On the farm – SpongeBob soil

I’m sure many of us will have been watching what has been going on in Australia this summer with increasing dread, especially as our own mercury has continued to climb.

As I write, it is already seven weeks since any significant rain, after a year of rainfall being more than 20 per cent below normal. Temperatures consistently in the thirties and strong winds don’t help soil moisture retention. Our landscape looks increasingly like Australia. Of course, we’ve had droughts before, but arguably they are becoming the norm rather than the exception, especially here in the north.

This has major relevance for our food production systems, which depend on our previously reliable rainfall and year-round pasture growth. So is there anything that we can do to help build more resilience into our soils and improve moisture retention? The answer is yes, a lot. In fact, building more hydration into our soils is also the remedy for achieving global cooling.

There are two key aspects and, ideally, they need to be done together for best effect. The first is to restore the hydrology of any wetlands left in our farmed landscape. We have lost the vast majority of our wetlands to drainage, but, unfortunately, while this may give us a little more winter grazing, it severely compromises our summer grazing by dropping the water table. Once this is coupled with shorter plant root depths (see how this has happened below), we are in trouble. Wetlands aren’t only important wildlife habitats, they are crucial “kidneys” for the health of our farmland as a whole, by helping maintain adequate soil hydration, as well as filtering sediment and toxins from waterways.

The second aspect is the soil structure itself. To build water retention capability we need more humus in our soils, which means more carbon. To achieve this we need to harness the power of sunlight through plant photosynthesis, combined with the powers of fungal mycelia (threads) in a healthy soil. This crucial relationship is what builds soil humus. The plants are able to make liquid sugars from water and carbon dioxide, powered by sunlight, and they exchange these for other minerals, nutrients and moisture. The fungi and other soil microbes take these liquid carbons down into the soil where they form humus. In this way it is possible to not only increase soil humus, but to actually grow topsoil, and relatively quickly – years, not millennia.

To encourage the soil fungi and other micro-organisms, which are required for a healthy soil structure, we need to reduce the amounts of chemical inputs. Unfortunately, these are toxic to much of our soil microbiology and contribute to impoverished soil health, soil losses by erosion, and hence also to shorter plant root depths. It becomes a self-reinforcing cycle that is hard to break out of. The good news is that there are plenty of fertilisers and other inputs that actually feed the soil biology rather than harming it, and in that way we can contribute to soil moisture retention as well as global cooling.
Not bad for a wee sponge, eh Bob?

Internationally respected soil microbiologist Walter Jehne will speak at NorthTec, Whangarei on March 2. Visit northlandclimatechange.org for details.

Bev Trowbridge