SEYMOUR – A project conducted in 12 northeast and east central Wisconsin counties in the early summer of 2016 was designed to detect the differences between agricultural production methods, the application of liquid dairy manure, the decomposition of plant debris and the response of soil microbes.
The project was carried out by Extension Service agriculture agents from June 20 to July 15. They buried cotton cloths at five different sites in their localities: in a woodland, in agricultural fields with differing crop rotation and tillage practices and at a site of their choice as a way to identify differences in the rate of decomposition of the plant residues.
A report on the findings was given at the 2017 annual meeting of the Outagamie County Forage Council by Shawano County agriculture agent Jamie Patton. As a specialist in soil science, she asks everyone to realize that “soil is alive” thanks to its extensive microbial system.
Patton's initial take on the results, which are yet to be completed, is that there is a definite “manure, microbe, money” connection for crop production in favor of reduced tillage on heavier soils. The role of manure in the scenario is to support the activity of bacteria that provide a quick breakdown of the plant residue and convert it to mineralized and useable nutrients for the subsequent crops.
No tillage or minimum tillage serves a different purpose in that it boosts the fungal activity in the soil, Patton indicated. She explained that fungi provide the glue which holds soil particles or aggregates together, thereby improving soil health, boosting water storage capability and lending to nutrient uptake for plants.
The ideal is to have a one to one ratio of fungi and bacteria in agricultural soils, Patton stated. As was clearly indicated with the placement of the cotton cloths in woodlands, where fungi thrive, the decomposition rate at those sites was much slower, she reported.
The fungi are ideal for the slow decomposition of leaves and wood in forests and for the decomposition of lignin and shells, Patton observed. As a result, not much naturally sourced nitrogen is produced in woodlands, she noted.
Slow decomposition in woodlands results in a high carbon to nitrogen ratio, Patton continued. This means that forests store carbon and build organic matter in the soil much faster than occurs on agricultural land, she said.
Before it was converted to agricultural production within the past two centuries, much of the soil in the area had organic matter of about 8 percent – a number that has since fallen to less than one half of that in most cases, Patton pointed out.
Natural nitrogen load
Within the approximately two ton of bacteria in soil per acre are the rhizobia which fix nitrogen and make it available for plants, Patton indicated. She cited research which shows that healthy soil will provide 71 percent of the nitrogen needed to grow corn and 77 percent of it when there is a corn and soybean rotation.
“Did you know that?” Patton asked. “That's amazing.” She had applied those numbers to the production of corn silage with the equivalent of 150 bushels of corn grain per acre, resulting in the per acre removal of 171 pounds of nitrogen, 71 pounds of phosphorus, 187 pounds of potassium, 16 pounds of sulfur and 0.25 pound of zinc.
In the spring of 2016, the slow uptick of the microbial activity in the soil was evident in the early weeks of corn growth in some areas, Patton recalled. She pointed out that the lack of such activity is not visual in the soil.
During the 2016 project, there were definite differences, quite obvious along a north/south line, on the rates of decomposition in the agricultural fields, Patton reported. She cited the differences in soils — sandy in the north and heavier loam or clay in the south — as a possible reason.
In general, the counties to the north had the most decomposition where there was a combination of tillage, an application of manure, and a corn and soybean rotation, Patton pointed out. She added that manure is essential to adding to the biomass in sandy soils.
“Manure is my favorite fertilizer when used at the right time and place,” Patton remarked. She also mentioned that plant debris from cover crops helps to support the bacterial activity that supplies nutrients to plants.