Adding organic matter or carbon
Randall Reeder
  

If OSU Extension were to conduct a poll of Ohio farmers with these two questions, the results might surprise you.

1. Are you in favor of sequestering carbon to help prevent global warming?

2. Is increasing organic matter in your soil good for crops?

The first question would likely get many negative answers because there is a lot of argument on the global warming issue. The second question would get nearly a 100% positive answer.

Here's the surprise: from a farming standpoint, it's the same question. Granted, a professional pollster might disagree with my wording of the questions. But for a farmer, sequestering carbon is adding organic matter.

A soil with high organic matter is more productive than the same soil where much of the organic matter has been "burned" through tillage and poor management practices. And the good news is that organic matter can be restored to about three-fourths of natural levels with best farming practices.

Plowing and erosion
Organic matter (carbon) has been lost from our cropland mainly through plowing, which makes soil more likely to erode. Water erosion, the major issue in Ohio, and wind erosion, as exemplified by the Dust Bowl in the Plains, are the major culprits worldwide.

USDA research shows that carbon dioxide gas is lost directly from tilled soil in proportion to the volume of soil loosened. Subsoiling a foot deep can lose more carbon than than plowing 8 inches deep; strip-till loses even less, and pure no-till planting loses the least. These losses are unrelated to residue cover.

Minimizing erosion is an important step to reversing the loss and building soil quality. And that usually requires leaving residue on the surface or planting a cover crop.

This article is not intended to be anti-tillage. However, it is extremely difficult to build up organic matter with annual plowing. It might be possible to find a system with livestock manure, cover crops and high-yielding crops that could manage to increase organic matter with plowing every few years, but I wouldn't bet on it.

Pioneers and the Dust Bowl
When the dust storms were at their worst in the spring of 1935, Will Rogers took a verbal shot at the pioneers on his weekly radio broadcast, "The old pioneer was a guy that wanted to plow up land that should have been left to grass. He wanted to cut a tree down, but he never did plant one. All he had was an ax, and a plow and a gun, and he just went out and lived off nature. He thought it was nature he was living off of, but really he was living off future generations."

You  may not agree completely with Will's assessment; pioneers on the tough prairie grassland had great difficulty growing anything until a blacksmith named John Deere put a steel moldboard on their old cast iron plows. But civilization has advanced in the last 150 years, and herbicides and high-tech machinery make moldboard lowing unnecessary on most soils. In fact, on competitive advantage many South American farmers have is that native grassland was converted directly to no-till soybeans and/or corn, and has never been tilled.

We know from historic tillage plots at the University of Illinois and University of Missouri that a century of plowing can reduce soil organic matter levels to half of their natural amounts. Since the OSU-OARDC tillage plots at Wooster were established in 1962, continuous no-till nearly doubled the organic matter in the tip 2 inches, while plowing has reduced it by a third.

Soil carbon research
The Ohio State University is fortunate to have on its faculty Rattan Lal, an internationally acclaimed expert on soil carbon. He wrote in Science magazine (June 11, 2004) that "soil organic carbon is an extremely valuable natural resource. Irrespective the climate debate, the soil organic carbon stock must be restored, enhanced and improved" to achieve food security.

As part of Lal's research, Extension educators in 11 counties have taken soil smaples on a variety of soil types and management practices, ranging from annual plowing to permanent pasture and woodlan. Preliminary analysis shows the value of adding manure and less or zero tillage.

Differences in soil carbon in permanent woodlands clearly show how soils have different carbon sequestering capacities. For example, Hoytville samples contained about 50% more carbon than Ellsworth, Mahoning, Chillicothe, and Ravenna soils, and twice as much as Canfield. Carbon levels in cropland with conservation tillage were roughly three-fourths of the woodland levels. Some folks might therefore argue we should maximize carbon sequestration and reverse global warming by converting farmland to woodland. But remember, we've go to eat, and a diet of nuts and tree fruit would be mighty limiting.

The bottom line is that adding organic matter to farmland is good for soil quality and crop yields, both short term and long term. Continuous no-till is about the only sure-fire way to do it. Cover crops and manure also help raise carbon levels. If you want to sequester carbon to reduce global warming (and possibly receive small annual payment) think of it as a bonus for being a good farmer.

Randall Reeder, associate professor and Extension agricultural engineer, can be reached at 614-292-6648 or reeder.1@osu.edu

 

This column is provided by the OSU Department of Food, Agricultural, and Biological Engineering.