More humus – higher biomass activity – more stable soil aggregates – but also more weeds
A long-term plot trial established at Frick, Switzerland in 2002 has been used to study the impact of reduced tillage on soil fertility and yields under organic farming conditions. Additional factors varied in the trial are biodynamic preparations and the form of livestock manure applied, allowing for potential interactions between the three influencing variables to be determined.
Soil cultivation using the traditional mouldboard plough in Central Europe severely disturbs the soil every year as the biologically most active topsoil is inverted and thus buried while biologically less active subsoil is brought to the surface, often leading to slaking.
It is for this reason that non-inversion soil cultivation has been advocated time and again. Reduced tillage is well researched and well established in integrated production where the absence of ploughing is balanced out with the aid of herbicides, fungicides, molluscicides and highly soluble nitrogen fertilizers.
In organic farming however, the use of the mouldboard plough appeared to be indispensable for weed and pest control as well as for seedbed preparation, despite its ecologically disruptive impact. Experiences and research trial results in relation to reduced tillage are still scarce but it has become evident that rhizomatous weeds can cause tremendous problems after only a few years of reduced tillage.
In the trial described here we have optimized reduced tillage. Depending on the situation, either a chisel plough or a stubble cleaner are used. A mouldboard plough is used in control plots. The trial is being carried out under normal field conditions using standard farm machinery in a replicated split plot design with subplots nested in large strip-like main plots. It is integrated into the FiBL experimental farm and assistance is being provided by biodynamic farmers as well as by a range of researchers.
Yields under reduced tillage were 10% lower than in the ploughed control in Years 1-3; 20-30% higher in Years 4-7 and 7% lower in years 8-11. Thus, mean yields under reduced tillage over eleven years were 7% higher. Moreover, soils under reduced tillage had 17% more humus (0-10 cm), 37% more microbial biomass, better soil structure and greater water retention capacity. Protein content in cereals was not reduced in the reduced tillage plots.
At the same time however weed infestation was found to be higher in reduced tillage plots. Bindweed, a noxious weed at our site, occurs locally concentrated and so far has been present in both reduced tillage and control plots (for scientific publications see below).
The biodynamic preparations are a cornerstone of biodynamic agriculture. Despite decades of research and practical experience much remains unknown about their effects. The Swiss biodynamic farming association (Schweizer Verein für biologisch-dynamische Landwirtschaft) approached FiBL with a request to investigate and document the preparations’ effects in field trials. Practitioners are particularly interested to know whether biodynamic preparations can only exert their effects in FYM/slurry systems or whether they also work in slurry-only systems.
Field observations had led some farmers to assume that biodynamic preparations can improve soil structure which in turn would make it easier to dispense with ploughing in organic farming.
The use of biodynamic preparations yielded only some limited effects in some years. In the soil, some statistically significant differences could be shown in the microbial C/N ratio, pointing to changes in the ratio between fungi and bacteria.
Slurry-only systems provide benefits in terms of farm economics and labour efficiency. Such systems are often already in place when farmers convert to organic or biodynamic production. In biodynamic farming, however, the use of composted farmyard manure is well established (see DOK trial). The two strategies for fertilizer use differ in their objectives:
To date there had not been any comparative investigations of these two fertilizer use strategies in conjunction with different soil cultivation techniques.
So far we have only been able to ascertain that the use of slurry-only compared to the use of composted farmyard manure resulted in higher cereal yields and higher cereal protein contents.
As part of the trial at Frick, greenhouse gas emissions are currently being measured in the various cultivation and fertilizer use variants.
Data from a number of trials in Europe are evaluated in meta-analyses as part of the TILMAN-ORG and BKBA (soil and climate-friendly organic tillage farming) projects: yields and soil organic matter are the main focus of these analyses.