Soils & GHG benefits and climate change adaptation
Remember “Net GHG Accounting” from a change in practice means counting all three GHG (CO2, CH4, and N2O) together. We have organized This section in “offense” for c-sequestration opportunities from soil health and “defense” for managing nitrous oxide emissions for soil health practices.
Offense: Soil Carbon Sequestration Strategies:
Reduce tillage. Increases soil carbon and soil health when practiced over many years.
Soil carbon can be lost quickly if tillage is later increased making it difficult to qualify as
‘permanent’ mitigation of GHG.
Add crop residues. Increases soil carbon, especially combined with reduced tillage. Improves soil health, including tilth. Excess residues on the soil surface can keep soil too cool and wet in spring, and can interfere with planting or early crop growth.
Add manure, compost, or biochar. Increases soil carbon, especially combined with reduced tillage. Improves soil health, including tilth. Transporting these materials from off the farm can be difficult and costly. Biochar (via pyrolysis) may offer significant potential, but public–private demonstration projects need to be implemented to determine feasibility and value on a large scale.
Add cover crops or double crops. Having crops cover the soil and build additional root systems for more of the year increases soil health and soil carbon. Cover crops require time and money to manage. Double crops increase total yield, but may reduce yields of the primary crop.
Convert land from annual to perennial crops.
Perennial crops, pasture, and tree root systems sequester soil carbon, use nutrients more efficiently, reduce erosion, and reduce GHG emissions. It may be difficult to find appropriate on–farm use or markets for some perennial crops.
DEFENSE: Nitrous oxide reducing strategies (N-use efficiency)
Develop a comprehensive nutrient management plan (CNMP).
A comprehensive nutrient management plan (CNMP) can help prevent erosion, water contamination, air contamination, and GHG emissions. It can be challenging to account for nutrients from prior application of manure, residues, compost, cover crops, crop rotations and other soil amendment. The CNMP must be kept up to date with changes in livestock numbers, cropping systems, management practices (e.g. manure management & livestock feed).
Optimize N fertilizer source.
Using the appropriate chemical form and formulation increases crop N use efficiency and reduces losses. Cost, availability, and logistics limit practical choices of fertilizer source. Coatings or inhibitors are expensive and not always effective.
Optimize N fertilizer placement.
Incorporating fertilizer into soil can reduce losses due to volatilization, particularly of urea and anhydrous ammonia. Placing fertilizer at depth or in bands can in some cases increase N2O losses, particularly if timing, source, and rate are not optimal.
Optimize N fertilizer time.
Applying most N fertilizer as side–dress reduces N2O and increases yield. Fertilizer requirements vary yearly; use of an adaptive in–season N rate helps manage variability.
Optimize N fertilizer rate.
Using appropriate source, placement, and timing, and rate, all reduce the total rate, reducing N losses including N2O. Fertilizer requirements vary yearly; use of an adaptive in–season N rate and timing can help manage this variability.
Reduce use of synthetic N fertilizer.
Synthetic N production requires lots of energy and emits GHGs; reducing its use reduces upstream GHG emissions. Synthetic N fertilizer is valuable and useful as part of a comprehensive nutrient plan.
Use appropriate crop rotations.
Crop rotations can increase yields and profitability, and if legumes are included, reduce N fertilizer requirements. Farm management and marketing may limit the choices of profitable and appropriate crop rotations.
Use a winter cover crop for annual crops.
Cover crops reduce nitrate in soil, reduce erosion, N leaching, and N2O emission, but must account for N availability from cover crop for subsequent crop. Cost and logistics may be challenging for both planting and termination of cover crops, including interactions with tillage practices.
Make your farm more energy efficient.
