Soil Agronomy

Agronomy is the science and technology of producing and using plants for food, fuel, fibre, and land reclamation in an efficient safe manner. Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science. Agronomy is the application of a combination of sciences like biology, chemistry, economics, ecology, earth science, and genetics. Agronomists today are involved with many issues including producing food, creating healthier food, managing environmental impact of agriculture, and extracting energy from plants. Agronomists often specialize in areas such as crop rotation, irrigation and drainage, plant breeding, plant physiology, soil classification, soil fertility, weed control, and insect and pest control.

Agronomists use biotechnology to extend and expedite the development of desired characteristics of particular plants to particular soils. Biotechnology is often a lab activity requiring field testing of the soils using the history of the soils in question. That is what chemicals and what crops have been used on the soils in the past.

In addition to increasing crop yields through better soil management agronomists use biotechnology to help increase the fertility of the soil. Fertility goes hand in hand with productivity.

Agronomists study sustainable ways to make soils more productive and profitable. They classify soils and analyse them to determine whether they contain nutrients vital to plant growth. Common macronutrients analysed include compounds of nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur. Soil is also assessed for several micronutrients, like zinc and boron. The percentage of organic matter, soil pH, and nutrient holding capacity (cation exchange capacity) are tested and analysed. Agronomists will interpret these lab reports and make recommendations to balance soil nutrients for optimal plant growth. (See Composts and Elements for Growing.)


Agroecology is the management of agricultural systems with an emphasis on ecological and environmental perspectives of the soil. This area is closely associated with work in the areas of sustainable agriculture, organic farming, alternative food systems and the development of alternative cropping systems based on permaculture.

Soil conservation is a set of management strategies to lessen the affects or reduce totally the soils alteration from chemicals due to overuse, acidification, salinization or other soil contamination.

Agronomists are also involved in the development of methods to preserve the soil and to decrease the effects of erosion by wind and water. Agronomists also seek ways to use the soil more effectively in solving other problems which include the disposal of human and animal wastes; water pollution; and also the build up in the soil of pesticides and herbicides.

A technique called contour ploughing and contour ripping is the ploughing and ripping across a slope, is commonly incorporated into farm and forestry plans to prevent soil erosion and to conserve rainfall rather than have the water runoff causing erosion through scouring. Contour farming was practiced by the ancient Phoenicians, and is known to be effective for slopes between 2 and 12 percent. Contour plowing can increase crop yields from 10 to 50 percent, partially as a result from greater soil moisture retention.

Terrace farming was practiced by the ancient Chinese and is very effective on steeper slopes. Terracing is the practice of creating near level layers on a hillside setting. Terraced farming is more common on small farms and in countries where labour is cheap or where land use is paramount, since mechanized equipment is difficult to deploy in these situations. Terrace farming can increase crop yields from 20 to 50 percent, partially as a result from greater soil moisture retention.

Terrace farming in Nan Chong County Southern Sichuan Province.

No tilling is a new technique now used to help prevent erosion especially in agro forestry. This method incorporates deep ripping across slopes or cross ripping techniques on level land. Cross ripping breaks the soil especially hard clays or cluggy clays. It mixes a small amount of the top soil and allows for deep penetration of water which would normally run off. Cross ripping also allows better root development along more than one plane. Planting of the trees is done where the rip lines intersect each other. We incorporated this method at Nana Glen with excellent results on clay over shale. The trees were planted ahead of the wet season and never watered or fertilized following the initial planting.

Tough soil binding grasses planted along contours can be utilized on steeper slopes at regular intervals to prevent or reduce soil runoff.

For better effect, contour drains of depths up to 1 metre deep may help retain the soil and prevent permanent wash off. These usually need regular maintenance to remove the soil and debris and cart it back up the slope. Another method is to incorporate a 500mm to meter deep pond with gentle grassed sloping sides on the upstream side of dams to prevent siltation. We did this at Nana Glen and with other strategies never had to clean it out in the 20 years we owned the orchard.

Windbreaks are central to the ability of surface soils to retain their integrity, soil moisture retention both with respect to erosive forces and chemical change from nutrient depletion. They are created by planting sufficiently dense rows of trees and shrubs on the windward exposure of an agricultural field subject to wind erosion. Evergreen species are preferred to achieve year round protection. Properly positioned and planted windbreaks using the correct trees and shrubs will prevent wind erosion, retain soil moisture and will not affect either crops or animal farming activities. Tests carried out by the Western Australian Agricultural Department actually showed an increase in production from crops and better quality meat from animals ranging amongst windbreaks were incorporated into the farming plan. Windbreaks also assisted in regulating temperatures keeping the plots warmer in winter and cooler in summer.

Crop rotation is simply the conventional alternation of crops on a given field, so that nutrient depletion is avoided from repetitive chemical uptake/deposition of single crop growth. The inter and intra planting of legumes and Asteraceae species like the various marigolds Tagetes erecta have proven very successful in increasing nitrogen and decreasing detrimental fungal diseases and nematodes in the soil. We utilized white Haifa Clover Trifolium repens with Stinking Roger Tagetes minuta to great effect in the orchard while maintaining a full grass cover right up to the trunks of the trees.

Perimeter Runoff Control:

Trees, shrubs and ground-covers are effective perimeter treatment for soil erosion prevention, by insuring any surface flows are impeded. A special form of this perimeter or inter-row treatment is the use of a “grass way” that both channels and dissipates runoff through surface friction, impeding surface quick runoff, and encouraging infiltration of the slowed surface water.

Salinity Management: The ions responsible for salination are: Na+, K+, Ca2+, Mg2+ and Cl-. Salinity is estimated to affect about one third of all the earth’s arable land. Soil salinity adversely affects the metabolism of most crops, and erosion effects usually follow vegetation failure.

Salinity in soil is first caused by poor irrigating methods. It occurs when the crops are irrigated with saline water. It can also occur when irrigation is done during periods of high evaporation dry atmospheric conditions or high temperatures. During the evaporation process the water from the soil evaporates leaving the salt behind causing salinization. Salinization causes the soil structure to break down causing infertility. It also causes movement of water from the plants to the soil under unfavourable conditions like during heat waves thus reducing the plants health to the point of death. Our dam water when initially tested was 400 parts per million sodium positive ions. As citrus are low salt tolerant we aware of what this meant as our soil was also marginal for citrus until the soils health could be turned around. This is one of the reasons we used the micro jets to capture the moisture of night fogs which were common in our district. The additional moisture over 39mm was captured coupled with very low evaporative rates meant that we had in affect lowered the salt concentrates to a level acceptable to the trees.

The second method is that of over irrigating which causes the saline ground water deep below the surface to rise into the root zone of the crops or trees causing their eventual demise. This type of salinity occurs on drylands from overirrigation and in areas with shallow saline water tables. In the case of over irrigation, salts are deposited in upper soil layers as a byproduct of most soil infiltration; excessive irrigation merely increases the rate of salt deposition. The best-known case of shallow saline water table capillary action occurred in Egypt after the 1970 construction of the Aswan Dam. Many areas of southern, western and central Australia are subject to this kind of salinity.

The use of humic acids may prevent excess salination, especially in localities where excessive irrigation was practiced. The mechanism involved is that humic acids can fix both anions and cations and eliminate them from root zones. In some cases it may be valuable to find plants that can tolerate saline conditions to use as surface cover until salinity can be reduced; there are a number of such saline tolerant plants that are native to Australia like the saltbushes (Atriplex semibacatta) and Senna artisimioides.

The third problem will be felt as a result of Global Warming where land is going to be inundated from the ocean. This will mainly affect good low lying coastal land.

Soil Organisms: When worms excrete in the form of castings, a balanced selection of minerals and plant nutrients is made into a form accessible for root uptake. Research from the USA points to earthworm castings having five times more available nitrogen, seven times more available phosphates and eleven times more available potash than the surrounding upper150 mm of soil. The weight of casts produced may be greater than 4.5 kg per worm per year depending on the species. By burrowing, the earthworm inadvertently creates soil porosity, creating channels enhancing the processes of aeration, moisture retention and drainage. Fungi can increase the root surface area of a plant by up to 60 times. This aides in moisture uptake in dry periods and the uptake of certain minerals. In exchange the fungi receive waste products from the plant. A true symbiotic relationship. Fungi have been known to transport aspirin from healthy plants to diseased plants aiding in recovery. It is being studied at he moment that aspirin to a plant is akin to penicillin to humans.

Red stinkhorn, Aseroe rubra left & Cortinarius sp. right a more conventional looking fungi are just two of the 25,000 fungi in Australia that work tirelessly in breaking down organic matter in the soil and assisting higher order plants in nutrient take up by increasing the plants root surface area by up to 60 times.,2000).

Mineralization of the Soil: To allow plants full benefits of their phytonutrient potential, active mineralization of the soil is sometimes undertaken. This can be in the natural form of adding crushed rock, compost or the addition of chemical soil supplements. In either case the purpose is to combat mineral depletion of the soil. There are a broad range of minerals that can be added including common substances such as phosphorus and more exotic substances such as zinc and selenium. There is extensive research on the phase transitions of minerals in soil with aqueous contact.

The process of flooding can bring significant quantities of sediment to an alluvial plain. While this effect may not be desirable if floods endanger life or if the eroded sediment originates from productive land, this process of addition to a floodplain is a natural process that can rejuvenate soil chemistry through mineralization, macronutrients addition and organic matter.

Agriculture Soil Conservation

On the Farm:

  1. Practice no till farming. With no till farming, crops are allowed to remain rather than being plowed under at the end of the season. This practice keeps soils anchored in place rather than having bare ground exposed to wind and water during the non growing period. It also saves on time and money on buying fuel and repairs.
  • Use terrace farming. This type of farming uses the topography of the land to slow water flow through a series of terraces. This manipulates the water flow preventing it from gathering speed and washing soil away from farmlands.
  • Practice contour farming. Contour farming replicates the effects of terrace farming, but on a smaller scale. Rather than planting crops in straight vertical rows, crops are planted following the contour of the landscape. Crops planted up and down hillsides create pathways for water to flow. Crops planted parallel to the land slow the flow of water that prevents soil erosion.

Round the Home:

  1. Reduce impervious surfaces. Impervious surfaces like driveways and patios allow precipitation to flow freely over them. Water flow gains momentum when moving over such surfaces and can then erode stream banks and lakeshores. A good compromise is to use paving stones rather than a concrete slab for your patio to allow the water to percolate down into the soil. Another method is to have a slight side slope on the driveway so the water runs sideways and does not collect all in one place. The use of swales will help stop the momentum and allow water to percolate downwards on the property.
  • Plant a rain garden. A rain garden is a shallow depression in your yard, which will collect precipitation or run off. They work better in more impervious soils. It prevents soil erosion and gives you an opportunity to grow plants which prefer a little more water during the wet season. This is my favourite and saves heaps on water in both cost and time.

3. Collect Rain Water. You can divert your roof rain water into rainwater tanks for use in the future. Your roof, after all, is another impervious surface. You can use the water you collect for your garden or fish tanks. We then use the fish tank water on the garden so around and around it goes. In this way, you can conserve water and soil. another method is to construct swailes so tha run off water slows and penetrates the soil.

Parks, Gardens and Farms:

  1. Plant windbreaks. Suggest to the local authority to do some additional native landscaping in which you would be willing to plant and maintain. In addition to preventing erosion, these plantings will lower wind velocities around your home helping to protect it from wind damage.

2. Restore wetlands. Wetlands are one of the most effective ways to prevent soil erosion. Wetlands or ephemeral pools act as natural sponges, absorbing rainwater and preventing it from carrying the soil away. They also provide great habitats for birds and other wildlife help prevent water pollution and retain moisture in the surrounding soil for longer periods.

3. Plant buffer zones along stream and seasonal stream banks. Buffer zones help hold stream banks intact during times of flooding. They also prevent runoff from entering waterways. Buffer zones would include a mixture of grasses, shrubs, and trees. Most local authorities have Green Groups or concerned citizens wishing to participate in revegetating and maintenance projects and welcome the input.

4. Re establish forest cover. The re-establishment of natural forest cover provides an extensive, tree-root network that offers a long-term solution to soil erosion. It can function both as a windbreak and a means to anchor soils in place. Again most local authorities have Green Groups or concerned citizens wishing to participate in revegetating and maintenance projects and welcome the input.

5. Arrange to have someone-else’s organic waste to be delivered and used on the block. We use woodchip when the electricity authority is clearing powerlines. This saves additional transport and is cheaper than buying from town.

6. Don’t burn mulch it. Burning adds to atmospheric CO2 and dissipates a lot of the minerals into the atmosphere away from the block.

Further Comments from Readers:

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