Innovative Nutrient Management Options for Sustainable Pasture Land Intensification

Progress report for LS19-317

Project Type: Research and Education
Funds awarded in 2019: $296,352.00
Projected End Date: 03/31/2023
Grant Recipient: University of Arkansas
Region: Southern
State: Arkansas
Principal Investigator:
Michael Popp
University of Arkansas
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Project Information


Cow-calf and stocker cattle operations often face a shortage of grazable forage on pastures during summer, early fall and winter. To provide access to high quality, grazable, and sustainable forage, we plan to study the feasibility of an integrated system using sub-surface poultry litter application on pasture in tandem with planting a mix of summer annuals and legumes to increase both the efficiency and level of nutrient application. This will enhance both forage quality and quantity for grazing. In addition to spring-planted annuals we also wish to investigate the potential for fall planting winter annuals for winter and early spring grazing. Those plantings will also benefit from the spring litter application given the slow release nature of nutrients with litter. In comparison to conventional perennial pasture forage species, our least intensive system, these annuals are expected in increase nutrient uptake from the soil and thereby extend the grazing season, while keeping nutrients below the soil surface. With litter applied sub-surface, we can expect to avoid nutrient runoff, increase water infiltration and soil water-holding capacity given greater root growth and eventual increase in soil organic matter.

Experiments will be conducted at research centers and four cooperating farms where crops are selected based on landscape suitability. Variation in crop mix options and animal type will allow comparison of profitability and income risk. To assist with this task, a cattle decision support system exists that can: 1. model forage growth and cattle her nutrition needs on a monthly basis; 2. calculate greenhouse gas emissions of varying production practices; and 3. perform what-if analyses concerning key economic and environmental performance indicators. However, it is currently not equipped to analyze detailed fertilizer application and annual sod seeding practices.

Therefore, we will evaluate innovative agro-grasslands management approaches by: 1. examining profitability and risks of added forage production using organic litter to extend the grazing season which is expected to lower hay feeding and attendant fuel use; 2. determining the feasibility of using innovative equipment to incorporate both litter and planting crops in a single equipment pass to allow greater use of nutrient rich manures on pastures; 3. matching crop needs to spatially variable landscape attributes to sustainably manage yield potential, soil moisture, and net GHG emissions while increasing beef output that can be marketed as grass-fed and/organic; 4. comparing forage soybean and cowpea sown in conjunction with brown mid-rib sorghum-sudan grass and a ryegrass/cereal rye/wheat and legume mix as winter annuals for livestock grazing (cows, stocker cattle and sheep); and 5. calibrating and modifying the existing cattle DSS tool with producer input to enhance user-friendliness.

Adoption of more annuals and custom, sub-surface applied litter could impact many producers of all operation sizes throughout agro-grasslands in the Southern humid region of the U.S. where approximately one third of all agricultural land is dedicated to pasture and hay. Outreach activities will share successes, pitfalls, and bottlenecks observed across varying degrees of pasture use intensity proposed in this holistic research system.

Project Objectives:
  • To determine the impact of summer annuals on grazing days and animal weight gain in bermudagrass-dominated systems.
  • Assess forage production potential of different summer annuals and winter annuals under sod-seeded conditions without grazing.
  • Measure changes in soil health across holistic pasture management systems varying in grazing intensity and soil fertility amendment practices under both research and farm conditions.
  • Conduct producer field trials to assess field performance of sub-surface poultry litter application equipment that is modified to plant at the same time.
  • Calibrate and modify existing decision support software to provide greater planning support for cattle operations using producer feedback about needed modifications to improve user-friendliness.


Materials and methods:

In 2020 forage and pasture trials met with significant weather issues as well as changes in site location as discussed below in the research and results discussion. We are excited to report that cattle facilities were refurbished (in fall of 2020) after the tornado had rendered the facilities inoperable for 2020.  Unfortunately that meant no cattle trials for 2020. Producer fields near Farmington, AR were treated with sub-surface applied litter as per attached media Spring Litter Subsurface near Farmington and planted to BMR sorghum sudangrass (SS), cowpeas (CP), and forage soybean (FS) on May 6, 2020. With unanticipated strong competition from cool season grasses followed by a 2 month period of warmer than usual weather without rainfall, pasture efforts at both fields on that site did not lead to observations of grazing success as the summer annuals did not establish as expected. Similarly, planting and sub-surface litter application occurred at the West Fork location on May 8, 2020. With early competition from cool season grasses followed by lesser than expected precipitation, the field was left to rest until August after an initial grazing of cool season grasses lessened competition for SS to emerge and thrive.  At the West Fork location 3 fall grazings of SS were considered a success for extending fall season grazing with summer annuals. The Alma, AR location had unfavorable weather conditions leading to planting delays and poultry litter that was delivered to the field's side, even though tarpped to avoid introduction of moisture from the soil and from rainfall (bottom and top of pile), turned out to be too moist for use in the sub-surface litter applicator.  As such, SS was planted by the producer in conjunction with commercial fertilizer so the producer could graze the field.  The Alma, AR location had a successful grazing season throughout the summer with cattle gaining at 3-4 lbs per d. 

Figure 1. Fall Applied litter into stubble form left over summer annuals in conjunction with broadcasted winter wheat planting.

Part of the Alma location was then treated with sub-surface poultry litter after SS residue was disked and winter wheat seed had been broadcasted on Oct. 8, 2020. 

Producer fields were soil sampled in February (5, 6 and 21) of 2020 but with COVID, results of these analyses were not available prior to litter application.  We applied litter at ~3.5 tons/acre to ensure sufficient nutrient availability on fields for both 2020 and 2021 given 2-yr N-P-K availability from litter applications and expensive transport of sub-surface litter application equipment.  Forage trials were planted at the USDA ARS Booneville site not until mid-June given wet weather conditions.  Sod-seeded plantings into bermudagrass failed as a result of too much competition and hence forage trials for 2020 were abandoned. Soil sampling was again conducted in early March (5, 6) of 2021. At the time of sampling, the field at Alma showed a much better winter wheat stand where poultry litter had been applied below the surface in the fall. Results for these soil sampling dates are not available at the time of this writing.  Soils were again sampled on March (2,4) in 2022 with results for all samplings not available at this time.

For the 2021 production season at the USDA ARS Booneville site both pasture and forage trials were conducted successfully.  The grazing study evaluated three different options for summer forages, a warm season perennial pasture typical of most Arkansas pastures (bermudagrass, crabgrass, broomsedge, and some warm season annuals such as foxtails) , sorghum-sudangrass only, and a sorghum-sudangrass plus cowpea mixture (“mixtures” were created with alternating drill passes of sorghum-sudangrass and cowpeas) (Figure 2).

Perennial Warm Season Pasture
Perennial warm season pasture
Sorghum Sudan Grass Only
Sorghum Sudan Grass Only
SS & Cowpea
Figure 2. Sorghum Sudan Grass & Cow Pea Mixture

The cool, wet spring in 2021 resulted in a late start to grazing the warm season perennial pasture (June 10) and a late planting for the warm season annuals (June 16-17). Grazing started on annual species on July 15. Eight stocker steers weighing an average of 680 lb at the beginning of the study, were assigned to each 4.5-acre pasture. Cattle were rotated approximately every 10 days on 4 paddocks resulting in a 30-d rest period.

Research results and discussion:

Farmer participants were updated of progress to date in on Feb. 10, 2020 at a in-person meeting at the USDA ARS Dale Bumpers Small Farms Research Center.  Fields for on-farm research were identified and soil-sampled subsequent to that meeting and sources of poultry litter for application were identified.

Forage trials were conducted as planned for 2019.  However, planting was delayed given frequent substantial rainfall events during the planting season such that poultry litter application would have lead to extensive field rutting.  Planting was delayed to May 28, 2019 in Booneville, AR and was not completed until June 21 at Fayetteville, AR.  At the Booneville location, we experienced difficulties with establishing cowpea (CP) and forage soybean (FS) given herbicide residual from prior year's applications.  At Fayetteville, residual herbicide action affected Sorghum sudangrass (SS) and significant competition from bermudagrass lead to abandonment of trials at Fayetteville.  At Booneville we did get stands of sorghum sudangrass but had only limited success with the legumes.  Forage data was therefore not collected at either site given delayed planting and unanticipated residual herbicide damage.  However, cows were allowed to graze out nearly mature stands of SS and completely removed the forage in 2 d indicating that forage produced is palatable and preferred to bermudagrass. To suppress weeds, repeated glyphosate applications were made at Booneville on April 12 and May 20.  The second application suppressed weeds and also set back bermudagrass. Given the lack of aggressive forage growth of CP and FS with the residual from prior year's Grazon, the suppression of bermudagrass led to significant weed growth in the absence of CP and FS.  Hence, a practice of repeated glyphosate applications will not be practiced in the future. Further, from observations in 2019, given differences in plant height, some shading effects for alternate row planting of SS with CP and/or FS may be an issue that will be observable for plantings to be conducted in 2020.

Pasture trials intended for 2019 met with significant problems.  Administrative actions, unknown to the investigators at the time of proposal submission, led to a severance of research ties with the University of Arkansas Monticello research station where pasture trials were to be conducted.  Our backup plan was the Savoy research station facilities near the University of Arkansas at Fayetteville.  Those plans failed upon realization that poultry litter use was not acceptable at Savoy given that research station's long term focus on solely using swine manure.  As a result, pasture trials were canceled for 2019.  SARE administration was notified using verbal communication.  Inevitable delays for pasture trials will be addressed by applying for a no-cost extension of one year's duration to allow for conducting pasture research trials at the Booneville facilities that were refurbished for this purpose this past year.  At the time of this writing cattle have been secured for 2020 pasture trials, with pasture paddocks newly fenced, new shade structures and a complete overhaul of handling facilities, alley ways and road access and watering sites.  A tornado in 2020 impacted the pasture trials as described above.

Given the relocation of pasture trials to Booneville, and the failure of forage trials in 2019 given unfavorable weather conditions as well as herbicide residual difficulties (2019 Forage and Pasture Update), the research team decided to conduct pasture trials and forage trials at Booneville for 2020-2022 and dropping the Fayetteville forage trial site to conduct more extensive and frequent sampling at the Booneville site that will now coincide with the pasture trials given change in site from Monticello or Savoy. As discussed above forage trials in 2020 were a failure with delayed planting and excessive competition from bermudagrass. Forage trials for 2021 and 2022 will now match the pasture trials in location and years. 

On-farm research with collaborating farmer producers is not impacted by changes in experimental research as on-farm trials were originally targeted to commence by 2020. On-farm trials met with both successes and failures as described above.  Work for 2021 farm trials is under way.  Producer interest is strong despite setbacks suffered in 2020.

Finally, modifications to the decision support software (DSS) tool have begun.  FORCAP is a uniquely comprehensive spreadsheet-based DSS that has been available since 2012 on-line at  As currently available, the tool allows users to analyze the impact of changing fertilizer amounts and forage species composition on hay and pasture ground, given a host of cow-calf management practices.  However, individual pasture paddock or hay field management practices are not possible. Only overall farm changes are possible.  As such, we have commenced to modify FORCAP by guiding the user through step-by-step decisions to allow for user specification of grazing access, forage species selection, planting, fertilizer, etc. management decisions on individual pastures and hay fields while reducing some of the options related to livestock management currently available.  The approach was presented to producers at our February meeting and met with approval.  We expect to have a prototype of this revamped tool ready for producer feedback in the coming year.  By late summer of 2020 efforts to continue to modify FORCAP were placed on hold as modifications to the tool were too significant and forage as well as cattle performance information to date were not available.  In it's place we began work on a spreadsheet-based decision aid to compare sub-surface litter application to commercial fertilizer and/or broadcast litter.  A draft (not for public consumption at this time) has been sent to Candace Pollock-Moore, SSARE, via e-mail. 

A manuscript was submitted to the Journal of Applied Farm Economics which is currently under second review.  That manuscript details how the Litter-Soil Calculator, decision support software comparing the relative profitability of broadcasting or sub-surfaced litter to commercial fertilizer under a variety of farm size and equipment specifications, can be used.  The plan is to post the decision aid along with FORCAP and other decision aids for eventual access by producers. 

Grazing started on annual species on July 15, 2021. Eight stocker steers weighing an average of 680 lb at the beginning of the study, were assigned to each 4.5-acre pasture. Cattle were rotated approximately every 10 days on 4 paddocks resulting in a 30-d rest period. Grazing ended early on all treatments because of drought in early fall. Grazing on perennial warm season pastures and two sorghum-sudangrass plus cowpea pastures ended on September 9 (Figure 4). Sorghum-sudangrass pastures were grazed until September 21 because of forage mass accumulation that occurred prior to drought (Figure 4).  Therefore, the grazing sessions for each treatment averaged 91 days for the perennial warm season, 68 days for sorghum-sudangrass only, and 60 days for sorghum-sudangrass plus cowpea. Averaged over the entire grazing season, ADG was 1.7 lb/d in the perennial warm season treatment, 2.1lb/d in the sorghum-sudangrass treatment, and 2.3 lb/d in the sorghum-sudangrass plus cowpea treatment. Gain per acre was 277, 256, and 243 lb/acre for the perennial warm season pasture, sorghum-sudangrass only, and sorghum-sudangrass plus cowpea treatments, respectively. Late planting resulted in short grazing seasons for the annual systems. Though ADG was superior in the annual systems, the greater grazing days in the perennial warm season pasture resulted in greater gain per acre in 2021. 

Later Graze Out
Sorghum Sudan Grass had more growth for later graze out
Early Graze Out on Perennial Pasture
Figure 4. Perennial and mixed pasture plots grazed out sooner than ...

The small-plot forage trials evaluated production of monocultures sorghum-sudangrass and cowpeas, and a mixture of sorghum-sudangrass and cowpeas planted in the same row, with poultry litter applied via broadcast, injected below the soil surface, or no litter application. Subsurface application was completed with a mechanized applicator that forms a trench and deposits litter in the trench, the trench is then covered with soil. The bands are 5 cm wide and 7.6 cm deep, configured with 38 cm band spacings. In subsurface plots, the drill was set to plant between the litter bands to prevent any burn from the litter that could hinder germination or seedling growth (Figure 5). Broadcast applied litter was applied by hand. The litter rate was 6.7 t/ha. All species were planted in 38 cm rows, seeding rates were 22.4 kg/ha for sorghum-sudangrass alone, 56.0 kg/ha for cowpeas alone, and for the sorghum-sudangrass and cow pea mixture, seeding rates for both were 22.4 kg/ha mixed in the same box. Plots were planted and fertilized on June 24, the first harvest occurred on August 4, and the second harvest on September 22.

Seed Placement
Figure 5. Litter bands and planting rows

The averages of first year of results show that subsurface application produced the highest yields for all species and mixtures, followed by surface applied litter (Table 1). Across all treatments, sorghum-sudangrass monocultures had the highest yields of 1505 kg/ha, compared to sorghum-sudangrass and cowpeas mixtures at 1115 kg/ha, and lastly cowpea plots averaged 210 kg ha. All yields, including the sorghum-sudangrass monocultures were low. This is because of the late planting date of June 24 and drought that occurred in late August through September. This project will be repeated next year, but no additional litter will be applied. In this way, we can evaluate if injected litter results in greater yields in the second year compared to surface applied litter.

Table 1. Yields for sorghum-sudangrass, cowpeas, and mixtures of sorghum-sudangrass and cowpeas at USDA-ARS DBSFRC in Booneville, AR in 2021.

Application Method


































*SS=sorghum-sudangrass, CP=cowpea, SSCP=sorghum-sudangrass and cowpea










Participation Summary
4 Farmers participating in research

Educational & Outreach Activities

1 Consultations

Participation Summary:

Education/outreach description:

We did have a farmer collaborator meeting to present activities to date and coordinate on-farm trials slated for 2020 and 2021. During that meeting we decided to curtail poultry litter application to a single application in the first year to serve nutrient needs for both years.  This will allow cost savings and is possible given the slow release nature of poultry litter nutrients and greater flexibility for summer annuals plantings.  Specific fields on collaborator farms were identified and soil sampled to assist with planting and ruminant stocking rate recommendations for 2020.  

In March of 2022 we video taped producer collaborators to share their experiences.  We plan to work on these videos to develop materials for extending findings once the summer research trials in Booneville are complete near the end of 2022.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.