What can spectroscopy, geophysics and imaging tell us about the status of our crop and soils management practices?
Getting a clear and quantifiable picture of soil heath and measuring the impact of certain crop management and cultivation practices on soils is notoriously difficult. The AHDB-funded Crop Rotations programme is exploring how technologies used in the fields of imagery and geophysics can be applied to better understand soils to help fill the knowledge gap.
Fingerprinting the profile of agricultural soils
An important measure of soil health is organic matter content. “Fourier Transform Infra-red (FTIR) spectroscopy is like chemical fingerprinting and can give us insights into the soil organic matter content of soils very accurately” said Dr Jean Robertson, Head of Infrared Spectroscopy at the James Hutton Institute (JHI). “Using FTIR, we were able to capture subtle but evident differences between the addition of farm yard manure and inorganic fertilisers over time, at Rothamsted’s long term experimental sites.”
Another important measure for assessing soil health is porosity. “Soil pores structure affects water behaviour in soil and has an impact on how fast roots can elongate into the soil” explained Dr Tracey Valentine, root biologist at JHI. Multispectral imaging, a tool commonly used for remote-sensing above ground, has the potential to be used as a tool for assessing soil porosity. “Already, we are seeing promising results from the comparison between an intact and repacked soil core” said Dr Valentine.
These technologies are still in their early stages and some more work is needed to see them form part of the soil health tool kit for farmers in the future. But already, experiments have shown that there are some interesting insights to be gained.
Applying the laws of geophysics to soils
One aspect of geophysics that is fast gaining traction in agriculture is soil electrical conductivity. “It is essentially a measure of how easily an electrical current can flow through soil” explained Dr Andy Binley, Professor of geophysics at Lancaster University. “Because current flows through fluid, wet soils show higher conductivity than dry soils; so soil conductivity can be used as a proxy for soil moisture, dryness and compaction”.
“It is a popular method because it is non-invasive, provides rapid results and can sense to several metres depth” emphasised Prof Binley. “In our potato field experiment, the drier and more compacted soils were less conductive than the wetter and less compacted soils. We also related this data to the impact such characteristics can have on the plants above ground – the uncompacted well-watered soil was associated with the densest plant canopy.”
“It’s interesting because soil conductivity is already commercially available. However, what is on the market provides more of a qualitative snapshot. Going forward we want to be able to provide more quantitative information from measurements over time” concluded Prof Binley.
Establishing crop management zones
Effectively identifying field variability is an important starting point to implement a more targeted approach to managing inputs and crops. Dr Alice Milne, agricultural systems modeller at Rothamsted Research, has been mining potato yield monitor data and NDVI (a type of vegetation index) to identify whether crop management zones can be established. The data suggests that this is possible with both types of data but significant differences between zones were not always observed in all fields tested.
“NDVI data only gets us so far. It’s the following step of management decision-making that is important for farmers. To determine how to manage each of these different zones, it’s really important to integrate other sources of information into the process, together with farmer knowledge” concluded Dr Milne.