Noted US scientist says zero-till best for the environment

In addition, tillage is detrimental to fungi/bacteria ratios that are vital to carbon and nitrogen storage. Minnesota, US, research suggests carbon dioxide emissions related to tillage are proportional to the volume of soil disturbed.

These reflect some of the views of Minnesota retired United States Department of Agriculture, Agricultural Research Service, soil scientist Dr Don Reicosky when addressing the USA 2019 National No-Tillage Conference.

He stresses that a cloud of CO2 rises behind any tillage tool and that the invisible gas is indicative of soil organic matter loss, a loss that negatively affects soil fertility, water infiltration, soil biology and overall soil structure.

These views are consistent with Australian researchers who have studied tillage and cropping systems over the last 40 years.

Australian research has, for example, shown that no-till or zero-till combined with plant residue preservation, compared with cultivation farming, captures and stores more soil water, generally have higher yields, have more soil organic matter (including soil carbon), and dramatically reduces soil erosion.

Research Dr Reicosky and colleagues have been involved with compared five tillage practices against no-till, which included only a tractor pass through the plot to provide the same compaction that other cultivation treatments would experience.

The research found that a significant portion of CO2 loss came immediately after tillage and was proportional to the volume of soil disturbed.

Dr Reicosky stresses that intensive tillage with a deeply-engaged tillage tool is a double negative from a carbon footprint standpoint. More diesel exhaust entering the atmosphere and more CO2 from the burp of CO2 escaping from the soil explains this finding". Soil is lost not because we farm, it's lost because of how we farm" Don Reicosky stresses.

Dr Reicosky reports that long-term studies from the late nineteenth century to about 2000 in Illinois and Missouri show, regardless of cropping systems, land on research plots farmed continuously over more than a century have shown steady declines in soil organic matter (SOM). Tillage is the prime suspect in the carbon loss shown in these studies, along with similar findings at other USA land-grant universities. Significantly less carbon is lost in systems with the least tillage.

In a case for more pasture in a farming system Dr Reicosky notes that in addition to removing a third of available carbon at harvest to feed ourselves and our animals, we've also changed from growing perennial species that put 60-90 per cent of their biomass below ground to annual species that put only 15-20pc of their biomass below ground. We have less carbon being returned to the soil.

Don Reicosky says using an implement like a moldboard plough (common in the US) or disk harrow further exacerbates carbon loss by disturbing soil and the biological activity that enables carbon and nutrient cycling synergies.

Carbon and nitrogen storage depends upon the ratio of various fungi to bacteria in the soil, and the fungi are much more susceptible to tillage damage Dr Reicosky notes.

"If we want to store more carbon and nitrogen for subsequent crops, we must try to maximize this ratio," he said.

"Any type of tillage will damage the fragile hyphae filaments on soil fungi and that works against optimum ratios," he explains.

"Another soil ingredient that thrives in the presence of soil fungi, and by being left alone, is glomalin, a glue-like carbohydrate that helps bind soil particles together to form larger beneficial aggregates, which allow water and oxygen infiltration around roots."

US research shows no-till management allowed glomalin to more than double in three years of no soil disturbance, he explains. Where soil had not been disturbed for 15 years, glomalin content was four times as great.

"This tells me we have to do something to protect soil fungi, and right now the best thing we can do is reduce soil disturbance," Don Reicosky stresses.

Next week: Rapid drought pasture recovery.