Soil CO2 Respiration: It’s More than Soil Health

1) PLANTS may require up to 150 lbs/acre of CO2 per day 2) SOIL may supply between 30 lb/a to 200 lb/a  CO2 3) ROOTS: Root respiration also supplies more CO2 to the soil system 4) AIR: 10 cubic acres of air are needed to satisfy the CO2 for one acre of wheat 5) ALL: Under healthy conditions, the soil-plant cycle is a unified system

Soil CO2 respiration should be center-stage in the emerging Soil Health discussion, according to Brinton who addressed a recent Soil Renaissance gathering in Oklahoma City. He showed early data from the Swedish soil ecologist Lundegårdh who first quantified plant CO2 demand due to photosynthesis and contrasted it with soil CO2 respiration. A biologically active soil was able to cover the plant’s carbon budget but depleted soils did not come close. CO2 in air must make up the deficit. Calculations show that wheat at full growth would need to filter 10 cubic acres of air (and corn 38 cubic acres) to support an acre of carbon yield. This means CO2 could be a temporarily limiting nutrient like nitrogen or phosphorus,- which plant physiologists have long known but is not popularly recognized.

While many assume carbon is simply coming from air, Brinton stressed that “we’re overlooking the role that healthy soil respiration plays in directly sustaining plants with sufficient CO2 for photosynthesis – and right where plants need it”. Lundegårdh complained in a 1926 Soil Science article that “unfortunately mineral nutrients are getting all the attention”- still true today. During intense plant canopy development it is possible that biologically depleted soils do not furnish sufficient CO2 from soil efflux for the full crop potential. Combine this with recent evidence that plant nutrient uptake – especially nitrate – comes at a biological CO2 cost, and soil-plant respiration emerges as a vital indicator of a truly productive soil crop system. In this way Brinton thinks CO2 respiration may be of central significance in plant productivity, “separate and above” other soil biology or soil health parameters. Brinton developed Solvita as a means to enable more cost-effective measuring of soil CO2. “We foresee increases in yields from healthier soil due to improved plant CO2 exchanges”.

Brinton presented the topic also in a ASA-SSSA hosted Webinar available thrugh August 2014 at:  https://www.soils.org/videos/play/certified/education/soil-health-respiration.flv .