Evaluation of forage soybeans to provide simultaneous benefits: A high-protein dairy forage and a legume cover crop?

Final Report for ONE05-040

Project Type: Partnership
Funds awarded in 2005: $9,800.00
Projected End Date: 12/31/2006
Matching Non-Federal Funds: $2,548.00
Region: Northeast
State: Maine
Project Leader:
Mark Hutchinson
University of Maine Extension
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Project Information


(Note to the resder: Graphs and chart data referred to in the text can be requested by sending e-mail to [email protected]. Refer to project ONE05-040)

The integration of crop and livestock enterprises has the potential to improve economic and environmental sustainability. The use of forage soybeans (Glycine max L. Merr) were evaluated as potential dairy forage and as a rotational crop in a vegetable production system.

A randomized complete block experiment was established using four varieties of forage soybeans in 2004 and 2005. Yields and nutritional value were analyzed. Sweet corn (c.v. Temptation) was grown following the forage soybeans in 2005 and 2006. Yield and stalk nitrate data were collected and analyzed.

There was no significant difference in forage soybean varieties for yield or nutritional value. However, the cows chose Stine 3300 in when offered all four varieties.
There was no significant difference in sweet corn yield between the four forage soybean varieties. Stalk nitrate data indicated excessive N plant uptake. This information could be used to better manage N applications in following years.


This SARE project highlighted the integration of crop and livestock enterprises to improve sustainability. Forage soybeans (Glycine max L. Merr) were evaluated as potential dairy forage in Maine and as a rotational crop in a vegetable production system.

Maine dairy farmers are interested in developing high protein annual forages to include in their dairy ration. An annual high producing forage would provide dairy farmers more flexibility in their crop rotations. Many dairy farmers have diversified by growing vegetable crops themselves or by land sharing with a vegetable producer. Sweet corn is often the crop of choice.
Sweet corn is a nitrogen (N) intensive crop. Producers are interested in reducing soil N inputs to improve the economics and environmental sustainability of sweet corn production. Legumes are often used in rotation as a potential N supply for the following crop. A fertilizer replacement study was conducted to determine the N contributions from a previous soybean crop.
This project was to evaluate how vegetable and dairy producers could share cropland for the mutual benefits of improving soil health, decrease traditional nutrient inputs, provide high quality dairy forage and increase economic viability.

Project Objectives:

Objective 1. Evaluate the forage quality of four soybean varieties as an annual forage for dairy production.

Objective 2. Determine the N fertilizer replacement value of a soybean crop prior to sweet corn.

Performance target 1: As a result of two workshop presentations, ten dairy farmers will plant a total of 250 acres of forage soybeans as an annual source of high quality dairy forage.

Performance target 2: As a result of two workshop presentations, 3 vegetable growers will include forage soybeans into their crop rotation.


Materials and methods:

This study required two growing seasons, year one was forage soybeans followed by sweet corn grown in year two. The project was replicated over a three year period.
The research design was a randomized split plot design with 4 main plot treatments and 4 subplot treatments. Main plots were 30’ X 200’ and subplots were 30’ X 50’.
Main treatments were four varieties of forage soybeans (Glycine max L. Merr): Derry, Tyrone, Tara and Stine 3300. Subplot treatments were nitrogen application rates in year two: 0, 40, 80, 120 lbs of N/ acre.

In June 2004, main plots were established on Scio soil type (very fine sandy loam) in China, Maine. Gramoxone was applied at 1.75 pints/acre before planting. Four varieties of forage soybeans were no-till drilled into pumpkin residue with 7” row spacing with a seeding rate of approximately 175,000 seeds per acre. Dual (1.5 pint/acre) and Prowl (2.0 pints/acre) with crop oil (3 pints /100gals/4 acres) was applied as a post emergent herbicide. No soil amendments were added. Soil pH was 5.9. Soil organic matter was 6.2.

Forage subsamples were collected on August 25, September 3 and September 13, 2005. Wet weights, dry weights and complete forage analysis were collected on each sample. In 2005, the experiment was repeated in China, Maine on Paxton-Charlton soil type. Forage soybeans were planted on June 3. Forage samples were collected on August 17 and August 25. In 2005, each forage soybean variety was individually wrapped for silage on August 26. Ensiled samples were collected on October 1. Forage samples from all 3 dates were sent to Dairy Herd One for complete nutrient analysis.

In the year following forage soybeans, sweet corn was planted. The soil was prepared for planting using zone tillage (7” tilled stripe) with 30” row spacing. Temptation (SE 74 days) sweet corn (Zea mays), 12 rows per main plot, was planted using a traditional 4 row corn planter in both years. Planting dates were May 11, 2005 and May 17, 2006. Extensive rain in 2005, before and after planting, resulted in a poor plant stand density for several main plots. In 2005, no fertilizer was added to the plots at pre-plant or at planting. In 2006, phosphorous and potassium was applied at planting to meet soil analysis recommendations.
A pre-emergent herbicide (Dual 1.5 pints/acre) was applied both years to control weed pressure. Integrated pest management practices were used to during the growing season and supported by the University of Maine Sweet Corn IPM program.

Nitrogen response subplots (30’ X 50’) were randomly established in sweet corn main plots. Four different rates of nitrogen (0, 40, 80,120 lbs of N/acre) were randomly side-dressed by hand when the sweet corn reached a height of 8-12”. This occurred July 7 2005 and July 3 2006. Urea (46-0-0) was used as the N source. A significant rain event followed within 24 hrs after the 2005 application with no precipitation following the 2006 application.

Soil nitrate test were collected and analyzed in 2005 for each subplot. Yield harvests occurred on August 11 2005 and August 8 2006. Number of marketable ears, total ear weight, stalks weight and stalk nitrate data were harvested from 1/1000 acre from middle two rows of the subplots.

Research conclusions:

Forage Soybean Yields:

Forage soybeans would not be recommended as an annual forage for dairy production. Annual yield was lower then traditional annual forage crops and much more difficult to wilt down and produce baleage. However the dairy farmer found that heifers did very well on the forage soybeans. Forage soybean yields ranged from 5.2-7.9 tons of dry matter (DM) per acre after being ensiled for 60 days.

Yield and feed analysis results were similar to 2004. There was no significant statistical difference in the forages. However the cows seemed to prefer the Stine variety according to the farmer. His observation was that in all but the Stine variety there was a lot of waste feed, specifically woody stems.

Sweet Corn Yields

There was no statistical difference in sweet corn yields in 2005 and 2006 across forage soybean varieties. Sweet corn yields were between 1000 to 1916 dozen ears of marketable corn per acre. An additional 80 lbs of N maximized yield potentials in both crop seasons (Figure 1).

The experimental design did not allow us to measurement how much N the forage soybeans actually contributed. It can be assumed from other research that there is little or no contribution from the forage soybeans because maximum yields at the expected N application rate of 80 lbs of N/acre.

However, there was noticeable difference in soil tilth and good weed control. The long soybean taproot appeared to loosen the soil and break up hard pans. The decaying roots also provided humus for the formation of soil peds.

Stalk Nitrate Results:

Stalk nitrate often referred to as the end of season cornstalk test. The test is a post mortem analysis tool used to determine plant tissue nitrogen left in the lower stalk after harvest. The test allows growers to determine if their crop nitrogen management was appropriate for that growing season. Stalk nitrate levels were at or above optimal levels for all treatments and varieties (Figure 2). However the critical levels for stalk nitrates were determined for grain corn which would be harvested later in the season. A later harvest would mean more of the nitrate in the lower stalk may have been translocated to the grain kernels. Because sweet corn is harvested at an earlier maturity level the nitrate may not have moved up to ear.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

This project was presented at the 2005 & 2006 Annual Maine Fruit and Vegetable School (2 locations with 68 participants). Information was presented as part of a program at the 2006 Maine Agricultural Trade Show. Information was shared at the New England In-Service training for Agricultural Professionals (Certified Crop Advisors- American Society of Agronomy) in February of 2004.

Project Outcomes

Project outcomes:

Farmer Adoption

Producers have continued to swap 25-30 acres of land after the project. Both partners realized benefits to this relationship. They are exploring ways to increase the number of acres. Two additional producers are investigating forage soybeans for organic milk because of it weed control advantages.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Evaluate blends of annual feeds for dairy production. Need to evaluate different legumes for rotations in vegetable and livestock integration systems.

A classic fertilizer replacement study utilizing a small grain along with forage soybeans would allow us to determine the actual N .

Stalk nitrate critical levels were established for grain corn by Iowa State University (Blackmer & Mallarino, 1996). Research needs to be
conducted to determine if these are the same critical levels for sweet corn.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.