Starting back in first decade of this century, the buzz words of carbon sequestration has appeared in articles and has become frequently discussed with farmers in the USDA’s Farm Service Agency and NRCS offices as one of the methods to reduce or offset carbon emissions.
Mike Peteren, Orthman Manufacturing agronomist
During this same period, some of the Farm Bureau folks got quite involved and brokered deals to monitor soil organic matter (SOM) and for growers to involve these better conservation practices on the farm, they could store carbon by leaving the previous crop residue on the surface throughout the year.
Strip-till, zero tillage, direct seeding, no-till and mulch till — all somewhat differing practices on the tillage side of things prior to seeding — return of residues to the soil for slowed breakdown and slow release to the soil complex.
With these methods of returning and storing soil carbon, the potential to offset the losses across the globe due to burning carbon-based fossil fuels at a ever-advancing rate, and carbon based gases being released into the atmosphere, is becoming a reality.
Slash-and-burn methods in South America and parts of Africa have been a traditional way to clear forest for cropland, but this releases very valuable carbon material into the atmosphere. Here in the U.S., we’ve adopted better and wiser conservation measures to simplify and drastically reduce the types of pre-plant tillage, which was inverting and burying prior-year residues but exposing years and years of prior-stored carbon, and much of it was oxidizing away and above.
Bigger Roots Store More Carbon
Scientists have calculated that with practices such as strip-till and direct seeding, growers can store tons of carbon in the top few inches of the soil, but what about all those roots, root exudates, lignin and cellulosic materials from 0 to 7 feet?
At Orthman Mfg., we’ve observed rooting magnified with strip-till due to a quicker start in the spring to maximize the number of roots expressed below ground.
In soil pits, we’ve measured corn roots in continuous strip-till and see that it allows deeper root expansion into the soil. That’s because as temperatures heat up during the growing season, the roots tend to follow the cooler soil temperatures deep into the soil profile.
Studies at the University of Georgia show that corn roots extend vertically at specific soil temperatures. This is in addition to the lateral root development of corn plants. By gaining more root dimension in linear length, the corn plants can accumulate more grams of dry matter below ground to depths mentioned above.
Roots And Residue Store Carbon
In eastern Colorado, in very deep loam and silt-loam soils, we’ve found deeper-rooted corn hybrids with more than 38,100 linear inches of roots. With other hybrids, we’ve measured roots that are 9,500 to 20,000 linear inches. The amount of carbon below the surface in the roots far exceeds the residue that remains on the surface after the ears of corn are harvested.
With strip-till and precision fertilizer placement, we’re gaining much more soil-carbon material than what’s possible with full-width tillage systems.
For example, when we first started the strip-till research at Lexington, Neb., in 2007, our soil samples from the first 4 inches of the soil had soil organic matter of 2.1 to 2.3%. But when we sampled again this spring very near to where we first sampled 5 years ago, the organic matter was now 2.7-3.1%.
We do not graze the corn stalks with cattle, which can reduce corn residues by 50% on the soil surface. We leave the corn stalks standing, 13 to 20 inches tall, and we don’t shred them in the spring. These longer and taller stalks keep winter winds from blowing residues away and off into the adjoining fields and ditches.
We estimate that 5.5 to 7.8 tons per acre of residue remain after harvest. Maintaining this quantity of residue does have its own concerns. But by keeping this residue, we have more water stored, more carbon returning into the surface and an increased population of microbes. And the old roots are decomposing slowly to become humus, which is a treat for burrowing insects and soil microbes.
Farmers strip-tilling their ground can be sure they are doing their part to minimize carbon dioxide emissions, sequester carbon, improve the soil-life system and improve the health and vigor of their soils to produce crops for many, many years to come.