Sustainable Agriculture Literature Review - Boulder County

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Nutrient Management
In most cropping systems, applied nitrogen from fertilizers, manures, biosolids, and
other sources is not always used effectively by crops. Excess or unused nitrogen in the
soil is very susceptible 75 to forming and emitting N2O, a GHG that is 310 times stronger
than CO2. 76, 77 It is important to note that all forms of nitrogen applications can contribute
to nitrogen losses and N2O emissions. By improving the nitrogen use efficiency in crops,
N2O emissions and GHG emissions from nitrogen fertilizer manufacture can be
significantly reduced. 78 Specific practices that improve nitrogen use efficiency and help
to reduce leaching or nitrogen emissions include:
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79, 80, 81, 82, 83
- Adjusting application rates based on precise estimation of crop needs (e.g.,
precision agriculture)
- Using slow- or controlled-release fertilizer forms of nitrification inhibitors
(which slow the microbial processes leading to N2O formation)
- Applying nitrogen when least susceptible to loss, often just prior to plant
uptake (improved timing)
- Placing the nitrogen more precisely into the soil to make it more accessible to
crops’ roots
- Avoiding nitrogen applications in excess of immediate plant requirements
For more information on nitrogen fertilizers, see sections 4.3 Fertilizers as Water
Pollutants and 6.2 Fertilizers.
Enhancing Removals - Agronomy
Increasing yields and generating higher inputs of carbon residue through improved
84, 85
agronomic practices help to increase the amount of carbon sequestered in soil.
Practices like improving crop varieties, extending crop rotations (especially those with
perennial crops), and minimizing bare and fallow land help keep more carbon below
ground and out of the atmosphere. 86, 87, 88, 89 Adding more nutrients when the soil is
deficient can help promote soil carbon gains 90 by increasing productivity, however, when
these benefits are achieved through synthetic nitrogen fertilizer applications they can be
offset by higher N2O emissions from soils and CO2 emissions during the synthetic
fertilizer manufacture process. 91, 92, 93 The manufacture of synthetically derived inputs
like fertilizers and pesticides produce carbon emissions due to the use of fossil fuels to
produce, manufacture, and transport synthetic inputs.
While the climate impact of synthetic fertilizers and pesticides is well documented in the
literature, the climate impact of organic fertilizers and pesticides is not well documented
and is an area where additional research is needed. 94 The climate impact of organic
inputs is not zero since organic fertilizers have a number of energy requirements, which
are discussed further in section 2.1 Breakdown of Energy Use. There are also energy
and climate impacts from the production, transportation, and application of organic
pesticides. A study evaluating the environmental impact of organic and synthetic
pesticides found that organic pest management practices are not necessarily more
environmentally sustainable than conventional ones in regards to environmental impact.
The authors concluded that in order to optimize environmental sustainability, individual
tactics can be evaluated for their environmental impact in the context of an integrated
approach. 95
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