Compiled by: Etienne Bruwer, Ruan Gagiano, and Renier Bothma, Agronomists at Kynoch

Dryland agriculture, where crops rely on natural rainfall instead of irrigation, demands meticulous soil management and precise nutrient strategies—particularly for maize and soybean production. A critical framework to achieve optimal yields is the 4Rs of nutrient management: applying the right source, at the right rate, at the right time, and in the right place. Additionally, managing soil compaction—a prevalent issue in dryland systems—is essential to ensure sustainable crop performance.

The 4Rs of Nutrient Management

1. Right Source

Selecting the appropriate fertiliser type is vital for maximising nutrient efficiency. Maize thrives with nitrogen-rich fertilisers, whereas soybeans—being nitrogen-fixing crops—require sufficient phosphorus and potassium to reach their full potential.

For Maize: Nitrogen-based fertilisers, such as coated urea, are recommended for their ability to minimise nutrient losses due to volatilisation.

For Soybeans: Phosphorus and potassium applications are essential for promoting robust growth. Additionally, inoculants can enhance nitrogen fixation, which plays a key role in supporting plant health and productivity.

2. Right Rate

The fertiliser application rate should be based on soil test results to address nutrient deficiencies effectively.

For Maize: Fertiliser quantities must be adjusted according to soil test data, historical yield patterns, and projected rainfall.

For Soybeans: Although soybeans require less nitrogen due to biological fixation, soil analysis should inform the optimal application of phosphorus and potassium to support growth and yield.

3. Right Time

Applying fertiliser at the appropriate time is particularly important in dryland systems, where water availability may vary.

For Maize: Split nitrogen applications—first at planting and later during key growth stages—ensure that nutrients are available when the plant needs them most, maximising uptake efficiency.

For Soybeans: Fertiliser should ideally be applied before or early in the growing season to ensure that roots can access nutrients crucial for establishment and development.

4. Right Place

Correct placement of fertiliser minimises nutrient loss and ensures efficient delivery to the root zone.

For Maize: Placing fertiliser close to the roots reduces losses from volatilisation or runoff, especially under dry conditions.

For Soybeans: Phosphorus and potassium should be positioned near the roots to ensure these essential nutrients are readily available as the plant matures.

Addressing Soil Compaction

Soil compaction poses a significant challenge in dryland systems, as it limits root penetration, impedes water infiltration, and reduces airflow in the soil profile. Managing compaction effectively is critical for improving water uptake and maintaining optimal yields.

Strategies to Prevent and Mitigate Soil Compaction

• Reduce Tillage: Minimising tillage preserves soil structure, facilitating water retention and promoting healthy root growth.
• Implement Cover Crops: Deep-rooted cover crops such as radishes naturally break up compacted layers while improving water infiltration and moisture conservation.
• Adopt Controlled Traffic Farming (CTF): Restricting machinery to specific paths prevents widespread compaction, allowing better root development in non-compacted zones.
• Subsoiling: In severe cases, subsoiling can help fracture compacted layers; however, this practice must be applied cautiously to avoid disrupting the soil’s moisture-holding capacity.
• Incorporate Organic Matter: Adding organic material, such as crop residues or compost, enhances soil structure and reduces compaction. Organic matter also improves the soil’s water-holding capacity, which is especially beneficial in dryland systems.

Conclusion

Achieving high yields in dryland maize and soybean production requires a dual focus on nutrient management and soil health. By applying the 4Rs—right source, rate, timing, and placement—farmers can optimise fertiliser efficiency. At the same time, managing soil compaction through reduced tillage, cover crops, and organic matter enrichment enhances soil resilience, ensuring sustained productivity under challenging environmental conditions.

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Soil is not just a passive environment where plants grow, but a dynamic, living system that plays a critical role in agricultural success. While it is often perceived as a vast reservoir of water, nutrients, microbes, and organic matter, assuming that plants will simply draw from these resources as needed, this viewpoint oversimplifies the true complexity of soil-plant interaction. For farmers seeking to optimise crop yields and soil efficiency, it is vital to grasp the fundamental processes that govern the relationship between soil properties, root systems, and nutrient availability. By deepening our understanding of these factors, we can unlock the full potential of our land, improve plant health, and maximise the return on agricultural investments.

The Importance of Soil Chemistry in Plant Growth

At the core of soil and plant interaction lies soil chemistry. The ability of soil to supply essential nutrients, facilitate water movement, and support microbial life directly influences plant growth and productivity. Understanding the chemical properties of soil, such as pH, cation exchange capacity (CEC), and organic matter content, allows farmers to make informed decisions regarding fertiliser application and soil management.

Soil pH, for instance, significantly impacts nutrient availability. In highly acidic or alkaline soils, certain nutrients become less available to plants, resulting in poor growth. By adjusting soil pH through the application of lime or sulphur, farmers can ensure that nutrients are in their most bioavailable form, enabling crops to take up nutrients more efficiently. Cation exchange capacity is another key factor, as it reflects the soil’s ability to hold and exchange nutrients. Soils with high CEC have a greater capacity to retain essential cations such as potassium, magnesium, and calcium, reducing nutrient leaching and improving plant uptake.

Soil Structure and Its Impact on Root Development

Soil structure—the arrangement of soil particles into aggregates—also plays a crucial role in plant growth. Well-structured soils have good aeration, water-holding capacity, and root penetration, allowing roots to explore a larger volume of soil and access more nutrients. Compacted soils, on the other hand, restrict root growth, reduce water infiltration, and limit oxygen availability, all of which negatively affect plant health.

Farmers can improve soil structure by incorporating organic matter, such as compost or cover crops, into their fields. Organic matter acts as a binding agent, promoting the formation of stable soil aggregates. Additionally, no-till or reduced-till farming practices can help maintain soil structure by minimising soil disturbance and promoting the activity of soil organisms like earthworms, which play a key role in creating channels for water and air movement.

Nutrient Uptake Mechanisms: How Plants Absorb Essential Elements

To understand how plants interact with soil, it is essential to explore the mechanisms by which they absorb nutrients. Nutrient uptake is not a passive process; rather, it involves a combination of root growth, soil properties, and chemical interactions. There are three primary mechanisms through which plants acquire nutrients: interception, mass flow, and diffusion.

1. Interception: Direct Root Contact with Nutrients

Interception occurs when plant roots physically encounter nutrients as they grow through the soil. Although this mechanism only accounts for a small percentage of nutrient uptake—approximately 1% for maize—it plays a role in absorbing nutrients such as phosphorus, potassium, and zinc. The efficiency of interception depends on root density, soil structure, and the availability of nutrients in the soil. In well-structured soils with an abundance of organic matter, root growth is more extensive, increasing the chances of direct contact with essential nutrients.

2. Mass Flow: Nutrients Carried by Water

Mass flow is the movement of nutrients dissolved in soil water towards the roots as plants take up water. This mechanism is particularly important for the uptake of nutrients that are mobile in the soil, such as nitrogen (in the form of nitrate), calcium, and sulphur. In environments with adequate rainfall or irrigation, mass flow is a dominant mechanism for nutrient uptake. However, in dry conditions, the effectiveness of mass flow decreases, making it important for farmers to monitor soil moisture levels and adjust irrigation practices accordingly.

3. Diffusion: Movement of Nutrients from High to Low Concentration

Diffusion is the movement of nutrients from areas of higher concentration to areas of lower concentration, driven by a concentration gradient. This mechanism is particularly important for nutrients like phosphorus, potassium, and zinc, which are less mobile in the soil. These nutrients are often bound to soil particles and need to diffuse through the soil solution to reach plant roots. Farmers can improve diffusion by placing fertilisers close to the root zone, ensuring that nutrients are within reach of the growing roots.

The Role of the Rhizosphere in Nutrient Availability

The rhizosphere—the narrow region of soil surrounding plant roots—is a hotspot of biological activity and plays a critical role in nutrient availability. Root exudates, which include sugars, amino acids, and organic acids, are released into the rhizosphere and influence nutrient availability in several ways.

Root Exudates and Microbial Interactions

Root exudates feed soil microbes, which, in turn, play a vital role in nutrient cycling. For example, bacteria in the rhizosphere can convert organic forms of nitrogen into plant-available forms like ammonium and nitrate. Similarly, mycorrhizal fungi form symbiotic relationships with plant roots, extending their hyphae into the soil to access nutrients like phosphorus that would otherwise be out of reach.

Chelation and Nutrient Solubility

Certain root exudates, particularly organic acids, can chelate (bind) metal ions like zinc, iron, manganese, and copper, making them more soluble and available for plant uptake. This process is especially important in soils with high pH, where these micronutrients may be present but not in a form that plants can easily absorb. Chelation improves the bioavailability of these essential nutrients, promoting healthier plant growth and development.

pH Modification in the Rhizosphere

Plants can actively modify the pH of their rhizosphere by releasing hydrogen ions (H+) or bicarbonates (HCO3-), depending on the nutrient needs and soil conditions. For example, in response to low phosphorus availability, plant roots may release organic acids that lower the rhizosphere pH, increasing the solubility of phosphorus and making it easier for plants to absorb. By understanding how plants interact with their rhizosphere, farmers can tailor their fertilisation practices to ensure that nutrients are available in the right form and at the right time.

Precision Fertilisation: Maximising Efficiency and Minimising Waste

Precision fertilisation is a key component of modern farming practices that aims to apply the right amount of nutrients at the right time and place. By understanding the mechanisms of nutrient uptake and the role of the rhizosphere, farmers can make informed decisions about fertiliser application, ensuring that nutrients are used efficiently and sustainably.

For example, nutrients that rely on diffusion, such as phosphorus and potassium, are most effective when placed near the root zone at planting. In contrast, nutrients that are mobile in the soil, like nitrogen and sulphur, can be broadcast or applied through fertigation. Tailoring fertilisation strategies to the specific needs of the crop and soil conditions not only improves nutrient use efficiency but also reduces the risk of nutrient runoff and environmental pollution.

Conclusion: Enhancing Crop Performance Through Soil-Plant Interaction

Optimising soil and plant interaction is key to improving agricultural productivity and sustainability. By understanding the complex processes that govern nutrient uptake, farmers can implement more effective soil management and fertilisation practices. This knowledge allows for better utilisation of resources, reducing input costs while increasing crop yields. Kynoch Fertilizer’s range of enhanced-efficiency fertilisers, along with expert agronomic advice, can help farmers optimise their fertilisation programmes for long-term success.

For personalised advice on improving nutrient management and soil health, contact Kynoch Fertilizer’s experienced agriculturalists on 011 317 2000 or info@kynoch.co.za

Compiled by: Hentie Cilliers or Chris Schmidt from Kynoch Fertilizer

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References

• Barber, S.A. (1995). Soil Nutrient Bioavailability: A Mechanistic Approach. 2nd edition. John Wiley & Sons.
• Marschner, H. (1995). Mineral Nutrition of Higher Plants (2nd edition). Academic Press, San Diego.
• McKenzie, B.M., Mullins, C.E., Tisdall, J.M., Bengough, A.G. (2012). Root-soil friction: Quantification provides evidence for measurable benefits for manipulation of root-tip traits. Plant Cell Environ, 36, 1085-1092.
• Mengel, K. (1995). Roots, Growth and Nutrient Uptake. Department of Agronomy publication # AGRY-95-08 (Rev. May-95). Purdue University, USA. Link. Accessed on 27 August 2024.

The post Unlocking Soil-Plant Interaction: Boost Crop Growth with Enhanced Fertilisation Strategies first appeared on Kynoch Fertilizer.

The multifunctionality of this phenomenon is evident in its roles in nutrient cycling, biological pest control, and the regulation of water and air availability, which are influenced by a combination of physical, chemical and biological factors.

The multifunctionality of this phenomenon is evident in its roles in nutrient cycling, biological pest control, and the regulation of water and air availability, which are influenced by a combination of physical, chemical and biological factors.

The complex relationship between soil health, water quality, and climate change can involve multiple perspectives, resulting in a complicated theoretical mixture.

This overview focuses on farmers and their soil at grassroots level, with sustainability in mind within our practical reality. What steps can the farmer take to begin improving soil health?

Add organic matter to the soil
In South Africa, the levels of organic matter in soils are very low, with approximately 58% of soils containing less than 0,5% organic carbon. The amount of organic matter varies depending on factors such as climate, vegetation, topography and soil texture.

Increasing the organic matter in the soil will have direct and indirect benefits for soil quality. Microbes break down plant residues in the soil to convert them into carbon.

The availability of inorganic nitrogen, soil water conditions, and temperature all have an impact on the rate of decomposition. Increased cultivation can lead to a faster breakdown and depletion of carbon. Therefore, it is recommended to minimise tillage and promote root growth by using seaweed extracts, adding calcium, magnesium, zinc and boron, as well as using humic acid (liquid carbon).

Micro-organisms in the soil
There are two main approaches that could be followed:

Add microbes to the soil: Adding microbes to the soil can have beneficial effects. This can be achieved by using granular fertiliser that is coated with microbes, applying organic material that contains microbes, or using liquids that contain microbes. Dry products can be spread evenly over the soil or placed in specific areas.

Feed microbes already in the soil: There is a large population of micro-organisms in the soil, estimated to be around 100 billion per gram of soil. When plant roots are in the soil, they come into contact with these microbes. The highest activity of microbes is typically found in the top 20cm of soil. Therefore, it is beneficial to provide carbon sources such as humic acid and fulvic acid to feed these microbes.

Add ‘housing’ for microbes
Carbon, such as biochar, organic roughs, or humic acids, can be utilised as a soil amendment to enhance crop growth by regulating soil conditions. This is due to its distinctive qualities, including a large surface area, a rich pore structure, an abundance of oxygen-containing functional groups, and a high cation exchange capacity.

Spray microbes on plants
Each plant possesses a microbiome that consists of fungi, viruses and bacteria, which play crucial roles in the plant’s functioning and survival. These micro-organisms can be found in various areas, such as the root zone (known as the rhizosphere), the internal environment of the plant (endosphere), and the above-ground surfaces (phyllosphere).

Farmers have the option to introduce microbes to the plant’s above-ground growth through foliar sprays or to the soil through soil drenches.

Irrigation
The practice of wetting soil profiles and subsequently withholding water for an adequate duration to facilitate the re-establishment of oxygen in the soil is considered a beneficial approach, as it effectively mitigates the occurrence of prolonged anaerobic conditions.

Conclusion
Lastly, it is worth noting that crop rotation is a highly effective management strategy that exerts a significant influence on microbial diversity within the soil.

Author: Dr Chris Schmidt

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Mankind is dependent on the soil for its needs for food and fibre for humans, feed for livestock, and, of late, contributing to our energy supply with crops grown primarily for biofuels. Soil is a dynamic and multifunctional living system that exists as a relatively thin layer on the Earth’s crust. (Singh & Ryan 2015).  Soil is not an inert growing medium – it is a living and life-giving natural resource. It is teaming with billions of bacteria, fungi, and other microbes that are the foundation of an elegant symbiotic ecosystem (USDA).

Soil health is defined as the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans (USDA).

As world population and food production demands rise, keeping our soil healthy and productive is of paramount importance. By farming using soil health principles and systems that include no-till, cover cropping, and diverse rotations, more and more farmers are increasing their soil’s organic matter (SOM) and improving microbial activity. As a result, farmers are sequestering more carbon, increasing water infiltration, improving wildlife and pollinator habitat—all while harvesting better profits and often better yields (USDA).

Soil Organic Carbon (SOC) found in the living matter in soils acts as a sink that traps and stores CO₂ – a major contributor to global warming. Soils represent the largest terrestrial pool of carbon: each hectare can store up to 50 – 300 tonnes of carbon (UNCCD 2014).

By increasing crop yields and productivity on available arable land, fertilisers help protect carbon-rich forests, peatlands, wetlands and grasslands by minimizing land use changes. Increased productivity through fertiliser use has spared 1 billion hectares of virgin land from cultivation between 1961 and 2005 and saved the equivalent of 317 – 590 billion tonnes of CO₂ emissions (the same as total global pre-1800 CO₂ emission levels) (Burney et.al. 2010).

With better management, farmland soil could also store up to an extra 1.85 billion tonnes of carbon each year (7 billion tonnes of CO₂): around the same amount of CO₂ emitted every year by the global transport sector (Zomer et. al. 2017).

The best way to capture more carbon on farmland is to use fertilisers to optimize plant growth and yields and leave crop residues in the field after harvest.

For every 2 – 3 tonnes of carbon stored above ground in plants, one (1) or more tonnes of carbon are generally stored below ground in the roots and root exudates.

Applying fertilisers following the 4R nutrient stewardship principles (Right nutrient source at the Right rate, at the Right time and in Right place) enhances nutrient use efficiency, which reduces nutrient losses to the environment, including in the form of greenhouse gases. Effective and efficient fertilization is a vital part of the climate-smart agricultural practices that could reduce global emissions by 5.5 to 6 billion tonnes of CO₂ equivalent per year: around the same as removing 1,500 coal-fired power plants from the energy sector (Smith et. al. 2007).

To help fight climate change we need to use fertilisers globally to grow more crops on existing farmland to protect carbon stored in wild ecosystems and increase the carbon stored in our agricultural soils (IFA 2018).

References:

• Bijay Singh and John Ryan 2015. Managing Fertilisers to Enhance Soil Health. First edition, IFA, Paris, France, May 2015. Copyright 2015 IFA.
• International Fertiliser Association (IFA) 2018. Integrated Plant Nutrient Management
• Jennifer A. Burney, Steven J. Davisc, and David B. Lobella, 2010.  Greenhouse gas mitigation by agricultural intensification.  Proceedings of the National Academy of Sciences (PNAS), June 15, 2010 107 (26) 12052-12057.
• Smith, P., D. Martino, Z. Cai, D. Gwary, H. Janzen, P. Kumar, B. McCarl, S. Ogle, F. O’Mara,  C.  Rice, B. Scholes, O. Sirotenko, 2007: Agriculture. In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
• UNCCD (2014) The land in numbers: Livelihoods at the tipping point. 2014. Secretariat of the United Nations Convention to Combat Desertification ISBN: 978-92-95043-90-9
• United States Department of Agriculture: Natural Resources Conservation Service: Soil Health.
• Zomer, R.J., Bossio, D.A., Sommer, R., & V. Verchot, (2017). Global Sequestration Potential of Increased Organic Carbon in Cropland Soils. Sci Rep 7, 15554.

Author: Graham Peddie from Kynoch Fertilizer

Soil Health in Sustainable Agriculture

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