Interest and utilization of cover crops continues to grow due to benefits including reduction of soil erosion, managing soil moisture, weed suppression, and increasing long-term soil productivity. It is important for North Dakota farmers to have NDSU recommendations from in-state field research, for proper seeding rates of rye based on fall establishment dates, and their goals of using rye as a cover crop prior to soybean production. Study 1 is within the scope of two ND Soybean Council research priorities: Weed #1. Weed management and #4. Soil management.
Fertilizer prices and supply, including phosphorus (P), continues to be a major crop production issue. A P fertilizer use option is a preplant P application for corn at rates to allow adequate plant nutrition for soybean the following year. NDSU Extension’s current suggestion regarding this strategy is based on other land-grant university information. Data from Study 2 will address this lack of ND research and is within the scope of ND Soybean Council research priorities: #4. Soil management – P recommendation.
Data from both studies conducted at the CREC will be shared with ND farmers and crop advisers to improve soil productivity and plant nutrition, while potentially increasing profitability of soybean production.

*Study 1. Examine winter rye fall seeding rate and date combinations:
1. Measure rye plant population and ground cover, soil moisture levels, and weed suppression prior to and/or during soybean production. 2. Measure soybean response (plant growth, and seed yield and quality) to the rye treatments.
*Study 2.
1. Measure soybean response to prior-year P application (for corn and soybean crops) compared to preplant P application during year of soybean production.

The two field studies will aid in providing research-based recommendations:
*Study 1 - Target rye stand density, based on producer goals with the cover crop, while maintaining soybean yield.
*Study 2 - Potentially increase efficient application and use of P for soybean production.

Update:
Winter Rye Cover Crop Establishment Options and Soybean Response to Prior-Year Phosphorus Application
Greg Endres (principle investigator); Leo Bortolon, Mike Ostlie and Kristin Simons (co-investigators)

Overview and objectives:

1. Winter rye seeding dates and rates: Research-based recommendations are needed on proper rye seeding dates and rates based on goals of North Dakota farmers for the cover crop. Objective was to identify optimum rye plant population based on combinations of fall seeding dates and rates with rye as a preplant cover crop preceding soybean considering impact on soil factors, weed control and soybean seed yield.
2. Response to prior-year application of phosphorus fertilizer: North Dakota research is needed to determine if one application of phosphorus (P) fertilizer the prior year of soybean production is effective versus annual P applications. If so, this would reduce costs of fertilizer application and incorporation for soybean. Study objective was to examine soybean response on low-P testing soil to preplant, broadcast-applied P fertilizer the prior year for corn plus soybean versus an annual application for corn followed by soybean.
Completed work:
• Trial 1: Four years of the study were completed at the Carrington Research Extension Center (REC). The trial for generating 2023 data was established continuing with the following six treatments: Winter rye was seeded on September 22 and October 14, 2022 at 25, 50 and 75 lb/A. At mid-May 2023, rye stand had low and variable density. Trial was abandoned due to inability to generate useful data.
• Trial 2: Four site years of the study were completed during 2021-23 at Carrington and North Central (Minot) RECs. P soil analysis: Carrington=2-7 ppm (very low-low) and 7.7-8 pH; and Minot=8 ppm (medium) and 6.5 pH. Treatments: 1) untreated check, 2) Preplant-applied P fertilizer applied for corn followed by P application the following year for soybean, 3) P applied for corn plus soybean during year of corn production. P fertilizer was applied as 0-46-0 (triple superphosphate) based on NDSU Extension recommendations for low-testing soils for corn and soybean production.
Results:
• Trial 1: Averaged across four years, rye plant density measured in May before soybean planting ranged from 137,800 plants/A (3 plants/ft2) with late seeding and the low seeding rate, to 598,300 plants/A (14 plants/ft2) with seeding at the early date and 75 lb/A rate. Ground cover averaged 9% with late seeding dates and low seeding rate compared to 27% with early seeding dates and greatest seeding rate. Green and yellow foxtail suppression was greatest, averaging 73% over three trials, with seeding early and at the greatest rate, when evaluated about one month after soybean planting. Soybean plant density and development, and seed yield (4-year trial average = 51.9 bu/A) and quality generally were similar among treatments.
• Trial 2:
o Carrington (three site-years) - Soybean plant development (emergence, flower and physiological maturity dates) were generally similar among treatments each year. Plant populations were similar among treatments. Seed quality (test weight, seed count, and seed oil and protein content) generally were similar among treatments. Seed yield: 1) untreated check=40.8 bu/A, 2) P application each year=44.4 bu/A, and 3) Total P application during corn year=43.8 bu/A. Yield increased with P application compared to the untreated check (LSD [0.10]=2.8 bu/A) but was similar between the P application strategies.
o Minot (one site-year) – Soybean yield, test weight, and seed protein and oil were similar among treatments.

Work to be completed:
• Research reports will be written and shared with audiences using Carrington REC annual reports and websites, and ND Soybean Council 2023 annual research report.
• Presentations developed and discussed during 2023-24 winter meetings with farmers and crop advisers.
Summary:
• Trial 1: Based on this study, winter rye seeded during early fall (last-half of September) at 75 lb/A provides the greatest potential for following spring ground cover (benefits include reduction of soil erosion and excess soil moisture management) and weed suppression, while having no negative impact on soybean production when rye is properly managed.
• Trial 2: Under conditions of this study, the results indicate application of P fertilizer at NDSU recommended amounts in the preceding year of soybean production is an acceptable alternative strategy versus in-season P application for the crop.

View uploaded report

Updated June 24, 2024:
Research Overview and Objectives:

1. Winter rye fall seeding dates and rates: Farmers that use rye as a cover crop preceding soybean require recommendations on fall seeding dates and rates to meet goals including soil management and other benefits. Rye cover crop planting dates can range from August to November, and planting rates may range from 20 to 90 lb/acre. The study objective is to determine appropriate rye seeding rate and established stand preceding soybean production including ground cover, soil moisture, and weed suppression with rye.
2. Response to prior-year application of phosphorus (P) fertilizer: Preplant phosphorus (P) fertilizer application the prior year of soybean production, typically on corn ground with one total application rate for corn and subsequent soybean production, is a common strategy in eastern cornbelt states. Advantages include reducing fertilizer input costs with one less trip across the field, and possibly more flexibility with available fertilizer supply and prices.
Study objective is to examine soybean yield response on low-P testing soil to preplant, broadcast-applied P fertilizer the prior year for corn plus soybean versus an annual application for corn followed by soybean. This research, not previously conducted in North Dakota, will help verify use of this strategy as a productive fertilizer program.
Study objective was to examine soybean response on low or very low P testing soils to preplant-applied P for corn plus soybean the year prior to soybean production versus P application for corn followed by P application the next year for soybean.
Materials and Methods:
• Study 1: The field study commenced during the fall of 2018 at the NDSU Carrington Research Extension Center (REC) with two planting dates and three planting rates of winter rye. Initial rye planting dates range from September 17 to October 2, and second planting dates range from October 8 to November 1. Planting rates are 25, 50 and 75 lb per acre. Rye was direct-seeded with a no-till drill and terminated by glyphosate near soybean planting time. Soybean were grown using best management practices. Soil, weed control and soybean performance notes were taken.
• Study 2: The field study was conducted in 2021-23 at Carrington and in 2022 at North Central (Minot) RECs. P soil analysis: Carrington=low (7 and 4 ppm) and Minot=medium (8 ppm). Study discussion will continue only for Carrington trials as soil P levels were appropriate based on study objectives (low or very low P levels).


Experimental design was a randomized complete block with four replications. Treatments: 1) untreated check, 2) P preplant broadcast-applied, based on soil analysis and NDSU fertilizer rate recommendations, for corn; followed by P application the following year for soybean, and 3) P applied the initial year for corn plus soybean. The dryland trials were established on conventionally tilled Heimdal-Emrick loam soil with 3.0-3.4% organic matter, 7.7-8.0 pH (0- to 6-inch depth) and 2-7 ppm P (very low-low soil level; Olsen test). Triple super phosphate (0-46-0) was preplant broadcast applied and incorporated prior to crop planting each year.

‘DKC32-12RIB’ corn was planted in 30-inch rows with the following planting and harvest dates: May 26 and Oct. 7, 2020; May 10 and Nov. 2, 2021; and May 26 and Nov 2, 2022. Corn grain yield averaged 66.5 bu/A in 2021 and 130.3 bu/A in 2022 with no differences among treatments for each trial. ‘AG03X7’ soybean were planted in 30-inch rows on May 18, 2021 resulting in established average stand of 123,500 plants/A and harvested Sept. 23; ‘AG03XF2’ soybean were planted in 22-inch rows on June 2, 2022 resulting in 146,900 plants/A and harvested Oct. 4; and ‘AG03XF2’ soybean were planted in 30-inch rows on June 2, 2023 resulting in 101,400 plants/A and harvested Oct. 12.

View uploaded report

Research Results and Discussion:
• Study 1: Four years (2019-22) of data have currently been collected. Data includes rye plant population, ground cover, weed suppression and soybean performance. The following is a summary of preliminary data:
o Averaged across years, rye plant density and ground cover measured during May (prior to soybean planting) ranged from 137,800 to 598,300 plants per acre, and 9 to 27%, respectively, among combinations of rye seeding dates and rates. The greatest rye plant density (598,300 plants per acre; 14 plants per square ft) and ground cover (27%) resulted from the first planting date and 75 lb per acre planting rate.
o Averaged across three years (2020-22), green and yellow foxtail suppression ranged from 51-73% among the six rye treatments, with the greatest suppression (73%) occurring with the first rye planting date and 75 lb per acre planting rate. In 2020, kochia suppression was greatest (79-83%) with the early rye planting date and 50 or 75 lb per acre planting rates.
o Averaged across four years, soybean plant density and development, and seed yield (average of 52 bu per acre) and quality were similar among rye treatments.

• Study 2: Soybean plant development (emergence, flower and physiological maturity dates) were generally similar among treatments each year. Plant populations were similar among treatments. Plant canopy, measured mid-July to mid-Aug. during the R2-6 growth stages, generally was slightly greater with sequentially applied P compared to the untreated check. Seed quality (test weight, seed count, and seed oil and protein content) generally were similar among treatments.

Soybean seed yield averaged among the three Carrington trials: 1) untreated check = 40.8 bu/A, 2) P application each year = 44.4 bu/A, and 3) Total P application during corn year = 43.8 bu/A. Yield increased with P application compared to the untreated check (LSD [0.10] = 2.8 bu/A) but was similar between the P application strategies.
Benefits to ND Soybean Farmers and the Industry:
• Study 1: Study data indicates planting winter rye as a cover crop during the last-half of September versus later in the fall at 75 lb per acre provides the best potential for optimizing factors measured in the study. Soybean performance, with proper management using rye cover crop, will be consistent with traditional production methods. Data is now available for crop advisers and farmers to determine appropriate rye planting dates and rates based on their goals with the cover crop.
• Study 2: Under conditions of this study, including very low to low soil P levels and soil pH ranging from 7.7-8, the results indicate application of P fertilizer at NDSU recommended amounts in the preceding year of soybean production is an acceptable alternative strategy versus in-season P application for the crop. This will save fertilizer application and mechanical incorporation costs due to one vs. two applications over two years. In addition, this may add more flexibility for farmers while making input decisions on P fertilizer supplies and prices.

*Study 1. Results will help farmers answer the following question: What is the best rye seeding rate based on fall seeding dates and following season factors affecting soybean production including ground cover, soil moisture, and weed suppression with rye? The information will help farmers select proper rye seeding rate and fall date based on their cover crop goals and resource management.
*Study 2. Results will help farmers answer the following question: Can P fertilizer be preplant, broadcast applied on low P-testing soil for both corn and soybean during the corn production year? If yes, this would 1) eliminate fertilizer application and incorporation costs for soybean, 2) potentially reduce P fertilizer cost for soybean, and 3) potentially increase P response by soybean.