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Reclamation of a burned forest soil with municipal waste compost: macronutrient dynamic and improved vegetation cover recovery
Bioresource Technology 76 (2001) 221±227
Reclamation of a burned forest soil with municipal waste compost: macronutrient dynamic and improved vegetation cover recovery C. Guerrero a, I. G omez b, R. Moral a, J. Mataix-Solera a, J. Mataix-Beneyto a, T. Hern andez c,* a
Department of Agrochemistry and Environment, University of Miguel Hern andez, 03202 Elche, Spain Department of Agrochemistry and Biochemistry, University of Alicante, P.O. Box 99, 03080 Alicante, Spain Department of Soil and Water Conservation and Organic Waste Management, CEBAS-CSIC, P.O. Box 4195, 30080 Murcia, Spain b
c
Received 6 May 2000; received in revised form 25 July 2000; accepted 31 July 2000
Abstract The reclamation of burned soils in Mediterranean environments is of paramount importance in order to increase the levels of soil protection and minimise erosion and soil loss. The changes produced in the content of total organic carbon (TOC), N (Kjeldahl) and available P, K, Ca and Mg by the addition of dierent doses of a municipal solid waste compost to a burned soil were evaluated during one year. The eect of organic amendment on the improvement in the vegetation cover after one year was also evaluated. The organic amendment, particularly at a high dose, increased the TOC and N-Kjeldahl content of the soil in a closely related way. The levels of available K in soil were also enhanced by the organic amendment. Although the eects on all three parameters tended to decrease with time, their values in the amended soils were higher than in the control soil, which clearly indicates the improvement in the chemical quality of the soil brought about by the organic amendment. The available P content did not seem to be in¯uenced by organic treatment, while available Mg levels were higher than in the control during the ®rst 4 months following organic amendment. The application of compost to the burned soil improved its fertility and favoured rapid vegetal recovery, thus minimising the risk of soil erosion. Ó 2000 Published by Elsevier Science Ltd. Keywords: Forest ®re; Municipal solid waste compost; Macronutrients; Organic matter; Soil restoration; Vegetation cover
1. Introduction Forest wild®res constitute a serious environmental problem not only due to the destruction of vegetation but also because of the degradation that may be induced in a soil as a consequence of the changes produced in its properties. Wild®res can strongly modify the abiotic and biotic characteristics of soil, altering its structure (DõazFierros et al., 1989), physico-chemical properties (pH, EC), C and macronutrient levels (White et al., 1973; St Jhon and Rundel, 1976; Hern andez et al., 1997), microbiota and vegetation cover (Chandler et al., 1983; Carballas et al., 1993; V azquez et al., 1993, 1996). The degree of the alteration produced in these biotic and abiotic factors depends on the frequency and intensity of ®re such alterations being particularly important in the surface horizons (Kutiel and Shaviv, 1989).
*
Corresponding author. E-mail address: [email protected] (T. HernaÂndez).
Fire may directly consume part or all of the standing plant material and litter as well as the organic matter in the upper layers of soil. Nutrients contained in the organic matter are either made more available or can be volatilised and lost from the site. Some of the soluble nutrients deposited in the ash, if not immediately absorbed by plants, may be lost from the site by erosion (DeBano and Conrad, 1978) or leaching into the groundwater (Pritchett and Fisher, 1987). The indirect eects of ®re on nutrients may include changes in N2 ®xation rates, mycorrhizal relationships and the hydrologic exportation of nutrients by mobilisation and water movement through the ecosystem. Although ®re aects the cycling of all plant nutrients, its eect on N is particularly important because N is a limiting nutrient (Hellmers et al., 1955) and is easily lost by volatilisation. Fire induces phosphorus mineralisation in the soil and the subsequent formation of soluble forms, which are easily leached. Moreover, increased erosion may increase the loss of P in particulate forms (Soto et al., 1991).
0960-8524/01/$ - see front matter Ó 2000 Published by Elsevier Science Ltd. PII: S 0 9 6 0 - 8 5 2 4 ( 0 0 ) 0 0 1 2 5 - 5
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The loss of organic matter through ®re, as well as the eect of ®re on microbiota and the diminution in vegetation and soil cover, will favour surface soil erosion, particularly in semiarid and Mediterranean forests, causing alterations in the biological cycling of nutrients (Raison, 1979; Chandler et al., 1983; Kutiel and Naveh, 1987; Pritchett and Fisher, 1987). Fire may aect different chemical and physical properties of the soil, increasing runo and promoting erosion processes. Erosion following a ®re usually results in much higher nutrient and soil losses than are found in other ecosystems (Boerner, 1992). Fertility is modi®ed not only immediately after the ®re but also in the longer term, which consequently has a negative eect on the recovery of the soil and the forest vegetation. The removal of top soil due to erosion and the depletion in fertility delay the recovery of the original vegetation type, or may even prevent it, thus enhancing the deserti®cation process. In order to minimise any damage caused to the soil by wild®res, the ash layer must be stabilised, the vegetation re-established and the soil structure improved as soon as possible. To this end, the addition of organic materials with a high macro and micronutrient content and a diverse microbial population can help in the re-establishment of a soil's pre-burning characteristics, favouring plant development and reducing the time needed to reach suitable levels of soil protection (Villar et al., 1998). Vazquez et al. (1996) observed that the addition to a burned soil of poultry manure at high doses signi®cantly improved both the stability of the aggregates and the yield of all leguminous and gramineous species tested. The aim of this work was to evaluate the ecacy of the addition of a municipal solid waste compost in improving the vegetation recovery of a burned soil and any in¯uence it might have had on organic matter and macronutrient dynamics. 2. Methods The experiment was carried out in a forest soil which had been burned ®ve months previously, located in Bocairente (Valencia, Spain), at 38°440 900 N and 0°420 900 W. The soil was a Calcic Rhodoxeralf (Soil Survey Sta, 1990), and the site (730 m above sea level) had a <2% slope and SE orientation. No live vegetation was observed, and the soil had a Munsell colour of 7.5 YR 4/4 (dry) and 10 YR 3/2 (wet) due to the ash cover. During the experimental period the average air temperature was 15:3°C, the average daily minimum temperature being 8:9°C and the average daily maximum temperature 21:7°C; the mean annual rainfall was 440 mm. The non-burned adjacent areas presented a Mediterranean sclerophyllous vegetation with widely dispersed trees (Pinus halepensis Miller, Pinus pinaster
Table 1 Main characteristics of the soil and municipal solid waste (MSW) compost used Parameters
Soil
MSW compost
pH Electrical conductivity (mS mÿ1 ) Sand (%) Silt (%) Clay (%) Ca CO3 (%) Active lime (%) Total organic carbon (g kgÿ1 ) N-Kjeldahl (g kgÿ1 ) Ammonium (mg kgÿ1 ) Nitrates (mg kgÿ1 ) Chlorides (mg kgÿ1 ) Sulphates (g kgÿ1 ) C/N relation Available content Pa (mg kgÿ1 ) Kb (g kgÿ1 ) Cab (g kgÿ1 ) Mgb (g kgÿ1 ) Nab (g kgÿ1 ) Fec (mg kgÿ1 ) Cuc (mg kgÿ1 ) Mnc (mg kgÿ1 ) Znc (mg kgÿ1 )
8.13 16.1 44.1 34.8 21.1 21.5 10.6 29.1 2.31 11.6 58 36 7.3 12.6
5.83 931 ) ) ) ) ) 200.3 16.4 20.5 < 0:1 6820 8010 12.3
3.60 0.45 5.31 0.17 0.11 11.9 0.7 13.5 1.13
) 2.38 30 2.13 3.97 378 45 285 47
a
Extracted with 0:5 M Na HCO3 . Extracted with 1 N ammonium acetate. c Extracted with 5 mM DTPA (diethylentriaminpentaacetic acid). b
Aiton, Quercus rotundifolia Lam., Olea europaea L.) and a high shrub cover (Quercus coccifera L., Rosmarinus ocinalis L., Ulex parvi¯orus Pourret, Daphne gnidium L., Cistus albidus L., Dorycnium pentaphyllum Scop.). The study was performed in 10 m2 plots randomly located in a burned area of 3000 m2 . Four treatments were established by adding dierent doses of a municipal solid waste (MSW) compost from a town composting plant in Valdeming omez, Madrid, Spain, to the burned soil. The application rates of 0, 0.5, 1, and 2 kg compost mÿ2 soil (dry basis) shall be referred to as C (control), MSW1, MSW2 and MSW3 treatments, respectively. Compost was uniformly incorporated into the soil surface. All the treatments were carried out in quadruplicate. Samples were taken 15, 30, 60, 90, 120, 150, 240, 300, and 360 days after compost application. Each sample consisted of a mixture of eight subsamples (200 cm3 soil cores) randomly collected at 0±15 cm depth. Vegetal residues such as charred twigs, tree branches etc., were removed from the subsamples before they were mixed. The characteristics of the soil and MSW compost are shown in Table 1. 2.1. Soil chemical analysis The soil samples were air dried and sieved through a 2 mm mesh before analysis. Total organic carbon (TOC)
C. Guerrero et al. / Bioresource Technology 76 (2001) 221±227
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The levels of TOC at the dierent sampling times were generally higher in the treated than in the untreated soils, particularly at higher doses (Fig. 1). The soil TOC content tended to decrease with time probably due to organic matter mineralisation processes. In the control soil, the TOC levels decreased gradually from the beginning of the experiment, while in the amended soils, particularly MSW2 and MSW3, the organic matter was mineralised more slowly, the diminution in their TOC
content only being noticeable 300±360 days after organic amendment. This can be explained by the relative stability of the organic matter of the MSW compost due to the composting process undergone by the organic waste, and is in agreement with the ®ndings of other authors in incubation experiments (Pascual, 1995, Moreno, 1997). The greater plant biomasss developed during the experimental period in the amended soils with respect to the untreated soil could also have contributed to the maintenance of TOC levels through the contribution of root exudates and plant debris. One year after organic amendment, the TOC levels in the amended soils, particularly in MSW2 and MSW3, remained higher than in the untreated soil. This is a positive development from a soil quality point of view, since organic matter improves a soil's characteristics through its eect on chemical, biological and physical properties. The organic matter incorporated with the MSW compost is used as energy source by soil microorganisms, thus favouring microbial recovery, which contributes to soil aggregation (Lynch, 1984; Oades, 1993). Apart from this indirect eect on microbial population activity, organic amendment also has a direct eect on the microbial population due to the diverse microorganisms incorporated with the MSW compost (5200 105 CFU gÿ1 of viable aerobic bacteria and 6800 CFU gÿ1 of viable aerobic fungi). Dõaz-Ravi~ na et al. (1996) observed a large increase in bacterial activity, after a long lag (up to 8 weeks), following the addition of poultry manure to a heated soil. In a previous work (Guerrero et al., 2000), we also observed an increase in bacterial and fungal populations following the addition of MSW compost to a burned soil. Soil organic amendment increased the nitrogen content of the burned soil, particularly in MSW2 and MSW3 (Fig. 2), which was to be expected due to the high N content of the MSW compost (16.4 g kgÿ1 ). The nitrogen content of the amended soils remained higher than that of the control throughout the experimental period, the dierences being, in general, statistically
Fig. 1. Changes with time in the total organic carbon (TOC) content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
Fig. 2. Changes with time in the Kjeldahl-nitrogen content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
was determined by Walkley±Black's method (Walkley and Black, 1934). K, Ca and Mg were extracted from the soil with 1 N ammonium acetate, following the indications of Knudsen et al. (1982), and determined by ¯ame atomic absorption spectrometry (FAAS). Kjeldahlnitrogen was determined by the Bremner and Breitenbeck (1983) method and available P was measured by Burriel±Hernando's extraction method following the indications of Dõez (1982). 2.2. Vegetal analysis One year after the organic amendment all phytomass developed in the plots was cropped and the most abundant vegetal species were quanti®ed and analysed. Vegetal biomass was dried at 65°C and ground before analysis. The P, K, Ca, Mg and oligoelement contents of the plants were determined in the nitric-perchloric (1:1) digestion extract. P was determined by the Murphy and Riley (1962) method and K, Ca, Mg and oligoelements by FAAS. Nitrogen was determined as mentioned above for the soil. Data were interpreted using analysis of variance and means were compared by using least signi®cant dierence values (Tukey's test). 3. Results and discussion 3.1. Chemical changes
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established vegetation. In an incubation experiment Giusquiani et al. (1995) observed that the levels of available P obtained by adding a MSW compost remained constant throughout the 12 month of the experiment. Pascual (1995), too, observed that soils amended with a MSW compost showed only slight ¯uctuations in P content over one year period. The organic amendments of our experiment increased the available K content in the soil, particularly at the high dose (MSW3) (Fig. 4). In general, the amended soils showed statistically signi®cant higher levels of available K than the unamended burned soil at all the dierent sampling times. Although the available K content diminished with time, the levels of available K in all the treated soils one year after the application of compost were still greater than in the untreated soil. These results are in agreement with those obtained by Albadalejo et al. (1994) in degraded soils amended with MSW. Only the soil amended with the high dose of compost (MSW3) showed initial levels of Ca (extractable with ammonium acetate) signi®cantly higher than in the control (Fig. 5). Apart from the ®rst samples, the Ca content of the treated soils showed no correlation with
signi®cant. As in the case of the TOC, Kjeldahl-N in the untreated soil decreased gradually with time, while in the treated soils the N content was only seen to have decreased by the end of the experimental period. This suggests that mineralisation processes predominated in the control soil, N being lost by leaching (in the form of nitrate) or evaporation (in the form of NH 4 ). In the amended soils the stimulation of microbial development and activity induced by the added compost meant that N ®xation and immobilisation processes initially predominated over the mineralisation processes, the losses of N being less noticeable. Pascual (1995) and Castellanos and Pratt (1981) also observed a slight N mineralisation in soils amended with urban waste composts. Since Kjeldahl-nitrogen levels in treated and untreated soils followed a quite similar pattern to TOC, the C/N relation during the experimental period remained constant, the values of this ratio generally followed the pattern: C > MSW1 > MSW2 > MSW3. The lower C/N values in the amended soils points to the existence in the compost of a more humi®ed organic matter than that existing in the burned soil and con®rm the contribution of dead roots and incompletely burned plant debris in the high carbon content observed in burned soils after ®re. As shown in Fig. 3, the addition of MSW compost initially increased the available P content in the soil although not to a statistically signi®cant extent. This fact, can be explained by the low concentration of this nutrient in the compost added (1180 mg kgÿ1 ), which is 10-fold lower than other MSW composts described in the literature (Giusquiani et al., 1995). The time course trend of available P was similar in all the treatments throughout the year and showed no statistically signi®cant dierences with the levels in the control soil. Although there were slight dierences between individual samples, these dierences were not statistically dierent, which suggests that the gradual mineralisation of organic P compensates the mineral P which is gradually lost through precipitation or absorption by the newly
Fig. 4. Changes with time in the available potassium content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
Fig. 3. Changes with time in the available phosphorous content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
Fig. 5. Changes with time in the available calcium content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
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Table 2 Percentage increase in yield (dry matter) in treated soils with respect to untreated soils, harvested 360 days after compost applicationa Dorycnium pentaphyllum Rosmarinus ocinalis Cistus albidus
MSW1
MSW2
MSW3
8.8 10.7 6.3
12.1 22.4 11.7
24.9 39.1 19.0
a
MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil.
Fig. 6. Changes with time in the available magnesium content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
the dose of compost added. In both the treated and control soils, the Ca content varied during the year, although it behaved dierently in both (Fig. 5). All the treated soils behaved in a similar way through the sampling period, but dierently to the control soil. This suggests that compost application modi®ed Ca availability, especially because of the changes in pH caused by organic matter mineralisation. At the last sampling times, all the amended soils showed higher Ca values than the control. The magnesium availability was positively in¯uenced by compost application, but only at the ®rst samplings (up to 4 months after compost addition) (Fig. 6). The concentrations of Mg of treated soils were not proportional to the compost application rates. 3.2. Plant cover development The addition of the MSW compost favoured vegetal cover recovery in a dose-dependent form. One year after organic amendment all the treated plots showed greater plant development than the unamended soil, a fact that would greatly contribute to the protection of a soil against erosion processes. This improvement in vegetation cover was a result of an improvement of the physical, microbiological and chemical properties of the soil due to the organic amendment. The most abundant vegetal species to be found growing in the dierent plots one year after the addition of organic amendment were Rosmarinus ocinalis, Dorcynium pentaphyllum and Cistus albidus, in that order (Table 2). The addition of the compost stimulated N absorption by plants, particularly at the high dose (Table 3), the increases in yield in MSW3 with respect to the control ranging from 10.2% to 53%, depending on the vegetal species. This higher N absorption led to a higher N concentration in leaves for Dorycinium and Rosmarinus, while in Cistus dierences with the control was manifested by a higher N concentration in roots stems (Table 3).
The plants growing in treated soils also showed a higher P content than those growing in the control soil (Table 3), the increases in MSW3 with respect to the control ranging from 7.5% to 39.5%, depending on the vegetal species. In this case, the dierences were observed in both leaves and roots stems (with the exception of Cistus albidus which only showed a higher P concentration than the control in leaves). The absorption of K seemed to be particularly stimulated by the organic amendment, the K content of plants growing in the MSW3 soil increasing by 17.2± 103% the levels observed in the plants growing in the control soil. In all the vegetal species the K content measured in leaves and in the rest of the plant (root stem) was in general, signi®cantly higher than in the plants growing in the control soil (Table 3). In general, the organic amendment did not in¯uence the absorption of Ca or Mg by the plants, although a higher Fe concentration was observed in the leaves and roots stems of plants growing in the treated soils. The in¯uence of the organic treatment on the absorption of the other oligoelements diered according to the vegetal species. For example, Dorycnium pentaphyllum growing in SW2 and SW3 showed a signi®cant increase in the levels of Cu and Zn in leaves, while Cistus albidus increased its absorption of Zn and Mg and Rosmarinus ocinalis increased its absorption of Zn alone. To summarise, the organic amendment stimulated the absorption of macro and micronutrients by plants. This led to a stronger recovery of the vegetation cover, which is important for protecting the soil against erosion processes.
4. Conclusions The results of this study indicate that MSW compost is useful for the reclamation of a burned soil since it increases the levels of soil organic matter and nutrients, encouraging the recovery rate of the vegetation cover which will protect the soil against erosion processes. An organic amendment applied immediately after burning will not only protect the soil against erosion but prepare the soil for subsequent reforestation with appropriate forest species. The use of MSW compost, therefore,
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Table 3 Nutrient status of spontaneous vegetation cropped in the experimental areaa Element
Treatment C
Treatment MSW1
MSW2
MSW3
N (%) P (mg kgÿ1 ) Ca (g kgÿ1 ) K (g kgÿ1 ) Mg (g kgÿ1 ) Na (g kgÿ1 ) Fe (mg kgÿ1 ) Cu (mg kgÿ1 ) Mn (mg kgÿ1 ) Zn (mg kgÿ1 )
Leaf of Dorycnium pentaphyllum 1.47a 1.57b 1.61b 679a 833b 945c 19.22 22.97 20.22 4.43a 4.40a 5.56b 2.91 2.95 3.00 0.54a 0.71b 0.71b 348.2a 330.1a 436.7b 6.3a 6.5a 7.5a 106.4 108.6 122.7 19.7a 23.9ab 27.7b
1.71c 921c 21.87 5.72b 3.14 0.71b 444.2b 14.2b 124.0 27.9b
N (%) P mg kgÿ1 Ca g kgÿ1 K g kgÿ1 Mg g kgÿ1 Na g kgÿ1 Fe mg kgÿ1 Cu mg kgÿ1 Mn mg kgÿ1 Zn mg kgÿ1
Leaf of Rosmarinus ocinalis 0.58a 0.88b 0.92b 819a 825a 829a 21.41 20.64 20.22 11.36a 17.54b 20.86bc 7.04 6.25 6.19 3.80a 4.87ab 5.44b 374c 355b 356b 12.5 13.1 21.5 36.9 33.6 37.1 37.1a 45.7b 58.1c
1.13c 916b 19.61 23.17c 6.48 9.64c 345a 16.4 31.5 77.9d
N (%) P mg kgÿ1 Ca g kgÿ1 K g kgÿ1 Mg g kgÿ1 Na g kgÿ1 Fe mg kgÿ1 Cu mg kgÿ1 Mn mg kgÿ1 Zn mg kgÿ1
Leaf of Cistus albidus 0.88 0.90 788a 841b 26.30 25.64 9.14a 11.85b 4.73a 5.00ab 4.80a 5.14a 988c 967c 16.6 18.8 45.1b 41.4ab 23.4a 44.0b
0.95 904c 26.05 9.91b 4.65a 6.34b 558a 15.7 33.1a 63.2c
a
0.92 897c 27.42 11.12b 5.51b 6.50b 832b 17.5 37.5a 49.1b 2
F
ns
b
ns
ns
ns
ns
ns ns
ns
ns
ns
C
MSW1
Root stem 0.86a 543a 7.30a 5.62a 0.82 0.67 328.8 6.0 18.2 12.9
of Dorycnium pentaphyllum 0.93b 0.93a 0.95b 638b 670b 784c 7.73a 8.09ab 9.18b 5.77a 5.65a 6.06b 1.08 1.08 1.11 0.70 0.70 0.73 285.2 280.2 230.1 5.0 4.8 5.2 20.4 20.5 20.6 16.6 17.1 21.3
MSW2
MSW3
Root stem 0.47a 571a 15.04 13.11a 3.01 6.81a 513c 12.0 21.0 24.0a
of Rosmarinus ocinalis 0.47a 0.53b 706b 805c 14.25 15.49 20.99b 25.35c 2.69 2.67 7.01a 6.38a 423b 390ab 13.1 15.6 18.6 21.3 23.8a 39.0b
0.48a 820c 13.63 26.53c 2.75 10.24b 356a 16.3 15.3 33.4b
Root stem 0.49a 601b 15.32 6.32a 2.88 3.88a 999d 9.7 32.6b 21.9a
of Cistus albidus 0.46a 0.58b 628b 557a 16.32 14.83 11.07c 10.00bc 2.96 2.77 4.73b 3.97ab 823c 375b 10.6 8.0 30.9b 22.1a 38.3b 25.8a
0.56b 590b 15.43 8.51b 2.75 4.50b 292a 9.3 25.7a 30.7b
F
ns ns ns ns ns ns
ns
ns
ns ns
ns
ns
ns
C: burned soil; MSW1: 0.5 kg of compost per m burned soil; MSW2: 1 kg of compost per m of burned soil; MSW3: 2 kg of compost per m2 of burned soil. b ns: not signi®cant at P 6 0:05. * Signi®cant dierences at P 6 0:01 respectively. ** Signi®cant dierences at P 6 0:05 respectively. *** Signi®cant dierences at P 6 0:001 respectively.
seems to be a promising, cost-eective and ecologically acceptable method for the reclamation of forest soils degraded by wild®res. References Albadalejo, J., Stocking, M., Diaz, E., Castillo, V., 1994. Land rehabilitation by urban refuse amendments in a semi-arid environment: eect on soil chemical properties. Soil Technol. 7, 249±260. Boerner, R.E.J., 1992. Fire and nutrient cycling in temperate ecosystems. Bio. Sci. 32, 187±192. Bremner, J.M., Breitenbeck, G.A., 1983. A simple method for determination of ammonium in semimicro-kjeldahl analysis of soils and plant materials using a block digester. Commun. Soil Sci. Plant Anal. 14, 905±913. Carballas, M., Acea, M.J., Cabaneiro, C., Trasar, C., Villar, M.C., Diaz-Ravi~ na, M., Fern andez, I., Prieto, A., Saa, A., V azquez, F.J., Zehner, R., Carballas, T., 1993. Organic matter, nitrogen, phos-
2
phorus and microbial population evolution in forest humiferous acid soils after wild®res. In: Trabaud, L., Prodon, R. (Eds.), Fire in Mediterranean Ecosystems. Ecosystems Research Report 5. Commission of the European Communities, pp. 379±385. Castellanos, J.Z., Pratt, P.F., 1981. Mineralization of manure nitrogen-correlation with laboratory indexes. Soil Sci. Soc. Am. J. 45, 354±357. Chandler, C., Cheney, P., Thomas, P., Trabaud, L., Williams, D. (Eds.), 1983. Fire in forestry. In: Forest Fire Behaviour and Eects, vol. I. Wiley, New York, pp. 171±202. DeBano, L.F., Conrad, C.E., 1978. The eect of ®re on nutrients in a chaparral ecosystem. Ecology 59, 489±497. Dõaz-Fierros, F., Benito, E., Vega, J.A., Castelao, A., Soto, B., Perez, R., Taboada, T., 1989. Solute loss and soil erosion in burnt soil from Galicia, N.W. Spain. In: Goldammer, J.G., Jenkins, M.J. (Eds.), Fire in Ecosystem Dynamics: Mediterranean and Northern Perspectives. S.P.B. Academic Publishing, The Hague, pp. 103± 116. Dõaz-Ravi~ na, M., Prieto, A., Baath, E., 1996. Bacterial activity in a forest soil after soil heating and organic amendments measured by
C. Guerrero et al. / Bioresource Technology 76 (2001) 221±227 the thymidine and leucine incorporation techniques. Soil Biol. Biochem. 28, 419±426. Dõez, J.A., 1982. Consideraciones sobre la utilizaci on de la tecnica extractiva de Burriel y Hernando para la evaluaci on del P asimilable en suelos. Anal. Edaf. Agrobiol. 41, 1345±1353. Giusquiani, P.L., Pagliai, M., Gigliotti, G., Businelli, D., Benetti, A., 1995. Urban waste compost: eects on physical chemical and biochemical soil properties. J. Environ. Qual. 24, 175±182. Guerrero, C., G omez, I., Mataix-Solera, J., Moral, R., MataixBeneyto, J., Hernandez, T., 2000. Eect of solid waste compost on microbiological and physical properties of a burned soil in ®eld experiments. Biol. Fertil. Soils (in press). Hellmers, H., Bonner, J.F., Kelleher, J.M., 1955. Soils fertility: A watershed management problem in the San Gabriel Mountains of Southern California. Soil Sci. 80, 189±197. Hernandez, T., Garcõa, C., Reinhardt, I., 1997. Short-term eect of wild®re on the chemical, biochemical and microbiological properties of Mediterranean pine forest soils. Biol. Fertil. Soils 25, 109±116. Knudsen, D., Peterson, G.A., Pratt, P.F. (Eds.), 1982. Lithium, Sodium and Potassium. In: ASA-SSSA, Methods of soil analysis, Madison, pp. 225±246. Kutiel, P., Naveh, Z., 1987. Soils properties beneath Pinus halepensis and Quercus calliprinos trees on burnt and unburnt mixed forest on Mt. Carmel, Israel. Forest Eco. and Management 20, 11±24. Kutiel, P., Shaviv, A., 1989. Changes of soil N±P status in laboratory simulated forest ®re. Plant and Soil 120, 57±63. Lynch, J.M., 1984. Interactions between biological processes, cultivation and soil's structure. Plant and Soil 76, 307±318. Moreno, J.L., 1997. Uso de composts de lodo de depuradora para la mejora de la calidad de los suelos de zonas aridas. Efecto de su contaminaci on metalica. PhD thesis. Faculty of Chemistry. University of Murcia, Spain. Murphy, J., Riley, J.P., 1962. A modi®ed single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta. 27, 31±36. Oades, J.M., 1993. The role of biology in the formation, stabilization and degradation of soil structure. In: Brussard, L., Kooistra, M.J.
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(Eds.), International Workshop on Methods of Research on Soil Structure. Soil Biota Interrelationships. Geoderma vol. 56, pp. 377±400. Pascual, J.A., 1995. Efectividad de los residuos org anicos urbanos en la mejora de la calidad de suelos aridos: aspectos biol ogicos y bioquimicos. PhD thesis. Faculty of Biology, University of Murcia, Spain. Pritchett, W.L., Fisher, R.F., 1987. Properties and Management of Forest Soils. Wiley, New York. Raison, R.J., 1979. Modi®cation of the soil environment by vegetation ®res, with particular reference to nitrogen transformations: a review. Plant and Soil 51, 73±108. St Jhon, T.V., Rundel, P.W., 1976. The role of ®re as a mineralizing agent in a Sierran Coniferous Forest. Oecologia 25, 35±45. Soil Survey Sta. 1990, Keys to soil taxonomy. SMSS Technical Monograph no. 19. Virginia Politechnic Institute and State University. Soto, B., Benito, E., Perez, R., Basanta, R., Diaz-Fierros, F., 1991. Alterations in surface runo due to forest ®res. In: Sala, M., Rubio, J.L. (Eds.), Abstracts of the International Conference on Soil Erosion and Degradation as a Consequence of Forest Fires. European Society for Soil Conservation, Barcelona, pp. 29. V azquez, F.J., Acea, M.J., Carballas, T., 1993. Soil microbial populations after wild®re. FEMS Microb. Ecol. 13, 93±104. V azquez, F.J., Petrikova, V., Villar, M.C., Carballas, T., 1996. Use of poultry manure and plant cultivation for the reclamation of burnt soils. Biol. Fertil. Soils 22, 265±271. Villar, M.C., Gonzalez-Prieto, S.J., Carballas, T., 1998. Evaluation of three organic wastes for reclaiming burnt soils: Improvement in the recovery of vegetation cover and soil fertility in pot experiments. Biol. Fertl. Soils 26, 1222±1229. Walkley, A., Black, I.A., 1934. An examination of the Degtjare method for determining soil O.M. and a proposed modi®cation of the chromic acid titration method. Soil Sci. 37, 29±38. White, E.M., Thompson, W.W., Gartner, F.R., 1973. Heat eects on nutrient release from soils under Ponderosa Pine. J. Range Manag. 26, 22±24.
Reclamation of a burned forest soil with municipal waste compost: macronutrient dynamic and improved vegetation cover recovery C. Guerrero a, I. G omez b, R. Moral a, J. Mataix-Solera a, J. Mataix-Beneyto a, T. Hern andez c,* a
Department of Agrochemistry and Environment, University of Miguel Hern andez, 03202 Elche, Spain Department of Agrochemistry and Biochemistry, University of Alicante, P.O. Box 99, 03080 Alicante, Spain Department of Soil and Water Conservation and Organic Waste Management, CEBAS-CSIC, P.O. Box 4195, 30080 Murcia, Spain b
c
Received 6 May 2000; received in revised form 25 July 2000; accepted 31 July 2000
Abstract The reclamation of burned soils in Mediterranean environments is of paramount importance in order to increase the levels of soil protection and minimise erosion and soil loss. The changes produced in the content of total organic carbon (TOC), N (Kjeldahl) and available P, K, Ca and Mg by the addition of dierent doses of a municipal solid waste compost to a burned soil were evaluated during one year. The eect of organic amendment on the improvement in the vegetation cover after one year was also evaluated. The organic amendment, particularly at a high dose, increased the TOC and N-Kjeldahl content of the soil in a closely related way. The levels of available K in soil were also enhanced by the organic amendment. Although the eects on all three parameters tended to decrease with time, their values in the amended soils were higher than in the control soil, which clearly indicates the improvement in the chemical quality of the soil brought about by the organic amendment. The available P content did not seem to be in¯uenced by organic treatment, while available Mg levels were higher than in the control during the ®rst 4 months following organic amendment. The application of compost to the burned soil improved its fertility and favoured rapid vegetal recovery, thus minimising the risk of soil erosion. Ó 2000 Published by Elsevier Science Ltd. Keywords: Forest ®re; Municipal solid waste compost; Macronutrients; Organic matter; Soil restoration; Vegetation cover
1. Introduction Forest wild®res constitute a serious environmental problem not only due to the destruction of vegetation but also because of the degradation that may be induced in a soil as a consequence of the changes produced in its properties. Wild®res can strongly modify the abiotic and biotic characteristics of soil, altering its structure (DõazFierros et al., 1989), physico-chemical properties (pH, EC), C and macronutrient levels (White et al., 1973; St Jhon and Rundel, 1976; Hern andez et al., 1997), microbiota and vegetation cover (Chandler et al., 1983; Carballas et al., 1993; V azquez et al., 1993, 1996). The degree of the alteration produced in these biotic and abiotic factors depends on the frequency and intensity of ®re such alterations being particularly important in the surface horizons (Kutiel and Shaviv, 1989).
*
Corresponding author. E-mail address: [email protected] (T. HernaÂndez).
Fire may directly consume part or all of the standing plant material and litter as well as the organic matter in the upper layers of soil. Nutrients contained in the organic matter are either made more available or can be volatilised and lost from the site. Some of the soluble nutrients deposited in the ash, if not immediately absorbed by plants, may be lost from the site by erosion (DeBano and Conrad, 1978) or leaching into the groundwater (Pritchett and Fisher, 1987). The indirect eects of ®re on nutrients may include changes in N2 ®xation rates, mycorrhizal relationships and the hydrologic exportation of nutrients by mobilisation and water movement through the ecosystem. Although ®re aects the cycling of all plant nutrients, its eect on N is particularly important because N is a limiting nutrient (Hellmers et al., 1955) and is easily lost by volatilisation. Fire induces phosphorus mineralisation in the soil and the subsequent formation of soluble forms, which are easily leached. Moreover, increased erosion may increase the loss of P in particulate forms (Soto et al., 1991).
0960-8524/01/$ - see front matter Ó 2000 Published by Elsevier Science Ltd. PII: S 0 9 6 0 - 8 5 2 4 ( 0 0 ) 0 0 1 2 5 - 5
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The loss of organic matter through ®re, as well as the eect of ®re on microbiota and the diminution in vegetation and soil cover, will favour surface soil erosion, particularly in semiarid and Mediterranean forests, causing alterations in the biological cycling of nutrients (Raison, 1979; Chandler et al., 1983; Kutiel and Naveh, 1987; Pritchett and Fisher, 1987). Fire may aect different chemical and physical properties of the soil, increasing runo and promoting erosion processes. Erosion following a ®re usually results in much higher nutrient and soil losses than are found in other ecosystems (Boerner, 1992). Fertility is modi®ed not only immediately after the ®re but also in the longer term, which consequently has a negative eect on the recovery of the soil and the forest vegetation. The removal of top soil due to erosion and the depletion in fertility delay the recovery of the original vegetation type, or may even prevent it, thus enhancing the deserti®cation process. In order to minimise any damage caused to the soil by wild®res, the ash layer must be stabilised, the vegetation re-established and the soil structure improved as soon as possible. To this end, the addition of organic materials with a high macro and micronutrient content and a diverse microbial population can help in the re-establishment of a soil's pre-burning characteristics, favouring plant development and reducing the time needed to reach suitable levels of soil protection (Villar et al., 1998). Vazquez et al. (1996) observed that the addition to a burned soil of poultry manure at high doses signi®cantly improved both the stability of the aggregates and the yield of all leguminous and gramineous species tested. The aim of this work was to evaluate the ecacy of the addition of a municipal solid waste compost in improving the vegetation recovery of a burned soil and any in¯uence it might have had on organic matter and macronutrient dynamics. 2. Methods The experiment was carried out in a forest soil which had been burned ®ve months previously, located in Bocairente (Valencia, Spain), at 38°440 900 N and 0°420 900 W. The soil was a Calcic Rhodoxeralf (Soil Survey Sta, 1990), and the site (730 m above sea level) had a <2% slope and SE orientation. No live vegetation was observed, and the soil had a Munsell colour of 7.5 YR 4/4 (dry) and 10 YR 3/2 (wet) due to the ash cover. During the experimental period the average air temperature was 15:3°C, the average daily minimum temperature being 8:9°C and the average daily maximum temperature 21:7°C; the mean annual rainfall was 440 mm. The non-burned adjacent areas presented a Mediterranean sclerophyllous vegetation with widely dispersed trees (Pinus halepensis Miller, Pinus pinaster
Table 1 Main characteristics of the soil and municipal solid waste (MSW) compost used Parameters
Soil
MSW compost
pH Electrical conductivity (mS mÿ1 ) Sand (%) Silt (%) Clay (%) Ca CO3 (%) Active lime (%) Total organic carbon (g kgÿ1 ) N-Kjeldahl (g kgÿ1 ) Ammonium (mg kgÿ1 ) Nitrates (mg kgÿ1 ) Chlorides (mg kgÿ1 ) Sulphates (g kgÿ1 ) C/N relation Available content Pa (mg kgÿ1 ) Kb (g kgÿ1 ) Cab (g kgÿ1 ) Mgb (g kgÿ1 ) Nab (g kgÿ1 ) Fec (mg kgÿ1 ) Cuc (mg kgÿ1 ) Mnc (mg kgÿ1 ) Znc (mg kgÿ1 )
8.13 16.1 44.1 34.8 21.1 21.5 10.6 29.1 2.31 11.6 58 36 7.3 12.6
5.83 931 ) ) ) ) ) 200.3 16.4 20.5 < 0:1 6820 8010 12.3
3.60 0.45 5.31 0.17 0.11 11.9 0.7 13.5 1.13
) 2.38 30 2.13 3.97 378 45 285 47
a
Extracted with 0:5 M Na HCO3 . Extracted with 1 N ammonium acetate. c Extracted with 5 mM DTPA (diethylentriaminpentaacetic acid). b
Aiton, Quercus rotundifolia Lam., Olea europaea L.) and a high shrub cover (Quercus coccifera L., Rosmarinus ocinalis L., Ulex parvi¯orus Pourret, Daphne gnidium L., Cistus albidus L., Dorycnium pentaphyllum Scop.). The study was performed in 10 m2 plots randomly located in a burned area of 3000 m2 . Four treatments were established by adding dierent doses of a municipal solid waste (MSW) compost from a town composting plant in Valdeming omez, Madrid, Spain, to the burned soil. The application rates of 0, 0.5, 1, and 2 kg compost mÿ2 soil (dry basis) shall be referred to as C (control), MSW1, MSW2 and MSW3 treatments, respectively. Compost was uniformly incorporated into the soil surface. All the treatments were carried out in quadruplicate. Samples were taken 15, 30, 60, 90, 120, 150, 240, 300, and 360 days after compost application. Each sample consisted of a mixture of eight subsamples (200 cm3 soil cores) randomly collected at 0±15 cm depth. Vegetal residues such as charred twigs, tree branches etc., were removed from the subsamples before they were mixed. The characteristics of the soil and MSW compost are shown in Table 1. 2.1. Soil chemical analysis The soil samples were air dried and sieved through a 2 mm mesh before analysis. Total organic carbon (TOC)
C. Guerrero et al. / Bioresource Technology 76 (2001) 221±227
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The levels of TOC at the dierent sampling times were generally higher in the treated than in the untreated soils, particularly at higher doses (Fig. 1). The soil TOC content tended to decrease with time probably due to organic matter mineralisation processes. In the control soil, the TOC levels decreased gradually from the beginning of the experiment, while in the amended soils, particularly MSW2 and MSW3, the organic matter was mineralised more slowly, the diminution in their TOC
content only being noticeable 300±360 days after organic amendment. This can be explained by the relative stability of the organic matter of the MSW compost due to the composting process undergone by the organic waste, and is in agreement with the ®ndings of other authors in incubation experiments (Pascual, 1995, Moreno, 1997). The greater plant biomasss developed during the experimental period in the amended soils with respect to the untreated soil could also have contributed to the maintenance of TOC levels through the contribution of root exudates and plant debris. One year after organic amendment, the TOC levels in the amended soils, particularly in MSW2 and MSW3, remained higher than in the untreated soil. This is a positive development from a soil quality point of view, since organic matter improves a soil's characteristics through its eect on chemical, biological and physical properties. The organic matter incorporated with the MSW compost is used as energy source by soil microorganisms, thus favouring microbial recovery, which contributes to soil aggregation (Lynch, 1984; Oades, 1993). Apart from this indirect eect on microbial population activity, organic amendment also has a direct eect on the microbial population due to the diverse microorganisms incorporated with the MSW compost (5200 105 CFU gÿ1 of viable aerobic bacteria and 6800 CFU gÿ1 of viable aerobic fungi). Dõaz-Ravi~ na et al. (1996) observed a large increase in bacterial activity, after a long lag (up to 8 weeks), following the addition of poultry manure to a heated soil. In a previous work (Guerrero et al., 2000), we also observed an increase in bacterial and fungal populations following the addition of MSW compost to a burned soil. Soil organic amendment increased the nitrogen content of the burned soil, particularly in MSW2 and MSW3 (Fig. 2), which was to be expected due to the high N content of the MSW compost (16.4 g kgÿ1 ). The nitrogen content of the amended soils remained higher than that of the control throughout the experimental period, the dierences being, in general, statistically
Fig. 1. Changes with time in the total organic carbon (TOC) content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
Fig. 2. Changes with time in the Kjeldahl-nitrogen content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
was determined by Walkley±Black's method (Walkley and Black, 1934). K, Ca and Mg were extracted from the soil with 1 N ammonium acetate, following the indications of Knudsen et al. (1982), and determined by ¯ame atomic absorption spectrometry (FAAS). Kjeldahlnitrogen was determined by the Bremner and Breitenbeck (1983) method and available P was measured by Burriel±Hernando's extraction method following the indications of Dõez (1982). 2.2. Vegetal analysis One year after the organic amendment all phytomass developed in the plots was cropped and the most abundant vegetal species were quanti®ed and analysed. Vegetal biomass was dried at 65°C and ground before analysis. The P, K, Ca, Mg and oligoelement contents of the plants were determined in the nitric-perchloric (1:1) digestion extract. P was determined by the Murphy and Riley (1962) method and K, Ca, Mg and oligoelements by FAAS. Nitrogen was determined as mentioned above for the soil. Data were interpreted using analysis of variance and means were compared by using least signi®cant dierence values (Tukey's test). 3. Results and discussion 3.1. Chemical changes
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established vegetation. In an incubation experiment Giusquiani et al. (1995) observed that the levels of available P obtained by adding a MSW compost remained constant throughout the 12 month of the experiment. Pascual (1995), too, observed that soils amended with a MSW compost showed only slight ¯uctuations in P content over one year period. The organic amendments of our experiment increased the available K content in the soil, particularly at the high dose (MSW3) (Fig. 4). In general, the amended soils showed statistically signi®cant higher levels of available K than the unamended burned soil at all the dierent sampling times. Although the available K content diminished with time, the levels of available K in all the treated soils one year after the application of compost were still greater than in the untreated soil. These results are in agreement with those obtained by Albadalejo et al. (1994) in degraded soils amended with MSW. Only the soil amended with the high dose of compost (MSW3) showed initial levels of Ca (extractable with ammonium acetate) signi®cantly higher than in the control (Fig. 5). Apart from the ®rst samples, the Ca content of the treated soils showed no correlation with
signi®cant. As in the case of the TOC, Kjeldahl-N in the untreated soil decreased gradually with time, while in the treated soils the N content was only seen to have decreased by the end of the experimental period. This suggests that mineralisation processes predominated in the control soil, N being lost by leaching (in the form of nitrate) or evaporation (in the form of NH 4 ). In the amended soils the stimulation of microbial development and activity induced by the added compost meant that N ®xation and immobilisation processes initially predominated over the mineralisation processes, the losses of N being less noticeable. Pascual (1995) and Castellanos and Pratt (1981) also observed a slight N mineralisation in soils amended with urban waste composts. Since Kjeldahl-nitrogen levels in treated and untreated soils followed a quite similar pattern to TOC, the C/N relation during the experimental period remained constant, the values of this ratio generally followed the pattern: C > MSW1 > MSW2 > MSW3. The lower C/N values in the amended soils points to the existence in the compost of a more humi®ed organic matter than that existing in the burned soil and con®rm the contribution of dead roots and incompletely burned plant debris in the high carbon content observed in burned soils after ®re. As shown in Fig. 3, the addition of MSW compost initially increased the available P content in the soil although not to a statistically signi®cant extent. This fact, can be explained by the low concentration of this nutrient in the compost added (1180 mg kgÿ1 ), which is 10-fold lower than other MSW composts described in the literature (Giusquiani et al., 1995). The time course trend of available P was similar in all the treatments throughout the year and showed no statistically signi®cant dierences with the levels in the control soil. Although there were slight dierences between individual samples, these dierences were not statistically dierent, which suggests that the gradual mineralisation of organic P compensates the mineral P which is gradually lost through precipitation or absorption by the newly
Fig. 4. Changes with time in the available potassium content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
Fig. 3. Changes with time in the available phosphorous content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
Fig. 5. Changes with time in the available calcium content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
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Table 2 Percentage increase in yield (dry matter) in treated soils with respect to untreated soils, harvested 360 days after compost applicationa Dorycnium pentaphyllum Rosmarinus ocinalis Cistus albidus
MSW1
MSW2
MSW3
8.8 10.7 6.3
12.1 22.4 11.7
24.9 39.1 19.0
a
MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil.
Fig. 6. Changes with time in the available magnesium content of the soil studied (control: burned soil; MSW1: 0.5 kg of compost per m2 burned soil; MSW2: 1 kg of compost per m2 of burned soil; MSW3: 2 kg of compost per m2 of burned soil; LSD: least signi®cant dierence, P 6 0:05).
the dose of compost added. In both the treated and control soils, the Ca content varied during the year, although it behaved dierently in both (Fig. 5). All the treated soils behaved in a similar way through the sampling period, but dierently to the control soil. This suggests that compost application modi®ed Ca availability, especially because of the changes in pH caused by organic matter mineralisation. At the last sampling times, all the amended soils showed higher Ca values than the control. The magnesium availability was positively in¯uenced by compost application, but only at the ®rst samplings (up to 4 months after compost addition) (Fig. 6). The concentrations of Mg of treated soils were not proportional to the compost application rates. 3.2. Plant cover development The addition of the MSW compost favoured vegetal cover recovery in a dose-dependent form. One year after organic amendment all the treated plots showed greater plant development than the unamended soil, a fact that would greatly contribute to the protection of a soil against erosion processes. This improvement in vegetation cover was a result of an improvement of the physical, microbiological and chemical properties of the soil due to the organic amendment. The most abundant vegetal species to be found growing in the dierent plots one year after the addition of organic amendment were Rosmarinus ocinalis, Dorcynium pentaphyllum and Cistus albidus, in that order (Table 2). The addition of the compost stimulated N absorption by plants, particularly at the high dose (Table 3), the increases in yield in MSW3 with respect to the control ranging from 10.2% to 53%, depending on the vegetal species. This higher N absorption led to a higher N concentration in leaves for Dorycinium and Rosmarinus, while in Cistus dierences with the control was manifested by a higher N concentration in roots stems (Table 3).
The plants growing in treated soils also showed a higher P content than those growing in the control soil (Table 3), the increases in MSW3 with respect to the control ranging from 7.5% to 39.5%, depending on the vegetal species. In this case, the dierences were observed in both leaves and roots stems (with the exception of Cistus albidus which only showed a higher P concentration than the control in leaves). The absorption of K seemed to be particularly stimulated by the organic amendment, the K content of plants growing in the MSW3 soil increasing by 17.2± 103% the levels observed in the plants growing in the control soil. In all the vegetal species the K content measured in leaves and in the rest of the plant (root stem) was in general, signi®cantly higher than in the plants growing in the control soil (Table 3). In general, the organic amendment did not in¯uence the absorption of Ca or Mg by the plants, although a higher Fe concentration was observed in the leaves and roots stems of plants growing in the treated soils. The in¯uence of the organic treatment on the absorption of the other oligoelements diered according to the vegetal species. For example, Dorycnium pentaphyllum growing in SW2 and SW3 showed a signi®cant increase in the levels of Cu and Zn in leaves, while Cistus albidus increased its absorption of Zn and Mg and Rosmarinus ocinalis increased its absorption of Zn alone. To summarise, the organic amendment stimulated the absorption of macro and micronutrients by plants. This led to a stronger recovery of the vegetation cover, which is important for protecting the soil against erosion processes.
4. Conclusions The results of this study indicate that MSW compost is useful for the reclamation of a burned soil since it increases the levels of soil organic matter and nutrients, encouraging the recovery rate of the vegetation cover which will protect the soil against erosion processes. An organic amendment applied immediately after burning will not only protect the soil against erosion but prepare the soil for subsequent reforestation with appropriate forest species. The use of MSW compost, therefore,
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Table 3 Nutrient status of spontaneous vegetation cropped in the experimental areaa Element
Treatment C
Treatment MSW1
MSW2
MSW3
N (%) P (mg kgÿ1 ) Ca (g kgÿ1 ) K (g kgÿ1 ) Mg (g kgÿ1 ) Na (g kgÿ1 ) Fe (mg kgÿ1 ) Cu (mg kgÿ1 ) Mn (mg kgÿ1 ) Zn (mg kgÿ1 )
Leaf of Dorycnium pentaphyllum 1.47a 1.57b 1.61b 679a 833b 945c 19.22 22.97 20.22 4.43a 4.40a 5.56b 2.91 2.95 3.00 0.54a 0.71b 0.71b 348.2a 330.1a 436.7b 6.3a 6.5a 7.5a 106.4 108.6 122.7 19.7a 23.9ab 27.7b
1.71c 921c 21.87 5.72b 3.14 0.71b 444.2b 14.2b 124.0 27.9b
N (%) P mg kgÿ1 Ca g kgÿ1 K g kgÿ1 Mg g kgÿ1 Na g kgÿ1 Fe mg kgÿ1 Cu mg kgÿ1 Mn mg kgÿ1 Zn mg kgÿ1
Leaf of Rosmarinus ocinalis 0.58a 0.88b 0.92b 819a 825a 829a 21.41 20.64 20.22 11.36a 17.54b 20.86bc 7.04 6.25 6.19 3.80a 4.87ab 5.44b 374c 355b 356b 12.5 13.1 21.5 36.9 33.6 37.1 37.1a 45.7b 58.1c
1.13c 916b 19.61 23.17c 6.48 9.64c 345a 16.4 31.5 77.9d
N (%) P mg kgÿ1 Ca g kgÿ1 K g kgÿ1 Mg g kgÿ1 Na g kgÿ1 Fe mg kgÿ1 Cu mg kgÿ1 Mn mg kgÿ1 Zn mg kgÿ1
Leaf of Cistus albidus 0.88 0.90 788a 841b 26.30 25.64 9.14a 11.85b 4.73a 5.00ab 4.80a 5.14a 988c 967c 16.6 18.8 45.1b 41.4ab 23.4a 44.0b
0.95 904c 26.05 9.91b 4.65a 6.34b 558a 15.7 33.1a 63.2c
a
0.92 897c 27.42 11.12b 5.51b 6.50b 832b 17.5 37.5a 49.1b 2
F
ns
b
ns
ns
ns
ns
ns ns
ns
ns
ns
C
MSW1
Root stem 0.86a 543a 7.30a 5.62a 0.82 0.67 328.8 6.0 18.2 12.9
of Dorycnium pentaphyllum 0.93b 0.93a 0.95b 638b 670b 784c 7.73a 8.09ab 9.18b 5.77a 5.65a 6.06b 1.08 1.08 1.11 0.70 0.70 0.73 285.2 280.2 230.1 5.0 4.8 5.2 20.4 20.5 20.6 16.6 17.1 21.3
MSW2
MSW3
Root stem 0.47a 571a 15.04 13.11a 3.01 6.81a 513c 12.0 21.0 24.0a
of Rosmarinus ocinalis 0.47a 0.53b 706b 805c 14.25 15.49 20.99b 25.35c 2.69 2.67 7.01a 6.38a 423b 390ab 13.1 15.6 18.6 21.3 23.8a 39.0b
0.48a 820c 13.63 26.53c 2.75 10.24b 356a 16.3 15.3 33.4b
Root stem 0.49a 601b 15.32 6.32a 2.88 3.88a 999d 9.7 32.6b 21.9a
of Cistus albidus 0.46a 0.58b 628b 557a 16.32 14.83 11.07c 10.00bc 2.96 2.77 4.73b 3.97ab 823c 375b 10.6 8.0 30.9b 22.1a 38.3b 25.8a
0.56b 590b 15.43 8.51b 2.75 4.50b 292a 9.3 25.7a 30.7b
F
ns ns ns ns ns ns
ns
ns
ns ns
ns
ns
ns
C: burned soil; MSW1: 0.5 kg of compost per m burned soil; MSW2: 1 kg of compost per m of burned soil; MSW3: 2 kg of compost per m2 of burned soil. b ns: not signi®cant at P 6 0:05. * Signi®cant dierences at P 6 0:01 respectively. ** Signi®cant dierences at P 6 0:05 respectively. *** Signi®cant dierences at P 6 0:001 respectively.
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