Flood-repair is one situation that will benefit more from full tillage of the soil rather than no-tillage (or direct drilling), says the New Zealand specialist soil scientist John Baker.
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 observes. Flood waters are usually being 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,” continues Dr Baker. He firmly recommends allowing this mud is to let it 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 remarks. “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 of straw and working this into the soil too.”
But, Dr Baker strongly emphasises, 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 points out that there is a new generation of low-disturbance no-tillage machines available that will handle virtually any level of surface residues and minimize 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, insists Dr Baker, a regime of continuous low-disturbance no-tillage will maximize the accumulation of soil organic matter with all of its advantages, not the least of which will be improved crop yields.