After months of planning, the field kit was finally deployed, but did the expectations live up to reality?
After months of planning, liaising with project partners, mitigating for a global pandemic, and hiring my partner as a research assistant to overcome challenges associated with social distancing, we were finally ready to deploy our sensors in the field. We were tasked with deploying a total of 15 soil moisture sensors across two fields at two different locations over the course of a week and to collect around 50 20cm soil cores. Ambitious? Certainly - the one week became three.
Installing soil moisture probes
Before deploying the sensors in the field, each sensor had to be manually programmed to ensure it worked and that it would record moisture measurements. The sensors provide a range of instantaneous moisture readings (as prescribed by the user) with depth which are transmitted back to an in-situ logger (although wireless data transmission options are available for ££) via cables. When installing cable networks on active farmland there are few options available for protecting both the equipment and the farmer. These options were: 1) to bury the cable below the depth of cultivation and drilling (20cm or so); 2) laying the cable at the surface and avoiding it during farming operations; or, 3) laying the cable at the surface and returning to disconnect during essential operations. An added complication with installing equipment on active farmland is the subsurface drainage network which needs to be taken into account when burying equipment in the soil. Following some detailed mapping and discussions with the farmer, we opted to bury cable at one of our sites and keep it at the surface at the other.
The gravity of digging 330 m of trench and 0.2 m in depth only struck home after excavating about 5 m of this mammoth trench. When digging through knee high pea crops on clay-rich soils in the rain, not even the greatest will in the world can overcome the frustration of peeling pea and clay platelets from your boots every couple of minutes. Needless to say, these were a tough few days for the team. BUT, we succeeded; laid the cables and installed the sensors.
Soil Core Extraction
The second essential piece of work that had to be undertaken during this initial field visit was the extraction of pre-treatment soil cores. This involved inserting 50 20cm coring tubes (made from plastic downpipe) into the soil with as little disturbance as possible (after Carr et al. 2020's recent findings). Although this method is particularly time consuming (compared to percussive techniques), it was adopted to maintain the integrity of the cores, which is important for later analysis. Once extracted, these were sealed using a combination of parafilm, freezer bags, and bubble wrap, and stored in the orientation in which they were extracted. Due to COVID-19, the lab-based analysis of the cores has been slightly delayed, but we are hoping they won't change too much during this time.
Now, just to do it all over again, and again...