Sustainable Agriculture Literature Review - Boulder County

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3.3 Water Conservation
To create desirable crop growth it is necessary to have good soil conditions that provide
optimum soil aeration, water infiltration, water percolation, water movement, and
permeability as well as uniform root development. Additionally, good soil quality helps to
reduce runoff and decrease potential soil erosion. The USDA National Irrigation Guide
identified improvements to soil quality that would help increase water use efficiency:
eliminating excess tillage operations, avoiding field operations while soil water content is
high, using organic material or crop residue, and using grass and legumes in rotation. 255
Mitigation of compaction layers is also important for water movement in soil.
Compaction Layers
Soil compaction occurs when soil particles are pressed together, reducing the pore
space between them. Fine textured soils (clayey and silty) are more vulnerable than
coarse textured soils (sandy) to compaction. Compaction results in decreased infiltration
and percolation, which leads to an increase in runoff and water erosion potential while
also reducing the effective rooting zone. One important factor that influences soil
compaction is the water content of the soil. For example, dry soil is more resistant to
compaction. 256 The most significant soil compaction occurs during tilling, harvesting, and
grazing when soils are wet. Soil compaction can extend to 20 inches below the
surface. 257 Although wheel traffic is a more obvious and direct cause for compaction,
tillage operations are also a factor. 258 Tillage practices can “break up soil structure,
speed the decomposition and loss of organic matter, increase the threat of erosion,
destroy the habitat of helpful organisms, and cause compaction.” 259
A number of actions can be taken to mitigate the compaction of layers. Additions of
organic matter, such as manure and compost, can have many positive affects on soil
including protection from erosion and compaction. 260 Soil stability and biodiversity also
aid in the prevention of soil compaction. 261 Deep ripping subsoiling at appropriate soil
moisture conditions can break apart compaction layers, but require 30-75 horsepower
per shank, depending on the soil type. Clay soils are very difficult to break up. 262
Although certain tillage operations can lead to compaction, it is possible to decrease soil
compaction in combination with executing conservation tillage systems. 263
A series of compaction tests were completed at the Central Great Plains Research
Station near Akron, Colorado. The study was performed due to concerns that the
practice of no-till, in the long-term, could result in increased soil compaction and possible
degradation of the soil. 264 A decrease in the soil’s least limiting water range was found to
have a direct impact on yield loss. 265 Understanding compaction characteristics of the
soil and the response of the crop to soil physical conditions is vital for farmers when
making informed decisions on field management. 266 The study’s findings support that soil
compaction has the potential to limit crop production. The economic considerations of
soil compaction are difficult to quantify since they can be both direct and indirect. 267
The choice of tillage practice for water conservation purposes depends on a wide range
of factors, including soil erodibility (soil texture, slope, organic matter content), the
irrigation system used, the equipment available, and rotation with other crops. Tillage
methods should be selected based upon which practice eliminates all or the most runoff
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