Source: This post was originally published on Agresol
Reducing nitrogen fertiliser is an essential step for farmers seeking to cut costs, promote environmental health, and build sustainable soil systems. Over-reliance on synthetic nitrogen fertilisers has not only increased production costs but also led to nutrient imbalances, soil degradation, and greenhouse gas emissions. Fortunately, there are effective, nature-based methods to reduce nitrogen fertiliser inputs without sacrificing crop yield or soil health. In this guide, we’ll explore five key strategies:
- Growing legume crops
- Cover/Catch crops
- Microbial solutions
- Storing N as Amino Acids
- Using Humic substances
These can help farmers naturally boost soil fertility and reduce the need for synthetic nitrogen, meaning lower input costs and most importantly, more profit for you!
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1 – Biological Nitrogen Fixation With Legumes
Legume crops are one of the most effective and natural ways to reduce nitrogen fertiliser inputs in farming systems. These plants, including beans, peas, lentils, and clover, have a unique ability to fix nitrogen from the atmosphere into the soil through a symbiotic relationship with nitrogen-fixing bacteria called Rhizobium.
This means legumes can naturally produce their own nitrogen AND increase the nitrogen content in the soil for the following crop. Additionally, legumes can share their nitrogen with nearby crops via mycorrhizal fungi networks.
How Legumes Work to Fix Nitrogen
Legumes have specialized root nodules where Rhizobium bacteria live. These bacteria take nitrogen from the air and convert it into a form that plants can absorb, specifically ammonium or nitrate. This process is known as biological nitrogen fixation (BNF). By incorporating legumes into a crop rotation or as cover crops, farmers can significantly reduce the need for synthetic nitrogen fertiliser.
For reference, depending climate, rainfall, species and biomass production, legumes can produce up to 300kg of FREE nitrogen and although if used as the cash crop, some of that nitrogen remains in the paddock for the following crop.
Using Legumes
- Crop Rotation: Incorporate legumes into your rotation, alternating them with other crops like cereals or vegetables. This helps maintain soil fertility and reduces the risk of nutrient depletion.
- Cover Cropping: Plant legumes as cover crops in fallow periods or between main crop cycles. This provides nitrogen fixation throughout the year and helps prevent soil erosion. For example, in the photo below is a mostly clover cover crop that produced more than 200 kg N/ha.
- Inoculation: Ensure that legume seeds are inoculated with the correct Rhizobium strains for optimal nitrogen fixation. If legumes are grown in a field for the first time, inoculation may be necessary to establish a robust nitrogen-fixing bacteria population.
By using legumes as a tool for nitrogen fixation, you can reduce you nitrogen fertiliser inputs for the legume crop itself as well as produce nitrogen for the following crop.
2 – Scavenging N with Cover/ Catch Crops
- Cover crops play a vital role in managing nitrogen (N) in the soil, particularly in scavenging excess nitrogen and preventing nutrient losses. Nitrogen scavenging by cover crops can help optimize nitrogen use efficiency, reduce the need for synthetic fertilisers, and protect water quality. Here’s an in-depth look at how cover crops contribute to nitrogen management:
What is Nitrogen Scavenging by Cover Crops?
Nitrogen scavenging refers to the ability of cover crops (or a catch crop) to absorb and take up nitrogen from the soil, particularly after a cash crop has been harvested. This process helps to prevent nitrogen leaching, a phenomenon where nitrogen moves beyond the root zone and potentially contaminates groundwater or nearby waterways. Cover crops act as a buffer, reducing nitrogen losses and improving nitrogen retention in the soil.
This is particularly useful as the cover crops convert nitrogen from nitrate and ammonia into amino acids which are stored in a stable for and can act as a flow release once the cover crop has been terminated. Crops like radish and turnips rapidly decay to release nitrogen back into the soil for the following crop. To understand more about the importance of nitrogen form for plant health check out our blog about John Kempf’s Plan Health Pyramid.
Types of Cover Crops That Are Effective for Nitrogen Scavenging
Cereal Rye, Oats and Barley:
- Rye, oats and barley are great cover crops for nitrogen scavenging for the upper layers of the soil. They grow quickly in the Autumn and can absorb a significant amount of nitrogen. Rye also helps reduce nitrogen leaching during the off-season, making it an ideal cover crop for protecting water quality.ng in regions with winter rains.
- Millet and Sorghum:
- Similar to above, millet and sorghum are grasses that grow quickly and scavenge nitrogen from the top layers of the soil. However, Millet and sorghum are summer growing crops that can be used after a winter cash crop.
- Radish, Turnip and Mustard:
- While primarily used for soil aeration, radish, turnips and mustard also have a great ability to scavenge nitrogen, especially in deeper soil layers. It can access nitrogen that would otherwise be lost to leaching and bring it to the surface, where it becomes available to other crops.
3 – Microbes As a Nitrogen Source
In the pursuit of sustainable agriculture, one of the most promising innovations lies in understanding and harnessing the complex interactions between plants and microbes. There are three particular relationships that are useful in sourcing Nitrogen for crops:
- The Rhizophagy Cycle
- Free-Living Nitrogen-Fixing Microbes
- Mycorrhizal Fungi Networks
What is the Rhizophagy Cycle?
The rhizophagy cycle refers to the process by which plants consume beneficial microbes, via their roots to obtain nutrients by removing the microbe’s outer layer, this is rich source of many nutrients particularly nitrogen. The microbe then moves back into the soil via root hairs to then rebuild their outer layers to then re-enter into the plant root. It involves a complex series of microbial activities that aid in nutrient delivery to the plant.
The Role of Free-Living Nitrogen-Fixing Microbes
In addition to the well-known rhizobial symbiosis, there are a variety of free-living nitrogen-fixing microbes that also contribute to the nitrogen cycle in the soil. These microbes can be found in the soil environment, where they fix nitrogen independently of plant roots. Their presence is crucial in boosting nitrogen levels for crops, especially in systems where legumes or other nitrogen-fixing plants are not present.
Key Free-Living Nitrogen-Fixing Microbes
Azotobacter:
- Azotobacter is a genus of free-living bacteria that plays a significant role in nitrogen fixation in soils. These bacteria do not require a host plant to fix nitrogen but can form partnerships with plants by releasing the fixed nitrogen into the soil, where it can be absorbed by plants. Azotobacter is particularly beneficial in well-aerated soils where it thrives and supports the soil’s nitrogen needs.
Azospirillum:
- Azospirillum is another genus of free-living nitrogen-fixing bacteria found in the rhizosphere of many plants. These bacteria are often associated with grasses and cereal crops and can contribute to improved plant growth by fixing nitrogen and producing growth hormones that promote root development.
Cyanobacteria:
- Cyanobacteria, also known as blue-green algae, are capable of fixing nitrogen in aquatic environments as well as in soil. They play an important role in both flooded and dryland farming systems. In rice paddies, for instance, cyanobacteria can fix nitrogen and contribute to the fertility of the field.
Clostridium:
- This genus includes nitrogen-fixing bacteria that can function in both aerobic and anaerobic environments. These microbes are particularly valuable in soils that undergo fluctuating moisture conditions, as they can fix nitrogen even when oxygen levels are low.
Klebsiella:
- Klebsiella is a nitrogen-fixing bacterium that can thrive in a range of environments, including both the soil and within plant roots. By fixing nitrogen in the rhizosphere, Klebsiella bacteria help provide plants with the nitrogen they need for healthy growth.
The Role of Mycorrhizal Fungi in Nitrogen Cycling
Mycorrhizal fungi are essential players in the nitrogen cycle and work symbiotically with plants to improve nutrient uptake. While they are primarily known for assisting in the uptake of phosphorus and water, recent studies suggest that they also contribute to nitrogen cycling by enhancing plant access to nitrogen sources in the soil.
How Mycorrhizal Fungi Contribute to Nitrogen Cycling
Nutrient Uptake: Mycorrhizal fungi expand the plant’s root system, creating a vast network of hyphae that can access nutrients, including nitrogen, from the soil more efficiently. This is particularly beneficial in nutrient-poor soils, where nitrogen may be present but not readily available to plants.
Nitrogen Transfer: Mycorrhizal fungi are capable of absorbing nitrogen from the soil and transferring it to the plant in exchange for carbohydrates. This mutualistic relationship boosts plant growth and helps reduce the need for external nitrogen inputs.
Soil Microbial Interactions: Mycorrhizal fungi also play a role in promoting the activity of other nitrogen-fixing microbes in the soil. By enhancing soil health and fostering a thriving microbial community, mycorrhizal fungi help increase the overall nitrogen availability for plants.
Improving Microbial relationships
The benefits above only come from a strong microbial population. To build a strong and robust population practices like no-till, minimise chemicals, biological inoculants and cover cropping need to be used.
4 – Storing Nitrogen As Amino Acids
As a way to reduce nitrogen fertiliser, one of the most effective strategies is to improve nitrogen cycling in the soil and store losable nitrogen as stable amino acids. Traditionally, nitrogen is supplied to plants through synthetic fertilisers, which can leach below the root zone or volatilize back into nitrogen gas. An alternative lies in the natural process of converting nitrogen into amino acids, an essential component for plant growth. This process can be enhanced through the use of microbes and good nutrition, making it a promising method to reduce nitrogen fertiliser. The general rule of thumb is to double the required nitrogen for a crop as 50% of the nitrogen will be lost. However, when the nitrogen is converted into amino acids in microbial biomass, the loss of nitrogen is reduced allowing for a low release to the crop.
Converting N into Amino Acids
When applying nitrogen, a ratio of 300 C:10N:1S with some additional Mo to assist in the conversion of nitrate into ammonia. The carbon provides microbes with the energy required to preform this function and sulfur is required in the building of specific amino acids.
With this mix, add a biostimulate and a microbial inoculant to rapidly convert N into a stable form.With rough estimates, this should reduce nitrogen loss by over 30% allowing you to effectively reduce N inputs.
5 – Adding Humic Substances To Nitrogen Applications
Incorporating humic substances into nitrogen fertilizer applications can significantly improve nitrogen retention and reduce nutrient loss in the soil. Humic substances, which include humic acids, fulvic acids, and humin, are rich in cation and anion exchange sites that enable them to bind to different forms of nitrogen, such as nitrate (anion) and ammonium (cation), and hold onto them more effectively. This helps in preventing nitrogen from being lost to volatilization, leaching, or other forms of loss, ensuring that nitrogen remains available to plants for longer periods.
As discussed in the transcript, one of the key issues with traditional nitrogen fertilizers is that up to 30% of nitrogen can be lost through leaching or volatilization after application. When nitrogen is combined with humic substances, the slow-release properties of these substances ensure that nitrogen is gradually made available to plants, reducing the risk of nitrogen loss and increasing the overall efficiency of the fertilizer.
Summary To Reducing Nitrogen Fertiliser
By adopting the methods above you can effectively reduce nitrogen fertiliser inputs to reduce input costs while maintaining yields. Key strategies for reducing nitrogen fertilizer use include:
- Legume Crops: These nitrogen-fixing plants naturally enrich the soil, reducing the need for added nitrogen fertilizers.
- Cover Crops: These plants help scavenge excess nitrogen, preventing leaching and improving soil structure.
- Microbial Applications: Free-living microbes and mycorrhizal fungi play an essential role in converting atmospheric nitrogen into usable forms, enhancing nitrogen availability for plants.
- Storing N as Amino Acids: By applying 300C to 10N to 1S with some Mo and microbes, N is stored as Amino Acids in microbial biomass.
- Humic Substances: Adding humic substances to fertilizer applications helps retain nitrogen in the soil, promoting slow release and reducing nitrogen loss.
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The post 5 Ways To Reduce Nitrogen Fertiliser appeared first on Agresol.
