Perennial Turfgrass Cover Crops in Maize Production Systems
Cost and time are the primary barriers preventing farmers from adopting cover crops in Iowa. Despite winter rye being able to reduce nitrate loss by nearly 50 percent, the cover crop is sometimes correlated with a yield loss in the following corn crop when terminated too close to the time of corn planting. However, terminating winter rye early to avoid yield loss in corn limits how much nitrate the cover crop can sequester. These challenges reduce the benefits and cost-effectiveness of cover crops.
Perennial grasses utilized as living ground cover could potentially overcome barriers experienced with annual cover crops. Ideally, a perennial cover crop would grow actively during the autumn and spring but become inactive during the summer when corn and soybeans experience the most growth, reducing competition with the main crop. Active growth of perennial grasses in autumn would increase nutrient accumulation that otherwise would have been lost through leaching or runoff. Previous research with cool-season grasses indicate that a Kentucky bluegrass cover crop grown concurrently with conventionally managed corn can produce comparable yields to a control with no cover crop. Current research corroborates these findings and suggests that Sandberg bluegrass cover crops can perform similarly.
In addition to their advantages over annual cover crops, perennial grass cover crops can restore valuable ecosystem services such as increased water infiltration, reduced soil erosion and decreased nitrogen and phosphorus losses to the environment. Researchers propose to evaluate the economic and environmental impacts of these relatively new perennial cover crop systems. The team will use suitable cool-season grass candidates identified through current research efforts, with a focus on investigating their above and below-ground nutrient dynamics and ability to reduce nonpoint nutrient pollution.
Three replications of 15 selected varieties of Kentucky bluegrass and Sandberg bluegrass will be planted into field plots along with a no-grass control at the Sorenson Farm near Ames, Iowa. Following successful establishment of grass plots, corn will be planted into tilled strips of grass at conventional rates and spacing. Growth of both grass and corn will be measured biweekly, with corn yield collected at the end of the field season. Soil testing and leaf tissue sample analyses for N and P concentrations will be conducted on a biweekly basis and data analyzed. At the end of the project, findings will be shared in an extension publication and at relevant conferences.
Data on the percentage cover of the groundcover crops as well as maize plant height were taken monthly on a total of 12 treatments/cultivars with four replications.
Five cultivars/treatments, i.e. Mercury, Granite, Jackrabbit, Award/Bluecoat, Poa bulbosa and the control (no groundcover) were chosen for soil analysis to monitor nutrient cycling. A sample was obtained by combining four randomized cores taken within each treatment when maize plants were at V6, R1, post-grain filling and post-harvest stages. Each treatment was broken down into two subsections, in-row and under living mulch, and each core was separated into three different depths. Analyses of ammonium and nitrate content in soil samples are currently being conducted. Damages to the research field due to derecho in 2020 were observed. Data on maize grain yield and lodging due to derecho were collected and are being analyzed.
Outreach this period included 6 presentations, which took place at a field day in September 2020, a workshop in conjunction with the annual international Tri-Societies meeting, and poster and oral presentations at the annual meeting of the Crop Science Society of America．
On April 7, 2020, base fertilizers (80lb P and 100lb K and 150lb N) was applied. On April 20, 2020, grass-free strips were created by tilling into each plot of grass and maize planting was done on April 22, 2020 with the hybrid DeKalb DB57-75RIB at approximately 34,000 seeds/acre. Herbicides of Prowl H2O and 2, 4-D was applied on the same day. On June 2, 2020 glyphosate was applied to the maize rows with a hooded sprayer to avoid damages to the perennial groundcovers.
The cultivars/treatments chosen for soil analysis to monitor nutrient cycling were Mercury, Granite, Jackrabbit, Award/Bluecoat, Poa bulbosa and the control group (no living mulch). These cultivars were chosen based upon their quality of stand and overall health using color as an indicator. Data was obtained on baseline nutrient concentrations for the research site at the 0-15 cm and 15-30 cm depths. For each treatment, a sample was obtained by combining four randomized cores taken within each treatment. Each treatment was broken down into two subsections, in-row and under living mulch and four randomized samples were taken from each subsection when maize plants were at V6 stage in mid-June. Each core was separated into three different depths to allow monitoring of nutrient cycling within the different root zones, i.e. those dominated by mainly turfgrass roots (0-15 cm), the shared zone (15-30 cm) and those dominated mainly by maize roots (30-45 cm). Soil sampling will again be done when maize plants are at R1 and post-harvest to track plant available nitrate, ammonium and phosphorous. Nutrient analysis will be conducted in lab and will be compared among treatment as well as with results from the baseline nutrient analyses.
Meanwhile, data on growth and development of maize plant and perennial groundcover including maize staging, plant height, percentage of perennial groundcover were taken monthly during the growing season. In the next growing season we plan to implement plant root simulators and lysimeters in addition to standard soil sampling to provide a better idea of available nutrients and losses to leaching through the soil profile in plots with perennial groundcover vs. the no-groundcover control.
Starting May 2020, a recent ISU soil science major graduate joined Dr. Fei’s group and and will focus his master’s research on this INRC-funded project.
This project aims to investigate the above- and below-ground nutrient dynamics and the potential of using perennial ground cover (PGC) to reduce nonpoint nitrogen and phosphorus pollution. Two cool-season perennial grass species, Kentucky bluegrass (Poa pratensis) and bulbous bluegrass (Poa bulbosa), a species with a distinct and extended summer dormancy, are grown as PGC in otherwise conventionally grown corn.
A field trial was established at the Sorenson Research Farm near Boone, Sept. 7, 2019. The experiment consists of 12 treatments with four replications. Each treatment is either a single cultivar of Kentucky bluegrass or bulbous bluegrass (PB 55), or a 2-cultivar Kentucky bluegrass blend. The control is non-grass plot with bare soil. The selected Kentucky bluegrass cultivars represent the diversity present in available commercial cultivars. Seeding rate for Kentucky bluegrass was approximately 2 lbs. per 1000 square feet while the seeding rate for bulbous bluegrass was 14 lbs. per 1000 square feet. Plots are 20 feet by 22.5 feet.
Preliminary observation indicated that uniform germination has taken place for all treatments except for the plots seeded to two Kentucky bluegrass cultivars (Geronimo and Blue Ghost), which had poor stand establishment and late germination. Soil samples used to establish baseline nutrient concentrations were collected shortly after grass seeding. For each replication, three sets of soil cores were taken at the 0-15 cm and 15-30 cm depth. The cores from each depth were combined and sent to AgSource Laboratories in Ellsworth, Iowa, for analysis.
Outreach this period included 2 presentations.