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

Commodities

• Agronomic: annual ryegrass, buckwheat, cotton, grass (misc. annual), grass (misc. perennial), rye, sorghum (milo), vetches

Practices

• Crop Production: conservation tillage, continuous cropping, cover crops, cropping systems, crop rotation, fertilizers, no-till, nutrient cycling, water management
• Education and Training: demonstration, extension, on-farm/ranch research, participatory research
• Soil Management: nutrient mineralization, soil analysis, soil quality/health

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.