*Soil Solution Chemistry in Different Land-Use Systems in the Northeast Brazilian Amazon DOI: http://dx.doi.org/10.5772/intechopen.101856*


**Table 2.** *Concentrations*

*30 cm and 60 cm. PC = pasture Cumaru; PSJ = pasture São João; SFC = secondary Forest Cumaru; SFSJ = secondary Forest São João; AFSC = agroforestry*

*AFSSJ = agroforestry*

*mulch agriculture*

 *system São João; RVC = riparian vegetation Cumaru; RVSJ = riparian vegetation São João; CMC =* 

 *São João; SBC =* 

*slash-and-burn*

 *agriculture*

 *Cumaru; SBSJ =* 

*slash-and-burn*

 *agriculture*

 *São João.*

 *of the chemical variables analyzed (mean and standard deviation)*

 *in the soil solutions of the areas studied in each basin in the different land-use classes at depths of*

 *system Cumaru;*

*chop-and-mulch*

 *agriculture*

 *Cumaru; CMSJ = chop-and-*

#### *Carbon Sequestration*

forest—a maximum of 198 mL and a minimum of 30 mL. In turn, for the analyses of the cations and anions, the greatest volumes were collected in the areas of riparian vegetation, AFSs, and chop-and-mulch agriculture, with a maximum volume of 850 mL and a minimum of 30 mL.

### **3.3 Spatial variability of nitrogen**

The highest concentrations of nitrogen chemical species were found in the areas of slash-and-burn agriculture (**Tables 2** and **4**). The maximum concentration of NO3 in the SBC was 8.227 mg L<sup>1</sup> (at depth of 30 cm), while the concentration of NH4 <sup>+</sup> in this same area was 0.929 mg L<sup>1</sup> (at 60 cm), and DON was 2.44 mg L<sup>1</sup> (at 30 cm), as shown in **Table 3**. In turn, smaller concentrations of nitrogen occurred in the areas of chop-and-mulch agriculture and riparian vegetation. The concentrations of NO3 , considering the land-use systems, were higher than those of NH4 <sup>+</sup> and DON.

As can be observed in **Table 3**, there were significant differences according to the Kruskal-Wallis test in the mean values of the areas studied in the different land uses (p ≤ 0.05) for DOC, NO3 , and NH4 + . The results of the ANOVA (p-value = 0.000) provided sufficient evidence that the means were also different for DON, where α = 0.05. According to the Tukey test, the AFS and riparian vegetation in Cumaru, as well as the pasture and riparian vegetation in São João, were different in relation to the other areas.

The boxplots in **Figure 3** present the variation of DON between the areas studied, where some discrepant data can be observed. In the Cumaru basin, it was highest in the areas of agroforestry system (AFSC) and riparian vegetation (RVC), while in São João the lowest values of DON were in the areas with secondary forest (SFSJ), pasture


**Table 3.**

*Statistical tests of the variables DOC, DON, NO3 , and NH4 + .*


#### **Table 4.**

*Presence of nutrients with highest concentrations (indicated by X) in the soil solution extracts according to land-use systems.*

#### **Figure 3.**

*Boxplots of the concentrations of dissolved organic nitrogen (DON) in the soil solution in the different areas studied after mathematical transformation (1/DON).*

(PSJ), and agroforestry system (AFSSJ) in relation to the areas in Cumaru with the same land use.

#### **3.4 Variability of DOC and DON in areas with different land-use systems**

At a depth of 30 cm, there were higher concentrations of DOC in all land-use classes, but with slash-and-burn agriculture standing out more specifically in the *Soil Solution Chemistry in Different Land-Use Systems in the Northeast Brazilian Amazon DOI: http://dx.doi.org/10.5772/intechopen.101856*

#### **Figure 4.**

*Temporal and spatial variation of concentrations of dissolved organic carbon and nitrogen (in mg L<sup>1</sup> ) in soil solution samples collected at depths of 30 and 60 cm in the sampling areas with different land-use classes in the watersheds studied.*

**Figure 5.**

*The ratio between dissolved organic carbon and nitrogen in the agrosystems in the Cumaru and São João watersheds at depths of 30 cm and 60 cm.*

periods of drought and transition from rainy to dry, with values above 20 mg L<sup>1</sup> . In turn, the riparian vegetation was in the second place regarding the magnitude of the concentrations of DOC. At a depth of 60 cm, slash-and-burn agriculture presented values greater than 10 mg L<sup>1</sup> of DOC in all climate periods (**Figure 4**).

In the pasture areas, the concentrations of DOC and DON were greater than 5 mg L<sup>1</sup> at both depths in the two transition periods and the rainy period, with no significant differences between depths. The DOC concentrations were lowest in the agroforestry system areas at both depths. With respect to climate, the DOC concentrations were greater in the dry period in all six land-use systems studied.

The DOC/DON ratio, in turn, was highest in the slash-and-burn agriculture areas and lowest in the riparian vegetation, AFS, and secondary forest areas (**Figure 5**).



*Soil Solution Chemistry in Different Land-Use Systems in the Northeast Brazilian Amazon DOI: http://dx.doi.org/10.5772/intechopen.101856*

**Table 5.**

*Average concentrations of nutrients present in the soil solution in the Cumaru and São João basins in areas with slash-and-burn agriculture, riparian vegetation, secondary forest, chop-and-mulch agriculture, pasture, and agroforestry system.*
