Flood-damaged soil benefits from full tillage
Many growers and livestock farmers will be looking at the sad state of their soils this spring after the soggy winter, writes Heather Briggs.
There are lots of different advisers out there, and each can help growers with their particular on-farm problems.
But, to get an overall view I have been talking to New Zealand specialist soil scientist John Baker, who was nominated twice for the World Food Prize and whose technology is recognised by the United States Department of Agriculture and the Food and Agriculture Organisation of the United Nations.
Stripped
He told me that flood-repair is one situation that will benefit more from full tillage of the soil rather than no-tillage (or direct drilling).
Any organic matter and soil microbial life in that eroded soil will have been stripped out and washed away, so it is the time to take exceptional remedial action, he told me.
Flood waters are usually heavily charged with silt washed from land upstream leaving behind almost inert, silt-laden "dirty water".
When this is allowed to pond for any length of time the silt will slowly settle out and deposit itself as fine mud on the soil surface,.
Dr Baker firmly recommends allowing this mud to dry until it is workable and then turning it into productive soil.
The problem is that because it is devoid of organic matter, soil microbes, air and structure, it is not a good idea to contemplate no-tillage initially, he told me, adding that the best first thing to do is to mix it with the top soil beneath it by aggressive tillage.
Ploughing is ideal but even rotary hoeing is acceptable.
The underlying top soil will provide a source of microbes and organic matter, and the tillage will aerate the soil. The process may be accelerated by spreading manure and straw, and working this into the soil too.
When I spoke to him, Dr Baker also strongly emphasised this mixing by tillage should only be done once, as it is a destructive process in itself and is very much a case of 'short term pain for long term gain'. After the first mixing, the regime should then turn to minimum-disturbance no-tillage with as much organic matter return as possible in the form of animal manure or crop residues (straw).
He pointed out that there is a new generation of low-disturbance no-tillage machines available that will handle virtually any level of surface residues and minimise the physical disturbance of the soil that has just been mixed.
The residues from then on are best left to decompose on the surface of the ground where soil fauna (including earthworms and other micro-organisms) will incorporate it into the soil without disturbing it, which would otherwise oxidise the organic matter that is already there.
Thereafter, Dr Baker insisted, a regime of continuous low-disturbance no-tillage will maximise the accumulation of soil organic matter with all of its advantages, not the least of which will be improved crop yields.
* Heather Briggs is the former manager of an agricultural growers' co-op who now works in the agri-PR sector.
