Cover crops have become quite popular in recent years, not only from a soil conservation and water quality perspective, but also due to their potential to be an additional forage source for livestock producers.
To better understand how cover crops can be used as a potential forage source, Iowa State University Extension and Outreach started a grazing cover crop project in the fall of 2015 at the McNay Research Farm near Chariton and the Allee Research Farm near Newell.
The focus of the project is to evaluate cattle performance and potential grazing days on a cereal rye cover crop as well as assess the impact grazing has on the aspects of soil health cover crops provide, such as helping to reduce compaction and build organic matter.
Prior to planting the rye cover crop last fall, baseline soil measurements were taken including bulk density and soil moisture. The same soil measurements were repeated this spring prior to grazing and after grazing the rye cover crop. The bulk density measurements taken from one of the grazed fields are summarized in Table 1 and soil moisture measurements in Table 2.
Table 1. Bulk density measurements.
Table 2. Soil moisture data.
Rye drilled after behind soybean harvest in the last week of October and during the first week of November at the McNay Farm yielded approximately 2 tons (DM) whereas rye aerial seeded into standing corn at the Allee Farm yielded less than 1 ton (DM).
Preliminary results of grazing cover crop
Due to excessive moisture this year, cattle turnout was delayed and grazing days only equated to a two to three week period. Although performance is hard to determine on such a short window, preliminary average daily gain (ADG) is evaluated to approximately 1.00 lb/hd/day while grazing. Initial nutrient analysis of the rye suggests that cattle grazing a lush, green cover crop need to have access to dry forage such as hay as they can physically not eat enough fresh forage to meet their nutrient requirements.
Part of this project was to evaluate what one may expect with soil compaction from grazing. Soil types in a field as well as soil moisture conditions when grazing the cover crops can be linked to what one may expect for soil compaction.
One method that can be used to determine soil compaction is by measuring soil bulk density, which is a reflection of soil porosity. Compacted soils have higher bulk densities, and less soil porosity, that restrict water infiltration and plant root growth. Soil texture also affects bulk density. More information on soil bulk density can be found in the NRCS publication, "Soil Quality Indicators: Bulk Density" or "Soil Bulk Density/Moisture/Aeration"
The preliminary results from the McNay Research farm show that cereal rye cover crop reduced bulk density and soil compaction, but bulk density increased after grazing the rye cover crop. Prior to grazing the rye cover crop and during grazing, the soil moisture content was at or above field capacity (40%). The increase in soil compaction after grazing the rye cover crop is not surprising, given the wet soil conditions of the poorly drained soils at the McNay Research Farm. These conditions are very conducive to soil compaction during grazing.
Looking at the bulk density results and the soil texture of the field (silt loam or silty clay loam), the bulk density results still fall in the range bulk densities considered as ideal for plant growth according to the NRCS's general relationships with soil texture and bulk densities, which would be less than 1.40 g/cm3.
Management tips for grazing cover crops
- Ways to manage soil compaction due to grazing cover crops include removing livestock if soil conditions are too wet or by utilizing rotational or strip grazing.
- With grazing cover crops or using them for forage, it is important to consider herbicide restrictions, and how that may or may not limit the ability to graze or use cover crops as a forage source.
This preliminary year has been a learning curve for all involved in this project. Funding will be sought to continue this project for the next three years to help learn more and provide research-based information to help producers make management decisions on grazing cover crops and the sustainability of this integrated crop-livestock system.
Special thanks to:
Dr. Dan Loy (Iowa Beef Center Director), Dr. Mahdi Al-Kaisi (ISU Extension Soil Scientist), Dr. David Kwaw-Mensah (Research Associate Soil Management/Environment), Joe Sellers (ISU Extension Beef Specialist), Beth Doran (ISU Extension Beef Specialist), Paul Kassel (ISU Extension Field Agronomist), and personnel at McNay and Allele Research Farms for their assistance on this project.