Using Subsoiling to Reduce Soil Compaction in Pastures

Collaborator: Mackay Ross, Cleardale

Research Coordinator: Dr. Akim Omokanye

Research Technician: Dr. Lekshmi Sreekumar

From: Peace Country Beef & Forage Association 2016 Annual Report


On beef cattle operations, at some point, forage production of hay fields and pastures will no longer meet minimum production expectations based on previous years’ production. This could be due to several factors such as reduced stand vigour, invasion of less productive plant species, over grazing, reduced soil fertility and general poor soil health. The consistent use of heavy machinery for conserved forage production practices (hay, haylage, greenfeed or silage production) or cattle trampling in pastures have been identified as factors responsible for compacted soil layers in beef cattle production systems. Compacted soils could restrict water infiltration into soil, root penetration and nutrient uptake, and reduce soil respiration by reducing pore space and limiting oxygen diffusion. The overall effect of compacted and unhealthy soil is reduced forage yield.


Rejuvenation of old forage stands is always a complex and costly challenge for beef cattle producers. Studies have shown that subsoiling could be used to loosen the compacted soil layers, allowing roots to penetrate deeper into the soil profile, increasing water infiltration and retention, increasing air spaces in the soil and improving conditions conducive to biological activity and overall soil health. Subsoiling fractures compacted soil without adversely disturbing plant life, topsoil, and surface residue. In choosing the type of subsoiler, the objectives of the operation and the field characteristics must be taken into account. The objective of this study was to conduct a preliminary assessment on the suitability of different types of subsoilers (in combination with or without rolling) for reducing soil compaction, improving water infiltration and increasing 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. Soil moisture content from 0-6” soil depth with gravimetric method

4. Forage DM yield and nutritional value


Results and Interpretation

Soil Moisture (Table 1)

The soil moisture content was significantly affected by subsoiling treatments. A combination of Agrowplow subsoiling plus rolling gave the highest soil moisture content (20.3%), while the control recorded the lowest moisture content (15.4%).

The higher soil moisture content obtained for all subsoiling treatments (subsoiling alone or subsoiling + rolling) over control, clearly shows the benefits of subsoiling pasture paddock for soil water storage.


Infiltration (Table 1)

Soil infiltration refers to the ability of the soil to allow water to move into and through the soil profile. Infiltration allows the soil to temporarily store water, making it available for use by plants and soil organisms. The infiltration rate is a measure of how fast water enters the soil, typically expressed in inches per hour. If the rate is too slow, it can result in ponding in level areas, surface runoff, erosion in sloping areas, and can lead to flooding or inadequate moisture for crop production. Sufficient water must infiltrate the soil profile for optimum crop production.


In our study, water infiltration rate was highest for Agrowplow + Rolling (3.84 inches/hour), followed by Agrowplow alone (3.07 inches/hr), and water infiltration was lowest for control (0.29 inches/hr). Generally, the Agrowplow seemed to allow more water to infiltrate at a higher rate than the Sumo type of subsoiler, but a combination of Agrowplow + rolling seemed to have more beneficial soil water intake effects. The mean infiltration rate following subsoiling alone (Sumo & Agrowplo, 2.26 inches/hr) was lower than the mean infiltration rate following subsoiling + rolling (Sumo & Agrowplo + rolling, 2.33 inches/hr). Agrowplow + rolling appeared to improve infiltration rate better than Agrowplow alone by 0.77 inches/hr. This was not the case with Sumo + rolling over Sumo alone.


Soil acts as a sponge to take up and retain water. 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). Looking at Table 2, with an infiltration rate of 3.84 inches/hr recorded for Agrowplow + rolling, it shows that Agrowplow + rolling had a moderately rapid water infiltration. On the other hand, the control, which had 0.29 inches/hr seems to show a moderately slow infiltration. Overall, our results show that subsoiling alone or a combination of subsoiling + rolling improved infiltration more than control. A high infiltration rate is generally desirable for plant growth and the environment. The results obtained in this study for subsoiling treatments compared to control clearly show that infiltration rate can be improved temporarily with tillage such as subsoiling that breaks the compaction layer, fractures dense soil profiles, and improves soil physical quality.

Compaction

Readings of 400 to 500 PSI would indicate potential soil compaction. With a compaction reading of 312 PSI for the control, the pasture paddock used for this study did not seem to have a serious compaction issue. However, subsoiling alone or with rolling was still able to reduce soil compaction compared to control. But subsoiling + rolling with both Sumo and Agrowplow seemed to reduce compaction better than subsoiling alone. This therefore confirms that tillage such as subsoiling can be used to reduce compaction issues on pasture paddocks.

Looking at each subsoiler type alone or a combination of subsoiling with rolling as well as control (Figure 1), control appeared to be consistently higher than all subsoiling treatments at every soil depth from 0 to 12”. Generally, at <150 PSI from 0-12” for Sumo and Agrowplow with and without rolling indicate a lack of any compaction issues.

Soil penetrometers, designed to test soil strengths when a rod is pushed into the ground, can be used in some applications to identify compacted layers and how well subsoiling operations fracture the soil.


Determining the optimum time to subsoil depends on several factors, including maximizing belowground soil disruption, minimizing aboveground soil disruption, and minimizing tillage energy requirements.

Soil compaction (>400 PSI) can have a number of negative effects on soil quality and crop production including the following:

1. causes soil pore spaces to become smaller

2. reduces water infiltration rate into soil

3. decreases the rate that water will penetrate into the soil root zone and subsoil

4. increases the potential for surface water ponding, water runoff, surface soil waterlogging and soil erosion

5. reduces the ability of soil to hold water & air, which are necessary for plant root growth and function

6. impedes root growth and limits the volume of soil explored by roots

7. decreases the ability of crops to take up nutrients and water efficiently from soil

8. reduces crop yield potential

For more information on Agricultural Soil Compaction: Causes and Management (Agdex 510-1. October 2010), please visit http://www1.agric.gov.ab.ca/$Department/deptdocs.nsf/all/agdex13331


Forage yield (Table 1)

Agrowplow alone improved forage DM yield (2229 lbs/acre) better than Sumo alone (1653 lbs/acre) or any of the subsoilers + rolling (Table 1). Control had the lowest forage DM yield (1306 lbs/acre) and control had 347 to 923 lbs /acre less DM yield than subsoiling treatments.


The better forage yield obtained from subsoiling treatments compared to control could be a reflection of high soil moisture, improved infiltration rate and reduced compaction.


Forage quality (Table 3)

The forage crude protein (CP) content appeared to be higher for Agrowplow + rolling than any other subsoiling treatment as well as control (Table 3). Generally, the CP obtained for control and the subsoiling treatments was 16% CP or more, indicating that all treatments as well as control had exceeded the CP requirements of growing & finishing calves (12-14% CP) and mature beef cattle (11% CP). The site contained a lot of clover stands and could be responsible for high CP content in the forage across the field.


The forage energy (TDN) was generally >60% TDN for all treatments, and they seemed to be enough for mature beef cattle’s energy requirements.


The forage Ca, P, Mg and K did not show any consistent pattern with respect to the treatments tested. All the minerals measured here were adequate for a dry gestating cow. For a lactating cow, all treatments tested fell short of meeting the P requirement.

Overall, subsoiling alone or with rolling did not seem to have improved forage quality in this study.

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