Subsoiling to Reduce Soil Compaction in Pastures

Collaborator: MacKay Ross, Clear Hills County

Research Technician: Dr. Lekshmi Sreekumar

From: Peace Country Beef & Forage Association 2017 Annual Report


Forage production in various beef cattle operations is declining year after year. This decline in forage production is attributed to several factors such as climate, soil compaction, decline in soil fertility, weed competition and reduced stand vigour. The consistent use of heavy machinery and cattle trampling in pastures have been identified as factors responsible for compacted soil layers in beef cattle production systems. Heavily compacted soils contain few large pores and have a reduced rate of both water infiltration and drainage from the compacted layer. Finally, while soil compaction increases soil strength, the plant roots must exert greater force to penetrate the compacted layer. The overall effect of compacted and unhealthy soil is reduced forage yield.


Subsoiling can break compacted soil layers without disturbing plant life, topsoil or surface residue. Studies have shown that fracturing compacted soil promotes root penetration by reducing soil density and strength, improving moisture infiltration and retention, and increasing the air spaces in the soil. Success depends on the type of equipment selected, its configuration, and the speed with which it is pulled through the ground. No one piece of equipment or configuration works best for all situations and soil conditions, making it difficult to define exact specifications for subsoiling equipment and operation. The objective of this study was to conduct an assessment on the suitability of different types of subsoilers (in combination with or without rolling) for reducing soil compaction, increasing soil infiltration and increasing the forage yield.


Methods:

An on-farm study was conducted from fall (October 2015) to summer (July 2016) on a pasture paddock in Cleardale. The paddock was initially seeded to creeping red fescue. Alsike clover was later broadcast (12 years later, 2011) onto the paddock.


A demonstration strip design was used. We used 2 types of subsoilers - a Sumo (GLS-Grassland) subsoiler and an Agrowplow (Model AP91). The subsoiling treatments consisted of the following:

  1. Sumo alone – subsoiling to a depth of 12’’

  2. Sumo + rolling - subsoiling to a depth of 12’’ followed by rolling

  3. Agrowplow alone - subsoiling to a depth of 12’’

  4. Agrowplow + rolling - subsoiling to a depth of 12’’ followed by rolling

  5. Control (check)

The treatments were implemented in early fall on October 9, 2015.


At approximately 9 months after subsoiling, the following field measurements were taken on July 7, 2016:

  1. Water infiltration with aluminized coated rings of 6’’ diameter and 5 ¼’’ height.

  2. Compaction reading with a digital penetrometer at 1” interval to a soil depth of 12”

  3. Forage moisture content 4. Forage DM yield and nutritional value

The measurements were taken again on August 24, 2017 after the pasture had been grazed four times in 2017, at intervals of 2-6 days with 20-25 cow/calf pairs.


Results and Interpretation:

Infiltration (Table 1)

Infiltration rate is a measure of how fast water enters the soil and is typically expressed in inches per hour. The highest infiltration rate of 1.23 inches/hr was recorded with Agrowplow alone followed by Agrowplow-Rolled (0.96 inches/hr). The Lowest infiltration rate was recorded for control (0.08 inches/ hr). Between the Agrowplow and sumo subsoiler (alone or in combination), the Agrowplow seems to be more efficient in increasing the infiltration rate compared with sumo. Sumo rolled seems to have higher infiltration rate (0.89 inches/hr as compared with sumo alone (0.86 inches/hr).


The downward movement of water within the soil is called percolation, permeability or hydraulic conductivity. Permeability also varies with soil texture and structure. Permeability is generally rated from very rapid to very slow (Table 2). The infiltration rate of 1.23 inches/hr that was recorded for Agrowplow and 0.96 inches/hr recorded for Agrowplow-Rolled seems to show moderate water infiltration. Similar results were achieved with the Sumo alone and in combination with rolling. With the infiltration rate of 0.08 inches/hr recorded for control, the control clearly had slow water infiltration. The moderate infiltration rate attained with the subsoilers as compared with control indicates that subsoiling can reduce compaction a considerable amount, and facilitate better water infiltration, root penetration and forage production.


Forage Moisture &Dry Matter Yield (Table 1)

The highest forage moisture percent (86%) was recorded with Sumo-Rolled followed by Sumo (85%) and lowest in Agrowplow (79%). The lower water infiltration rates with Sumo and Sumo-Rolled resulted in higher moisture content in forages, compared to Agrowplow. The highest dry matter yield (957 lbs/acre) was recorded for Agrowplow-Rolled, compared with Sumo-Rolled (936 lbs/acre) followed by Agrowplow alone (909 lbs/acre). Again the data shows the effectiveness of Agrowplow-Rolled in mitigating soil compaction and increasing the forage yield.

Compaction

Soil compaction is measured by soil penetrometers in psi. Penetrometers measure soil strength and their movement through the soil, which is related to the soil’s resistance to root penetration. Plant roots, however, grow around obstacles and can exert tremendous local pressure on soil pores so that penetrometers can only provide a relative root resistance value. Readings of 400-500 psi indicate potential soil compaction.


Here from figure 1, the compaction reading of 420 psi with the control indicate that soil compaction is an issue in this particular beef cattle production system, which results in lower forage productivity. Use of different subsoilers seemed to reduce the compaction values as compared to control. The highest reduction in compaction occurs under Agrowplow, followed by Agrowplow-rolled. In a nutshell, Agrowplow alone or in combination with rolling is found to be more effective in reducing the soil compaction as compared with the Sumo subsoiler.

Conclusion

Subsoiling proved to be an effective tool for reducing soil compaction, increasing soil water infiltration, improving plant nutrient absorption, and increasing forage productivity.

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