Agriculture Reference
In-Depth Information
No added P
0.9
Disturbed
0.8
Undisturbed
0.7
0.6
0.5
0.4
0.3
1
2
3
Cycle
+ 160 µgP g
-1
Soil
0.9
0.8
0.7
0.6
0.5
0.4
1
2
3
Cycle
Figure 7.1
Shoot growth response of maize grown in greenhouse pots for three cycles of 3 weeks
each. After shoot harvest, the soil in the pots was either removed and remixed or left undisturbed.
All pots had the same population of native AM fungi at the start of the first cycle. (Adapted from
Fairchild, G.L., and M.H. Miller. 1990. Vesicular-arbuscular mycorrhizas and the soil-disturbance-
induced reduction of nutrient absorption in maize. III. Influence of phosphorous amendments to
soils.
New Phytologist
114:641-650.)
P application (McGonigle and Miller, 1996). Other factors present in the field environment,
not fully explored in greenhouse studies, resulted in the enhancement of early season AM
fungus colonization and P uptake not translating into increased plant growth and yield in
no-tilled versus conventionally tilled soils. Despite the importance of early season P nutri-
tion of crops such as maize (Grant et al., 2001), the cooler soil temperatures in no-tilled soils
due to shading by crop residues contributes to reduced early season plant development.
As would be expected, disturbance of the soil such as by moldboard plowing, which
inverts the soil column 135°, also affects the distribution of AM fungi within the soil pro-
file. No-till soils under continuous wheat cultivation had more spores of AM fungi in the
surface 80 mm of soil and fewer in the 80- to 150-mm layer than did soils from convention-
ally tilled plots due to mechanical inversion of the soil (Smith, 1978), even though the total
number of spores was not affected. The density of propagules of AM fungi declines with
soil depth (Jakobsen and Nielson, 1983; Oehl et al., 2005), and they are more numerous in
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