Developing Soil Carbon Balance (SCB) in a Long-Term Row Crop Production System

Commodities

Practices

South Texas soils are predominantly low in organic matter content
and often face serious nutrient loss challenges during crop
production. Record low rainfall in the last few years in South
Texas has also become an imperative area of concern. A long-term
research field at Texas A&M AgriLife has been practicing
cotton-sorghum crop rotations over the last 30 years. However, an
integration of cover crop mixtures (annual ryegrass, Austrian
winter pea, tillage radish, hairy vetch, buckwheat, and oat) with
two different tillage (no till vs conventional till) methods was
initiated four years ago to experience the ecosystem services
those cover crops has to offer, specifically in regard to adding
organic matter in the soil. However, a soil carbon balance (SCB)
considering both C inputs and outputs in that field has not yet
been developed.

This study will: a) evaluate the efficacy of cover crop mixtures
to add soil carbon and develop SCB b) account for meteorological
parameters and soil physicochemical properties to better
understand SCB and c) provide experimental and experiential
learning opportunity to the graduate student about sustainable
farming. We will use a LI-7810/7820
CH₄/CO₂/N₂O/H₂O Trace
Gas Analyzer to measure greenhouse gas emissions for two crop
seasons. One-meter-deep cores samples will be collected to
measure carbon content in soils at different depths. Total carbon
contributed and total carbon released from different treatments
will be used to calculate SCB.

The outcomes of this experiment will be disseminated through
presentations at conferences, peer-reviewed article publications,
webinars, farmers field-day demonstrations, and classroom
presentations.

This project will follow a system-based research approach (as
outlined in the SARE website) where agricultural sustainability
will be introduced and analyzed in a conventional farming system
(long-term cotton and sorghum rotations). This project will
address the key research question: “Are cover crop mixtures
capable of providing ecosystem services in a semi-arid row crop
production system?” Specific objectives are:

Objective # 1. To develop a soil
carbon budget under six cover crop mixtures (annual ryegrass,
Austrian winter pea, tillage radish, hairy vetch, buckwheat, and
oat) and tillage practices (no till and conventional tillage) in
a long-term row crop (cotton and sorghum) production farming.
One-meter soil cores will be collected and divided into five
segments (depth of 0-5 cm, 5-10 cm, 10-30 cm, 30-60 cm, and 60-90
cm) for soil C analysis and eventually to feed into a DAYCENT
model in the future. Other soil cores will be collected to
measure the field bulk density of soil at those five depths. Seed
mix of these cover crops were selected based on the grower’s
recommendations and the performance of those cover crops in the
semi-arid climate. Specifically, we selected a mixture of
legumes (hairy vetch and Austrian winter
pea), grasses (annual ryegrass, oat, and
buckwheat) and broad leaf (tillage radish
or Daikon radish) cover crops for efficient use of the soil
moisture and nutrients at different soil depths. We are
anticipating a possibility to continuing this study even after
finishing this two-year project.

Hypothesis 1A: Cover crop mixtures will have positive
impacts on soil carbon balance (net C accumulation) in the field
compared to the plots without cover crops.

Hypothesis 1B: No tillage (under CC treatments) will
retain more soil carbon than conventional tillage (under CC
treatments)

Objective # 2: To consider the
effect of meteorological parameters (temperature, rainfall,
relative humidity, and wind speed) and soil physicochemical
properties (gravimetric water content, water filled pore space,
organic matter content, bulk density, soil pH, and cation
exchange capacity) on soil C balance. Meteorological
parameters can largely influence carbon emission and accumulation
in soil. PI’s previous project have shown a significant effect of
meteorological parameters on trace gas emissions from soil in row
crop production system (Dattamudi, 2015).

Hypothesis 2: Meteorological parameters and soil
properties will have a significant effect on soil respiration and
cover crop residue decomposition (to add organic matter in the
soil) which will subsequently influence the soil C balance.

Objective # 3: To disseminate
information and knowledge among the growers, other stakeholders,
and fellow classmates through grower meetings, extension
activities, conference presentations, classroom demonstrations,
and peer-reviewed publications. Additionally, social media
platforms such as Facebook, Instagram, College website, College
Newsletter, and LinkedIn will be used to disseminate the research
outcomes of this study.

Hypothesis 3: Knowledge dissemination will provide more
information to the growers and other agricultural stakeholders
about the influence of cover crop treatments and conservational
tillage practices (no-till) on soil carbon dynamics.