There is increasing demand for the production of low carbon intensity (CI) soybeans (and corn). Livestock feeders want low CI feed ingredients, food companies want low CI food ingredients, and renewable liquid fuel producers want low CI feedstocks. Producers of biodiesel and renewable diesel are highly incentivized to lower their fuel CI scores through existing and emerging low carbon fuel standard (LCFS) initiatives, and the emerging market for sustainable aviation fuel (SAF) could be a significant market for low CI feedstocks such as soybeans.

CI values for soybeans represent the carbon footprint required to produce a bushel of soybeans. CI values are generally measured in grams carbon dioxide equivalent (CO2e) per megajoule (MJ) of energy. It is a straight forward process to convert CI value to grams CO2e per bushel of soybeans. Drivers of CI values for soybeans include the amount and type of energy used to produce soybeans (i.e., energy for machinery, transportation, etc.), energy used to produce soybean inputs such as phosphorus and potassium fertilizer along with pesticides, and the level of nitrous oxide emissions in the field. Nitrous oxide (N2O) emissions represent the largest component of the soybean CI value. In fact, the Argonne Laboratory Greenhous Gas (GREET) model, estimates that N2O accounts for 75 percent of the soybean CI value.
The average soybean planting date in Iowa is later than optimum. Moving the soybean planting date to the optimum will reduce the CI score of soybean production, but current estimates do not account for the full reduction. Co-investigator Castellano’s research team, funded by the United Soybean Board, used process modeling over the last 30 years to estimate how moving the average soybean planting date from the county average to the county optimum would affect CI score. The average planting date was determined from USDA statistics and the optimum planting date was taken as the average planting date for corn. The difference in planting dates was typically about 10 days and allowed planting of a longer maturity group.

In this work, the reduction in CI score owing to earlier planting was almost wholly attributed to higher yields from planting earlier with a longer maturity group variety. However, the CI score of soybeans is affected by yield and by N2O emissions from the soil, and the model did not reflex N2O emission reductions from the field (among other smaller effects). In contrast to the model output, theory suggests earlier planting should reduce N2O emissions from the field because earlier planting leads to earlier soil N uptake, which is well known to reduce N2O emissions. And, N2O emissions from the field account for about 75 percent of the CI score for soybean production.

Hence, there is a need to further test and improve models of soybean N dynamics to quantify N2O emissions and ensure soybean growers are properly credited for efficiency improvements owing to earlier planting. We hypothesize that earlier planting will indeed reduce N2O emissions from the soil because earlier crop growth will immobilize more nitrate from the soil. Consistent with this hypothesis, our previous ISA-funded work on nitrogen fixation has shown that soybeans rely almost wholly on soil nitrogen rather than fixed nitrogen until reproductive growth stages that occur much later in the season. And, it is well understood that the primary cause of environmental N losses in Iowa corn and soybean cropping systems is the lack of significant plant N demand in the early spring.

One potential constraint to planting soybeans earlier in Iowa is the high amount of corn residue on the field in no-till, corn-soybean rotations. Corn residue from corn production has been trending upward, in part, due to higher corn populations. Higher corn populations are helping to drive yields higher but the increasing residue poses challenges when planting soybeans the following season. One approach to addressing this challenge is to remove some of the corn residue. The harvested residue could be used for cattle feed or for industrial uses. For example, the Verbio ethanol operation near Nevada, IA has a program to pay growers for baled corn stover.
How can Iowa soybean growers improve their ability to get soybeans planted earlier in the spring? They will need equipment (i.e., planters, etc.) available early in the spring and soil conditions will need to be suitable (i.e., acceptable soil temperature and moisture). Salin 247 is focused on providing growers dedicated equipment for planting soybeans early and planting into no-till ground with cover crops. Partial removal of corn stalks should also help allow earlier soybean planting in the spring.

This proposed project will evaluate the impact of early-planted, no-till soybeans in a corn-soybean rotation on soybean yield as well as on soybean carbon intensity values. The impact of partial corn residue removal will also be evaluated. This project will be the third year of a Salin 247/ISA Research Project, but it will also be a collaborative effort with the Department of Agronomy at Iowa State University. Dr. Dave Krog from Salin 247 will be the co-investigator along with Dr. Michael Castellano from Iowa State University.

Project objectives include:
(1) Evaluate the soybean yield and soybean carbon intensity (CI) impact of planting no-till soybeans early in the spring
(2) Evaluate the impact of corn stover partial removal in the fall prior to soybean planting on the soil suitability for planting and on soybean yield and soybean CI values
(3) Complete an economic evaluation of early-planted, no-till soybeans under the two corn stover management options
(4) Evaluate the performance (e.g., acres planted per day, energy use, navigation performance) of an 8-row, autonomous Salin 247 planter
(5) Conduct the trials on actual Iowa farm fields
(6) Communicate the project results to the Iowa soybean industry

Key project deliverables will include:
- Semi-annual ISA update reports
- A comprehensive report of the project findings (pdf format)
- Presentation slides describing the project and its findings (PPT format)
- Presentation of project findings to selected ISA audiences

Update:
ISA 2023/24 Research Project
Estimating crop yields and carbon intensities from earlier planted soybeans and potential synergies with partial corn residue harvest
Update Report by Salin 247, Inc.
for the
Iowa Soybean Association
April 1, 2024

Project objectives
The primary objectives of the “Estimating crop yields and carbon intensities from earlier planted soybeans and potential synergies with partial corn residue harvest” project are to (1) evaluate the soybean yield and soybean carbon intensity (CI) impact of planting soybeans early in the spring, (2) evaluate the impact of corn stover partial removal prior to soybean planting on the soil suitability for planting and on soybean yield and soybean CI values, (3) complete an economic evaluation of early-planted, soybeans under the two corn stover management options, (4) evaluate the performance (e.g., acres planted per day, energy use, navigation performance) of an autonomous Salin 247 planter, (5) conduct the trials on actual Iowa farm fields, and (6) communicate the project results to the Iowa soybean industry.
Summary of project progress
• The original plan was to build and use for the project an 8-row autonomous planter. Instead, a second 4-row (30” row spacing) planter (V3) has been built. Based on learnings from last season, the new machine has several enhancements compared to the planter (V2) last season. Both 4-row planters will be used for the project
• Verbio agreed to help find project fields, and they provided a list of candidate growers, but none of those options worked out
• Several candidate growers/fields were tentatively enrolled in the project last fall but four of those options ultimately did not work out
• There was an original goal of six fields. Nine fields have been selected with an average size of 22 acres
• Four of the nine fields will have corn stover removal treatments
• Two of the nine fields have been strip-tilled
• Two of the nine fields will have fall and spring tillage
• One field has cover crops
• RTK GPS drone images have been taken and stitched for each of the nine fields
• Shape files of plot areas have been created in Ag Leader SMS software
• Project plots in fields have not yet been physically flagged but will get flagged in the next week or so
• Plot shape files have been sent to ISU so soil sampling can be scheduled and soil sensor installations can begin
• Planting details are being gathered from growers including desired planting population, number of end rows, how that are going to provide seed, and other information
• We will start the “early” planting as soon after April 1 that conditions are suitable. There is one grower that would not like us to plant prior to April 15, the FCIC’s “earliest planting date” for northern Iowa.
• ISU will install soil sensors shortly before and shortly after planting.

Salin 247 autonomous planters
For the 2024 OFT project, Salin 247 will be using two autonomous, 4-row (30” row) planters (named V2 and V3). The planter (v2) used for last year’s ISA project has been upgraded to address GPS and controller issues from last season. A new planter (V3) has been built with several upgrades including all-wheel steering (V2 is a skid steer machine), suspension system, telescoping toolbar, upgraded batteries, upgraded hydraulic system, and electronic improvements. Both planters will be using upgraded navigation software.
Salin 247 has also developed new path planning software. The software allows us to more efficiently and accurately create path plans for planting and for post-emerge operations. Our new approach requires that we obtain RTK GPS coordinates of each trial field. High resolution coordinates help improve the accuracy of navigation.

Status of project tasks
The focus of work to-date has been on project planning. Below is the list of key project tasks along with a status update where applicable. Early planting of soybeans will begin as soon after April 1 that soil conditions are suitable (i.e., soil temps greater than 50 degrees Fahrenheit and around 35% soil moisture at planting depth), and the grower gives their approval. One grower does not want us to planter prior to April 15, the FCIC’s earliest planting date to be eligible for replant seed cost coverage.

Project task status as of April 1, 2024
Broad tasks Key tasks Description
Project planning and grower recruitment Collaboration with ISA Research Center for Farm Innovation Work with the RCFI on the details of an implementation plan including designing the trials and recruiting growers for the project
Status: ISA agronomists worked to identify potential collaborative growers. Two growers were recruited for the project.
Collaborate with Verbio on finding growers Verbio, a cellulosic energy producer in Neveda, IA, agreed to help us find collaborative growers for the project
Status: Verbio was not able to recruit any growers for the project.
One-on-one conversations with potential collaborator growers Identify a set of potential collaborative growers during the summer of 2023 and speak with them one-on-one about the trail protocols and expectations. Get firm commitments from six growers and two to three backup growers prior to 2023 harvest.
Status: Commitments have been made by 8 growers for 9 trial fields (one grower will have 2 plots).
2023 fall field work Arrange for corn stover removal on collaborative farm fields
Make arrangements for custom corn stover removal on designated areas of collaborative farm fields and at specified removal rates
Status: We did not need to do any corn stover removal in the fall. Selected growers already had done removals.
Conduct corn stover removal Complete the corn stover removal and transportation to market
Status: Stover removal not needed last fall.
Planter design, construction, & testing Planter design Based on learnings from past and current ISA-funded projects, Salin 247 has concluded that a 20-foot toolbar planter (i.e., 8 30” rows) has economic advantages over a 10-foot planter toolbar (i.e., 4 30” rows). Significant design changes and a different energy management approach are needed to accommodate a 20-foot planter toolbar.
Status: Instead of building an 8-row planter, two 4-row planters will be used.
Planter construction Source components needed for the 20-foot planter toolbar and construct an 8 30” row autonomous planter that will plant at 5.5 mph (i.e., plant at ~10 acres per hour)
Status: The second 4-row planter has been built and is being tested. The new planter has many enhancements based on learnings from last season.
Planter testing Prior to starting project planting, conduct appropriate testing in the shop and in the Salin 247 test field
Status: Field testing of both planters is still underway as of 4/1/2024.
2024 spring work Obtain high resolution field boundaries & field maps & create navigation paths Using a drone with RTK GPS and a high resolution camera, capture high resolution field images
Stitch images into one high-resolution field map.
Identify project plot area for each field
Generate navigation paths for planting
Create shape files for plot areas and for the navigation paths
Define early planted and late planted areas of the plots
Status: High resolution field maps have been created for each of the nine project fields. Plot areas have been identified. Not all early and late areas have been identified yet
Soil testing ISU plans to take soil samples on selected fields.
Status: Soil samples have not yet been taken, but the plan is to take them prior to planting. ISU will schedule this task.
Install soil temperature and moisture sensors Soil temperature and moisture sensors will be installed. Iowa State University will select the appropriate sensors to be used
Status: Iowa State has ordered and received 72 soil sensors. They will be installed shortly before or shortly after planting. ISU wants to install the sensors on 3 project fields.
Soil temperature and moisture data collection Weekly soil temperature and moisture data for all 24 treatments will be begin in early spring and continue through the growing season
Early-season planting Soybeans will be planted on half of each of the six cooperator fields early in the season (as soon as soil moisture conditions allow)
Later-season planting Soybeans will be planted on the other half of the six fields at least 14 days past the early-season planting date for each respective field
Planter performance data collection Planter performance data (e.g., acres planted per hour, energy use, navigation accuracy) will be collected during planting
2024 growing season work Soil nitrate nitrogen data collection Weekly soil nitrate nitrogen levels will be collected for each of the 24 treatments starting one to two weeks prior to planting and extending through the growing season
Weather data collection Temperature and rainfall data will be collected throughout the growing season. Temperature data will come from the closest weather reporting site, and rainfall data will come from Climate Corporation reported rainfall estimates by field
Status: Climate Corporation data collection will begin April 1.
2024 fall work Crop yield data collection Cooperator growers will collect yield monitor data and provide it via a designated data format
Modeling, data analysis and project communications Data management and analysis Complete the collection and cleaning of all field data and complete the data analysis for the project
Semi-annual reporting Provide two updates via the ISA semi-annual reporting process
Field day A field day will be scheduled for the summer of 2024 to provide an update on the project and report planting performance findings
Final report A final report of project findings will be prepared and provided to the ISA once all harvest data has been collected and the data analysis completed by December 2024


Trial fields
Below is a table listing the nine project fields. These nine fields are being provided by eight different growers. Note that one of the “growers” (Field 1) is Iowa State University.



The original aim was to find six no-till fields where half of the field would have 50% residue removal. We were able to identify seven no-till fields but only five had an option to do 50% residue removal. Recently we learned that strip-till was done on two of the fields (Field 1 & 6). We were planning to do residue removal on one of those fields, but it was determined not to be feasible. The table below provides some useful information on the nine project fields. All the fields grew corn in 2023.

Field trial design
Below is a depiction of the original field trial design with two planting date treatments (“Early planted” and “Late planted”) as well as two corn stover removal treatments (“No fall stover removal” and “50% fall stover removal”). The size of plots is going to be determined by the size and shape of the selected fields.
Original field trial design


Note that two of the fields with residue removal needed an alternative design. Their design is shown below.


Planting schedule
The goal is to begin planting the “early” treatments as soon as soil conditions are suitable but after April 1. The timing of planting for any given field will also depend on the timing of pre-plant herbicide applications by the growers and by cover crop termination for fields that planted cover crops last fall. Planting could also be impacted by soil sampling scheduling.

Planter logistics
For most of the project fields, our plan is to operate both of our 4-row (30” row spacing) autonomous planters. This will require leasing a pickup and flatbed trailer.
Some growers would like to provide us seed in bulk but not have to tie up their seed tender. For those growers, we will have a bulk box where grower seed can be put prior to going to the field.

Data collection
Iowa State University is wanting to install soil sensors on three of the project fields. A total of 72 soil sensors are available. The sensors will be logging soil temperature, moisture, and other data several times each day.

View uploaded report

Updated December 11, 2024:
We have received collaborator grower yield data for four of the eight trial fields. Here are the steps needed for completing the project:
• ISU organizes soil sensor data collected in Fields 2, 3, and 4.
• Salin 247 collects and analyzes plot yield monitor data for the remaining four fields.
• Salin 247 summarizes all soils and relevant crop production practice data needed by ISU.
• ISU runs nitrous oxide emission models using soils, crop production practice, and weather data for each field.
• ISU calculates carbon intensity values for each plot in each field.
• Salin 247 generates a report with final project findings

View uploaded report 2

Summary
This report summarizes the findings of the project “Estimating Crop Yields and Carbon Intensities from Earlier Planted Soybeans and Potential Synergies with Partial Corn Residue Harvest.” The study assessed the effects of early versus later soybean planting and the potential benefits of partial corn residue removal prior to planting. On-farm trials were conducted across eight Iowa farms, with six growers successfully providing yield monitor data. Unfortunately, yield monitor malfunctions on two farms prevented data collection from those plots. Iowa State University collaborated on the project including providing process modeling estimates for soybean yields, nitrous oxide emissions, and nitrate leaching for all eight fields.

Key findings-
• Measured yields were an average 4% (2.7 bu/acre) higher for early-planted (first half of April) versus later planted soybeans
• Modeled yields were 22% higher on early-planted versus later-planted soybeans
• The value of early-planted soybeans based on measured yields was $27/acre while based on modeled yields was $144/acre
• Early-planted soybeans with residue removal yielded an average 13.8% (7.8 bu/acre) higher than later-planted without residue removal and was worth $64/acre
• Modeled nitrous oxide emissions were 13% lower for early-planted soybeans
• Carbon intensity (CI) scores were 9.5% lower for early-planted soybeans
• Early-planted soybeans are an opportunity for Iowa growers to increase yields, lower CI scores, increase net returns, and widen the soybean planting window

Other summary information-
• Early soybean planting occurred between April 5 and April 23, while later planting took place from April 24 to May 19. Within fields, the interval between early and late plantings ranged from 14 to 37 days.
• Early-planted soybeans were seeded into cool, wet soils, with average furrow temperatures ranging from 40°F to 59°F across the eight fields.
• Parts of two fields planted on April 5 recorded soil temperatures as low as 30°F.
• Measured early-planted soybeans yielded, on average, 4% (2.7 bu/acre) more than later-planted soybeans. Yield advantages for early planting ranged from -1.1 bu/acre (-1.5%) to 7.1 bu/acre (8.8%).
• Corn residue removal results were available for three fields, showing soybean yield improvements of 2.6%, 3.5%, and 22.2% compared to no residue removal
• Ecosystem process modeling estimated a 22% yield advantage for early-planted soybeans compared to later planting. The impact of residue removal was not modeled due to limited data.
• Early planting showed an average 13% reduction in nitrous oxide emissions and an average 9.5% reduction in carbon intensity value based on modeling results.
• Even though the impacts of residue removal were not modeled, research has shown removal reduces nitrous oxide emissions and, therefore, carbon intensity scores. Modeled nitrous oxide emissions would likely be more than 13% with residue removal.
• Modeled nitrate leaching was similar with early and late planting; however, residue harvest should decrease nitrate leaching and more measurements are needed to tune the model.
• Based on measured yields, corn stover removal prior to planting had an estimated net value of $59/acre after accounting for stover sales revenue and nutrient losses.
• No significant differences in harvest moisture levels were observed between early and later plantings.
• Early-planted soybeans across all fields exhibited slow emergence and slow early growth due to the cool, wet weather in April and early May. These conditions likely contributed to reducing early soybean yields.
• No significant disease or insect damage was observed in any of the plots.
• All fields experienced heavy rainfall in April and/or May, but only one field had ponding that led to soybean loss.
• The six no-till fields measured moderate soil compaction, requiring low to moderate air bag down force during planting. The tilled fields did not require added down force with air bags.
• The two tilled fields did not require additional down force on the planter.
• The Salin 247 autonomous planter increased soil compaction in its tracks only slightly in the top two inches of soil
• We conclude that early planted (i.e., early to mid-April) soybeans in Iowa show the potential to have higher yields, lower nitrous oxide emissions, lower carbon intensity values, and a higher net return than later planted soybeans.
• Partial corn residue removal on no-till, corn-soybean rotation soybeans resulted in moderately higher yields although yield data was limited in this study. Observations from the field suggest growers will be able to plant earlier when some corn residue is removed due to warmer and drier soil surface conditions.
• Negative impacts of corn residue removal are uneven distribution of remaining corn residue after partial removal, increased soil compaction from removal equipment, and removal of nutrients.
• No freezing damage was observed on emerged soybeans although freeze damage risk is increased with soybeans planted in early to mid-April in Iowa.
• Beyond the potential for higher yields and lower carbon intensity values, early planted soybeans also widen the planting window for soybeans in Iowa.
• Using a light-weight, autonomous planter likely allowed us to plant earlier in the season (and get back into the fields earlier after a 16-day rain delay starting in late April) since conditions throughout the planting season were relatively wet.

Autonomous planter performance-
Evaluating the performance of the Salin 247 autonomous planter is a secondary objective of the project. Salin 247 used its so-called V2 model to plant all eight project fields. Selected navigation and energy use data was collected along with a wide range of planting performance data. This is the third growing season for the V2 machine and it performed well with the exception of some GPS receiver issues. We would occasionally loose online RTK GPS correction data that is required by our machines. Over the course of the planting season, we were able to eventually create a solution that involves adding redundancies to receiving RTK correction. We have also taken a different approach to connecting to our machines through the Internet. We have now implemented the Starlink technology for accessing the Internet via a set of satellites. The GPS issue impacted our productivity in the field (i.e., acres planted/day), but we are feeling good about the new approach going forward.

General planting observations-
The following are some general observations from planting the early-planted soybean plots.
• When we started planting soybeans on April 5 (Fields 3 and 4 in Webster County), some soil temperature measurements in the furrow were as low as 30oF.
• Soils stayed relatively cool during the month of April, and early-planted soybeans were slow to emerge.
• Conditions during early planting were also relatively wet. Portions of fields with no corn residue removal were noticeably wet on the soil surface. This wetness did cause some problems with our row cleaners on two occasions in Field 4.
• Soybeans were planted at depths ranging from 1.5” to 2.25”. We did not observe seed being planted into dry soil in any of the trial fields.
• No-till fields required a moderate amount of down force using air bags on our planter. We did not add additional weight to the planter on any of the fields. Tilled fields (Fields 7 and 8) did not require additional air bag down force.
• The later planting date was delayed on many trial fields due to rainfall and wet conditions. Once the rain stopped in early May, we began planting again on May 12. We were able to start planting again one or two days before other growers were back in the field planting.
Growing season observations
Here are a few observations from the growing season.
• Early-planted soybeans were generally slow to emerge and showed slow early growth. This is likely due to cool, wet conditions early after planting.
• Soil crusting was not a problem for emergence.
• No major insect or disease issues were reported by growers although at least one field had slight early-season iron chlorosis in spots. Yellowing did not last long, however.
• By early July, it was difficult to distinguish early-planted from later-planted soybeans in many of the trial fields. When soybeans started to “turn” in September, there was a noticeable difference in planting date.
• Heavy rains fell on most of the project fields at some point during the growing season. Fortunately, only Field 6 experienced ponding that caused some soybean loss (on south end of field).
• Field 5 soybeans were unusually short at maturity. Cool weather in northern Webster County may have contributed to slower growth.
• Conditions for harvest were good so we didn’t have any weather-related harvest issues. Field 5 was the last to be harvested, and harvest moisture averaged 8.2 percent with no difference in early versus late plantings.

Grower Outreach-
Salin 247 participated in meetings, demonstrations, and field days in order to inform folks about this project. Key events included:
• Bunge/Syngenta Field Day
• Iowa State University/Pivot Bio Field Day
• Iowa State University Iowa Nitrogen Initiative (INI) Fields Day
• Ag Venture Alliance Field Day
• Precision Planting Field Days
• Precision Planting Agronomy/Autonomy Days
• Becks Becktology Days

Conclusions-
• Planting soybeans early (i.e., first half of April) is likely to result in higher yields compared to planting later (e.g., two to five weeks later). Our estimate based on 2024 results showed a 2.7 bu/acre (4.0%) early planting advantage. At today’s prices, this advantage is $27/acre.
• The actual realized early planted soybean advantage will depend on weather conditions. In 2024, conditions at and after early planting were wet and cool for all locations. Early planted soybeans got off to a slow start. Under more favorable April weather conditions, the early planted advantage could be higher.
• No early planted soybeans were impacted by a late frost, but this is clearly a risk for soybeans planted in early April.
• Results from this study suggest that Iowa soybeans could be planted much earlier than has historically done even if soil temperatures are below 50 degrees. Some furrow temperatures were as low as 30 degrees at the early planting dates. This would indicate a potentially wider planting window for soybeans in Iowa.
• Removing corn residue prior to planting resulted in an average 9% soybean yield increase, ranging from 2.6% to 22.2%. With residue removal, soils were warmer and drier which likely helped translate to higher yields.
• On the other hand, removing corn stover with round balers did increase surface soil compaction on two of the trial fields.
• Removal of corn stover with round balers also resulted in uneven distribution of remaining residue although there were no noticeable emergence and yield impacts from the unevenness.
• Process modeling results suggest the yield advantage from planting early is closer to 22% instead of the project measured value of 4%. Modeling also estimates nitrous oxides emissions that are 13% lower for early planted soybeans.
• Based on the project modeling work, the early planting impact on the soybean carbon intensity (CI) score was a reduction of 8.5%.
• Based on these findings, we believe Iowa soybean growers should consider planting their soybeans earlier than historically done. If they have only one planter, they should consider planting some or all soybeans before planting corn. Of course, weather conditions in any given year will influence planting timing.
• Beyond higher yields, planting soybeans early widens the planting window for soybeans.
• The primary risk to planting early is a late freeze. This risk combined with the cost of replanting was not considered in this project.
• Removing some corn residue prior to planting soybeans is likely to be beneficial. Nutrient removal does need to be taken into account, however. This work showed an advantage to corn residue removal but use of strip-tilling could have a similar positive impact on soybean yield with the benefit of not removing nutrients.
• We conclude that early planted (i.e., early to mid-April) soybeans in Iowa show the potential to have higher yields, lower nitrous oxide emissions, lower carbon intensity values, and a higher net return than later planted soybeans.
• Partial corn residue removal on no-till, corn-soybean rotation soybeans resulted in moderately higher yields although yield data was limited in this study. Observations from the field suggest growers will be able to plant earlier when some corn residue is removed due to warmer and drier soil surface conditions.
• Negative impacts of corn residue removal are uneven distribution of remaining corn residue after partial removal, increased soil compaction from removal equipment, and removal of nutrients.
• No freezing damage was observed on emerged soybeans although freeze damage risk is increased with soybeans planted in early to mid-April in Iowa.
• Beyond the potential for higher yields and lower carbon intensity values, early planted soybeans also widen the planting window for soybeans in Iowa.
• Using a light-weight, autonomous planter likely allowed us to plant earlier in the season (and get back into the fields earlier after a 16-day rain delay starting in late April) since conditions throughout the planting season were relatively wet.
• This work is based on one season of experience and data collection on a limited number of fields in Iowa. It would be valuable to extend this work to future growing seasons and varying weather conditions.

Refer to the attached final report for more information including the set of tables and figures.

Studies have shown that Iowa growers plant their soybeans later than the optimal planting date. Planting earlier and closer to the optimal date has the potential to increase soybean yields. In addition, there is some evidence that planting soybeans earlier will help reduce nitrous oxide emissions associated with soybean production. Lower N2O emissions will lower the CI values of soybean production, and lower CI soybeans have the potential to receive a premium market price. It is, therefore, important that growers have the information and equipment needed that will enable them to plant earlier and benefit from higher soybean yields and higher soybean prices. If removing some corn stover prior to planting soybeans is shown to have a positive impact on planting suitability of the soil, this practice could also be shown to be profitable to growers.