Building soil organic matter has always been considered a good thing from an agricultural productivity, environmental and farm profitability perspective.
Soils are often extremely variable, even within a small area, not just in organic matter content but also aspects such as pH, clay content , and level of various nutrients such as phosphorus and nitrogen.
Raising soil carbon mainly focuses on the top 0 to 30cmm of soil with main gains in the top 0 to 10 and 0 to 20cm layer.
Organic matter can rise considerably in a year of good plant growth but can drop significantly in a drought, and certainly in a run of dry years like 2017 to 2019.
Organic matter is a constant variable as at any time some is being broken down by soil organisms , and some is being added to the soil via new plant material.
The wetter the environment the greater the capacity to increase soil carbon given suitable management.
Some of the major research sites have started from previously long cultivated cropping land and or pastures that probably were often overgrazed and not corrected for soil deficiencies nor had decent legume growth.
Research has found it’s hard to build soil carbon in cropping only systems, although zero till combined with stubble retention has come closest and in higher rainfall environments may be able to slowly build it.
Nutrient deficiencies need to be addressed with products that are able to supply that deficient element in an available form at a sufficient rate.