Sustainable Agriculture Literature Review - Boulder County

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A reduction in the use of synthetically derived fertilizers and inputs can effectively lower
emissions and increase the sequestration and storage of carbon in soils. 96 One of the
most applicable examples to Boulder County is the use of rotations with legume crops, 97
that help to reduce reliance on external nitrogen inputs, though even legumes have been
shown to increase N2O in some locations, negating some of the potential climate
benefits. 98 Additionally, the use of catch or cover crops provide temporary vegetative
cover between successive agricultural crops, or between rows, helping to sequester
carbon from the atmosphere and reduce N2O emission by extracting unused plant
99, 100
available nitrogen from the preceding crop.
The global warming potential of organic farming systems is considered to be smaller
than that of conventional systems when calculated per land area, but this difference
declines, when calculated per product unit based on comparative yields. 101 While
practices like cover crops, manure application, and conservation tillage can help to
reduce GHG emissions from synthetic fertilizers, there are additional increases in GHG
emissions from manure handling, compaction of soils resulting from the use of heavy
machinery, and in some instances increased fuel use. 102
Enhancing Removals - Tillage and Residue Management
Due to advances in weed control methods and farm machinery, many crops can now be
grown with conservation tillage. Since soil disturbance tends to stimulate soil carbon
losses through enhanced decomposition and erosion, 103 reduced- or no-till agricultural
practices often result in a gain of carbon to the soil, but not in all systems. 104, 105, 106 The
conversion of agricultural systems from continuous tillage (conventional tillage) to
minimal tillage could increase carbon storage in soils in Boulder County, lowering net
GHG emissions, 107, 108, 109 but producers are unlikely to make the conversion to minimal
tillage systems unless they are demonstrated as profitable. These limited tillage
practices are increasingly being used across cropping systems in a wide range of
locations, but have not seen wider-spread adoption due to concerns over potential
110, 111
financial benefits.
Many studies have assessed the viability of no-till systems, 112, 113 but few of these
studies have looked at no-till agriculture on irrigated lands, raising concerns over
inferring financial impacts from non-irrigated to irrigated lands. 114, 115, 116 Additionally, due
to the location specific impacts of low tillage practices on carbon sequestration, it is
important to focus on research conducted in a regionally appropriate area to Boulder
County. A five-year study 117 conducted just outside of Fort Collins, CO, gives a detailed
assessment of potential impacts from adoption of limited tillage practices on irrigated
land. Results from the study found that conversion of agricultural systems from
continuous tillage to no-tillage systems may lower the overall GHG impact and improve
net financial returns by avoiding over application of nitrogen fertilizer. Specifically, the
study found that
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