Agriculture Reference
In-Depth Information
B. inermis
95% C.I.
Uniform
A. sativa
95% C.I.
Uniform
low contrast
high contrast
Litter Quality Contrast Treatments
Figure 6.4 Proportion of the total root length of Bromus inermis (top) and Avena sativa (bottom)
located in patches of higher quality (i.e., lower C:N) litter when roots had free access to two patch
types that varied in quality. Capital letter treatment codes below each bar indicate the types of litter
patches (red clover shoots, red clover roots, green oat leaves, or senesced oat straw) available to roots
in each treatment, where BC equals red clover roots versus green oat leaves, BD equals red clover
roots versus oat straw, CD equals green oat leaves versus oat straw, AC equals red clover shoots ver-
sus green oat leaves, AB equals red clover shoots versus red clover roots, and AD equals red clover
shoots versus oat straw. The uniform line at 0.5 represents an even distribution of roots into each
patch type. The 95% C.I. (confidence interval) line represents the upper confidence interval around
the uniform distribution line. Treatment means falling on or below this 95% C.I. are statistically
indistinguishable from the uniform root length distribution (i.e., no selective foraging). Different
letters above the vertical bars indicate significant differences (Tukey-Kramer adjustment for mul-
tiple comparisons). Note that A. sativa plant biomass was on average about 10-fold that of B. inermis
at harvest (55 days after planting). This likely indicates that plant growth rate (i.e., N demand) rela-
tive to patch quality (i.e., N supply rate) controls root selective foraging.
N  mineralization by releasing labile root-derived compounds or specific signaling mol-
ecules into the rhizosphere (Drinkwater and Snapp, 2007). The management of crop resi-
due diversity and quality, as well as the spatial distribution of crop residue inputs, may
also provide opportunities for using priming to improve NUE. To get there, advances are
needed in crop variety development and in our understanding of litter decomposition,
root foraging behavior, and SOM dynamics, particularly interactions between SOM, min-
eral surfaces, and the formation and turnover of soil aggregates (Grandy and Neff, 2008;
Behrens et al., 2008; Schmidt et al., 2011). With these advances, we will build a foundation
 
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