Digging holes in pasture near Takaka recently provided a wealth of information. The site visited was an area close to the coast that had been regularly cropped for a number of years with the soil applied nutrients being conventional high analysis water soluble N, P, K, S, inputs.
Over a period of several years crop yields declined to the point where it was deemed no longer financially viable to continue cropping and the decision was made to return the area to pasture to be rotationally grazed.
The reason for the decline in yield was not the lack of major growth nutrients, but a steady decline in humus. Humus is the result of the breakdown, carried out by soil organisms, of plant matter. The decline of humus resulted from both regular cultivation with soil exposed to the atmosphere for prolonged periods and the probable overuse of soluble fertilisers particularly nitrogen.
My initial visit to the area was three years ago soon after the initial application of a remedial nutrient input programme based on local Golden Bay Dolomite, along with soft phosphate rock and elemental sulphur.
At that time, as it was at the time of the recent visit, there had been a great deal of heavy rain during the month prior. The soil had been hard underfoot, with few earthworm casts visible and the grass plants were growing with their crowns well above the soil surface. Although a sand based soil, there were puddles covering a significant area of the paddock.
Now the soil is soft underfoot, and feel is a valid measure when carried out regularly, with the surface almost entirely covered in worm casts, some of which were very large indicating the presence of deep burrowing worms along with others working closer to the surface.
Although recently grazed there were few obvious dung patches and only in the wetter hollows were urine patches obvious. The soil surface was more than 90% covered in a range of pasture species, all with their crowns close to the soil surface and there were no puddles although there had been heavy overnight rain.
Digging a number of holes to the subsoil depth of about 300mm, a little over a spade depth, showed that the majority of plant roots were going straight down. Many of the root ends at 250 – 300mm were white and fine indicating they had recently grown, with few darker roots indicating ongoing breakdown of old root mass.
There was no obvious break line at 75 – 100mm depth indicating the soils ability to rebound from the pressure exerted by stock feet. A truly healthy soil does not compact under rotational grazing regimes where stock are well fed and on areas for a maximum period of 48hours.
A walk to the fence line confirmed our judgement that soil health was excellent. The stock that were resident in the area and had recently grazed the paddock, were in outstanding health. Although they could have eaten more, had more feed been offered, they were all large framed animals with dark glossy coats and even without drenching there was not a dirty tail to be seen.
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