Soil monitoring

Introduction

The health of our farming or grazing enterprise is dependent on the condition of our soil. A healthy well balanced soil will produce high yielding crops and pastures and an unbalanced soil will not be able to provide nutrients when a crop requires feeding. Therefore, the first and most important step is to conduct a benchmark of the soil resources. Many farmers hand the job of soil testing to the local agronomist and expect him to take responsibility for their success. It is far better for the farmer to conduct his own testing and then discuss options with local agronomists.

  1. Important - ensure that the soil test is worth doing. If you only test for the basics, it may not help to resolve any issues at all. If you are going to the trouble of collecting a soil sample, do it right and pay for the right information. A basic test may cost $120 and a thorough test may be $160. Pay a bit more and get the right info.

  2. Important - pay for your own independent test to be conducted - this will give you peace of mind.

  3. Important - conduct a topsoil test (0-30 cm) to assess the plant establishment requirements and a subsoil test (30 - 60 cm) or even (30 - 90 cm) to assess the nutrients at depth.

  4. Each soil test lab uses different methods of measuring available nutrients - some use mild acid forms and some use stronger forms to release the nutrients. Whichever the lab uses, ensure that the test also provides a total amount of each nutrient (especially for phosphorous).

  5. Conduct a test in the worst soil type, the best soil type and a paddock you want to work on. This will give you the basic, good, bad and ugly.

  6. Where possible also conduct a microbiology test to assess the capacity and diversity of biology in your soils. You will need to ensure you have active growth and collect some root material in your sample.

  7. Most labs do not give recommendations - you will need a good agronomist to discuss the recommendations. Then look at options for the application of nutrients and amendments.

Soil Monitoring is divided into three major areas:

These three areas require different testing methodologies.

Collecting a sample

The soil sampling protocol is fairly standard today with two main options.

Generally a soil sample is no more than 300 - 400 grams for nutrients and maybe 100 grams for microbiology.

You will need to decide how many samples are required to get a representative sample.

Follow the link to a video showing how to take a soil sample. Soil collection video

Background to soils

The three key parameters of soil are:-

Look below the surface - Technology of Growing Grass

Nutrients - Chemistry

For many years, nitrogen, phosphorous and potassium (NPK) have been the only nutrients most agronomists concentrate on because these were the most limiting and soils were fairly balanced. However, today many agronomists are now looking to find the next most limiting factor which could be sulphur, zinc, boron or any number of nutrients. Therefore, it is worth knowing a little more. The chemistry of our soils is similar to that of a battery with positive and negative charges and transfer of nutrients via water as soluble salts. The ability for our soils to hold and release nutrients is called the Cation Exchange Capacity (CEC), while the key nutrients that hold onto the clay colloid include:

The second component and extremely important one is the humus, carbon or organic matter. Some soil tests give an organic matter %, others a carbon %. The humus is the portion of the organic matter that can hold onto nutrients, act like a sponge, filter or sieve to stop leaching or volatilisation. This sponge can also hold onto four times its own weight in water. In the past 200 years, we have lost at least 80% of this sponge and this is the key reason why our soils no longer manage droughts or floods well.

Other minerals in our soils include Sulphur, Zinc, Manganese, Copper, Boron, Iron, Molybdenum, Silicon, Cobalt and Selenium to name a few. Each mineral has a role within the soil and within the plant species as well as in the animal and humans. If one mineral is out of balance, it can severely impact on another minerals nutritional role.

pH or potential of hydrogen mostly known as the level of alkalinity or acidity of the soil is also a critical factor in nutrient flow from soil to plants. pH varies from about 3 (highly acid) to 6.5 - 7 (neutral) to 14(highly alkaline). Most minerals become more available to plants at the neutral level, while some minerals are more available in alkaline soils.

The most important Best Practice activity would be to conduct a soil nutrient test with a lab such as Environmental Analysis Laboratory (EAL) at Southern Cross University, Lismore.

Example soil test 2012 - EAL

Living soil - biology of soil

In the past 50 years, and still continuing, many scientists focus on what they can see on top of the ground and ignore the things we cannot see (eg. under the soil). It is difficult to find many specialists or extension staff who accept the biology in the soil is an issue, let alone how to manage for it. The soil is the place where it’s all happening, as the smallest change on top can make enormous changes beneath the surface. Our failing crops, root bound pastures and many diseases are established from the actions on top of the ground. The chain reaction is felt throughout the soil. Soil is as much a living thing as a physical entity. The soil provides a habitat for soil organisms; consequently the use and management of soils will have significant effects on species diversity and conservation of biodiversity.

Soil micro-organisms such as protozoa, nematodes, bacteria and fungi are essential to the functioning of our soil. Although, science in agriculture in the past has largely ignored the part we cannot see, climate change is at last bringing it to the table for discussion. The microbes carry out biochemical transformation and act as a source and sink for nutrients. These are the forgotten essential components for healthy soil.

Murphy (2000), summarises that soil microorganisms (bacteria and fungi) only make up a few percent of the total OM, but this still equates to hundreds of kilograms of living organisms per hectare. The microorganisms continually ‘turnover’ as individuals divide, grow and then die. Microorganisms use the dead OM in soil as food. As they breakdown the OM, any excess nutrients they don’t need are released into the soil in forms that plants can use. This process is called mineralisation. Soil animals such as earthworms also play an important role in breaking up OM into smaller pieces, but it is the micro-organisms that are responsible for the actual release of nutrients.

Example Biological analysis poor - CIAAF- Microbiology Laboratories Australia

Example Biological analysis good - CIAAF- Microbiology Laboratories Australia

Fungi

The “grazing web of life” (figure 5) shows the fungi are essential for healthy grazing systems due to the mycorrhizal (symbiotic) relationship formed with most pasture plants as the fungi extend the root system to source nutrients and water for itself and the host plant. The fungi receive energy from the roots in response to supplying nutrients. Up to 1.5 million species of fungi exist worldwide and still little is known of the real function they play. In an ideal grazing situation, the bacteria to fungi ratio should be approximately 1: 1

Organism

Kg/ha

Bacteria

1000

Fungi

2000

Algae

100

Protozoa

200

Nematodes

50

Worms

1000

Plant roots

2000

Figure . Weight of soil organisms in the top 15 centimetres of a fertile soil.
Organism Kilograms of live weight/Ha

Bacteria

Another symbiotic relationship between plants and microbes involves soil based bacteria. The best known common soil bacteria relationship, rhizobium, invades the root and multiplies within the cortex cells. Legume nitrogen fixation starts with the formation of a nodule (Lindemann 2003). The plant supplies all the necessary nutrients and energy for the bacteria. Within a week after infection, small nodules are visible with the naked eye, although the bacteria is only about one thousandth of a millimetre long. In the field, small nodules can be seen 2-3 weeks after planting, depending on legume species and germination conditions. When nodules are young and not yet fixing nitrogen, they are usually white or gray inside. As nodules grow in size, they gradually turn pink or reddish in colour, indicating nitrogen fixation has started. The pink or red colour is caused by leghaemoglobin (similar to haemoglobin in blood) that controls oxygen flow to the bacteria. A single gram of soil has also been estimated to contain several thousand species of bacteria (Torsvic et al et al 1994). Bacteria are also important in the decomposition of pasture into organic matter.

Protozoa and Nematodes.

Protozoa and nematodes also play an important role in the functioning of soil. As an example, protozoa are able to digest many bacteria and release large amounts of nitrogen for plant use. The number of individual soil animals in the soil is enormous. In all but the driest environments there are billions of protozoa per square metre (m2), millions of nematodes/m2 and 100 000’s of mites/m2. Data from east Beverly in Western Australia, found that there were approximately 800 million protozoa/m2, 900 000 nematodes/m2 and 130 000 mites/m2 in a soil under pasture.

Vadakattu (2004) explains that soil protozoa play a critical role in crop health by actively attacking pathogenic fungi such as rhizoctonia root rot and through the release of essential plant nutrients tied up in micro-organisms. The total biomass of living organisms in a healthy soil may exceed 20 tonnes per hectare and its diversity can be compared to that of a coral reef (Wallwork 1976)- only far more complex. Microorganisms utilize more than 70% of the annual plant production from intensively grazed pastures (Hutchinson and King 1982) and therefore play a huge role in the biochemical and physical environment of the soil. Best Practice recommendation is to conduct a soil test for microbial capacity.

BACK TO TOP

Based in Yeppoon, we're proud to service Queensland and New South Wales