6 reasons to reinvent our relationship with nitrogen fertilisers

Jan 27

By Kim Deans

Rising fertiliser prices and looming shortages are currently creating a situation where many farmers are looking into alternative options particularly with regards to nitrogen. Rather than looking for a quick fix, there are plenty of reasons to take a long term view and put in place strategies that will successfully reduce our reliance on nitrogen fertilisers that will also create a more resilient, regenerative and profitable farming system.

There is no question that nitrogen is essential for plant growth, this is obvious when we see the green flush of growth in response to applying nitrogen in any form on any scale. Nitrogen is a structural component of several essential plant parts and compounds including chlorophyll, nucleic acids (DNA, RNA) in each cell and proteins. As a result of these functions, applying nitrogen fertilisers creates visible responses in plant growth. By focusing only on these visible benefits from applying nitrogen the unintended consequences evident in declining soil health caused by applying nitrogen at ever increasing rates have largely gone unnoticed.

Some reasons (in addition to high prices and shortages of nitrogen fertilisers) that it could be time to reinvent our relationship with nitrogen fertilisers are:

1.Soil carbon levels

When we decide to improve soil health nitrogen is one of the first inputs that we must reinvent our relationship with due to the interrelationship between nitrogen and carbon cycles. Carbon is the life force in our soils and the foundation of physical, biological and mineral health. Our land management determines whether we sequester carbon or our soils lose carbon and add it to the atmosphere. Unfortunately most agricultural soils are losing more carbon than they are sequestering and have become dead, lifeless, anaerobic and unable to absorb or hold water. As carbon is depleted and soil health declines, these lifeless soils rely on ever increasing rates of fertiliser and pesticide inputs to produce a yield. The use of nitrogen fertilisers has played a role in creating this situation and it is impossible to profitably reduce our reliance on nitrogen inputs without addressing soil carbon restoration to improve overall soil health.

There are two main carbon cycles at work in the soil that we must understand when we consider our relationship with nitrogen fertilisers:

The short term decomposition cycle whereby organic materials like crop residues are broken down by the microbial community in the soil. This activity concentrates the carbon in the top of the soil and can be influenced by temperature, moisture, time of the day/year and the availability of food for microbes. Carbon in plant matter on the soil surface is prone to losses due to oxidation.

The liquid carbon pathway(2) which draws carbon deep into the soil. This is the carbon captured by plants during photosynthesis and delivered to the soil by plant root exudates. These exudates are traded with soil microbes for nutrients needed by the plant and play a vital role in plant nutrition and health. Root exudates are the cheapest, most efficient and most beneficial form of soil carbon for soil life. Studies on carbon conversion efficiency(2), (the percentage of carbon inputs biologically converted to stable soil carbon) have shown root derived carbon conversion efficiency averaged 46% in comparison to just 8% for carbon from above ground biomass. This is five times more efficient than the decomposition cycle!

There is a lot of information promoting the use of nitrogen fertilisers to restore soil carbon as this increases the biomass of plants produced to decompose and build soil organic matter. This approach focuses solely on the short term decomposition cycle, and overlooks how synthetic fertilisers alter soil microbial communities and inhibit the more efficient liquid carbon pathway (3).

“Rather than applying ‘more fertiliser’ the solution to deteriorating soil function lies in the adoption of management practices that increase levels of stable soil carbon. Organic carbon, organic nitrogen and moisture-holding capacity always move together. When levels of soil carbon increase, so too do levels of organic nitrogen and the ability of the soil to infiltrate and store water. Organic carbon holds between four and twenty times its own weight in water. In many environments, moisture availability (rather than nutrient availability) is the most limiting factor for production. Over time, improvements to soil carbon levels eliminate the need for inorganic fertilisers. “ Dr Christine Jones (2)

2. Soil aeration

Soil aeration is the most commonly ignored soil limitation in agriculture yet restoring soil structure and soil aeration through improving soil carbon and soil biological health will restore natures FREE nitrogen cycle. Nitrogen is the most common element in our atmosphere (78%), there are 74000 tonnes of nitrogen in the air above every hectare of land! We rarely see nitrogen deficient plants in nature (check out the road sides) so this is a sure indication that nature already knows how to get plants nitrogen needs met.

In healthy, aerated, biologically diverse soils nitrogen is not a major limit to production because these soils have the capacity to harvest nitrogen from the atmosphere via free living soil bacteria, algae and rhizobium in legume nodules which all fix atmospheric nitrogen and make it available for plants. Applying synthetic nitrogen can shut down these processes in the soil, as well as contributing to soil structural decline which creates low aeration (air is 78% N). There is a viscous cycle at play where the more synthetic nitrogen we apply, the more soil structure breaks down, soils become compacted and anaerobic and the more nitrogen we need to apply.

Natures nitrogen cycle is biologically driven. Applications of synthetic nitrogen alter soil microbial communities, interfering with their crucial role in the nitrogen cycle. Compacted soils with poor air flow reduce habitat for aerobic microbes including free living nitrogen fixers. Bacteria in the soil love to feast on nitrogen and consume and store this nitrogen inside them. Applications of nitrogen stimulate these bacterial populations, feasting on nitrogen means their populations become out of balance with soil fungi who perform important functions within the soil in relation to nutrient cycling, decomposition, disease suppression and water dynamic and will reduce nitrogen leaching. With nitrogen supplies from fertiliser increasing the population of bacteria, the bacteria also require more carbon and will consume soil carbon reserves to meet their energy requirements. Loss of soil carbon leads to soil structural decline, compaction, less water storage capacity (rainfall use efficiency), erosion and poor root growth.

How do you know if you have anaerobic soils? Dig a hole, observe and monitor soil structure and porosity. Look at the weeds growing on your land and what they indicate. There are a number of weeds that grow in anaerobic, compacted soils and have deep tap roots designed to break up soil compaction and cycle minerals from the subsoil. Dock, thistles, mallow, rushes & sedges are examples of indicators that soil is compacted and anaerobic.

3. Drought proofing and rainfall use efficiency

How effectively we make use of the rain that falls on our land is a key driver of farm profitability. Rainfall use efficiency investigations undertaken on 1700 farms in northern NSW Australia (1) found rainfall use efficiency varied from 6% to 70% with an average of just 21%. This clearly shows plenty of room for improvement. It is highly likely that this is far worse now.

Rainfall use efficiency relates directly back to soil carbon which as we have seen is impacted by our management of nitrogen. Agricultural systems that harness natures free nitrogen cycle also restore soil carbon as the two go hand in hand. Agricultural systems that rely on high rates of synthetic nitrogen inputs continually deplete the carbon in our soils. These degraded soils cannot absorb water when it rains. Water either runs off creating erosion and increasing the incidence of flooding, or the water sits on the soil surface, unable to infiltrate into the soil until it is lost to the system due to evaporation. With the water cycle broken, soils get progressively drier and we effectively create our own droughts.

4. Water quality and ecosystem health

Water quality decline is a chronic issue in agricultural landscapes and is another unintended consequence of the use of synthetic nitrogen fertilisers that largely goes unquestioned. The nutrient runoff from fertilisers is contributing to inland rivers becoming dead zones devoid of life. These nutrients, in combination with sunlight and warm waters trigger algal blooms. As the algae die off and are decomposed by bacteria, oxygen in the bottom waters drops to levels that can be deadly for aquatic organisms. Dead zones are common in the Earth’s oceans, The Gulf of Mexico dead zone is an area of water with less than 2 ppm dissolved oxygen at the mouth of the Mississippi River. This dead zone is caused by nutrient enrichment from the Mississippi River, particularly nitrogen and phosphorous, it’s area varies in size, but can cover up to 15,000 – 18,000 square kilometres. The largest dead zone ever recorded in the Gulf of Mexico was reported by National Geographic News in August 2017 and reached 22,729 square kilometres.

5. Weed problems

Many weeds are an indicator that the nitrogen cycle is broken and our soils are anaerobic and compacted. Anaerobic, compacted soils lead to lower numbers of protozoa and nematodes in the soil food web who consume bacteria and cycle the nitrogen stored and held by bacteria in the soil to make it available to plants. Without these higher order predators in the soil food web to consume and cycle the nitrogen accumulated in the bacteria, when bacteria die the nitrogen is released into the soil where it can be lost by leaching and also sends the signal for the germination of nitrate accumulating weeds. These weeds role in the ecosystem is to soak up the surplus nitrates where they will be incorporated into the plant material for cycling back through the system. Examples of nitrate accumulating weeds are nightshades, capeweed, nettles, fathen/lambs quarters and milk thistle. We spend a fortune on herbicides to control these weeds, only to unintentionally continue to accelerate the biological imbalances that created the perfect conditions for these weeds to thrive in the first place.

6. Pest and disease problems

Nitrogen-fixing bacteria produce ammonia, a form of inorganic nitrogen, inside soil aggregates and rhizosheaths, the protective cylinders that form around plant roots held together by plant root exudates. Rhizosheaths are rarely seen on root systems of industrially farmed plants which instead have bare root systems devoid of their microbiome. When you consider that roots are the digestive system of a plant and industrial agriculture has decimated the soil microbiome which is equivalent to our gut microbiome it is no wonder along with increasing rates of nitrogen applications we are seeing a correlating increase in the use of pesticides to combat the ever increasing pest and disease pressure on these unhealthy plants.

A biologically active rhizosphere converts the ammonia fixed into an amino acid or incorporates it into a humic polymer. These organic forms of nitrogen cannot be leached or volatilized. Amino acids can be transferred into plant roots by mycorrhizal fungi and joined together by the plant to form a complete protein. On the other hand, inorganic nitrogen applied as fertilizer often ends up in plants as nitrate or nitrite, which can result in incomplete or “funny” protein which makes plants more susceptible to insects and diseases.

When soil and plant health suffer this correlates further up the food chain with animal and human health as well. High rates of nitrogen fertilisers can contribute to copper deficiencies in animals which have been linked with scours, a number of diseases including Johnes disease and internal parasite infestations. Dairy farmers we have worked with have noticed huge gains in terms of cow health when they have improved soil health and reduced their reliance on high rates of nitrogen fertilisers.

Where to from here?

When we embark on a journey of getting off the nitrogen treadmill there are no quick fixes. This is not a process of substituting one input for another and expecting it to deliver the same result. We cannot solve the problem with the same kind of thinking that created it. We cannot buy soil structure, aeration or carbon. We can shift our mindset and make management decisions to improve soil structure, aeration and carbon. We can first acknowledge with self-compassion that we are dealing with the unintended consequences of what has been sold to us as best practice farming. We don’t know what we don’t know. When we know better we can commit to doing better.

Transition takes time

Transition is the process or a period of changing from one state or condition to another. When we look for ways to reduce synthetic nitrogen fertiliser use in high input industrial systems then we are transitioning from a system that is essentially addicted to nitrogen fertiliser to one where the natural nitrogen cycle is restored and functioning. It may sound harsh to claim that a system is “addicted” to inputs however when we consider how our farming systems have become dependent upon ever increasing rates of nitrogen fertiliser to function we are in the grip of an addictive cycle of purchasing an input that makes us need it more.

Once we commit to transitioning towards a system where we restore health to our soils so natures free nitrogen cycle can function again it is important to develop a strategy that is appropriate in our individual context. Don’t waste time randomly trying different inputs or ideas, there are no silver bullets. Transition is about principles applied in context, there is no recipe or one size fits all approach.

Systems need time to reboot so patience is essential. Implementing a regular soil health monitoring strategy that incorporates soil physical, biological and mineral health as a whole keeps us on track and help us to pick up any unintended consequences quickly. Monitoring is essential as when we are restoring soil health the changes can happen underneath the soil first, we don’t want to abandon ship too soon before we give the above ground changes a chance to emerge.

Going cold turkey on a high input system can lead to a crash in production and is not always a viable option. We would need to have the financial resources and mental capacity to weather this crash and instead may wish to spread the risk across our farm by taking a gradual approach or transitioning a small area first to learn and grow in confidence with a strategy for our context.

Transition tools for nitrogen

When considering cutting back our rates of synthetic nitrogen fertiliser the first step to doing less harm is to buffer soil applied nitrogen with humates (a carbon source). We may also decide to gradually reduce our rate of soil applied nitrogen (buffered with humates) and apply foliar nitrogen to meet crop requirements as guided by leaf testing. Foliar applications will do less harm to soil biology and make more efficient use of nitrogen fertilisers. This also helps us to apply nitrogen closer to crop needs. Paying attention to molybdenum and cobalt levels in our soil and plant leaf tests is also helpful, as these trace elements are essential for biological nitrogen fixation to occur.

Understanding our inputs

Many farmers looking for alternatives to urea this year in response to these price increases are investigating a range of products in an effort to replace urea. There are a wide range of inputs available. Taking time to research our options thoroughly helps ensure that our expectations of these products are realistic. It is vital to understand the purpose of the products we are applying. Fertilizers are applied to soil or plants to supply nutrients that promote plant growth. In contrast, bio-stimulants can contain metabolites, microbes, quorum signalling molecules, proteins, amino acids, plant growth hormones, enzymes, botanicals, humic substances and much more. Bio-stimulants can be applied to seeds, plants or the soil to stimulate natural processes that may enhance nutrient uptake, nutrient efficiency, stress tolerance or crop quality and yield as well as soil microbial communities.

Reinvention starts with us being willing to see a different point of view. The problems we face due to increasing costs of nitrogen fertilisers can be a symptom of declining soil health, poor soil aeration and dead lifeless soils. When nature’s free nitrogen cycle is not functioning farming systems become addicted to inputs. The only way off this treadmill is taking a long term view towards restoring soil health. Remember that it takes time to build back the physical and biological health in soil that has been lost.

The best time to take steps to restore soil health was yesterday, the second best time is now!

References:

(1) Gardiner & Gammie (2012) “Economics, productivity and natural resources in agricultural systems.” Proceedings of the 16thASA Conference. http://agronomyaustraliaproceedings.org/images/sampledata/2012/8054_6_gardiner.pdf

(1) Jones, Dr Christine Light Farming: Restoring carbon, organic nitrogen and biodiversity to agricultural soils

(2) Jones, Dr Christine Nitrogen the double edged sword

Recommended Reading:

Is your soil alive? Or barely breathing? by Angus Deans

Inputs explained with Lee Fieldhouse & David Hardwick

For the Love of Soil by Nicole Masters

The Myth of Fertiliser by Nicole Masters

Get more bang for your nitrogen buck by Nicole Masters

Dirt to Soil by Gabe Brown

6 keys to successfully using biological stimulants by Kim Deans

New Research: synthetic nitrogen destroys soil carbon undermines soil health GRIST 2010 by Tom Philpott

The sad story of nitrogen by Graeme Sait