Results from monitoring
Cover crop growth
As seen in the boxplot chart above, the canopy cover (percentage of the ground covered by the cover crops in each treatment) varied with the conventional annual ryegrass planted into cultivated soil getting most cover earliest, and the regenerative oats/vetch and lupin mix direct-drilled into uncultivated soil starting slowest. The regen cover crop mix still had gaps even at the end of September, by which time the ryegrass had been terminated in the hybrid plots and grazed in the conventional ones.
NOTE: Box plots show both the difference between treatments and the difference within a single treatment. The dark-blue box at the furthest left shows the range of ground cover percentages measured in the conventional system plots on the 14th of June. The centre and right dark-blue boxes show the same for the hybrid and regenerative systems plots. The stretched boxes and lines show there is a lot of variation within each system, and the different positions of the boxes show there is a lot of variation between the systems, with conventional having the most ground cover and regenerative having the least. The other colours show the same things at different times over the winter.
The amount of dry matter produced under each system, however, tells a different story.
In the box plot above, we see there was not very much difference in the dry mass of cover between the three growing systems in mid-August, although it looks as though the regenerative oats/vetch/lupin mix might be a little bit higher. Because there is quite a lot of overlap between the three treatments (growing systems) we found there was not a significant statistical difference. That means we couldn’t be sure they were actually different to one another. We stopped measuring the conventional system after August because it was being grazed by lambs. When we measured the hybrid plots again in September, before we sprayed them out to get ready for strip-tilling, we found they had increased a little, and were more even across the plots. By mid-October when we weighed the amount of biomass in the regenerative plots, we found there was a lot of material. This was what was needed for the planned mulch planting.
Cover crop nutrients
When the regenerative treatment cover crop was terminated, samples were sent to Hill Laboratories for testing. The levels of key macronutrients are shown in the chart below.
The chart shows that the nutrient levels in the regenerative plots are a little variable. In general, plot 3, which produced the least amount of biomass over the winter, also had comparatively lower nitrogen, phosphorus, potassium, sulphur, calcium and magnesium, when compared to the other three plots. We also found that the western end on plot 3 had the lowest baseline soil carbon level of any plot. We do not know yet what is behind these findings, so can only say there seems to be some correlation.
Slugs
Slug pressure was measured using the Oregon State University ‘Relative Slug Activity’ method. Four flowerpot bases were placed in each plot along the existing transect. Lids were left for several days. Slugs on each lid, and in the plant matter under each lid, were counted and weighed. This measure does not give ‘total number of slugs per hectare’, but it does provide a relative measure of slug pressure. The number of slugs per lid varied from 0 – 10, and the total weight varied from 0 – 7.5 g/lid.
As a result of monitoring, it was determined that slug controls should be applied prior to planting. The best time for this was before we mulched the regenerative cover crop, and we applied 10 kg/ha of IronMax using an Airborne Solutions drone.
Visual Soil Assessment
Visual Soil Assessment (VSA) was delayed due to high soil moisture conditions, but was completed over several days before groundwork commenced. Most VSAs were done in the plots, but some samples were dug out to ensure soil wasn’t disturbed by cultivation activities, and the assessments done in the shed.
All VSA results across all plots ranked as ‘Moderate’, with total scores ranging from 15.5 – 20.6.
The conventional ryegrass had been cultivated after the sweetcorn crop and had more, finer roots than the uncultivated regenerative oat/vetch/lupin crop. We noted that soil in the regenerative treatment plots was drier than in the other treatments. This makes sense, because the ryegrass was terminated much earlier than the oats mix, and therefore had much less evapotranspiration. In the regenerative treatment plots, the soil structure was blockier and harder to break up. This may be due to historical compaction issues and limited mechanical loosening (worsened by a wet season), or due to the oats taking up more moisture from the soil.