Grazing Management Practices to Enhance Soil Health in the Northern Great Plains

A three-year ICLS project was initiated during the spring of 2020. NDSU Extension partnered with producers to establish six demonstration sites located in central North Dakota, along with a host site on the main campus of NDSU. An annual forage crop was subjected to two grazing density treatments: 1) moderate and 2) high. Additionally, two forage utilization rates were evaluated: 1) 50% and 2) 75%. A non-grazed treatment served as the control. Treatments will be imposed for two years, followed by a cash crop.

Each location was developed to test grazing density treatments in a split-plot design. Three producers demonstrated the high stock density at two utilization rates (50% and 75%), while three producers demonstrated the moderate stock density at the same two utilization rates. The Fargo location provided a study of all treatments and utilization rates.

Forage Establishment

The annual forage crop planted by mid-June of 2020 and 2021 included and will include oats, sorghum sudangrass, foxtail millet, sunflower, radish, kale, turnip, flax and forage pea seed seeded at a rate of 18, 3, 2, 1.5, 1, 0.75, 0.75, 2 and 10 lbs/ac, respectively. Following two years of an annual forage crop, the planned cash crop will be corn planted in the spring of 2022.

Livestock and Grazing Management

Cattle were randomly assigned to grazing density treatments and carrying capacities were determined based on available forage production and estimated utilization. Stocking rates were determined by dividing the available forage by anticipated dry matter intake per day, then dividing by 30 days of planned grazing to predict the number of cows per plot. The available forage for 50% and 75% utilization treatments was calculated at 35% and 50% of the total forage produced, respectively (Meehan et al., 2018). The estimated dry matter intake was based on recommendations in the Beef Cattle Handbook (National Research Council, 2016). The moderate stock density was based on the recommended stocking rate for a 30 day period. The high stock density was set at double the moderate stock density and the grazing period reduced so as to ensure the treatment was not overgrazed. During 2020, turnout dates ranged from late August to early October.

Electric poly-wire and temporary posts were utilized as portable cross-fence to limit-graze livestock and maintain grazing efficiency. Each treatment was divided into four sections. Windbreak shelters were available for use and continued access to water was provided.

Soil Sampling

Soil samples were collected to characterize physical, chemical and biological properties. Soil physical properties included bulk density, infiltration and soil aggregate stability collected pre- and post-treatment. Six sub-samples were collected from a similar soil series within each treatment prior to seeding of annual forage crop. Samples were also collected from a nearby location that was managed as part of a traditional cash crop system. Soil chemical properties included soil nutrients, pH and organic matter collected annually with assessment of nutrient distribution occurring pre- and post-treatment only. Sub-samples for nutrient distribution were collected from each 1 acre sub-plot, whereas once yearly levels were extracted from a similar soil series within each treatment. Above ground residue was gently removed at each sampling site prior to conducting the sampling technique.

A soil core sampler with hammer attachment was used to measure bulk density at a depth of 0-6 inches. In calculating bulk density, the weight of the oven-dried soil was divided by the volume of the ring to determine lb/ft³.

Soil infiltration was determined by utilizing the Cornell Sprinkle Infiltrometer system (van Es and Shindelbeck, 2003). It consists of a portable rainfall simulator that is placed onto a single 9.5 inch inner diameter infiltration ring and allows for application of a simulated rainfall event. Field-saturated infiltrability reflects the steady-state infiltration capacity of the soil, after wet-up. It is based on the data collected at the end of the measurement period, or whenever steady-state conditions occur. Since the apparatus has a single ring, conversion factors from Reynolds and Elrick (1990) are needed to account for the three-dimensional flow at the bottom of the ring.

Soil aggregate stability samples were collected with a tiling spade to a depth of 0-6 inches. A manual wet sieving method by Six et al. (1998) was used to develop an automated method for assessing aggregate stability. Due to variation in soil across locations, the sand correction procedure by Mikha and Rice (2004) was applied to each sample to remove the sand fraction from the water stable aggregates total.

Soil nitrate nitrogen (NO₃-N), carbon (C), phosphorus (P), potassium, pH, organic matter (OM), sulfate-sulfur (SO₄-S), zinc and copper (Cu) were determined from samples collected at 0-6 and 6-12 inches with a 0.7 inch diameter soil probe. Soil nitrates (Vendrell and Zupancic, 2008) were measured using the Brinkmann PC910 Colorimeter. This colorimeter was also used to determine levels of P after applying the Olsen Test (Nathan and Gelderman, 2015). Potassium was measured using an atomic absorption spectrophotometer. Zinc and copper were extracted with diethylene triamine penta acetic acid and also measured with an atomic absorption spectrophotometer (Nathan and Gelderman, 2015). Recommended chemical soil test procedures for the North Central Region (Nathan and Gelderman, 2015) were used to analyze C, pH, OM and SO4-S.

Forage Production and Utilization

Forage production and utilization of the annual crop was estimated by clipping six 59-inch diameter hoops per experimental treatment. Clipping for peak biomass production occurred during the week prior to grazing and turnout dates ranged from late August to early October. Clipping to determine forage utilization occurred upon removal of cattle from the grazing treatments.

Livestock Performance

Beef cattle were stratified by a 2-day body weight and body condition score at the site in Fargo pre- and post-treatment, whereas cattle at the demonstration sites were scored for their body condition only. A visual scoring system developed by Wagner et al. (1988) was used to assess body condition.

Data Analysis

The demonstrations will be set-up utilizing a randomized split-plot design to evaluate the different stock densities at each location.  Data analysis will be conducted using SAS version 9.4.  Data will be analyzed to assess changes in soil physical properties, soil chemistry and soil biology, forage production, crop production and livestock production.

Economic Analysis

The economic analysis would evaluate the cost and/or revenue advantages of the grazing management practices being evaluated against a baseline system to determine if these strategies pay off based upon livestock and/or crop production advantages. The analysis will also evaluate the circumstances that make the ICLSs being demonstrated profitable or cost effective for producers. This analysis would be based upon historical and projected market prices and production costs for the systems.

Outreach Activities

NDSU Extension will partner with producers to establish several demonstration sites.  Producer involvement will provide a real world perspective of the effects grazing management practices have on ICLSs. The NDSU Central Grasslands Research Extension Center and the NDSU Main Station will also host  sites along with six livestock producers who practice ICLSs.  A series of café talks, workshops and tours will provide opportunities to disseminate results to producers, landowners, local organizations and other stakeholders during years one and two of the project. This outreach will provide stakeholders an opportunity to see the demonstrations in action and have discussions with our partner producers during the project. Other outreach efforts include, but are not limited to, journal articles, extension publications, bulletins, news articles, videos and social media. After project completion, two one-day workshops will be hosted around North Dakota by the project team and partners to comprehensively share what was learned during the on-farm demonstrations. This will allow an opportunity for all the producer partners to gather together and learn from one another as well. These workshops will be open to all local stakeholders as well as those throughout the Northern Great Plains.