We recently did some soil testing of our main growing areas. The last time we tested was 4 years ago so it was probably a bit overdue.
Growing veggies takes a lot from the soil so you will eventually develop mineral deficiencies and possibly also excesses if, for example, you add a lot of one type of compost.
Our market garden has two main zones. Top block where we have been farming for the longest and 4 years ago we converted this zone to a “no dig” deep compost growing system. The other zone is middle block which is larger, about 5 years younger and farmed using minimal disturbance. In both zones we minimise any activity that inverts soil, snipping out plants and weeds leaving the roots undisturbed to decompose in the soil and planting new crops by dibbing small holes just large enough to push seedlings into. The aim is to maintain the structure and microbiota of the soil.
Four years ago we tested the top block and middle block. This time we repeated the testing in these two blocks but also decided to test the paddocks, on the east and west side, as a way to see how much we have changed the soil by converting it to market gardens.
To do soil testing we take multiple samples from across the block, mix them all together and then test a sample from this so it is like getting an average measurement for the block.
One of the things we test for is the amount of organic matter present in the soil which is a useful indicator of the overall health and biological activity of the soil.
All of the samples from this year (and four years ago) show good levels of organic matter (above 6% is considered to be good) but it is interesting/disappointing to see that the levels have dropped in both top block and middle block over this four year period and both are lower than the surrounding paddocks.
Thinking about why this might be leads us to question if we might have become too good at weeding. While weeds need to be removed so that they don’t compete with the veg for nutrients, they also do provide a biodiverse soil covering that can sequester and nurture soil microbes. The high levels observed in the paddocks are most likely because this soil is always covered with a diversity of plants. The large drop in organic carbon levels in middle block may reflect that this zone was always more weedy and that it is only in the last few years that we have got on top of this…..maybe to the detriment of the soil?
It’s a compromise, this farming caper, planting monoculture rows of veg and keeping the weeds down make farming at scale more efficient but we need to think about how and when it might be better to leave the weeds (or at least or some of them) and maybe even mix up our plantings.
BP
