Vegetation influence on soil quality in a highly degraded tropical ...
Vegetation influence on soil quality in a highly degraded tropical ...
Vegetation influence on soil quality in a highly degraded tropical ...
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J. Agric. Univ. P.R. VOL. 88, NO. 1-2, JANUARY-APRIL 2004 21<br />
<strong>in</strong> a fluventic Dystrandept was approximately 2,000 and 1,300 mg C/<br />
kg, respectively (Henrot and Roberts<strong>on</strong>, 1994). In <strong>tropical</strong> forest <strong>soil</strong>s of<br />
Brazil, Costa Rica, Panama, and Hawaii, MBN ranged from n<strong>in</strong>e to 265<br />
mg N/kg (Vitousek and Mats<strong>on</strong>, 1988). The MBC and MBN values determ<strong>in</strong>ed<br />
<strong>in</strong> this study appear to be <strong>in</strong> the low range of values<br />
determ<strong>in</strong>ed <strong>in</strong> other studies for <strong>tropical</strong> <strong>soil</strong>s.<br />
Soil microbial respirati<strong>on</strong> was significantly higher under grasses<br />
than under legumes and bare <strong>soil</strong> (Table 3). No significant differences<br />
were found between legumes and bare <strong>soil</strong>. This f<strong>in</strong>d<strong>in</strong>g suggests that<br />
<strong>soil</strong>s under grasses have higher potentially m<strong>in</strong>eralizable C and N pools<br />
because of the <strong>in</strong>creased above- and below-ground biomass producti<strong>on</strong><br />
and subsequent decompositi<strong>on</strong> <strong>in</strong> <strong>soil</strong>, and producti<strong>on</strong> of root exudates<br />
(Groffman et al., 2001; O’D<strong>on</strong>nel et al., 2001). Higher <strong>soil</strong> respirati<strong>on</strong> (P<br />
< 0.05) was observed at the surface 0- to 5-cm than at 5- to 15-cm depth,<br />
because of stratificati<strong>on</strong> of aboveground biomass litter fall.<br />
The potentially m<strong>in</strong>eralizable nitrogen (PMN) pool represents a biologically<br />
active amount of N orig<strong>in</strong>at<strong>in</strong>g from various comp<strong>on</strong>ents of<br />
the SOM that could be m<strong>in</strong>eralized by <strong>in</strong>digenous microorganisms dur-<br />
TABLE 3. <str<strong>on</strong>g>Vegetati<strong>on</strong></str<strong>on</strong>g> effects <strong>on</strong> <strong>soil</strong> microbial parameters. Values for each <strong>in</strong>dividual<br />
species and c<strong>on</strong>trol are the means averaged across depth and time.<br />
Species Group MBC MBN MBC/MBN PMN<br />
Microbial<br />
respirati<strong>on</strong><br />
- - - - mg/kg - - - - mg N/kg mg CO2-C/kg A. procera Legume trees 140.2 23.17 13.4 21.4 131.9<br />
A. <strong>in</strong>ermis 131.3 15.88 11.0 23.5 115.1<br />
B. humidicola Grasses 185.0 24.24 10.7 34.7 152.0<br />
H. altissima 193.9 26.93 6.92 28.7 148.2<br />
A. glabrata Legume shrubs 111.5 20.81 7.68 20.4 134.6<br />
C. acutifolium 148.6 21.66 8.74 25.8 125.7<br />
C<strong>on</strong>trol Bare <strong>soil</strong> 135.0 20.43 11.3 41.7 119.4<br />
F-test NS1 NS<br />
C<strong>on</strong>trasts<br />
NS NS *<br />
<str<strong>on</strong>g>Vegetati<strong>on</strong></str<strong>on</strong>g> vs. bare <strong>soil</strong> NS NS ND2 28.0 132.4<br />
41.7 119.4<br />
Legumes vs. grasses 132.93 20.4 ND 22.8 126.8<br />
189.5 25.6<br />
31.7 150.1<br />
Grasses vs. bare <strong>soil</strong> 189.5 25.6 ND 31.7 150.1<br />
135.0 20.4<br />
41.7 119.4<br />
Legumes vs. bare <strong>soil</strong> NS NS ND 22.8<br />
41.7<br />
NS<br />
1 NS denotes n<strong>on</strong> significance at P < 0.05.<br />
2 ND denotes c<strong>on</strong>trast was not determ<strong>in</strong>ed.<br />
3 C<strong>on</strong>trast means are significantly different at P < 0.05.