Why do you think it’s more important than ever to look after our soil now?
Because of the intensification in modern farming practices, there’s increasing need for greater yields. This requirement puts a lot of stress on the soil, although compaction is an issue, in general less organic matter is being incorporated into the land, which is key for soil health.
Has soil health diminished?
In general, yes. It’s partly to do with the availability of organic matter and farmyard manure. If you have a mixed farm, then you have the availability of manure, but there are plenty of arable farms with no livestock. Another source of organic matter is straw, but this has a different value to what it did 30 years ago. Today, it’s often taken off the field, when before it would have been a matter of course to incorporate it back into the land.
Critically, there isn’t enough manure produced by livestock in the UK, to fertilise the soil we grow for other crops.
In cereals, the change mostly came in the 1960’s and 1970’s when we saw a ‘green revolution’, increased fertiliser use and new dwarf cereal cultivars resulted in reducing lodging, and making harvesting easier. At the same time, we had new crop protection products available to enhance crop yields.
The introduction of dwarf cultivars has also directly impacted on the amount of organic dead root material incorporated into the soil, because the roots of these varieties are smaller.
What impact have the changes in farming practices over the last 50 years meant for soil health?
The amount of root material incorporation has changed in 50 years. As a matter of course, root material has always been incorporated back into the land. The dead root material dies off and produces organic matter in the soil. The use of shorter cultivars with smaller roots means less root material, and therefore less organic matter.
What are the measures of soil health?
There are several different parameters associated with good soil health. These generally fall into three broad categories that are symbiotic, and relate very closely with one another. One key common factor they have is that they all benefit immensely from the presence of organic matter:
1. Biological: for soil to be at optimum health, it needs to have a diverse microbial population, and this is maintained by organic matter content. The more diverse the microbial population, the healthier the soil is, and the less likely it is for the crop to succumb to disease and for crop growth to be optimised.
2. Physical: compaction inhibits drainage and stops the soil breathing. Heavy machinery and tyre pressure all contribute to compaction, that’s why it’s important to spread the weight over the field as much as you can, and pay attention to lowering tyre pressure where possible.
3. Chemical: organic matter is also crucial to increasing the bio-chemical availability in the soil. The turnover of microbes and their activity in breaking down organic material involves chemical changes, physical fragmentation and the release of mineral nutrients. There needs to be a gradual release of nutrients into the soil.
How can we measure soil health?
I’m very interested in how we can measure soil health, but it’s a tricky area. Some scientists believe there’s no such thing as soil health because it’s so difficult to define. Optimum soil health for cereals might be very different to that required for legumes for instance. Soil scientists and agronomists understand there are different parameters associated with soil health.
Current soil analysis usually doesn’t consider things like soil health in terms of microbial population. The good news is that farmers will be able to have their soil tested for microbial diversity, very soon.
What about the future?
We know it’s crucial to incorporate organic matter, in the same way that it’s important to apply fertiliser, because even though the immediate gains of applying nitrogen are more apparent, in the long term, the health of crops will be improved.
However, the resources required are not always obtainable. Animal manure is not always available and straw has a premium value, and I’m a realist and a pragmatist – farmers do have to think about the bottom line.
Waste material from anaerobic digestion units could be utilised more, as could the employment of products like ‘Bio-char’. This is a name for charcoal from wood or plant material created from pyrolysis of biomass. It’s an organic slow release material, and incorporating it means the carbon is slowly broken down by microbes in the soil.
In the future a farmer may not just be applying fertiliser, but also in a mixture with organic matter to maintain soil health.