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.
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
The field trial established in 2019 investigating the suitability of additional Kentucky bluegrass (KBG) (Poa pratensis) cultivars and bulbous bluegrass PGC for maize production is now in its 4th year. In the fall of 2022, we added three entries, two cultivars of rough bluegrass (Poa trivialis) and one blend of Poa secunda (cultivars of Vale and Havana). The experiment now include 10 Kentucky bluegrass cultivars or cultivar blends and one cultivar of Radix hybrid bulbosa (PB55), in addition to the three new entries. All are grown as perennial groundcover with maize that are otherwise managed in conventional manner. Pioneer 1185 corn was planted on May 3, 2023. We plan to collect growth and development data of both the perennial groundcover and the corn plants.
Other Activities - 1 Field day
The field trial established in 2019 investigating the suitability of additional Kentucky bluegrass (KBG) (Poa pratensis) cultivars and bulbous bluegrass PGC for maize production is in its 3rd year. The experiment consists a total of 12 treatments/cultivars with four replications. Ten Kentucky bluegrass cultivars or cultivar blends and one cultivar of bulbous bluegrass (Poa bulbosa) are grown as perennial groundcover in otherwise conventionally grown corn. Data collected from 2022 were analyzed. Maize plant height in both July and August for the control and Poa bulbosa were not significantly different from one another. The no-PGC control had the highest gravimetric water content (GWC) during V6, but not significantly different from most other treatments at R1, all treatments had significantly higher access to moisture compared to previous years due to high amount of precipitation in the spring. The control and ‘Award/Bluecoat’ KBG had the highest levels of N availability during V6, although likely not practically significant due to the overall low levels as a result of excess soil moisture in the spring. Maize grain yields showed no statistical differences between treatments, although the no-PGC control yielded more than the Poa bulbosa treatment, which yielded more than the KBG treatments. The soil orthophosphate (H2PO4) concentrations data for 2022 is still being analyzed by a third party and data should be available by January, 2023.
Bartel, C.A., Moore, K.J., Fei, S.Z., Lenssen, A.W., Hintz, R.L. and Kling, S.M., 2022. Evaluating Strip and No-Till Maintenance of Perennial Groundcovers for Annual Grain Production. Crops, 2(3), pp.268-286. 2. Bartel, C.A., Moore, K.J., Fei, S.Z., Lenssen, A.W., Hintz, R.L. and Kling, S.M., 2022. Evaluating Chemical Suppression Treatments to Alter the Red: Far-Red Ratio in Perennial Groundcovers for Maize Production. Agronomy, 12(8), p.1854.
Proposal submitted (related to INRC work)
Understanding Summer Dormancy in Poa: A Physiological and Molecular Approach. USDA AFRI $649,986. PI: Fei, CoPI Moore 2. AI-Driven Climate Smart Agricultural Research and Demonstration Farm (AI-AgARENA), USDA AFRI CoPI: Fei
Data collected from 2021 were analyzed. Maize plant height in both July and August for the control and Poa bulbosa were not significantly different from one another, with the P. bulbosa being marginally taller, and on average 25% taller than all Kentucky bluegrass treatments, which were not significantly different from one another.
Grain Yield for the control and P. bulbosa were not significantly different from one another, with the P. bulbosa marginally out-yielding the control, yielding 159 bu/acre and 161 bu/acre respectively. All KBG treatments were not significantly different from one another, with an average grain yield of 92 bu/acre, a yield penalty of approximately 42%. In addition to the impact of PGC on maize yield, the above- and below-ground nutrient dynamics were also studied to quantify the impact of PGC in reducing nonpoint nitrogen and phosphorus pollution.
Gravimetric water content (GWC): When compared to the 2020 data, the GWC in 2021 was much more uniform with little variability between treatments, likely due to the extreme drought conditions. The common trend between 2020 and 2021 is that the control and P. bulbosa plots had higher GWC than all KBG plots, with the exception of R1 sampling which occurred mid-drought, so all treatments had essentially no free water.
Soil Nitrate: Similar to 2020, the highest degree of variability was observed at V6 sampling, with the control having the highest levels in both years. At V6, the control contained 59 mg/kg, while the PGC treatments ranged from 35-51 mg/kg. By post grain-filling (PGF) sampling all treatments had regressed to non-significant differences.
Soil Ammonium: The ammonium trends were similar to the nitrate, with high degrees of variability at V6 sampling regressing to non-significance by PGF. Interestingly, the control had the second lowest level of ammonium at V6 sampling at 7mg/kg, with only the Award/Bluecoat KBG mix having marginally lower concentrations. The Granite KBG and P. bulbosa had the highest concentrations, both around 18 mg/kg.
Soil Orthophosphate: Similar to 2020, the H2PO4 concentrations were higher under PGC than in corn rows. However, there was a high level of variability within treatment and samplings, leading to no strong observable trends.
Other activities during this project period included hosting a group of visitors from the Royal Barenbrug Company, Netherlands.
The field trial established in 2019 investigating the suitability of additional Kentucky bluegrass (Poa pratensis) cultivars and bulbous bluegrass perennial groundcover (PGC) for maize production is in its second year. The experiment consists of a total of 12 treatments/cultivars with four replications. Ten Kentucky bluegrass cultivars or cultivar blends and one cultivar of bulbous bluegrass (Poa bulbosa) are grown as perennial groundcover in otherwise conventionally grown corn.
Maize grain yields for the year of 2021 were analyzed and plots grown with bulbous bluegrass, even unsuppressed, is not statistically different from that of the control whereas Kentucky bluegrass greatly reduced grain yield. Besides the impact of PGC on maize yield, researchers also studied the above- and below-ground nutrient dynamics with the aim of quantifying the impact of PGC in reducing nonpoint nitrogen and phosphorus pollution. Gravimetric water content is significantly higher in soils from 0-15 cm where either bulbous bluegrass or no grass was grown when compared to Kentucky bluegrass during peak maize growth period in V6 and R1. Starting from R1, all PGC plots had significantly reduced nitrate in soils from 0-15 cm deep when compared to the no-grass control.
So far, bulbous bluegrass appears to provide the most nitrate leaching mitigation while providing the most competitive yields of all the PGC treatments.
Other activities included two presentations.
The field trial was established in 2019. The experiment consists a total of 12 treatments/cultivars with four replications. Maize grain yields for the year of 2020 were analyzed and plots grown with Poa bulbosa performed similarly to the no-grass control. During the project’s first year, only plots grown with P. bulbosa produced similar yields to the no-grass control.
Researchers analyzed gravimetric water content (GWC), NO3-, NH4+, and PO43 both in the maize row (IR) and under the living mulch (LM). Soil samples were collected from 0-15cm, 15-30cm, and 30-45cm in both IR and LM and analyzed separately within each depth.
GWC decreased across all treatments when moving from IR to LM. The smallest differential occurred in the no-grass control, which is likely due to there being no groundcover. At 0-15cm and 15-30cm depths, GWC was significantly higher in the no-grass control compared to all other treatments. Additionally, at these depths, GWC in plots with P. bulbosa were significantly higher than other KBG treatments, which were not different from each other. At the 30-45cm depth, GWC was significantly higher in the no-grass control than all other treatments.
NO3- generally decreased when moving from IR to LM with exception of Jackrabbit KBG and the Award+Bluecoat KBG mix. At 0-15cm and 15-30cm depths, the no-grass control and Mercury KBG performed similarly, having significantly higher NO3- concentration than all other treatments. At the 30-45cm depth, NO3- in the no-grass control was higher than all other treatments. NH4+ also decreased when moving from IR to LM, however, the magnitude that treatments decreased by differs drastically. At the 0-15cm and 15-30cm depths, the no-grass control has significantly higher NH4+ than all other treatments. Granite KBG had an outlier which draws its average higher. At the 30-45cm depth, no differences in NH4+ concentration were found.
PO43- increased when moving from IR to LM (Fig. 8). At the 0-15cm depth, plots with P. bulbosa had significantly lower PO43- than all other treatments except Jackrabbit KBG. All KBG were similar to one another. At the 15-30cm depth, PO43- concentration in the no-grass control was higher than Jackrabbit KBG and P. bulbosa but was lower than Mercury KBG. PO43- concentration in P. bulbosa was significantly lower than Mercury KBG, Granite KBG, and the no-grass control. At the 30-45cm depth, PO43- concentration in the no-grass control was only significantly higher than Jackrabbit KBG.
Other activities included two field days and two presentations, and a number of upcoming events and presentations are planned.
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.