If you cut your nitrogen by 80% tomorrow, would you expect your production to drop? Of course it would… if you did nothing else. Optimising nitrogen use is one of the holy grails in a drive to produce food for a booming world population, all whilst looking after the environment.

Across the world a growing number of farmers are successfully dropping their N to astoundingly low levels in an approach that provides a wide range of benefits. How is it that some farmers can dramatically reduce nitrogen without reducing production?

The journey starts with an appreciation of soil health’s role in driving the nitrogen cycle.

Soil Structure

If you ask most fertiliser reps what the number one yield limiting factor is, they’ll probably tell you it’s nitrogen. That’s actually inaccurate; try this… hold your hand tightly over your nose and mouth for a few minutes to see what your number one factor is.

It’s air.

It is just the same for your plants and soil microbes. Without adequate airflow, roots and microbes curl up and die and natural mineral and water cycles breakdown. Compacted and waterlogged soils lose valuable nutrients including N[i], and reduce those microbes responsible for providing N to your crops.

Improving yield starts with a soil that can breathe. Air, and water, moves into soil through the gaps in soil aggregates; the crumbs formed by soil microbes. Just like constructing an apartment building, microbes and earthworms make hallways, stairwells and living spaces. Poor soil structure turns these apartments into a tarmac. This loss of structure stalls the natural nitrogen cycle.

The recent State of the Environment report shows that 78% of dairy farms were badly affected by compaction in 2013. This is a double whammy for farmers and the environment, as compacted soils require more N and lose more N into the atmosphere and waterways[ii] [iii]. Research shows, that depending on the type of N used, up to ten times more N is lost from compacted soils[iv]; requiring more inputs to maintain production.[v]

Often when considering natural nitrogen inputs, farmers most often think of legumes, particularly clover and rhizobia for N fixation. However, in healthy soils among the most common organisms are free-living bacteria which fix nitrogen into the soil. These free-living N fixers require air, so compacted soils will have less of these important organisms.

The high use of soluble nitrogen creates a vicious cycle; putting farmers on a treadmill of decreasing returns due to the breakdown of soil carbon, thus a loss of humus and an increase of microbes which love to feed on N.  The loss of carbon creates the conditions for compaction, increasing runoff and erosion and limiting root growth. Just too really put the boot in, these soils then require more irrigation, creating more vulnerable farm systems.[vi]

How efficient is your N fertiliser?

Our modern farming practices are leaky and inefficient. In dairy systems only 15-35% of the N applied is actually made available to the plant, with the majority of applied N lost to the air and waterways (globally this figure is 5-15%)[vii]. There wouldn’t be many businesses happy with those kinds of inefficiencies, particularly for something which may be such a major input. So why do we tolerate it in farming?

Increasingly fertiliser companies are focusing on add-on products to improve N efficiencies, like DCD, Nitrapyrin and Agrotain. Even projections for best practices around nitrogen, the soundest estimates offer 60% efficiency at best.  These products will enable fertiliser companies to continue business as usual, without addressing the key issue; why do you need to add soluble N, and why is the nitrogen cycle not working optimally?

Additional disruption to natural N function has been introduced with chemical pasture topping and herbicide brown out practices using glyphosate which has an inhibiting effect on N fixation and promotes N.

The success of Biological Agriculture begins through building a foundation to enhance natural cycles, using proactive practices which address the root causes, versus reacting to symptoms. Fostering underground livestock is an essential ingredient to reducing N inputs. One key in profitably reducing N, is through the addition of carbon based biological foods and stimulants to improve soil structure and nitrogen storage[viii] while maintaining yields [ix] [x].

Plants require nitrogen in different forms throughout the growing season; applying large volumes of N at once is ineffective in supporting plants through the year. Biological production creates significantly less emissions and leaching[xi] [xii], while providing nitrogen in plant available forms when plants need it[xiii].

Microbiology and Soluble N

Many plant species are completely dependent on microbial partners for growth and survival.[xiv] High inputs of soluble N fertilisers dramatically change microbial communities; reducing organic N and C, microbial diversity and overstimulating bacteria.

Fungi to Bacteria (F:B) ratios are important for soil structure and pasture health. New research has also shown that soils higher in fungi reduce N leaching[xv] [xvi]. Mycorrhizae, a plant symbiotic fungus, have been shown to reduce leaching by 40%.[xvii]  These important fungi also produce a substance called glomalin, a relatively stable soil protein important in soil structure. [xviii] Degrading soil health and the addition of soluble N reduces the F:B ratio, creating more bacterial soils with time.

During the life and death processes which drive healthy biological systems, nitrogen goes through a variety of forms before being taken up by plant roots. Bacteria consume N and hold it in their bodies. If the soil foodweb has been compromised, through compaction or high soluble N applications, there is often lower predation from protozoa and nematodes[xix]. This means N becomes immobilised or bound in the soil, unavailable to plants.

Not all synthetic N is detrimental, adding small amounts of N (5 units/Ha) has actually been found to be beneficial for soil microbiology, acting as a catalyst to help stimulate the natural N cycle.

Research is showing that high yields can be maintained and inputs reduced through good management of soil, water, energy and biological resources. Studies have shown that the same corn yields were possible by reducing chemical inputs by half and cutting a third of costs.[xx] [xxi]

Feed your soil

Soils are an ecosystem; supporting and feeding soil microbes have huge benefits across the entire farm enterprise. Reducing nitrogen can be profitably and sensibly done through enhancing microbiology and soil health. With huge leaps forward for the environment and farming bottom lines.

Image by Integrity Soils. Use with permission.

REFERENCES

[i] Deurer, M., Grinev, D., Young, I., Clothier, B.E. and Müller, K. (2009). The impact of soil carbon management on soil macropore structure: a comparison of two apple orchard systems in New Zealand. European Journal of Soil Science Volume 60, Issue 6, pages 945–955

[ii] Bhandral, Rita, et al. “Transformation of nitrogen and nitrous oxide emission from grassland soils as affected by compaction.” Soil and Tillage Research 94.2 (2007): 482-492.

[iii] Lipiec, J., and W. Stepniewski. “Effects of soil compaction and tillage systems on uptake and losses of nutrients.” Soil and Tillage Research 35.1 (1995): 37-52.

[iv] Torbert, H. A., and C. W. Wood. “Effects of soil compaction and water‐filled pore space on soil microbial activity and N losses.” Communications in Soil Science & Plant Analysis 23.11-12 (1992): 1321-1331

[v] Hernández-Hernández, R. M., and D. López-Hernández. “Microbial biomass, mineral nitrogen and carbon content in savanna soil aggregates under conventional and no-tillage.” Soil Biology and Biochemistry 34.11 (2002): 1563-1570.

[vi] Khan, S. A., Mulvaney, R. L., Ellsworth, T. R., & Boast, C. W. (2007). The myth of nitrogen fertilization for soil carbon sequestration. Journal of Environmental Quality, 36(6), 1821-1832.

[vii] Gourley, C. J., Dougherty, W., Aarons, S., & Kelly, K. Improving nitrogen use efficiency: from planet to dairy paddock. www.massey.ac.nz/~flrc/workshops/14/Manuscripts/Paper_Gourley_2014.pdf

[viii] Poudel, D.D. Horwath, W.R. Mitchell J.P, & Temple, S.R. (2001) Impacts of cropping systems on soil nitrogen storage and loss.  Agric. Syst., 68 (2001), pp. 253–268

[ix] Kramer, A. W., Doane, T. A., Horwath, W. R., & Kessel, C. V. (2002). Combining fertilizer and organic inputs to synchronize N supply in alternative cropping systems in California. Agriculture, ecosystems & environment, 91(1), 233-243.

[x] Aguilera, E., Lassaletta, L., Sanz-Cobena, A., Garnier, J., & Vallejo, A. (2013). The potential of organic fertilizers and water management to reduce N2O emissions in Mediterranean climate cropping systems. A review. Agriculture, Ecosystems & Environment, 164, 32-52.

[xi] Oquist, K. A., J. S. Strock, and D. J. Mulla. “Influence of alternative and conventional farming practices on subsurface drainage and water quality.” Journal of Environmental Quality 36.4 (2007): 1194-1204.

[xii] Magesan, G. G., & McFadden, G. (2012). Nutrient leaching under conventional and biological dairy farming systems. Advanced Nutrient Management: Gains from the Past-Goals for the Future. (Eds LD Currie and C L. Christensen). http://flrc. massey. ac. nz/publications. html. Occasional Report, (25).

[xiii] Burger, M., & Jackson, L. E. (2003). Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates in organic and conventional cropping systems. Soil Biology and Biochemistry, 35(1), 29-36.

[xiv] Van Der Heijden, Marcel GA, Richard D. Bardgett, and Nico M. Van Straalen. “The unseen majority: soil microbes as drivers of plant diversity and productivity in terrestrial ecosystems.” Ecology letters 11.3 (2008): 296-310.

[xv] De Vries, F. T., Hoffland, E., van Eekeren, N., Brussaard, L., & Bloem, J. (2006). Fungal/bacterial ratios in grasslands with contrasting nitrogen management. Soil Biology and Biochemistry, 38(8), 2092-2103

[xvi] De Vries, F. T., Liiri, M. E., Bjørnlund, L., Bowker, M. A., Christensen, S., Setälä, H. M., & Bardgett, R. D. (2012). Land use alters the resistance and resilience of soil food webs to drought. Nature Climate Change, 2(4), 276-280

[xvii] Asghari HR, Cavagnaro TR (2012) Arbuscular mycorrhizas reduce nitrogen loss via leaching. PLoS ONE 7, e29825

[xviii] Rillig, M. C., Ramsey, P. W., Morris, S., & Paul, E. A. (2003). Glomalin, an arbuscular-mycorrhizal fungal soil protein, responds to land-use change. Plant and Soil, 253(2), 293-299.

[xix] Griffiths, B. S. (1994). Microbial-feeding nematodes and protozoa in soil: Their effects on microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere. Plant and Soil, 164(1), 25-33.

[xx] Pimentel, D., Culliney, T. W., Buttler, I. W., Reinemann, D. J., & Beckman, K. B. (1989). Low-input sustainable agriculture using ecological management practices. Agriculture, ecosystems & environment, 27(1), 3-24.

[xxi] Chivenge, Pauline, Bernard Vanlauwe, and Johan Six. “Does the combined application of organic and mineral nutrient sources influence maize productivity? A meta-analysis.” Plant and Soil 342.1-2 (2011): 1-30.