A comparison of row spacing, spray band pattern, and population density was compared using field corn grown in the second year of the living mulch (LM) system. Corn yields and clover re-establishment were greatest in narrow band and wide row treatments. Soil water content was less in LM compared to other cover crops, but nitrate leaching was lower in LM. Runoff, erosion, and nutrient loss was less in watersheds planted to (LM) compared to cereal rye. Interest in the project has been broad, including producers, other researchers, food industry groups, and politicians.
Objective 1: Identify the best row spacing, population density, and clover suppression combination for sweet corn production. Rationale for objective: The living mulch system for corn production provides obvious advantages to field corn production by suppressing weeds and providing biologically fixed nitrogen fertilizer. The savings are not only from reduced fertilizer and weed control cost, but we calculated labor inputs to be about half of that of conventionally grown corn. This provides clear advantages for larger-scaled sustainable conscious producers, but it does little for the limited resource farmers. Adapting the living mulch system for sweet corn production may be one way to extend the concept to the limited resource clientele.
Objective 2. Optimizing fall clover re-establishment within corn row spacing, strip-till band width, and population density variables. Rationale for objective: There is a delicate balance between competition by the corn and release of nitrogen by the clover. The major source of N in the living mulch system is from senescing clover leaves as the corn stem elongates and shades the clover. Narrow row spacing and higher population densities promote canopy conditions conducive to shading and are a principle of weed competition. It is unclear what the impact row spacing and population density will have on clover regeneration, hence the impetus for this objective. .
Objective 3. Obtain an approximation of how much N is transferred from white clover to corn in a living mulch system. Rationale for objective: We have one year of data where we have estimated the clover impact on N fertilization in corn. The experiment needs to be validated with additional years of data over multiple locations to demonstrate the robustness of the concept.
Objective 4. Determine the impact of the living mulch corn production system on water runoff and quality in an integrated crop/grazing system. Rationale for objective: The forage quality of corn stover is low and often insufficient for maintenance of gestating cows but could be improved in the presence of a highly digestible and high protein forage such as clover. Mulch crops are known to reduce water runoff and improve water quality in systems which livestock do not graze the crop residue but increases turbidity and coliform contamination when grazed. Having a mulch crop in the system may mitigate pollution potential by reducing runoff and turbidity of the water.
Objective 1: White clover was established as a pure stand in the fall of 2013. A 2 x 2 x 2 factorial of 30 or 36 inch row spacing, 8 or 16 inch herbicide band, and sweet corn (Seminis Obsession II, GENVT3P) population density of 18K or 24K plants per acre was planted with four replications on April 17, 2014. Atrazine and pendimethilin herbicides were applied at 1 lb ai per acre at corn emergence to control weeds within the banded dead clover rows. Plots were irrigated to prevent drought stress. No nitrogen fertilizer was applied. Corn was harvested from June 28 through July 10 and the number of ears, and ear length and width measured. Corn stover was removed and an applicaton of pendimethilin applied to prevent weeds and permit clover to re-establish in the plot areas. Clover re-establishment was monitored using a point fram quadrat to estimate basal cover.
Objective 2: White clover was established as a pure stand in the fall of 2013. A 2 x 2 x 2 factorial of 30 or 36 inch row spacing, 8 or 16 inch herbicide band, and field corn (DeKalb DKC64-69, GENVT3P) population density of 24K or 36K plants per acre was planted with 4 replications on April 17, 2014. Atrazine and pendimethilin herbicides were applied at 1 lb ai per acre at corn emergence to control weeds within the banded dead clover rows. Plots were irrigated to prevent drought stress. No nitrogen fertilizer was applied. Corn ears were removed from stalks at the black layer stage and shelled to obtain yield. Corn stover was removed after harvest and an application of pendimethilin applied to prevent weeds and permit clover to re-establish in the plot areas. Clover re-establishment was monitored using a point fram quadrat to estimate basal cover. Corn was re-established into the plots the following year.
Objective 3. Land was prepared by disking the soil twice, firmed and leveled with a cultipacker. ‘Wrens Abruzzi’ cereal rye (CR), ‘Dixie’ crimson clover (CC), and ‘Durana’ white clover (LM) were seeded by hand at rates of 90, 25, and 10 lbs seed/acre, respectively, on 17 October, 2014. Plots were cultipacked a second time to ensure good seed to soil contact. On 16 March and 8 April 2015, the CC and CR plots, respectively, were killed with a broadcast application of glyphosate and dicamba. The LM plots received a 8 inch banded herbicide application of the herbicides 36-inch rows 14 days prior to planting corn (DeKalb DKC64-69, GENVT3P). Corn was planted on 21 April, 2015 using a John Deere 7300 MaxEmerge no-till planter at a population density of 36,000/acre. All plots received a herbicide application of pendimethalin and atrazine at rates of 1 lb/A, at emergence. The CR, CC, and LM plots received 250 (50 at planting), 150, and 50 lbs/A N fertilizer, respectively at the sixth leaf stage.. Clover, corn, and soils were sampled weekly and analyzed for total N, and nitrate and ammonia in the soil, and plant available N calculated. The experiment was repeated in 2016.
Objective 4. Matched watersheds were planted to either LM or CR on October 20, 2014. On 1 April, 2015, 8-inch bands of glyphosate and dicamba were applied to kill the LM clover using a hooded sprayer on 36-inch rows. Glyphosate was broadcast applied to the CR watershed to terminate the cereal rye on 21 March, 2015. Corn (DeKalb DKC64-69, GENVT3P) was planted on 14 April, 2015, using a John Deere 7300 MaxEmerge no-till planter at 36,000 plants/A on both the P3 and P4 watersheds. Pendimethalin and atrazine were both applied one week later on both watersheds at 1.20 kg a.i. ha-1 and 1.12 kg a.i. ha-1, respectively. The CR watershed received a broadcast application of herbicide while the LM watershed received an application over the established bands of dead clover. Both watersheds were irrigated during the corn production period. Fiftly pound N/A was applied as liquid UAN at planting and 220 kg N ha-1 was applied at the V5 growth stage in the corn in the cereal rye cover crop. No supplemental N was applied in the living mulch. Both watersheds were harvested on 14 September, 2015. Immediately following harvest, each watershed was sub-divided into 4 equally sized paddocks and 6 pregnant heifers (900 lbs ea.) were used to graze and remove corn stover and residue in each watershed. The paddocks were grazed sequentially for 7 d each, giving each watershed 28 total days of grazing. Runoff from both watersheds was monitored for E. coli from September 2015 through February 2016. Water runoff collected using H-flumed from each watershed and subsamples were analyzed for suspended solids, toal N, total P, and E. coli. The P4 watershed was replanted with cereal ryegrass at the same rate as 2014 on 20 October, 2015 and the experiment repeated in 2016.
Objective 1: Treatments where the clover was sprayed in 16 inch bands gave the greatest number and largest ears of sweet corn irrespective of row width. The 18,000 plant/A population density gave the largest ears of corn, but they were fewer in number. However, summer weeds established into the plots, despite herbicide applications, and killed the clover. The experiment was repeated in the summer of 2015 with the same result. Therefore the LM system does not appear to be a viable production option for sweet corn in Georgia.
Objective 2. Clover continued to grow in between the banded herbicide treated areas until the corn provided approximately 40% light interception, at which time the clover mass steadily decreased until corn harvest. Clover recovery after corn harvest was inversely proportional to the amount of clover killed during the band-spray application of herbicides. Cover re-grew in all treatments where corn was planted to 36 inch rows in 2014, but only clover in the 36 inch row with the 8 inch herbicide band was able to fully regrow in 2015. Corn yields were least when corn was planted at lower population densities, but were not different among row spacing and herbicide band treatments in 2014. However, the 36-inch row spacing and 8 inch herbicide band gave greatest yields in 2015. Thus, we conclude that corn planted on 36 inch rows when the clover is sprayed in 8 inch bands is the most sustainable LM treatement of those tested.
Objective 3. Rainfall and temperatures were nearly normal in 2015, but 2016 was unusually hot and dry. Supplemental irrigation was able to meet evapotranspirative (ET) demand by the crop in 2015, but the ET exceeded rainfall and supplemental irrigation in 2016 despite twice weekly irrigation events. As a result, plant available N (PAN) was similar among cover crop treatments in 2015, but low rainfall and warmer tempertures of 2016 limited clover decomposition within the herbicide treated strips and the senesced clover leaves in between the corn rows. Corn yields were similar among the cover crop treatemnts in 2015 but lowest in the LM treatment in 2016 because of lower PAN. Subsurface water loss and N leaching in the LM treatment were lower than either the CR or CC treatments in both years.
Objective 4. Grazing cattle in the LM watershed utilized virtually all of the available clover and stubble available to them and those grazing the CR watershed consumed the corn residue and weeds. Cattle grazing the LM gained 1.2 lbs/day whil those grazing the CR watershed lost 0.65 lbs/day. The majority of water runoff from the two watershed occurred between October and March of each year. The LM watershed decreased water runoff compared to the CR watershed and it had fewer suspended solids. However, the solids present in the LM watershed were primarily organic and the nutrients of the organic solids and those of the mineral solids in the runoff from the CR watershed were not different from one another. Therefore the environmental benefit of the LM system is a reduction in water runoff and reduced suspended solids (especially the mineral fraction) but not due to nutrient runoff. Feces from cattle grazing the CR system were dry and depositied as dung piles on the soil surface. Feces from cattle the LM system had high water content and, consequently, spread across soil surface. This led to greater E. coli bacterial counts in the runoff from the LM watershed.
Field days, county meetings, webinar, and on-farm demonstrations were conducted throughout the project duration to transfer technology from the research project to end users. Student field trips were conducted annually as part of the Crop Science course taught at the University of Georgia, which was complemented with in-class discussions on background reasoning as to why the project is important, theory on cohabitation of corn and clover, data sharing and discussion.
One research article has been published by Agronomy Journal on the row spacing/herbicide banding objective, a second on ground water loss and nutrient leaching has been accepted by the Journal of Environmental Quality, and a third manuscript on the nitrogen dynamics between soil and crop has been submitted to the Agronomy Journal.
Educational & Outreach Activities
Each summer we host the annual J. Phil Campbell Research and Education Center corn boil. This is an event in which farmers, scientists, University administrators, are fed a meal consisting of sweet corn produced from the farm. A tour is hosted for participants to gain first-hand knowledge of the research programs conducted at J. Phil Campbell. Attendance ranges between 200 and 300 participants yearly, of which about 1/3 are farmers, 1/3 University scientists, administrators, staff and politicians, and about 1/3 are local residents who are interested in research projects at the Center.
A 35-Acre demonstration plot was planted in Lee County during the fall 2016 (corn crop in summer of 2017) with a field day for South Georgia farmers to see how the technology works. Twenty-two farmers attended the field day.
A field day was hosted at the North Georgia Research Farm (Floyd County) in the summer of 2015 to demonstrate how minor changes in agronomic practices have impacts on clover survival. Approximately 30 farmers attended.
The American Society of Agronomy highlighted our living mulch research and disseminated the story to over 30 news outlets (see at: https://www.soils.org/discover-soils/story/living-mulch-builds-profits-soil)
A webinar has been posted on the internet demonstrating the living mulch concept. (see at: https://www.youtube.com/watch?v=wyQWPGMJm7A)
While there are still specific practices that need to be perfected for the LM system, farmers are almost universal in orating the need for this research, how the system makes sense from a production/economic/environmental standpoint.
The J. Phil Campbell Sustainable Agricultural Research Center hosted a UGA “Corn Boil” on June 29, 2015. Fresh sweet corn was grown using the living mulch system for the corn boil meal, which consisted of hot dogs, homemade baked beans, chips, and drinks. Local industry leaders, farmers, grocers, Chamber of Commerce, State and Local politicians, and UGA faculty and administrators, were invited to attend. Over 100 guests attended the event. The system by which the sweet corn was produced was described at the field day.
The J. Phil Campbell Sustainable Agriculture Research Center hosted 3 field days over the course of the growing season. The field days had stops at the LM plots, cover crop plots, and organic agriculture plots. A total of 218 producers attended the field days. Questionnaires were distributed to growers and requested feedback for each stop at the field day. The LM plots consistently received the highest ratings of all stops on the tours.
Josh Andrews, a graduate student working on the living mulch project, presented his research data to over 50 research and extension scientists at the 2016 Southern Agricultural Workers annual conference held on Feb 6-8, in Atlanta. He received Third Place among all graduate student oral presentations at the meetings.
A factorial of two row spacings (30 and 36 inch), two herbicide banding widths (8 and 16 inches), and two population densities (24 and 36K plants/A) were tested in the second year of the living mulch system. Clover was the sole source of N for the corn in this study. Clover regrowth in narrow rows and wide bands was slow in winter and corn yields were less (5.54-8.62 MT/ha) than in wide rows with narrow bands (11.09 MT/ha). Thus, it is imperative to use wide row spacing and narrow spray band patterns for the living mulch system.
Three cover crop systems (cereal rye, crimson clover, and white clover living mulch) were established in the fall of 2014. Corn was planted into each in spring of 2015. The cereal rye plots received a full complement of 250 kg/ha N, the crimson clover 100 kg/ha N, and the living mulch plots no N fertilizer. Mulch residue, living mulch clover, and corn were sampled weekly to determine N supply and uptake within each plot during the summer of 2015. Soil moisture was measured within and between rows and water use calculated for corn within each production system. Between row soil moisture was less in LM plots than other plots until 45 DAP, after which there were not differences. Corn height was less in the living mulch plots until tasseling but were not different thereafter. Shading of white clover occurred at 45 DAP at which time white clover responded be senescing leaves. As a result, N uptake was lower in LM until 60 DAP but was similar thereafter. Corn yield (11.34 MT/ha) and water use efficiency (35 kg/ha/mm water) were not different among treatments.
Matched watersheds were planted to one of two cover crops: cereal rye or LM. H-flumes were instrumented with Teledyne sonic flow meters and ISCO Avalanche water samplers. Volume, sediments, and nutrients were measured in water runoff over the course of the 2015 growing season and compared to historical data from each. Historically the watershed planted to LM had 25% more runoff than the watershed planted to cereal rye. However, the difference between the two watersheds in 2015 was 5%. Thus, LM reduced water runoff. The watershed panted to LM historically had twice as much sediment in runoff than the watershed planted to cereal rye. Both cover crops reduced sediment in runoff by 90%+ compared to historical losses. However the LM watershed had 75% less sediment than the cereal rye watershed, and sediment losses in the LM watershed were 99.9% less than historical values. Nutrient losses from runoff were similar regardless of cover crop, primarily because sediment in the LM was nutrient rich organic matter.