Adapted from a 2015 Agriculture & Agri-Food Canada (AAFC) Factsheet. By Roger Henry, Vernon Rodd and Aaron Mills
Soybeans have become a significant agricultural cash crop in the Maritime region in the last five years, and interest in the crop continues to grow in both the organic and conventional farming sectors. Organic soybean production research has been conducted in PEI since 2008 at the AAFC Harrington Research Farm. This work has looked at tilled and no-till systems, finding that both offer a similar yield potential.
Organic soybeans demand a significant premium price in the marketplace, often double the conventional price. Currently, the price for food-grade organic beans is $1100/tonne. If farmers are able to achieve yields approaching 37 bushel or one tonne to the acre, the premium makes organic soybeans an attractive cash crop.
Choosing a field for organic soybeans
Ideally, any field for organic soybeans should have good fertility levels, good organic matter content and no major weed issues. Compost applied the fall before is the most such a field requires, and that’s not absolutely necessary.
Soybeans are a lazy legume. They will fix their own nitrogen (N) if they cannot find it in the soil, but if nitrogen is present, soybeans will not fix their own. We do not recommend additional N fertility on organic soybean crops, especially not if manure is applied in spring, because this will generally increase the weed pressure from nutrient-loving weeds such as lamb’s quarters, sow thistle and redroot pigweed.
Organic soybeans can be successfully grown in a tilled or no-till system. The main difference will be in the methods of weed control. The tilled system uses mechanical weed control methods, while the no-till system relies on a rye mulch for weed suppression.
Regardless of whether a no-till or tilled cropping system is used, an organic soybean cropping system must be designed to address weed issues throughout the growing season. The soybean crop is slow to emerge, especially in a cold spring. Developing a good crop canopy can often take eight weeks. This is a perfect time for weed growth to choke out the crop if a good weed control system is not in place. In addition, green weeds in the crop at harvest can clog equipment, stain the beans during harvest, or cause the crop to heat in storage. With adequate weed control, organic production can achieve yields approaching those of conventional production.
As with any crop that does not compete well against weeds, the key to a good clean stand is to get uniform germination and to have the crop canopy close in as early as possible, to limit the light and space for weeds. The soybean plants will fill in all available space over time, but initially the weeds have the advantage. As a general rule, the wider the plant spacing, the taller and bushier the soybean plants will grow as the canopy fills in.
Cropping System Options: No-till or Traditional Tillage?
No-Till Soybean Production System
This simple system, developed at the Rodale Institute in Pennsylvania, does not require mechanical weeding. To set up this system, one has to establish winter rye the previous fall in the field where soybeans are to be grown. The rye is allowed to grow the next spring, until it flowers (comes out “in head”); it is then aggressively rolled when half or more of the rye plants are in head. The timing of the rolling is important: if one does not wait until the rye is at 50% heading prior to rolling, much of the rye will regrow and be a nuisance at soybean harvest or choke out the soybean plants during the summer.
There is a proper crimper roller that will roll the rye in one pass—it is a water tank with flat bar welded on the outside of the tank, which crimps/cuts the rye plants as it rolls. We have found that a common land roller will also work, however. When using the land roller, roll the rye in one direction to bend it over, then re-roll the opposite way. This will tend to break the rye off at the base and prevent it from re-growing, which is what you want.
Once flattened, the rye forms a thick mulch that prevents weed growth, into which the soybeans can be drilled. Rye contains allelopathic compounds that effectively suppress the growth of other grasses and weeds, eliminating the need to weed. This works for soybeans because the rye’s allelopathic effect does not suppress legumes. We have also used this system successfully with field peas.
Traditional Tilled Planting: Row crop or solid stand planting
Seedbed preparation in the tilled system involves controlling initial flushes of annual weeds. Knowing the growth habits of annual weeds is necessary to destroy as many as possible before planting main crops. Most annual weeds will germinate in seven days or less in the warm spring weather, so it is recommended to cultivate the field twice, seven days apart. Following the second cultivation, plant immediately and roll. This process will kill two flushes of weeds and can be used for both the row crop and solid stand planting systems described below.
Row crop planting system
The row crop system requires the beans to be planted in 18–30” spaced rows, while leaving the headlands unplanted to allow for cultivation between the rows as the crop develops, in addition to fingerweeding* pre- and post-emergence. Weeds can be controlled with a traditional row cultivator until the plants are at least 12 inches high. Row spacing below 20 inches will require a guidance system on the three point hitch to ensure the tractor and cultivators stay in the center of the row and do not pull out soybean plants.
Soybeans generally take from 10 to 14 days to emerge, so there is a good window for fingerweeding before emergence. The field should be weeded before the soybeans emerge from the soil; a week after planting is usually ideal. If weeds are still an issue, the beans can be fingerweeded again when they are at the first trifoliate stage (see fig 5). Our research has shown that it is important not to fingerweed when the soybeans are emerging from the soil and during the cotyledon stage, as they are very easily killed with the weeding. Others have stated that fingerweeding can be as late as the hook stage of early emergence with no negative impacts. Research in Quebec recommends staying away from post-emergence fingerweeding until the first trifoliate stage.
*Fingerweeder, tyne weeder or flex-tine harrow are all names for the same weeder.
Solid stand planting system
In contrast, in a solid stand system, the entire field is planted using a 7-14” row spacing, which leaves fewer options for weed control. With solid stand plantings of beans, one cannot use any in-row cultivation; the only option for weed control is to use a fingerweeder or rotary hoe pre- and post-emergence, so it is critical to choose a field that has demonstrated low weed pressure, and then time the weeding well.
The most common row spacing for solid stand is 12-14”, which requires blocking off every second run in the grain drill. If you plant a solid stand in 6–7” rows, the rows do fill in more quickly, but the soybean plants generally do not grow as tall, which can result in pods that are too low to harvest. In humid, moist years, the narrow spacing can result in fungal disease problems. The beans should be planted no more than 1 inch deep. The land should be rolled following planting, to ensure better soil seed contact and more uniform germination.
Cropping System Comparison:
Should you choose a Traditional Tilled Cropping System or No-till Cropping System?
Review of the differences in planting systems
Planting. The tilled system allows for earlier planting and a longer planting window than the no-till system. The no-till system requires waiting until the rye flowers before planting the soybeans—early June here in PEI. We plant shorter-season beans,so that frost will not be an issue.
Equipment. The tilled system uses conventional cultivation and planting equipment, while the no-till requires an expensive no-till drill with aggressive front coulters to cut through the rye mat.
Traffic and tractor use. The tilled system requires many more passes over the field, 2-3 for seedbed preparation and 2-3 to cultivate the beans once planted, versus 2-3 pass total with the no-till system. Ultimately this gets into the question about cost of production. More passes mean more fuel use and more impact on soil quality with increased tillage and traffic. The farmer must decide what’s best for the soil and evaluate the investment in an expensive no-till drill.
Weeding options. When using the tilled system, the beans can be planted in a solid stand or in rows and cultivated. With the solid stand, the beans are planted at 7 or 14 inch row spacing and fingerweeded before and after the soybeans emerge. If the beans are planted in a wider spacing 18-30 inch rows, it allows for in-row cultivation before and after emergence, in addition to the fingerweeding. The no-till system relies on the rye mat to suppress weeds.
Establishing a solid stand. In the no-till system, rolling the rye adequately is critical to the beans establishing well. If the rye is not flattened, it will be hard to place the beans in the soil and emergence will suffer. With the tilled system, once a good seedbed is prepared, the establishment of the soybeans is relatively straightforward.
Yields. Whichever system is followed, the yields can be quite similar, provided there is a good plant population (50 plants/sq meter) and the weeds are controlled. If weeds get out of hand, yields can easily drop by 50%. A poor stand (e.g. 25 plants/sq meter) will not have nearly the yield potential compared to one with twice the plants, so achieving good emergence is also key to a successful crop. The table below shows the yields achieved using the various methods at the Harrington Farm (not all methods were used each year).
Yields achieved using different cropping systems
|Cropping system||Year||Kg/ha||Lbs/ac (bu/ac)|
|In-row (24″)||2014||1911||2100 (35)|
|Tilled solid stand||2008-2013||1340-2200*||1200-2000*|
The asterisk (*) in the table highlights potential yield differences from year to year, largely due to the level of weed control achieved.
The information and data provided in this fact sheet are based on using DH 420 soybeans, a variety typically used for making tofu.
We are impressed with organic soybean yields of 33-40 bu/acre under no-till management. Given current prices, organic soy is a highly profitable crop that also offers very good soil quality maintenance for production in the Maritimes.