June update
Most of June has involved watching cover crops grow! but we also completed a series of soil measurements including visual soil assessments (VSAs) and worm counts, and we have sampled for labile soil carbon.
To monitor the cover crops’ development, we have made weekly ground cover measurements since germination using the smartphone Canopeo app. Canopeo allows us to track growth many times without disturbing the crop in our key measurement plots.
We saw that the annual ryegrass in the conventional treatment plots reached a high ground cover percentage faster than the mixed oats, radish, vetch, sunflower mix in the hybrid and regenerative plots which are relatively sparsely planted. By the end of June, there was less difference, and the cover crops are much taller than the ryegrass. We intend grazing the ryegrass with lambs once the soil dries out some! The mixed covers will not be grazed. We will make harvest cuts and determine the actual dry biomass in all the plots before we terminate the cover crops.
We think we are starting to see changes in the VSA tests, generally in a positive direction. Three examples are shown below. But remember, one image from a test at one time of year is not enough to give statistically relevant answers!! What we do see is that annual ryegrass can give good nutty structure quite quickly. Given the different cultivation that the treatments were given before tomatoes, we are not too surprised to see some differences. The hybrid plots suffered from a rotary hoe while the soil was still wet, and the subsequent pan development remains noticeable. The soil moisture was ideal for VSA when we did these in early June, and that will have helped increase scores relative to those we did in wet soil in previous seasons.
Carbon in the soil takes many forms, including mineral/inorganic calcium carbonate, the main component of limestone. The organic carbon components are often thought of as fitting into one of two pools: the “stable” and “labile” fractions. The stable fraction, which may be protected by clay minerals or soil aggregates, or be chemically persistent, takes years to centuries to decompose and to build up so annual changes are very small. Labile carbon breaks down in days or years and is the portion of soil organic carbon that consists of soil microbial biomass carbon, dissolved organic matter, and easily oxidative organic matter. Because it can be readily decomposed by soil organisms, it is the fraction of soil organic carbon with the most rapid turnover times, and its oxidation drives the movement of CO2 between soils and atmosphere. It is an active source of nutrition and an indicator of change in the soil.
We are sampling all carbon at the beginning, middle and end of the Carbon Positive project. We are sampling for labile carbon a couple of times each year, basically in spring and autumn. We have been taking labile samples to 60cm depth, split into 0-15, 15-30, and 30-60cm bands. These are the very active root zone in the cultivated depth and the area below it, which still has significant root and micro-organism activity. As well as Hill Laboratories’ measurement of labile carbon percentage using the Hot Water Extractable Carbon method, we are determining the actual soil bulk density so we can accurately assess the tonnes of labile carbon per hectare. Hill Labs has a very informative technical note on soil carbon tests.
We also completed the Milestone 7 report which gives a lot of information about the development and outcomes of the process tomato crops we grew with Heinz-Watties last summer. Now we are reviewing our plans for the coming season and making sure things are ready.