SA Graan November 2015

November 2015

you can effectively be figuring out your soil’s quality and what the

plants and roots say about your soil. Walk your farm; choose the

best and worst places and observe soil profiles. An example of a

very practical test for producers is the “slaking test”, which makes

it possible to identify the quality of your soils in one easy exercise

(see

Photo 1

The jar on the left shows a degraded soil or “dirt” that collapses

when getting in contact with water, while a healthy soil on the right

infiltrates and holds all the water like a sponge.

Use appropriate indicators

Various speakers, such as Dr Rianto van Antwerpen (senior soil

scientists at SASRI) and Mr Victor Roberts (soil scientist at Cedara),

emphasised the use of an auditing system and/or indicators, meas-

uring the impact and progress of CA. Examples are: Soil struc-

ture, soil porosity, soil colour, number and colour of soil mottles,

earthworm counts and other soil fauna, soil cover at planting, crop

cover at six to eight weeks, soil depth, run-off and erosion, micro-

organisms and roots.

Again, it is of critical importance for producers to choose and use in-

dicators themselves, which will strengthen their discovery and learn-

ing process and help them to fully understand and take ownership of

important concepts and practices. This can even go as far as taking

a microscope to the field, identifying some of the weird and won-

derful creatures and very useful indicators, such as the Tardigrades

(commonly known as water bears or moss piglets) or soil mites (see

Photo 2

and

Photo 3

). Mr Ruhan Theunissen from Reitz, presented

how the quality of oil in a tractor’s engine could be an appropriate

“dipstick” to measure and compare between systems.

Understand soil life and biology…

And understand how to put that life

back into your soil

The pioneer CA producer from Winterton, Mr Ant Muirhead, widely

known as “Prof Muirhead”, supported by Prof Teague (see

Photo 4

called for the revival of soil biological capital, which is a subject

poorly understood by most, but central to soil health and sustaina-

ble agriculture. The growing academic understanding of soil biology

has slowly made its way onto producers’ fields. However, aggressive

tillage practices and excessive application of agro-chemicals, which

still prevails in most parts of the country, has largely destroyed our

soil biology. We will however have to put it back for CA systems to

function maximally.

1: A slaking test to assess soil health.

Photo: Hendrik Smith

2: Tardigrades, commonly known as water bears or moss piglets.

3: A soil mite, living in the upper layers of the soil.

Photo: Peter Webb

4: Ant Muirhead, Richard Teague and Phillip Theunissen participate in the panel discussion.

Photo:

Landbouweekblad

5: Beneficial mycorrhizal interactions with plant roots.

Photo: Dr Joanna Dames

“Producers could tap the multiple benefits of soil microbial sym-

bionts,” Prof Teague said. “We should be putting them back into

the game.”

One of the key concepts to understand and to repair is that of the soil

food web (SFW), which is the network and functioning of different

groups of soil biota and the connections between them. This process

is driven by photosynthesis, which uses carbon dioxide from the air,

combines it with water, and turns it into carbon, of which about 40%

is released as exudates by the roots into the soil, mostly in the form

of sugars, with some carbohydrates and proteins. These carbon

exudates are food or bait for soil microbes, which in return supply

soil mineral nutrients to the roots. Prof Teague discussed one of the

most important symbiotic relationships plants have, which is with

arbuscular (tree-like) mycorrhizal fungi. In this symbiosis the fungus

colonises two different environments – the roots of the host plant

and the surrounding soil – connecting the two with its long hyphae

(see

Photo 5

This enables the host plant to have an improved uptake of water and

mineral nutrients conducted along those hyphae. This relationship

has been documented in connection with many minerals, including

phosphorus, nitrogen, zinc and copper. One way of getting a handle

on soil biology, is to start measuring or analysing soil biological indi-

cators; some laboratories in South Africa have been rendering those

services for a while.

Weed management imperatives

A separate session on the challenges and solutions of weed and in-

sect management involved some agri-businesses in presenting their

best practices. As a summary of this session, Dr Charlie Reinhardt

(dean: Villa Academy), said that the benefits for sustainable crop

production that are associated with CA practices are unequivocal.

From a weed management perspective, however, it removes the im-

portant method of mechanical control from the producer’s “toolkit”.

This, to a large extent, makes practitioners of zero-tillage reliant on

chemical control (herbicides).

The practice of cover crops for weed suppression is gaining ground

in zero-tillage systems, for perfectly good reasons. It should be not-

ed that this biological way of weed management is mainly based

on chemistry. Dead plant material and live plants (weeds and crops)

exude biochemicals that can inhibit the growth and development of

not only plants (weeds and crops) but also micro-organisms. The

phenomenon is called “allelopathy”.