Abstract
Burning of the soils as a result of the burning of vegetation especially the forests are often due to human activities. Most zones which are affected with burning are arid and semi-arid regions. Libya is one of arid regions in the world because the annual rainfall does not exceed 650 mm per year except in a small area called Green mountain (Aljabal Alakhdar), which is receive an annual rainfall exceed than 400 mm. It is the only wet area in Libya, so it contains forest with plant diversity. This region (the area covered by this study), like any forest area in the Mediterranean region is exposed to encroachments such as burning parts of it to convert trees to charcoal or burning trees and turning them into agricultural land in other parts. Therefore, the aim of this study was to evaluate the effects of burning on the organic matter, chemical macro nutrients: total nitrogen, total phosphorus and exchangeable potassium that following burning in two areas in the Green Mountain, with those exposed to burning compared to those in adjacent unburned areas in one seaboard (Ras alhelal) and one mountainous (Marawah) site. The results of this study indicated that the soils in both sites, regardless of burning or depth fall into the silt loam category texture and the main separated particle size was the silt with low clay contents, also the results indicated that, the fire was not enough to change this texture. In the light of the results obtained, it is clear that soils of both study sites are characterized by low organic matter content. In addition, the results indicate that the average percentage of the organic matter in all layers at the seaboard site was higher than its average percentage in the equivalent layers at the mountainous site. According to the findings obtained from this study, there has been a strong impact of fire on total N especially in the new burnt (mountainous) site, which agrees reasonably well with the degrees of soil organic matter of both burned study sites. The expected way that total N would be lost in these soils by fire is in volatilization and particulate transfer to the atmosphere during burning. The results of total P in soils showed that there was more total P in the upper soil layer in the old-burnt site (seaboard) than the new-burnt (mountainous) site at the same depth. It should be noticed from the data that the amount of total P in the seaboard site was high compared with its amount in the mountainous site. As well the results showed that, exchangeable potassium was very limited probably due to its absence in the parent material of the soils and almost all that there is being absorbed by plants. The results indicate that the highest quantities of the exchangeable potassium were in the uppermost layers in both study sites, were particularly high in the mountainous site compared with the seaboard site and were markedly affected by burning in the top layer of the soil.
Highlights
IntroductionThe effect of fires on the nitrogen cycle in soils was clearly described by Neil et al [1]
The results indicate that the highest quantities of the exchangeable potassium were in the uppermost layers in both study sites, were high in the mountainous site compared with the seaboard site and were markedly affected by burning in the top layer of the soil
Particle size analysis showed that sand sized particles form between 24.6 and 30% of the mineral part of the sampled soils. These results confirmed by the ANOVA results which indicated that the differences were highly significant (p0.001) between the study sites in the clay, silt and sand contents, the differences were highly significant between different depths in clay content (Table 1)
Summary
The effect of fires on the nitrogen cycle in soils was clearly described by Neil et al [1]. They described the transformation of nitrogen under the effect of fires as occurring in several accelerated loss steps. They reported that between 400°C and 500°C volatilization caused 75% to 100% of nitrogen to be lost; between 300°C and 400°C, 50% to 75% is lost; from 200°C to 300°C, up to 50% of nitrogen is lost; and below 200°C only small amounts of nitrogen are lost. The problem is complicated by surface erosion, when the removal of NH4+ attached to clay particles occurs
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