Combining row crops and small-grain pastures to feed stocker calves and cow/calf pairs is becoming more common as a way to offset declining income from row crops alone. Grazing of annual crops induces concern in that cattle may degrade soil by trampling vegetation and compacting the surface by their hoof traffic. Lull (1959) estimated that mature cattle exerted about 24 pounds per square inch of static ground pressure. The potential for compaction damage is exacerbated on bare ground where there is no vegetation to absorb the pressure. Tilling and crop production expose soil to wind and water erosion, compaction, and decrease aggregate stability. Aggregate stability aids in erosion resistance (Fattet et al., 2011), facilitates root penetration (Fattet et al., 2011), increases soil aeration (Oades, 1984), and is critical in water infiltration (Franzluebbers, 2002) and retention (Saha and Kukal, 2013), especially in dryland agricultural systems. There are increasing conservation efforts to reduce erosion and increase aggregate stability by establishing stands that provide superior ground cover. In no-till areas, compaction by cattle trampling could reduce the success of stand establishment in the next cropping season. If producers implement conservation tillage methods such as no-till to reduce erosion, is there a cumulative effect on soil bulk density from trampling?
Texas High Plains agriculture largely depends on underground water from the Ogallala Aquifer for irrigation, wherein the consumption of this irrigation water is much faster than the aquifer’s recharge ability (Johnson et al., 2013). By converting portions of irrigated cropping systems to limited-irrigation small grain pastures for beef cattle, it can possibly prolong the life of the aquifer, as well as provide an additional source of income for an existing farm operation, when compared with a continuous monoculture of cotton in their production systems (Allen et al., 2005, 2012). High-intensity hoof action increases compaction, resulting in less infiltration and high bulk densities (Warren et al., 1986). Soil compaction severely limits infiltration of rain and, therefore, decreases the productivity of plants growing in the soil (Haveren, 1983; Gifford et al., 1977). The grazing of annual forages with conservation tillage efforts has raised concerns with soil compaction issues in annual systems. Grazing can enhance soil bulk densities, especially in previously tilled farmland. However, water infiltration rates can be sustained with proper grazing management practices, helping maintain adequate ground cover (Bisinger et al., 2015), as well as deferment of grazing to allow the soil to recover from grazing bouts.
This field experiment is testing the effects of trampling intermittently for an entire grazing season (May-August) by cattle on surface-soil compaction and bulk density, and on seedling establishment over time in no-till scenarios compared to a no-trampled control (ungrazed) plots which are also no-till. The seeding of pearl millet (Pennisetum glaucum) is being executed over 2 consecutive years (2018, 2019) on irrigated cropland. The study in 2018 was carried out at moderately heavy stocking densities to achieve a high consumption rate of vegetation and potentially compact the soil on approximately three, 2-acre paddocks. The pastures were used once a month alongside another grazing trial to give perennial grass systems a rest from the months of June until September. The last heavy grazing bout had doubled the stocking rates, and vegetation was consumed to a similar level of residual forage to that which was left previously. The aim is to determine if there is a cumulative effect of grazing when soil conservation efforts are implemented, such as no-till. The current practice of moderate to heavy grazing densities of stocker cattle on small grains through summer months is being simulated.
Data collection in the first year was taken after initial trampling, then every 60 days. Twenty soil cores, located along two permanent transects running perpendicular to each other, are being collected to determine the effects of trampling on remaining living plants, dead litter cover, and soil recovery from compaction until the next planting date, then repeated in the following year. After sufficient precipitation to induce emergence of the pearl millet, we will determine treatment effects (trampled by grazing vs. no grazing) on seedling emergence and relate those effects to soil bulk densities. Next to each bulk density core, a soil penetrometer reading will be taken. These readings will be conducted to compare compaction detection methods (bulk density and soil penetrometer) to determine which is most efficient for detecting compaction and their recovery rates. Conclusions of this study will be compiled into fact sheets which will be distributed to producers through the Texas Alliance for Water Conservation (TAWC) annual Water College, the Texas Tech and TAWC field days, and on social media.
Allen, V.G., et al. 2012. Integrating cotton and beef production in the Texas Southern High Plains.
Allen, V.G., et al. 2005. Integrating cotton and beef production to reduce water
withdrawal from the Ogallala aquifer in the Southern High Plains.
Bisinger, J. J., et al. 2014. Pasture size effects on the ability of off-stream water or restricted stream access to alter the spatial/temporal distribution of grazing beef cows.
Fattet et al., 2011. Effects of vegetation type on soil resistance to erosion: Relationship
between aggregate stability and shear strength.
Franzluebbers, A.J. 2002. Water infiltration and soil structure related to organic matter
and its stratification with depth.
Gifford, G. F. 1978. Hydrologic impact of grazing on infiltration: a critical review.
Haveren, B. P. 1983. Soil Bulk Density as Influenced by Grazing Intensity and Soil Type on a Shortgrass Prairie Site.
Johnson, P., J. et al. 2013. Integrating cotton and beef production in the Texas Southern High Plains: III. An economic evaluation.
Lull, 1959. Soil Compaction on Forest and Range Lands.
Oades, 1984. Soil organic matter and structural stability: mechanisms and implications
Saha and Kukal. 2015. Soil structural stability and water retention characteristics under
different land uses of degraded lower Himalayas of North-West India.
Objectives of this study are to quantify the effect of brief cattle trampling at moderate to heavy grazing densities on soil bulk density; to determine if cattle have a cumulative effect on soil bulk density in no-till systems; to quantify the amount of deferment time required for bulk densities to recover to acceptable levels; and to compare two methods of determining and monitoring soil compaction for deciding which of the two is most user-friendly and easiest for producers to use.
-Plot area was prepared in early March 2018 by:
-lightly disking to remove weeds.
-applying herbicide prior to planting to allow millet to outcompete pigweed.
-Pearl millet was planted in May 2018 and given time to establish.
-Grazing exclosures were placed in the center of each field for an untrampled control.
-Cattle intermittently grazed millet plots throughout June, July, and August.
-Stocking rates were doubled for the last grazing bout in September, and cattle were allowed to graze down residual forage as much as available.
-Two permanent transects were placed in each field running perpendicular to each other.
-20 soil samples were collected from the top 3 inches using 2 x 3 inch core sleeves, 10 evenly spaced along each transect. Initial samples were taken September 24th, 2018, then repeated every 60 days.
-5 soil samples using 3.5 x 7 cm core sleeves from each small grazing exclosure were taken to compare to the trampled treatment. Initial samples were taken September 24th, 2018, then repeated every 60 days.
-Penetrometer readings were taken next to each bulk-density core to a depth of 12 cm. The Field Scout penetrometer records resistance at 3, 6, 9, and 12 cm. (initial samples were taken September 24th, 2018, then repeated every 60 days)
-Soil samples are taken by tapping core sleeves into the ground using a board placed on top and a rubber mallet. Once the board lies flat across the soils surface, a shovel is used to dig the core sleeve from the soil profile. The soil is scraped from the bottom (so the soil is even within the core sleeve) wrapped with clear cellophane and taken to the laboratory for analysis.
-In the lab, cores are removed from their plastic wrap, dried at 105 degrees C for 48 hours and then weighed. Volumetric bulk density is then calculated using the dry weight of the soil divided by the volume of the core sleeve, and recorded in g-1 cm-3.
What is to come…
-Atrazine will be sprayed to prevent weeds in March 2019, and pearl millet will be no-till planted into the three paddocks.
-After germination and seedling emergence, seedling will be counted along the permanent transects using the Daubenmire frame method.
-Establishment and plant cover will be monitored along each transect in May, June, July, and August until treatments are applied.
-Once trampled, cattle will vacate plots, and soil sampling will continue.
Preliminary data for the first year show no difference between trampled and untrampled treatments in regard to soil bulk density. However, when examining individual soil bulk density cores along the transect, there was a slight increase in bulk density in areas that cattle utilized more heavily, namely, around water troughs and mineral tubs.
Educational & Outreach Activities
There have been no outreach programs yet. However, once data is analyzed for both this past year and the upcoming data collection year, the outcomes will be presented to TAWC producers and other TTU and TAWC outreach programs, as well as at professional society for agronomy symposiums.
The impact of this project is two-fold: Understanding the required deferment of grazing to mitigate compaction and re-establish the subsequent annual crops will be useful to help producers know how to improve soil health. It is also applicable to winter wheat pasture programs when wintering cows is lucrative during winter months. Since most producers have predominantly perennial warm-season species in their summer pastures, this could help reduce the cost of purchasing hay through the winter months while the grasses are dormant. Having a quick and objective way to identifying soil compaction risks in the field is crucial for sustainable management decisions, especially in no-tilled annual grain crop/livestock grazing production systems that help maintain proper watershed function and cropland vigor.