Farm Progress

Ask a CCA: Understand how water, light and nutrition influence soybean yield for high-yield soybeans.

March 20, 2017

4 Min Read
BOOST YIELD: The four main factors driving soybean yield are light (temperature), nutrition, water (drainage) and pest management.

By Geoffrey Trainer

What does it take to raise 100-bushel soybeans?

There have been many references to high-yield soybean management in farm publications and presentations over the last few years. There are five key points to maximizing soybean yield:
1. determinates of soybean yield
2. maximizing light interception
3. water use among growth stages
4. nutrient use
5. high-yield practices

These are all common points when talking with growers who are and have been successful in producing high yielding soybeans.

What are the factors that attribute to yield gain?

Soybean yields have increased over time. For example, from 1924 to 1979, the average yearly soybean rate of gain was 0.35 bushel per acre and from 1980 to 2010 was 0.50 bushel per acre. This increase has been accomplished through improved breeding methods and technologies. The research scientist’s overall goal is to increase the yearly soybean gain even more in the future.

The four main factors driving soybean yield are light (temperature), nutrition, water (drainage) and pest management. Understanding how water, light and nutrition influence soybean yield is important and essential in developing production practices for high-yield soybeans.

We must remember that water and drainage go hand in hand, and that light and temperature are somewhat linked. These four factors work together, and if one factor is out of balance, then soybean yield will be negatively affected. An example: If you have excellent fertility, adequate soil-water profile and maximize light interception, yet glyphosate-resistant weeds infest the field, your ability to maximize yield may be compromised.

As we begin to think about high-yield soybeans, we need to focus on four key factors:
• establish uniform plant stand (plants per acre)
• increase pod-set (pods per plant)
• increase number of seeds per pod
• maximize seed weight (seeds per pound)

Growers need to pay attention to details important for ensuring successful germination and seedling establishment. However, they often overlook factors that can influence pod set, which could be the stage of development with the highest upside potential to influence soybean yield. Factors that can influence pod set include carbohydrate reserves, nitrogen reserves, water balance, plant hormone levels and balance, heat, and nutritional status.

How do you maximize light interception?

As growers, if you can’t control sunlight intensity and interception, how can you maximize light interception? One key practice to influence the amount of light a soybean accumulates before reproductive growth is to adjust planting date and soybean relative maturity. This practice means early reproductive growth occurs before the onset of intense heat during the period leading up to the summer solstice when days are the longest. The goal should be to manage soybeans so they achieve critical R1 (beginning bloom) to R3 (beginning pod) growth stages just prior to the summer solstice when days are long and temperatures are mild.

During peak water demand, soybeans are thought to utilize more than 0.3 inch of water per day or 2.1 inches per week. This can actually be much higher if pod fill occurs during very hot periods. Water use is critical to understand if a grower irrigates their soybeans. Soybean water demand mimics that of corn during peak water usage.  

What’s the best fertility strategy to increase yields?

In regards to fertility, most recommendations are based off current soil test levels. If a nutrient falls below the critical value, a grower will likely get an economic response by applying that nutrient. This application means you are likely to get a response by applying that nutrient, but it does not ensure you will have maximum yields. Choosing to build nutrient levels to the high or very high range, and maintaining that level is more likely to produce consistent high yields regardless of crop.

Soybeans are a legume that benefit from the symbiotic relationship between the plant and nitrogen-fixing bacteria called rhizobia. Most studies show during ideal growing conditions rhizobia often are able to fix enough nitrogen, along with organic nitrogen, to supply a 60 bushel-per-acre soybean crop. DuPont Pioneer research has shown as yields increase to 80 bushels per acre and higher, a nitrogen deficit may result. DuPont Pioneer studies have shown that adding supplemental nitrogen to soybeans in 80 bushel-per-acre and greater environments, have shown a 4.5-bushel advantage.

There are several management practices that are common among growers that consistently raise high yielding soybeans. Some of these management practices include:
• planting high-yielding, well-positioned varieties
• using broad-spectrum seed treatment that includes fungicide, insecticide, rhizobia and biological growth promoters
• planting as early as possible
• building and maintaining fertility levels in your soil
• using supplemental N during seed fill, and foliar fungicide and insecticide at R3
• sampling tissues
• applying micronutrients as needed
• rotating between crops
• managing love-hate relationship between water and drainage
• scouting intensively (once a week prior to bloom, twice a week after)
• concluding with a timely harvest

Implementing practices mentioned above may help boost soybean yields to the next level.

Trainer is a CCA and product agronomist at DuPont Pioneer in Ohio. Email [email protected].



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