Nebraska researchers lead project identifying causes of yield gaps in US soybean production
A new paper published in Agricultural and Forest Meteorology details the University of Nebraska–Lincoln’s efforts to identify causes for yield gaps in soybean production systems in the north central region of the United States.
Average soybean yield in the north central region from 2010-2014 was 43 bushels per acre, yet some producers reached soybean yields over 80 bushels per acre.
The three-year study, led by Patricio Grassini, assistant professor in the Department of Agronomy and Horticulture, and Shawn Conley, associate professor in the Department of Agronomy at the University of Wisconsin, sought to identify causes of yield gaps over large agricultural areas and diverse climates and soils. Faculty from 10 land-grant universities looked at rainfed and irrigated soybean in the north central U.S., which accounts for roughly one-third of worldwide soybean production.
Grassini and his colleagues explored the use of producer survey data as an alternative approach to traditional field research to identify management practices that explain highest soybean yields for different combinations of climates and soils. In Nebraska the team relied on Nebraska’s Natural Resources Districts and 20 Nebraska Extension educators to obtain real-world producer data. In total, 3,568 soybean fields across 10 states were surveyed for this study, covering approximately 300,000 acres.
“Regional soybean yield was on average 22% and 13% below the yield potential estimated for rainfed and irrigated soybean,” said Grassini. “Sowing date, tillage and in-season foiliar fungicide and/or insecticide were identified as explanatory causes for yield variation.”
To reach these conclusions, researchers combined producer survey data with a spatial framework to measure yield gaps, identify management factors explaining the gaps and understand the biophysical drivers influencing yield responses to field management. According to Grassini, earlier sowing dates was the most consistent management factor leading to yield increases.
Juan Ignacio Rattalino, research assistant professor at Nebraska who authored the paper, sees this study as a proof of concept about the power of using producer data to identify opportunities for improving farm management and profit.
“There are a lot of studies about yield response to planting date but this is the first one to explain why such response varies across years and regions. We found that the yield benefit derived from earlier planting depends on the degree of water limitation during the period of pod setting in soybean,” Rattalino said.
The study was supported by $1.4 million from the North Central Soybean Research Program, with complementary funding from the Nebraska Soybean Board and Wisconsin Soybean Marketing Board. Other institutions involved include Iowa State University, Kansas State University, Michigan State University, North Dakota State University, Ohio State University, Purdue University, University of Illinois-Champaign, University of Minnesota and University of Wisconsin.
Over the last decade I have noticed a subtle shift across much of the northern soybean growing region towards planting later maturity group soybeans. This shift, either conscious or unconscious, may be attributed to earlier planting dates, relatively favorable fall harvest windows, and the drive for maximum yield as influenced by high commodity prices. As with all trends sooner or later, we have a correction year: 2014 was that year for many farmers. As farmers, consultants, and the battered and bruised seed suppliers sort through the plethora of product offerings for 2015, a common question arises: “In 2015, how much weight should we really give to maturity group in these seed decisions?”. For those of you with short attention spans like me, the short answer for soybean is not much….for the rest of you please read on to understand my reasoning.
In 2011, the WI Soybean Research Program published an article in the journal Crop Management entitled: “Optimal Soybean Maturity Groups for Seed Yield and Quality in WI” (Furseth et al, 2011). In this data set we looked at 893 varieties across 6 growing seasons (2004-2009) and three production regions in WI . Within each region we identified the optimal maturity group range for maximum yield. Those were 2.6-2.9, 2.1-2.4, and 2.0-2.2 for our southern, central and north central regions respectively. After I make this provocative statement this is usually where the audience either falls asleep, starts texting their neighbor about the lame and inept speaker (me), or uses the restroom and fails to hear as the great Paul Harvey would say ……the rest of the story.
Within each figure below you will also notice a maroon line directly below the black yield regression slope. This maroon line indicates the range of maturity groups that lie within 10% of maximum yield. These figures suggest that regardless of growing region in WI growers can select a variety that is almost one full maturity group earlier than the optimal maturity group range for maximum yield and still be within 10% of maximum yield.
These data further support Joe Lauer’s assertion that “Every hybrid (or in our case cultivar or variety) must stand on its own” (Happy Thanksgiving JGL, you were positively quoted in a soybean article). In our recently released 2014 WI Soybean Variety Test Results book the maturity group range that included a starred variety (starred varieties do not differ from the highest yield variety in that test) was 1.9-2.8, 1.1-2.4,and 0.9-2.0 in our southern, central and north central regions respectively. This amplifies my assertion that the “relative” maturity group rating is trumped by individual cultivar genetic yield potential.
Lastly, since I brought it up lets also discuss our “relative” soybean maturity group rating system. If anyone has ever observed a multi-company variety trial in the fall, they may have notice many differences in maturity amongst varieties that have the same MG rating. For example in our 2014 Southern Region Glyphosate Tolerant Soybean Test we noted a 7 day maturity date range among all the 2.4 maturity group varieties listed. This may not seem important at the end of September, but in years when we plant late (Table 1), have a cool growing season and apply a fungicide those few days may matter.
As seed decisions are made for 2015, it is fine to keep the relative maturity rating on your check list, just don’t have it near the top!
(Source – http://www.farms.com/news/should-we-be-using-soybean-maturity-group-as-a-tool-for-variety-selection-115951.aspx)
There’s no shortage of diseases waiting to descend on your soybean crop. No matter where you farm, managing disease requires integrated action from planting to harvesting. Scouting and record-keeping are two tools that – when used in addition to the information below – can help you save considerable yield.
The summaries below are guidelines and should be supplemented with information from your local extension on regional thresholds.
White mold: A fungus affecting Midwest farmers in cool conditions
Persistent and volatile white mold spreads via spores during flowering. It is an annual threat to soybeans in northern and near-northern states. Rotation is only a partial solution, as sclerotia can survive in the soil for up to 10 years, so spraying fungicide labeled for white mold control is recommended. While early planting and narrow rows have been shown to increase yield potential, these factors can also increase your risk of white mold. Consider your field history before deciding how to manage this disease.
Frogeye leaf spot: Growing prevalence and severity in southern states
Infection can occur at any stage of soybean development, but it occurs most often after flowering. Rotating out infected soybean fields for at least two years will help reduce risk. Fungicide seed treatments and fungicides applied after R1 can reduce disease severity. Applications made at R3 are considered most effective in southern states.
Brown stem rot: Incognito infection with symptoms hidden in roots
Since it requires somewhat cooler weather, brown stem rot mainly affects the north-central growing region. This disease may cause yield loss without producing striking symptoms. It is important to keep good notes on your fields to identify problem areas and to determine if the affected areas are becoming larger over the years. Varieties with resistance to brown stem rot should be used only when high disease pressure is anticipated in an infested field. Maintaining soil pH at 7.0 will reduce the risk of brown stem rot.
Charcoal rot: Heat-loving disease that strikes at early reproductive stages
This disease is common in the southern states and even in the Midwest during hot, dry seasons. Infection may occur early in the season, but symptoms typically do not develop until after flowering, when plants become stressed. Reduced tillage and rotation with a small grain, such as wheat or barley, are the best management practices. Identification is particularly important if it occurs in seed fields because infected seeds have lower germination.
Stem canker: Disease spreads field to field on contaminated farm equipment
Treat seed with fungicide that contains carboxin and thiram. The most vulnerable time for infection is the V3 stage, when three nodes are present on the main stem of the plant. The leaves of soybean plants exhibit a distinct yellowing, and later browning, between veins. As plants enter the middle pod-fill stages, cankers begin to form and the disease progresses until plants die. Avoid replanting in infested fields. Instead, plant a non-host (non-legume crop) for at least 2 years.
Soybean cyst nematode: Soybean susceptibility to diseases increased with SCN
In addition to its own effects on a soybean crop, soybean cyst nematode (SCN) can also make your plants more susceptible to contracting other diseases. By the time one nematode is seen on the roots or in soil, more are likely already in the field. One cyst can hold up to 500 eggs and 2 to 3 cycles can take place in just one soybean-growing season. Once SCN is detected in the soil, an integrated approach should be employed, including crop rotation and use of resistant varieties.
The keys to maximizing the economic returns from phosphorus (P) and potassium (K) fertilizer applications are a comprehensive soil testing program and maintaining P and K soil test levels above their respective critical levels. The critical level for a given nutrient is the soil test level at which 95 to 97 percent of the crop’s yield potential will be reached with no additional inputs of the nutrient.
The Michigan State University Extension nutrient recommendation scheme for P and K is shown in Figure 1. When soil test levels are less than the critical level, P and K fertilizer recommendations are higher than crop removal to build up the nutrient levels in the soil. At soil test levels between the critical level and the maintenance limit, P and K fertilizer recommendations are equal to crop removal. At soil test levels higher than the maintenance limit, P and K fertilizer recommendations are less than crop removal.
Figure 1. Michigan State University Extension’s phosphorus and potassium recommendation scheme.
The critical level for phosphorus is 15 ppm and the maintenance range for soybeans is 15 ppm, so P soil test levels should be maintained between 15 and 30 ppm. Because soybeans remove 0.8 pounds per bushel of P2O5, maintenance levels of P fertilizer are required to keep P soil test levels in this range. For a 60-bushel per acre soybean crop, this is 48 pounds per acre of actual P2O5 or 90 pounds per acre of monoammonium phosphate (MAP) or 100 pounds per acre of diammonium phosphate (DAP). Spring application of P fertilizers is recommended over fall application when soil pH levels exceed 7.4. This practice increases P fertilizer availability by reducing the amount of P tied up in the soil.
The critical K level is calculated by multiplying the cation exchange capacity (CEC) by 2.5 and adding 75. For example, the critical K level for a soil having a CEC of 12 meq per 100 g is 105 ppm [(12 x 2.5) + 75]. The maintenance range for soybeans is 30 ppm, so the K soil test level for this soil should be maintained between 105 ppm and 135 ppm. Because soybeans remove 1.4 pounds of K2O per bushel, the maintenance application rate for a 60-bushel per acre soybean crop is 84 pounds of actual K2O or 140 pounds of Muriate of potash (0-0-60) per acre. When applying K fertilizer prior to planting soybeans, spring applications are recommended over fall applications on coarse-textured soils having CECs less than 6 meq per 100 g and organic soils to avoid leaching losses.
Maintenance P and K fertilizer applications can be applied biannually in corn-soybean rotations under the following conditions:
Soil is a mineral soil.
Soil pH is less than 7.4 to reduce P tie up.
Fertilizer is applied prior to planting corn.
Application rate accounts for the P and K removed by both crops.
CEC is 6 meq per 100 g or higher to reduce K leaching.
The effect of various P and K fertilizer application methods (broadcast, deep banding, 2×2 starter and foliar) on soybean yields has been evaluated in university research trials. Broadcast applications have performed equal to or better than the other application methods when soil test levels are above the critical levels. When P and K soil test levels are below the critical levels, band applications are more efficient than broadcast applications.