The importance of observation when soil sampling

Fert Options
with Robin Boom
Agronomic Advisory Services

I enjoy walking around farms observing the pasture make up and vigour, and discussing my observations with farmers as I take soil samples.

Earlier today I took some samples off a run-off owned by a dairy farmer. Last year it looked to be struggling, mainly because fertiliser inputs had been minimal, with little clover and a dominance of low fertility grasses and obvious urine patches.

He applied a capital application of potassium and phosphorus and what a difference it made a year later.

There were good sized clover over the whole property and ryegrass was now the dominant species and the pastures were really pumping.

The farmer could see the big improvement himself, and with the healthy clovers the whole natural nitrogen cycle was working properly, rather than the anaemic looking pastures dotted with green urine patches observed a year before. It now looked as vibrant as his dairy farm.

It is one thing to get soil test data back from a laboratory, but this also needs to align with what you observe in the field, and that is why I found it strange that this spring Ballance reps were not taking many soil tests for farmers, but rather Hill Laboratories were employing their own staff to go around and take samples on behalf of Ballance reps.

I can see this as being a win-win for both companies, as it gives the Ballance reps more time to visit more of their clients and work on fertiliser recommendations using Overseer and econometric models, and Hill Laboratories win by getting more soil samples through their laboratory.

The problem I have with this model though is that it is important to actually walk through paddocks and make mental observations as you go on different parts of the farm, and by not observing the pastures first hand, an important link missing. Also when I push the soil probe into the soil, I can tell how tight or free the soil itself is, whether it is biologically alive or dead, and if there are compaction or drainage problems which in themselves can be just as important an issue as the chemistry of the soil.

Sometimes I find with dairy farms in particular that the chemistry may be at optimum levels, but there may be an absence of clovers, too much poa or weeds like mouse eared chickweed, shepherds purse, sorrel, yellow bristle grass or stinking mayweed which tell their own story. On other properties the pastures may be open for some other reason, such as drought, pests or the overuse of nitrogen. In such situations I may suggest pasture species need to be considered a priority instead of fertilisers.

On hill country pastures, the grass, clover and weed species found are even more diverse than dairy farms and this is often determined by soil fertility. Clovers which are stunted or discoloured, pale around the edges or have red markings are all indicative of different elements which are deficient. Similarly with grasses, the dominance of browntop, sweet vernal, crested dogstail, danthonia, rice grass, or chewings fescue, all of which are often termed ‘native grasses’, not because they are native to NZ because they are not, but because they are the ones that persist and survive on low nutrient levels, or ‘native’ background fertility. All of these species point to some factor of fertility which is limiting production, but it is more often the clovers which are the canary of  pastures, and ‘native grass’ dominance is caused by the absence of good legume growth, which fix free nitrogen which encourages the more productive grasses to compete.

Visual observations are vitally important in helping diagnose deficiency symptoms, a bit like a good vet can look at a cow and often tell what the issue is or a good GP can observe and push and prod to see what the ailment is. They will of course also use blood tests and other tissue tests to confirm their observations, as an agronomist will also confirm symptoms through laboratory analyses.

There also comes the question of what is tested for in the laboratory. Many farmers I believe are short-changed as their fertiliser rep will only look at six elements, yet plants need at least 16 elements to grow and animals at least 17. This is one of the reasons I use Brookside Laboratories based in Ohio as their standard tests analyse 13 elements and there are other elements or means of testing the soils for looking at nutrient levels which provide more and better information than just relying on the old Olsen P test and MAF Quick Tests. The Olsen P test was developed in the early 1950s by Dr Olsen of Colorado State University using baking soda for the alkaline soils of the American mid-west. The question which should be asked is why are we still using 1950s technology when there are more modern and better tests used internationally on acidic soils like ours.

ROBIN BOOM Member of the Institute of Professional Soil Scientists



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