University of Texas Rio Grande Valley:
Soil Infiltration

Texas-Coahuila-Tamaulipas-Nuevo Leon
Regional Workgroup

KEY PROJECT HIGHLIGHTS:

•	UTRGV Project demonstrated the benefits of
tillage and compost for improvement of
vegetation establishment to reduce runoff and
increase soil infiltration.

•	Project served as an on-hand, learning tool for
UTRGV students on agricultural practices

Urban development in the US-Mexico border region has
led to an increase in impervious surfaces and soil
compaction. Soils and substratum in the region contain an
appreciable amount of expansive clay, which is prone to
surface crusting and sealing. This change increases
stormwater runoff and the chances of urban flooding. The
wash-off of pollutants by runoff may also create sediment
and water quality problems for receiving waters. To
alleviate these problems, infiltration practices such as rain
gardens and bioswales have been adopted in the region.
Reducing runoff and increasing infiltration is highly
desirable in semi-arid region such as Lower Rio Grande
Valley.

The University of Texas Rio Grande Valley received
Border 2020 Program funds of approximately $49,600
USD, with an additional leverage amount close to $40,000
USD. The project focused on remediating urban
compacted soils to improve infiltration by adopting
agronomic practices (tillage and compost). Tillage is a
common practice used in agricultural lands to loosen and
mix the topsoil while compost amendment can reduce bulk
density and improve infiltration capacity of the soil. In this
project, tillage and compost amendment are hypothesized
to provide the greatest benefits in remediating compacted
soils, meeting the ultimate goals of reducing runoff,
increasing infiltration (and thereby groundwater
recharge), and improving vegetation establishment.

The objective of this project was to evaluate an urban soil
remediation method consisting of tillage and/or compost
amendment in a field-testing site (0.13 acre) located at the
UTRGV Edinburg campus. Specific tasks were three-fold:

•	Establish a field-testing site for evaluating soil
remediation methods;

•	Determine infiltration rate, bulk density,
penetration resistance, and runoff water quality;

•	Determine a turfgrass health indicator.

The site selected represented a typical urban soil that has
been graded and compacted by construction activities
(Fig. 1).

Tillage

1-month after hydroseeding

Figure 1. Site setup and tmfgrass establishment. (Top Left to Right:
Initial Site, Tillage, 1-month after hydroseeding; Bottom Left to Right:
Compost, Hydroseed, 4-month after hydroseeding)

The site received 4 different land treatments: 1) tillage
only, 2) compost only, 3) tillage + compost, and 4) no
tillage + no compost (Fig. 2).

N
A

W-< ~ E
V

Randomized Complete Block Design

A: Tillage + No compost

B: No tillage + Compost

C: Tillage + Compost

D: No tillage + Mo compost (control)

Figure 2. Randomized Complete Block Design for compost and tillage
treatments.

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UTRGV Soil Infiltration

After the land treatments, common Bermuda grass was
hydroseeded and in-ground irrigation was operated for
the first two months for the vegetation establishment.
The project team measured key soil physical properties
over time (infiltration rate, bulk density, and penetration
resistance) along with in-situ runoff experiments and turf
health to evaluate the treatment effects on remediating
urban compacted soils.

The project outcomes from the field-testing site were the
following:

•	Tillage was effective in reducing soil compaction (bulk
density and penetration resistance), but tilled soils were
reconsolidated during 21 months of monitoring period.

•	Compost amendment demonstrated its benefit for better
turf appearance (think, dark green) and improved
infiltration rate.

•	Both tillage and compost were effective for promoting
turfgrass growth and soil physical health. If tillage is not
applicable, just adding compost would help.

•	The longevity of tillage treatment is somewhat
questionable as bulk density tended to increase over
time. As a conventional lawn management, core
aeration would be desirable to minimize soil
compaction (e.g., once a year).

•	Applying compost and tillage did not pose any nutrient
loss concern in runoff water. It is important to note that
tilled and/or compost-amended plots has uneven
surface compared to control plots.

The project team presented their results at various
conferences and meetings. These included: 1) an oral
presentation at the 2019 Soil Science Society of America
Annual Meeting; 2) 2019 Rio Grande Valley Water
Quality Management & Planning Conference; 3) 2019
Border 2020 Gulf Task Force public meeting. In addition
to the field testing used as the project site, it also served as
outdoor classroom for UTRGV students in environmental
science, geology and soil science courses (Figure 3 and
Figure 4).

Figure 3. UTRGV students conducting experiments as part of
classroom hands on exercises on project site.

Figure 4. UTRGV students conducting experiments as part of
classroom hands on exercises on project site.

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