Perennial Turfgrass Cover Crops in Maize Production Systems

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

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 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.  

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.