey et al., 1995a).

Acceptability

Calves are quite selective when fed soybean silage in round bales and will not eat the stems. However, when the silage is chopped, consumption is good and refusals are minimal. Johnston and Bowman (2000) fed growing lambs on both chopped and round baled soybean silage and did not observe a problem with acceptability. When intercroped with maize, intake by sheep was similar to maize silage (Murphy et al., 1984.) They also found that the digestibility of DM, energy, protein, ADF and NDF was similar to maize silage. In Brazil, daily intake of CP by steers averaged 43 g higher from a mixed maize-soybean silage when compared to pure maize silage (Evangelista et al., 1991). Chopped soybean straw was consumed by mature ewes at 1.67% body weight (BW) compared to ground grass hay at 2.46% BW. Ground soybean straw consumption was intermediate at 1.98% BW (Gupta et al., 1973). When using grain type soybeans Coffey et al., (1995b) found silage harvested in the R2 and R4 stages had various degrees of mold, a displeasing odor, and a dark green and black colour. Soybean silage harvested in the R6 stage rarely had mold, retained a colour similar to freshly harvested forage, and had a pleasing odor.

Anti-quality factors

There appears to be no anti-quality factors from using soybeans for forage production. However, if soybean forage is harvested at growth stage R7, the concentration of ether extract in the diet may be high enough to result in a suppression of intake and fibre digestion. Therefore, soybean forage harvested at R7 should then be limited to a maximum of 50% of the diet (Brown, 1999; Hintz et al., 1992).

Grazing

Can be grazed by a range of livestock, e.g. dairy cows, but should be strip-grazed to avoid wastage. More likely, it will be zero grazed or ensiled to reduce field loss associated with grazing.

Main attributes

High forage yield in relatively short growth period of time. High nutritive value and good digestibility. Protein-rich. Highly acceptable feed with good intake characteristics for different classes of stock.

Main shortcomings

Not highly suited to long-term grassland-dominant areas on account of short-term nature and need to plough up grassland, though suited to grassland-arable rotations. Although work has been done by Johnston and Bowman (2000) in Canada and Koivisto et al., (2003) in the UK, more work needs to be done to determine to the suitability of these crops in regions with short or cool growing seasons.

LINKS

• Forage Soybean Cultivars
• Evaluation of forage soybeans in the United Kingdom
• Soybean Poster
• Tom Devine’s USDA Webpage
• Soybeans as a forage crop
• Soybeans for silage

Main References

Anil, L., J. Park, R.H. Phipps and F.A. Miller. 1998. Temperate intercropping of cereals for forage: a review of the potential for growth and utilisation with particular reference to the UK. Grass and Forage Science 53:301-317.

Coffey, K.P., G.V Granade, and J.L. Moyer. 1995a. Nutrient content of silages made from whole-plant soybeans. The Professional Animal Scientist 11:74-80.

Coffey, K.P., G.V Granade, and J.L. Moyer. 1995b. In vitro digestibility and preference by sheep for silages made from whole-plant soybeans. The Professional Animal Scientist 11:81.

Devine, T. E. and E. O. Hatley. 1998. Registration of 'Donegal' forage soybean. Crop Science 38:1719-1720.

Koivisto, J.M. T.E. Devine, G.P.F. Lane, C.A. Sawyer and H.J. Brown. 2003. Forage soybeans (Glycine max (L.) Merr.) in the United Kingdom: test of new cultivars. Agronomie (in press).

Martin, R.C. , Voldeng, H.D., and Smith, D.L. 1990. Intercropping corn and soybean for silage in cool temperate region: yield, protein and economic effects. Field Crop Research 23:295-310.

Other References

Brown, C. 1999. Soybeans as a forage crop. OMAFRA, Queen’s Printer of Ontario. (Available on-line at http://www.gov.on.ca/OMAFRA/english/crops/facts/soybean_forage.htm).

Caldwell, B. E. (ed.) 1973. Soybeans: Improvement, production, and uses. Agronomy Monograph 16. ASA, CSSA, SSSA, Madison, WI.

Devine, T. E., E. O. Hatley, and D. E. Starner. 1998a. Registration of 'Derry' forage soybean. Crop Science 38:1719.

Devine, T. E., E. O. Hatley, and D. E. Starner. 1998b. Registration of 'Tyrone' forage soybean. Crop Science 38:1720.

Evangelista, A.R., R. Garcia, J.A. Obeid and J.D. Galvao. 1991. Intercropping maize and soyabeans: forage yield, quality and nutritive value of silage. Revista da Sociedade Brasileira de Zootecnia 20:578-584.

Gupta, B.S., D.E. Johnson, F.C. Hinds and H.C. Minor. 1973. Forage potential of soybean straw. Agronomy Journal 538-541.

Hintz, R.W., K.A. Albrecht, and E.S. Oplinger. 1992. Yield and quality of soybean forage as affected by cultivar and management practices. Journal of American Society of Agronomy 84 (5):795 – 798.

Johnston, J. and M. Bowman. 2000. Comparison of Soybean Silage Test Results at New Liskeard in 1999 and 2000. New Liskeard Agricultural Research Station.

Lindemann, W.C. and C.R. Glover. 1999. Nitrogen fixation by legumes. (Available on-line at http://www.cahe.nmsu.edu/pubs/_a/a-129.pdf).

Marchiol, L., F. Miceli, M. Pinsona and G. Zerbi. 1992. Intercropping of soybean and maize for silage in northern Italy: Effect of nitrogen level and plant density on growth, yield and protein content. European Journal of Agronomy 1:207-211.

Munoz, A.E., E.C. Holt and R.W. Weaver. 1983. Yield and quality of soybean hay as influenced by stage of growth and plant density. Agronomy Journal 75:147-149.

Murphy, W.M., J.P. Welch, R.H. Palmer, B.E. Gilman, C.W. Albers and D.T. Dugdale. 1984. Digestibilities of silages made from corn interplanted with soybean or fababean. Journal of Dairy Science 67:1532-1534.

Peel, M.D. 1998. Crop rotations for increased productivity. North Dakota ext. Serv. NDSU. (Available on-line at http://www.ext.nodak.edu/extpubs/plantsci/crops/eb48-1.htm).

Putman, D.H., S.J. Herbert and A. Vargas. 1985. Intercropped corn-soybean density study. I. Yield complementarity. Experimental Agriculture 21:41-51.

Putman, D.H., S.J. Herbert and A. Vargas. 1986. Intercropped corn-soybean density study. II. Yield composition and protein. Expermental Agriculture 22:373-381.

Ritchie, S.W., J.J. Hanway, H.E. Thompson G.O. Benson. 1997 (reprint). How a soybean plant develops. Special Report 53. Iowa State Co-operative Extension, Iowa State Univeristy, Ames.

Smith, D.L. and Hume, D.J. 1987. Comparison of assay methods for N₂ fixation utilising white bean and soybean. Canadian Journal of Plant Science 67:11-19.

University of Wisconsin-Extension. 1999. Soybeans for hay or silage. University of Wisconsin-Extension. (Available on-line at http://www.uwex.edu/ces/forage/pubs/SOYBNFOR.html).

Upfold, R.A. and H.T. Olechowski. 1994. Soybean production. Ontario Ministry of Agriculture and Food, Publication 173. Queen’s Printer for Ontario, Toronto, ON.