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Effect of sulphur inoculated with Thiobacillus on soil salinity and growth of tropical tree legumes
Bioresource Technology 81 (2002) 53±59
Eect of sulphur inoculated with Thiobacillus on soil salinity and growth of tropical tree legumes N.P. Stamford *, A.J.N. Silva, A.D.S. Freitas, J.T. Ara ujo Filho Department of Agronomy, University Federal Rural of Pernambuco, 52171-900, Dois Irm~ aos, Recife, Pernambuco, Brazil Received 21 November 2000; received in revised form 14 June 2001; accepted 17 June 2001
Abstract A greenhouse experiment was carried out with the objective of evaluating the eects of the elementary sulphur inoculated with Thiobacillus, compared with gypsum, in the amendment of a alluvial sodic saline soil from the Brazilian semiarid region, irrigated with saline water and grown with the tropical legumes leucena and mimosa. The treatments consisted of levels of sulphur (0; 300 and 600 kg/ha) and gypsum (1200 and 2400 kg/ha), irrigation using dierent waters containing the salts NaHCO3 , MgCl2 , CaCl2 , NaCl and KCl, with dierent electrical conductivities (ECs: 0.2, 6.1 and 8.2 dS/m at 25°C). Based on the results it appears that saline water increased exchangeable Na , K , Ca2 ; Mg2 , and soil pH. Sulphur inoculated with Thiobacillus was more ecient than gypsum in the reduction of the exchangeable sodium of the soil and promoting leaching of salts, especially sodium. Sulphur inoculated with Thiobacillus reduced the EC of the soil saturation extract to levels below that adopted in soil classi®cation of sodic or saline sodic. Leucena was more tolerant to salinity and mimosa more resistant to acidity promoted by sulphur inoculated with Thiobacillus. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Sodic soil; Leucaena leucocephala; Mimosa caesalpiniaefolia; Salinity; Ameliorants
1. Introduction The sustainability of agriculture in arid and semiarid regions depends on the maintenance of salt content on the soil pro®le (Ayars et al., 1993). Salinity constitutes one of the most important processes that decline plant productivity, thus several studies have been carried out to evaluate the eect of salinity in economic crops (Homan et al., 1989; Shalhevet et al., 1995; Francßois, 1996). Research involving levels of soil salinity and of waters with dierent electrical conductivities (ECs) was developed to estimate the eects of the salts in soils and in plant growth in relation to productivity and quality of crop production (Mass et al., 1988; Miyamoto et al., 1986; Ayars et al., 1993). The areas aected by salinisation in Brazil are greater than four million hectares (Szabolcs, 1989), and potentially there are about nine million hectares of soil in the Brazilian Northeast saline and sodic, including as planossolos, solonetz, solonc* Corresponding author. Present address: Rua Jader de Andrade, 335 Casa forte, 52061-060 Recife-Pernambuco, Brazil. Tel.: +55-081-32684611. E-mail address: [email protected] (N.P. Stamford).
hack, alluvial saline and solodic soils (Pereira et al., 1985). Soil salinisation is a secondary process caused by the use of inadequate irrigation systems and especially de®cient soil drainage. Furthermore the quality of water used in irrigation can also enhance salinisation (Szabolcs, 1989). Irrigation represents the most viable alternative to increment plant yield in the Brazilian semiarid region, due to the occurrence of frequent water de®cits in soil and plant roots in drought periods. Nunes Filho et al. (1991) reported that the accumulation of water in dams, in the rainy period, and decrease of water volume by evaporation, in the dry period, can promote a quantitative and qualitative variation in salt content in the water used in irrigation. Thus the use of saline waters certainly contributes to soil salinisation, through the gradual process of salt accumulation (Ghassemi et al., 1995). Excess of salts in soils reduces plant development, increases the energy required for nutrients and water absorption, and requires a biochemical adjustment for the survival in stress conditions (Rhoades et al., 1992). Sodic and saline±sodic soils frequently present physical degradation and chemical changes that can result in damages with relationship to nutrient accumulation,
0960-8524/02/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 8 5 2 4 ( 0 1 ) 0 0 0 9 9 - 2
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N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
promoting de®ciency of some elements and toxicity by others (Naidu and Rengasamy, 1993). The eciency of corrective substances such as gypsum and organic matter frequently used in the amendment of sodic soils has been evaluated in several studies (Gupta and Abrol, 1990; Niazi et al., 1992; McKenzie et al., 1993). The chemical correctives used in saline and alkaline soils displace sodium and other ions of the soil exchange complex, and these cations leach from the soil pro®le (Miyamoto and Enriquez, 1990; Armstrong and Tanton, 1992). When elemental sulphur is used, a biological reaction takes place in soil, carried out by different species of Thiobacillus (sulphur oxidative bacteria), producing sulphuric acid that reduces soil pH (Garcia J unior, 1992). In a soil solution, the dissociated hydrogen ion can displace the sodium from clay particles thereby promoting its subsequent leaching, reducing the soil salinity (Rupela and Tauro, 1973). The main objective of this work was to evaluate the eciency of sulphur inoculated with Thiobacillus bacteria, compared to gypsum, in the amendment of an alluvial saline solodic soil of the Brazilian semiarid region. The in¯uence of waters with dierent levels of salinity (electrical conductivity) was observed as well as was the performance of tropical tree legumes cropped in the saline soil.
2. Methods 2.1. Plant and soil characteristics The experiment was carried out at a greenhouse with system to control the temperature at 30±35°C. A solodic alluvial soil with medium texture, described by Brasil (1972), was used. The soil (0±30 cm layer) was collected from the UFRPE Experimental Station in Serra Talhada, a semiarid region located in Pernambuco State, Northeast of Brazil, sieved (5 cm sieve), mixed and kept in clay pots to minimise the thermal shock resulting from excessive exposure to solar radiation. Analyses of soil, using the Embrapa (1997) methodology, showed the following results: pH H2 O 7:9, P (Mehlich extracted) 110 mg/kg, cations (mmolc /kg) ± Ca2 62; Mg2 24; K 9:2; Na 42; total N 0.09%; or-
ganic C 1.2% and EC (EC in soil extract 4.1 dS/m at 25°C). 2.2. Soil ameliorants and salinity levels Soil was treated with gypsum (G) as CaSO4 2H2 O and elemental sulphur inoculated with the sulphur oxidising bacteria Thiobacillus thiooxidans and T. ferrooxidans in the same rate of viable cells 106 =ml. Bacterial cultures were grown in 125 ml Erlenmeyer ¯asks using medium 9 K (Garcia J unior and Andrade, 1989) for 5 days at 180 rpm in a horizontal shaker at 30°C. Inoculation was applied at the rate of 1 ml/g of sulphur. To obtain the best results for bacterial oxidation, the soil was incubated for 15 days and watered daily using a slightly saline irrigation water source (0.2 dS/ml). During this period at intervals of 5 days, sucient water (2 l/pot) was applied to force leaching of salts particularly sodium. The levels of gypsum and sulphur were calculated according to Barros and Magalh~aes (1989), and included a minimal adjustment, based on previous assays, using the same soil, and on chemical analyses conducted after the incubation period. The levels of ameliorants applied (kg/ha) were: 300 and 600 for elemental sulphur and 600 and 1200 for gypsum CaSO4 2H2 O. There was a control treatment with no S or gypsum applied. The salinity levels of water used corresponded to EC 0.2 Sal0 , 6.1 Sal1 and 8.2 Sal2 ) dS/m at 25°C. The water used for irrigation contained the salts NaHCO3 , NaCl, MgCl2 , CaCl2 and KCl (Table 1). 2.3. Seed inoculation and experimental conditions The tree legume leucena (Leucaena leucocephala cv. K8) and mimosa (Mimosa caesalpiniaefolia) were used as plant tests and the seeds were furnished by the Centre of Agricultural Researches of the Semiarid Tropics (CPATSA/EMBRAPA). Seeds were surface-sterilised with 95% ethanol for 10 min, washed six times with sterilised water and soaked overnight to imbibe water. They were planted in trays containing peat vermiculite (2/1 ratio) and 10 days later the seedlings were transplanted into pots (2 seedlings/pot). The two legumes were inoculated with Bradyrhizobium strains adopted to salinity conditions in previous
Table 1 Chemical composition of irrigation water in relation to the dierent levels of electrical conductivity (EC), in relationship with the chemical analysis of water from the dam of UFRPE Experimental Station in the semiarid region of Pernambuco state
a b
EC (dS/m)a
SAR (mmol/l)1=2 b
Na
K
Ca2 mmolc =l
Mg2
Cl
HCO3
0.2 6.1 8.2
9.07 20.91 29.16
24 293 394
3 335 450
11 134 181
11 136 184
33 409 551
17 208 281
EC: electrical conductivity. SAR: sodium adsorption rate.
N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
experiments (Stamford et al., 2000). Leucena was inoculated with strains NFB 494 and NFB 601 and mimosa with NFB 577 and NFB 578 in mixture (1/1 ratio) with viable cells greater than 108 =g of peat inoculant. After the incubation period, soil water was kept at 80% of ®eld capacity, monitored by daily weighing, using the corresponding level of salinity (EC 0.2, 6.1 and 8.2 dS/m). Plants were harvested 90 days after transplanting and shoot dry matter weight was determined. 2.4. Soil and leaching solution analysis The day after leaching 100 ml of the solution in equilibrium with the exchangeable soil cations was collected for determination of pH, electrical conductivity and sodium content. At the end of the experiment, the soil in each treatment was assessed for determination of pH H2 O, cations (mmol/kg) Na , K , Ca2 , Mg2 and Al3 , following the Embrapa (1997) methodology. The EC of the saturation extract was determined using the methodology described by Ferreira (1997). 2.5. Statistical analysis The experiment was conducted in a completely randomised factorial design with four replications. The statistical calculations were done using the software SANEST, and the averages were compared by the Tukey test at the 5% probability level (Silva and Silva, 1982).
3. Results and discussion 3.1. Soluble sodium in the leaching solution The content of Na in the leaching solution obtained by application of 2.000 ml of water (EC 0.2 dS/m) is presented in Table 2. These data are in reference to the solution collected after leaching (100 ml/pot), in the periods of incubation (5, 10 and 15 days) with application of the soil correctives.
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In the ®rst period of incubation the eect of higher levels of sulphur inoculated with Thiobacillus was observed with occurrence of a small concentration of sodium in the leaching solution. This response suggested that in these treatments, the hydrogen ion liberated by sulphuric acid promoted the substitution of sodium retained in the exchangeable soil particles, which were leached when excess water was applied. During the 15 day incubation period the treatment with sulphur (1200 kg/ha) yielded a sodium concentration of 112 mg/l, that represented approximately 37% of the sodium content observed with 5 days of incubation (303 mg/l). This served as an indication of the eect of this treatment compared with gypsum. Gheyi et al. (1995), using sulphuric acid (1.2 t/ha), observed a greater eect of gypsum (30 t/ha), in the ®rst year, however the amount of gypsum applied was very high. The eect of gypsum was observed in the leaching solution after the 15 day incubation period. Several authors have previously observed eects of gypsum, especially when the percolation was promoted by rainwater, measured daily during 20 days (Ruiz et al., 1997). Similar results were obtained by Sampaio and Ruiz (1996) when leaching was parcelling out in six applications, with an interval of 22 days. These authors concluded that the application of water in a layer smaller than the volume of soil pores was sucient to reduce the cation content of saline soils, although reduction of exchangeable sodium in sodic soils should be considered more complex and would require application of a chemical corrective. Application of saline water with dierent levels of EC increased the concentration of exchangeable sodium in the soil, probably due to sodium applied as NaHCO3 and NaCl in the irrigation water. 3.2. Soil pH and exchangeable aluminium The results of soil pH and exchangeable cations are shown in Figs. 1±3, and the data represent averages obtained for leucena and mimosa legumes. Soil amendment with sulphur resulted in the presence of soluble aluminium in the soil which was probably due to
Table 2 Content of soluble sodium in the leaching solution in the incubation period with gypsum and sulphura Na (mg/l)
Soil ameliorant kg=ha Time of incubation (days): No addition (control) Gypsum 600 Gypsum 1200 Sulphur 300 Sulphur 600
5
10
15
363aA 354aA 334aA 337aA 303bA
256aB 244aB 217abB 234abB 184bB
240aB 143bC 133bC 131bC 112bB
Within topics, values followed by dierent letters are signi®cantly dierent at P 0:05, using the Tukey test. Upper case letters compare data in rows and lower case letters compare data in columns. a Inoculated with Thiobacillus, at 5, 10 and 15 days after incubation.
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N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
˚
Fig. 1. Eect of sulphur inoculated with Thiobacillus and gypsum on pH and exchangeable aluminium in saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
the relationship with pH and soil acidi®cation and the resulting displacement of exchangeable Al3 by the sulphuric acid hydrogen ion formed during sulphur oxidation by Thiobacillus bacteria (Garcia J unior, 1992). This eect could be harmful to plants growing in the amended soil, and care should be exercised in applying this soil amelioration strategy. The control treatment and soil amelioration using gypsum did not provide detectable values of exchangeable aluminium in soil. Sulphur inoculated with Thiobacillus resulted in the smallest pH values in the soil, occurring mainly in the level of 1200 kg/ha, where the pH was lowered to 3.5, indicating the presence of sulphur oxidising bacteria and sulphuric acid production. Irrigation with waters of dierent salinities yielded a signi®cant eect P < 0:05 on exchangeable aluminium and reduction was observed when water of greater salinity was applied (8.2 dS/m). The greater levels of water salinity increased soil pH potentially because of the Mg2 , Ca2 and K content in the water which contributed to carbonate or bicarbonate formation and, consequently, resulted in higher values of soil pH. These results are in agreement with Miyamoto et al. (1986) and
Fig. 2. Eect of sulphur inoculated with Thiobacillus and gypsum on exchangeable sodium and potassium in saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
Bajwa et al. (1993), using saline waters to irrigate loamy and clay loamy soils of a semiarid region. 3.3. Exchangeable sodium and potassium The eect of sulphur on exchangeable sodium and potassium was statistically signi®cant P < 0:05 and when applied in the highest level provided slight values of exchangeable sodium in all levels of salinity employed, indicating displacement of this element from the soil complex reaching the soil solution had occurred. Gypsum in the levels used showed smaller replacement of exchangeable sodium in the soil complex, that was not signi®cantly dierent (P 0:05) compared to the unamended control. Holanda et al. (1998) and Gheyi et al. (1995) observed eects of gypsum promoting the reduction in the exchangeable sodium, however these authors have used much higher levels of gypsum (30 t/ha). Based on the analysis of variance and the Tukey test there was an interaction between the factors of gypsum and sulphur versus water salinity. The treatment with lower level of sulphur (300 kg/ha) and unamended soil with higher salinity level (8.2 dS/m) accumulated more sodium in the soil, reaching the value of 1.70 and 1:48 cmolc =kg, respectively (Fig. 2). The treatment with larger level of sulphur (600 kg/ha) and a smaller salinity
N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
°
Fig. 3. Eect of sulphur inoculated with Thiobacillus and gypsum on exchangeable magnesium and calcium in saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
level (0.2 dS/m) presented the lowest level of exchangeable sodium in the soil 0:13 cmolc =kg. The lowest level of exchangeable potassium in soil was also observed when sulphur was employed. This showed the eect of Thiobacillus in the formation of H2 SO4 and consequently the displacement of potassium by the dissociated hydrogen ion. When a salinity level of 8.2 dS/m was applied, a greater concentration of potassium was accumulated. 3.4. Exchangeable calcium and magnesium Sulphur inoculated with Thiobacillus reduced soil exchangeable calcium, primarily when supplied at a level equivalent to 1200 kg/ha (Fig. 3). The higher values of exchangeable calcium obtained with the application of the two levels of gypsum were justi®ed by the fact that this ameliorant is an important source of calcium and the cations liberated to the soil solution are susceptible to leaching. Similar results were obtained by Moolman (1989) when evaluating the eects of gypsum for amendment of sodicity in soils of the Brazilian semiarid region.
57
The levels of water salinity used in this study, generally, did not in¯uence soil exchangeable calcium although a signi®cant interaction between water salinity and the soil correctives was observed P < 0:05. When the higher level of sulphur (600 kg/ha) inoculated with Thiobacillus was applied, soil calcium content decreased. This suggests that sulphuric acid formed from higher levels of sulphur not only removed sodium from the soil complex but also calcium, and both can be percolated from soil by leaching. These results are compatible with Rowell (1985) and Ferreyra and Coelho (1986), who concluded that washing the soil pro®le with a mixture of salts reduces the soil sodicity. Ayars et al. (1993) observed that the salts dissolved in the irrigation water increased the contents of magnesium, sulphate, borax and chlorine but maintained the levels of potassium and calcium in the soil after 4 years of irrigation. The eect of the treatments on the exchangeable magnesium in the soil was similar to calcium (Fig. 3). The smallest concentrations of exchangeable magnesium in the soil were observed when sulphur was applied diering signi®cantly in the treatment control and gypsum application P < 0:05. In relation to saline water addition, the content of magnesium in the soil was not signi®cantly aected P > 0:05. There was an observed interaction between water salinity and the treatments with sulphur, resulting in an increased magnesium content in the soil for the highest levels of water salinity and higher sulphur levels. 3.5. Electrical conductivity The results of EC of the soil saturation extract in the ®nal of the experiment yielded statistical dierences between the tree legumes leucena and mimosa P < 0:05. We observed that the levels of salinity in the irrigation water provided a signi®cant increase of EC of the soil for all the treatments (Table 3). The results are in agreement with Miyamoto et al. (1986), Mass et al. (1988), Homan et al. (1989) and Holanda et al. (1998). The smallest values of EC in the saturation extract were obtained when sulphur inoculated with Thiobacillus was applied, resulting in levels below the limit for classi®cation as saline soil (4 dS/m), in reference to Richards (1954). The treatment with larger salinity water Sal3 re¯ects the occurrence of sodium and other cations leached during the process of soil amendment. Comparing the values of EC in the soil saturation extract after growing leucena and mimosa tree legumes a signi®cant interaction could be observed between plants and chemical correctives. When sulphur inoculated with Thiobacillus was applied to leucena the values of EC were smaller compared to mimosa. In the treatment with gypsum the EC relationship with the growing legumes was inverted and lower values are observed in mimosa tree legume.
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N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
Table 3 Soil electrical conductivity (dS/m) determined at the end of the experiment Soil ameliorant
Leucena
Mimosa
Sal1 (0.2)
Sal2 (6.1)
Sal3 (8.2)
Sal1 (0.2)
Sal2 (6.1)
Sal3 (8.2)
No addition (control) Gypsum 600 Gypsum 1200 Sulphur 300 Sulphur 600
4.9aC 4.8aC 4.6abC 4.2bB 2.1cC
7.6aB 6.6bB 7.6aB 5.9cA 2.9dB
8.4aA 8.7aA 8.5aA 5.4bA 3.7cA
5.2aB 4.7bC 4.6bB 4.8bC 2.8cC
7.8aA 6.1bA 6.0bA 7.7aB 4.1cB
7.7bA 6.5cA 6.7cA 8.5aA 4.9dA
Within topics, values followed by dierent letters are signi®cantly dierent at P 0:05, using the Tukey test. Upper case letters compare data in rows and lower case letters compare data in columns.
3.6. Plant dry matter weight The production of dry matter of leucena and mimosa in the treatments with sulphur inoculated with Thiobacillus and irrigation and using dierent levels of saline water is presented in Fig. 4. There was a dierential response between mimosa and leucena in relationship to the application of chemical correctives and water salinity. Dry matter of mimosa was reduced as the conductivity of the irrigation water increased in the treatments without gypsum and was strongly reduced when gypsum was applied, independent of the irrigation water's EC.
Application of sulphur with Thiobacillus at the lowest level increased dry matter production. Leucena dry matter was not aected by the application of gypsum and by sulphur with Thiobacillus at the lowest level (300 kg/ha) and was independent of the water salinity. Sulphur applied at the highest level (600 kg/ha) reduced plant dry matter signi®cantly, independently of the water salinity. This suggested that mimosa is more susceptible to the salinity than leucena, but more tolerant to soil acidity. The same rate of tolerance was described by Stamford et al. (1997) in an acid soil of the rain forest, when growing mimosa was inoculated with ecient strains of Bradyrhizobium and fertilised with soluble phosphate. These factors should be taken into account for legume selection in acid soils or irrigated with saline water. We can conclude that irrigation with saline water can increase the content of exchangeable cations and soil pH. Sulphur inoculated with Thiobacillus is more ecient than gypsum in the displacement of sodium and other cations from the soil complex to leaching solution. Leucena and mimosa tree legumes respond dierently to salinity levels and soil ameliorants with leucena being more tolerant to salinity and mimosa more resistant to the acidity promoted by sulphur inoculated with Thiobacillus. Acknowledgements We are indebted to Conselho Nacional de desenvolvimento Cientõ®co e Tecnol ogico (CNPq) for the ®nancial support and the research fellowship conceded. References
Fig. 4. Eect of sulphur inoculated with Thiobacillus and gypsum on mimosa and leucena dry matter yield grown in a saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
Armstrong, A.S.B., Tanton, T.W., 1992. Gypsum applications to aggregated saline±sodic clay topsoils. J. Soil Sci. 43, 249±260. Ayars, J.E., Hutmacher, R.B., Schoneman, R.A., Vail, S.S., P¯aum, T., 1993. Long term use of saline water for irrigation. Irrig. Sci. 14, 27±34. Bajwa, M.S., Josan, A.S., Choodhary, O., 1993. Eect of frequency of sodic and saline-sodic irrigation and gypsum on the build-up of sodium in soil and crop yields. Irrig. Sci. 14, 21±26.
N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59 Barros, M.F.C., Magalh~aes, A.M., 1989. Avaliacßa~o de metodos de determinacß~ ao da necessidade de gesso em solos salino-s odicos. Rev. Bras. Ci. Solo. 13, 119±123. Brasil. 1972. Levantamento Explorat orio ± Reconhecimento de solos do Estado de Pernambuco. Departamento Nacional de Pesquisa Agropecu aria, Divis~ ao de Pesquisa Pedol ogica, Ministerio da Agricultura, Recife (DNPEA, Boletim Tecnico, 26; DRN-SUDENE, Serie Pedol ogica, 14). Empresa Brasileira de Pesquisa Agropecuaria, 1997. Manual de metodos de an alises de solo, second ed. Centro Nacional de Pesquisa de Solos, Rio de Janeiro, 212 pp. Ferreira, P.A., 1997. Aspectos fõsico-quõmicos do solo. In: Manejo e controle da salinidade na agricultura irrigada. Congresso brasileiro de engenharia agrõcola. Anais. Sociedade Brasileira de Engenharia Agrõcola, Campina Grande, pp. 36±67. Ferreyra, F.F.H., Coelho, M.A., 1986. Efeito de doses de gesso e subsolagem na produtividade de arroz em solo s odico. Rev. Bras. Ci. Solo. 10, 157±161. Francßois, L.E., 1996. Salinity eects on four sun¯ower hybrids. Agron. J. 88, 215±222. ~ es microbianas. Garcia J unior, O., 1992. O enxofre e suas transformacßo In: Cardoso, E.J.B., Tsai, S.M., Neves, M.C.P. (Eds.), Microbiologia do solo. Sociedade Brasileira de Ci^encia do Solo, Campinas, pp. 1±15. Garcia J unior, O., Andrade, T.R., 1989. Lixiviacß~ao de metais pesados por bacterias ± Princõpios basicos. UNESP, S~ao Paulo, 51 pp. Ghassemi, F., Jakeman, A.J., Nix, H.A. 1995. Salinization of land and water resources: humans causes, extent, management and case studies. Center for Resources and Environment Studies, Canberra, 526 pp. Gheyi, H.R., Azevedo, N.C.de., Batista, M.A., Santos, J.G.R., 1995. Comparacß~ ao de metodos na recuperacß~ao de arroz em solo s odico. Rev. Bras. Ci. Solo. 19, 173±178. Gupta, R.K., Abrol, I.P., 1990. Salt-aected soil: their reclamation and management for crop production. Adv. Soil Sci. 11, 223±228. Homan, G.J., Catlin, P.B., Mead, R.M., Johnson, R.S., Francßois, L.E., Goldhamer, D., 1989. Yield and foliar injury responses of mature plum trees to salinity. Irrig. Sci. 10, 215±229. Holanda, J.S., Vitti, G.C., Salviano, A.A.C., Medeiros, J.D.F., ~ es nas propriedades quõmicas de Amorim, J.R.A., 1998. Alteracßo um solo aluvial salino±s odico decorrentes da subsolagem e do uso de condicionadores. Rev. Bras. Ci. Solo. 22, 387±394. Mass, E.V., Donovan, T.J., Francois, L.E., 1988. Salt tolerance of irrigated guayule. Irrig. Sci. 9, 199±211. McKenzie, D.C., Abbot, T.S., Chan, K.I., Slavich, P.G., Hall, D.J.M., 1993. The nature, distribution and management of sodic soil in New South Wales. Aust. J. Soil Res. 31, 839±868. Miyamoto, S., Enriquez, C., 1990. Comparative eects of chemical amendments on salt and sodium leaching. Irrig. Sci. 11, 83±92. Miyamoto, S., Riley, T., Gobran, G., Petticlew, J., 1986. Eects of saline water irrigation on soil salinity, pecan tree growth and nut production. Irrig. Sci. 7, 83±95.
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Moolman, J.H., 1989. The eect of a change in irrigation water quality on the salt loads of the deep percolate of a saline sodic soil ± a computer simulation study. Irrig. Sci. 6, 19±28. Naidu, R., Rengasamy, P., 1993. Ion interactions and constraints to plant nutrition in Australian sodic soils. Aust. J. Soil Res. 31, 801± 819. Niazi, M.H.K., Hussain, N., Mehdi, S.M., Rashid, M., Khan, G.D., 1992. Ecacy of acid reclaimants in combination with nonconventional fertilizers for salinity control. In: Proceedings to Sixth International Drainage Symposium, Nashville, pp. 387±394. Nunes Filho, J., Guerra, C.A.M., Souza, A.R., Sa, V.A.L., Soares, M.J.C.C., 1991. Qualidade da agua de acßudes para ®ns de irrigacß~ao no sert~ao de Pernambuco, Brasõlia, pp. 35±39 (ITEM ± Irrigacß~ao e tecnologia moderna, 44). Pereira, J.R., Valdivieso, G.R., Cordeiro, G.G., 1985. Recuperacß~ao de solos afetados por s odio atraves do uso de gesso. In: Seminario Sobre o Uso de Fosfogesso na Agricultura, Brasõlia, pp. 85±105. Richards, L.A., 1954. Diagnosis and improvement of saline and alkali soils. Handbook, US Department of Agriculture, Washington, 60 US Government Printing Oce, 160 pp. Rhoades, J.D., Kandiah, A., Mashal, A.M., 1992. The use of saline water for crop production. Irrigation and drainage paper 48, Rome, FAO, 135 pp. Rowell, D.L., 1985. The reduction in sodicity during the displacement of mixed CaCl2 ±NaCl salts from soils by water. Irrig. Sci. 6, 1±18. Ruiz, H.A., Gheyi, H.R., Almeida, M.T., Ribeiro, A.C., 1997. Torta de ®ltro e vinhacßa na recuperacß~ao de um solo salino±s odico e no desenvolvimento de arroz irrigado. Rev. Bras. Ci. Solo. 21, 659± 665. Rupela, O.P., Tauro, P., 1973. Utilisation of Thiobacillus to reclaim alkali soils. Soil Biol. Biochem. 5, 899±901. ~es Sampaio, R.A., Ruiz, H.A., 1996. Caracterõsticas das solucßo ~es drenadas na recuperacß~ao de solos salino±s odicos com lixiviacßo parceladas. Rev. Bras. Ci. Solo. 20, 13±20. Shalhevet, J., Huck, M.G., Schroeder, B.P., 1995. Root and shoot growth responses to salinity in maize and soybean. Agron. J. 87, 512±516. Silva, J.A.A., Silva, J.P., 1982. Estatõstica experimental aplicada a ci^encia ¯orestal. Imprensa Universitaria, Recife, 305 pp. Stamford, N.P., Ortegas, J.A.D., Temprano, F., Santos, D.R., 1997. Eects of phosphorus fertilisation and Bradyrhizobium and mycorrhizal fungi inoculation on growth of Mimosa caesalpiniaefolia in an acid soil. Soil Biol. Biochem. 29, 959±964. Stamford, N.P., Ara ujo Filho, J.T., Silva, A.J.N., 2000. Growth and nitrogen ®xation of Leucaena leucocephala and Mimosa caesalpiniaefolia in a saline soil of Brazilian semi-arid region as aected by sulphur, gypsum and saline water. Trop. Grasslands 34, 1±6. Szabolcs, I., 1989. Salt-aected Soils. Library of Congress, Florida, 274 pp.
Eect of sulphur inoculated with Thiobacillus on soil salinity and growth of tropical tree legumes N.P. Stamford *, A.J.N. Silva, A.D.S. Freitas, J.T. Ara ujo Filho Department of Agronomy, University Federal Rural of Pernambuco, 52171-900, Dois Irm~ aos, Recife, Pernambuco, Brazil Received 21 November 2000; received in revised form 14 June 2001; accepted 17 June 2001
Abstract A greenhouse experiment was carried out with the objective of evaluating the eects of the elementary sulphur inoculated with Thiobacillus, compared with gypsum, in the amendment of a alluvial sodic saline soil from the Brazilian semiarid region, irrigated with saline water and grown with the tropical legumes leucena and mimosa. The treatments consisted of levels of sulphur (0; 300 and 600 kg/ha) and gypsum (1200 and 2400 kg/ha), irrigation using dierent waters containing the salts NaHCO3 , MgCl2 , CaCl2 , NaCl and KCl, with dierent electrical conductivities (ECs: 0.2, 6.1 and 8.2 dS/m at 25°C). Based on the results it appears that saline water increased exchangeable Na , K , Ca2 ; Mg2 , and soil pH. Sulphur inoculated with Thiobacillus was more ecient than gypsum in the reduction of the exchangeable sodium of the soil and promoting leaching of salts, especially sodium. Sulphur inoculated with Thiobacillus reduced the EC of the soil saturation extract to levels below that adopted in soil classi®cation of sodic or saline sodic. Leucena was more tolerant to salinity and mimosa more resistant to acidity promoted by sulphur inoculated with Thiobacillus. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Sodic soil; Leucaena leucocephala; Mimosa caesalpiniaefolia; Salinity; Ameliorants
1. Introduction The sustainability of agriculture in arid and semiarid regions depends on the maintenance of salt content on the soil pro®le (Ayars et al., 1993). Salinity constitutes one of the most important processes that decline plant productivity, thus several studies have been carried out to evaluate the eect of salinity in economic crops (Homan et al., 1989; Shalhevet et al., 1995; Francßois, 1996). Research involving levels of soil salinity and of waters with dierent electrical conductivities (ECs) was developed to estimate the eects of the salts in soils and in plant growth in relation to productivity and quality of crop production (Mass et al., 1988; Miyamoto et al., 1986; Ayars et al., 1993). The areas aected by salinisation in Brazil are greater than four million hectares (Szabolcs, 1989), and potentially there are about nine million hectares of soil in the Brazilian Northeast saline and sodic, including as planossolos, solonetz, solonc* Corresponding author. Present address: Rua Jader de Andrade, 335 Casa forte, 52061-060 Recife-Pernambuco, Brazil. Tel.: +55-081-32684611. E-mail address: [email protected] (N.P. Stamford).
hack, alluvial saline and solodic soils (Pereira et al., 1985). Soil salinisation is a secondary process caused by the use of inadequate irrigation systems and especially de®cient soil drainage. Furthermore the quality of water used in irrigation can also enhance salinisation (Szabolcs, 1989). Irrigation represents the most viable alternative to increment plant yield in the Brazilian semiarid region, due to the occurrence of frequent water de®cits in soil and plant roots in drought periods. Nunes Filho et al. (1991) reported that the accumulation of water in dams, in the rainy period, and decrease of water volume by evaporation, in the dry period, can promote a quantitative and qualitative variation in salt content in the water used in irrigation. Thus the use of saline waters certainly contributes to soil salinisation, through the gradual process of salt accumulation (Ghassemi et al., 1995). Excess of salts in soils reduces plant development, increases the energy required for nutrients and water absorption, and requires a biochemical adjustment for the survival in stress conditions (Rhoades et al., 1992). Sodic and saline±sodic soils frequently present physical degradation and chemical changes that can result in damages with relationship to nutrient accumulation,
0960-8524/02/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 8 5 2 4 ( 0 1 ) 0 0 0 9 9 - 2
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N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
promoting de®ciency of some elements and toxicity by others (Naidu and Rengasamy, 1993). The eciency of corrective substances such as gypsum and organic matter frequently used in the amendment of sodic soils has been evaluated in several studies (Gupta and Abrol, 1990; Niazi et al., 1992; McKenzie et al., 1993). The chemical correctives used in saline and alkaline soils displace sodium and other ions of the soil exchange complex, and these cations leach from the soil pro®le (Miyamoto and Enriquez, 1990; Armstrong and Tanton, 1992). When elemental sulphur is used, a biological reaction takes place in soil, carried out by different species of Thiobacillus (sulphur oxidative bacteria), producing sulphuric acid that reduces soil pH (Garcia J unior, 1992). In a soil solution, the dissociated hydrogen ion can displace the sodium from clay particles thereby promoting its subsequent leaching, reducing the soil salinity (Rupela and Tauro, 1973). The main objective of this work was to evaluate the eciency of sulphur inoculated with Thiobacillus bacteria, compared to gypsum, in the amendment of an alluvial saline solodic soil of the Brazilian semiarid region. The in¯uence of waters with dierent levels of salinity (electrical conductivity) was observed as well as was the performance of tropical tree legumes cropped in the saline soil.
2. Methods 2.1. Plant and soil characteristics The experiment was carried out at a greenhouse with system to control the temperature at 30±35°C. A solodic alluvial soil with medium texture, described by Brasil (1972), was used. The soil (0±30 cm layer) was collected from the UFRPE Experimental Station in Serra Talhada, a semiarid region located in Pernambuco State, Northeast of Brazil, sieved (5 cm sieve), mixed and kept in clay pots to minimise the thermal shock resulting from excessive exposure to solar radiation. Analyses of soil, using the Embrapa (1997) methodology, showed the following results: pH H2 O 7:9, P (Mehlich extracted) 110 mg/kg, cations (mmolc /kg) ± Ca2 62; Mg2 24; K 9:2; Na 42; total N 0.09%; or-
ganic C 1.2% and EC (EC in soil extract 4.1 dS/m at 25°C). 2.2. Soil ameliorants and salinity levels Soil was treated with gypsum (G) as CaSO4 2H2 O and elemental sulphur inoculated with the sulphur oxidising bacteria Thiobacillus thiooxidans and T. ferrooxidans in the same rate of viable cells 106 =ml. Bacterial cultures were grown in 125 ml Erlenmeyer ¯asks using medium 9 K (Garcia J unior and Andrade, 1989) for 5 days at 180 rpm in a horizontal shaker at 30°C. Inoculation was applied at the rate of 1 ml/g of sulphur. To obtain the best results for bacterial oxidation, the soil was incubated for 15 days and watered daily using a slightly saline irrigation water source (0.2 dS/ml). During this period at intervals of 5 days, sucient water (2 l/pot) was applied to force leaching of salts particularly sodium. The levels of gypsum and sulphur were calculated according to Barros and Magalh~aes (1989), and included a minimal adjustment, based on previous assays, using the same soil, and on chemical analyses conducted after the incubation period. The levels of ameliorants applied (kg/ha) were: 300 and 600 for elemental sulphur and 600 and 1200 for gypsum CaSO4 2H2 O. There was a control treatment with no S or gypsum applied. The salinity levels of water used corresponded to EC 0.2 Sal0 , 6.1 Sal1 and 8.2 Sal2 ) dS/m at 25°C. The water used for irrigation contained the salts NaHCO3 , NaCl, MgCl2 , CaCl2 and KCl (Table 1). 2.3. Seed inoculation and experimental conditions The tree legume leucena (Leucaena leucocephala cv. K8) and mimosa (Mimosa caesalpiniaefolia) were used as plant tests and the seeds were furnished by the Centre of Agricultural Researches of the Semiarid Tropics (CPATSA/EMBRAPA). Seeds were surface-sterilised with 95% ethanol for 10 min, washed six times with sterilised water and soaked overnight to imbibe water. They were planted in trays containing peat vermiculite (2/1 ratio) and 10 days later the seedlings were transplanted into pots (2 seedlings/pot). The two legumes were inoculated with Bradyrhizobium strains adopted to salinity conditions in previous
Table 1 Chemical composition of irrigation water in relation to the dierent levels of electrical conductivity (EC), in relationship with the chemical analysis of water from the dam of UFRPE Experimental Station in the semiarid region of Pernambuco state
a b
EC (dS/m)a
SAR (mmol/l)1=2 b
Na
K
Ca2 mmolc =l
Mg2
Cl
HCO3
0.2 6.1 8.2
9.07 20.91 29.16
24 293 394
3 335 450
11 134 181
11 136 184
33 409 551
17 208 281
EC: electrical conductivity. SAR: sodium adsorption rate.
N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
experiments (Stamford et al., 2000). Leucena was inoculated with strains NFB 494 and NFB 601 and mimosa with NFB 577 and NFB 578 in mixture (1/1 ratio) with viable cells greater than 108 =g of peat inoculant. After the incubation period, soil water was kept at 80% of ®eld capacity, monitored by daily weighing, using the corresponding level of salinity (EC 0.2, 6.1 and 8.2 dS/m). Plants were harvested 90 days after transplanting and shoot dry matter weight was determined. 2.4. Soil and leaching solution analysis The day after leaching 100 ml of the solution in equilibrium with the exchangeable soil cations was collected for determination of pH, electrical conductivity and sodium content. At the end of the experiment, the soil in each treatment was assessed for determination of pH H2 O, cations (mmol/kg) Na , K , Ca2 , Mg2 and Al3 , following the Embrapa (1997) methodology. The EC of the saturation extract was determined using the methodology described by Ferreira (1997). 2.5. Statistical analysis The experiment was conducted in a completely randomised factorial design with four replications. The statistical calculations were done using the software SANEST, and the averages were compared by the Tukey test at the 5% probability level (Silva and Silva, 1982).
3. Results and discussion 3.1. Soluble sodium in the leaching solution The content of Na in the leaching solution obtained by application of 2.000 ml of water (EC 0.2 dS/m) is presented in Table 2. These data are in reference to the solution collected after leaching (100 ml/pot), in the periods of incubation (5, 10 and 15 days) with application of the soil correctives.
55
In the ®rst period of incubation the eect of higher levels of sulphur inoculated with Thiobacillus was observed with occurrence of a small concentration of sodium in the leaching solution. This response suggested that in these treatments, the hydrogen ion liberated by sulphuric acid promoted the substitution of sodium retained in the exchangeable soil particles, which were leached when excess water was applied. During the 15 day incubation period the treatment with sulphur (1200 kg/ha) yielded a sodium concentration of 112 mg/l, that represented approximately 37% of the sodium content observed with 5 days of incubation (303 mg/l). This served as an indication of the eect of this treatment compared with gypsum. Gheyi et al. (1995), using sulphuric acid (1.2 t/ha), observed a greater eect of gypsum (30 t/ha), in the ®rst year, however the amount of gypsum applied was very high. The eect of gypsum was observed in the leaching solution after the 15 day incubation period. Several authors have previously observed eects of gypsum, especially when the percolation was promoted by rainwater, measured daily during 20 days (Ruiz et al., 1997). Similar results were obtained by Sampaio and Ruiz (1996) when leaching was parcelling out in six applications, with an interval of 22 days. These authors concluded that the application of water in a layer smaller than the volume of soil pores was sucient to reduce the cation content of saline soils, although reduction of exchangeable sodium in sodic soils should be considered more complex and would require application of a chemical corrective. Application of saline water with dierent levels of EC increased the concentration of exchangeable sodium in the soil, probably due to sodium applied as NaHCO3 and NaCl in the irrigation water. 3.2. Soil pH and exchangeable aluminium The results of soil pH and exchangeable cations are shown in Figs. 1±3, and the data represent averages obtained for leucena and mimosa legumes. Soil amendment with sulphur resulted in the presence of soluble aluminium in the soil which was probably due to
Table 2 Content of soluble sodium in the leaching solution in the incubation period with gypsum and sulphura Na (mg/l)
Soil ameliorant kg=ha Time of incubation (days): No addition (control) Gypsum 600 Gypsum 1200 Sulphur 300 Sulphur 600
5
10
15
363aA 354aA 334aA 337aA 303bA
256aB 244aB 217abB 234abB 184bB
240aB 143bC 133bC 131bC 112bB
Within topics, values followed by dierent letters are signi®cantly dierent at P 0:05, using the Tukey test. Upper case letters compare data in rows and lower case letters compare data in columns. a Inoculated with Thiobacillus, at 5, 10 and 15 days after incubation.
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N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
˚
Fig. 1. Eect of sulphur inoculated with Thiobacillus and gypsum on pH and exchangeable aluminium in saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
the relationship with pH and soil acidi®cation and the resulting displacement of exchangeable Al3 by the sulphuric acid hydrogen ion formed during sulphur oxidation by Thiobacillus bacteria (Garcia J unior, 1992). This eect could be harmful to plants growing in the amended soil, and care should be exercised in applying this soil amelioration strategy. The control treatment and soil amelioration using gypsum did not provide detectable values of exchangeable aluminium in soil. Sulphur inoculated with Thiobacillus resulted in the smallest pH values in the soil, occurring mainly in the level of 1200 kg/ha, where the pH was lowered to 3.5, indicating the presence of sulphur oxidising bacteria and sulphuric acid production. Irrigation with waters of dierent salinities yielded a signi®cant eect P < 0:05 on exchangeable aluminium and reduction was observed when water of greater salinity was applied (8.2 dS/m). The greater levels of water salinity increased soil pH potentially because of the Mg2 , Ca2 and K content in the water which contributed to carbonate or bicarbonate formation and, consequently, resulted in higher values of soil pH. These results are in agreement with Miyamoto et al. (1986) and
Fig. 2. Eect of sulphur inoculated with Thiobacillus and gypsum on exchangeable sodium and potassium in saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
Bajwa et al. (1993), using saline waters to irrigate loamy and clay loamy soils of a semiarid region. 3.3. Exchangeable sodium and potassium The eect of sulphur on exchangeable sodium and potassium was statistically signi®cant P < 0:05 and when applied in the highest level provided slight values of exchangeable sodium in all levels of salinity employed, indicating displacement of this element from the soil complex reaching the soil solution had occurred. Gypsum in the levels used showed smaller replacement of exchangeable sodium in the soil complex, that was not signi®cantly dierent (P 0:05) compared to the unamended control. Holanda et al. (1998) and Gheyi et al. (1995) observed eects of gypsum promoting the reduction in the exchangeable sodium, however these authors have used much higher levels of gypsum (30 t/ha). Based on the analysis of variance and the Tukey test there was an interaction between the factors of gypsum and sulphur versus water salinity. The treatment with lower level of sulphur (300 kg/ha) and unamended soil with higher salinity level (8.2 dS/m) accumulated more sodium in the soil, reaching the value of 1.70 and 1:48 cmolc =kg, respectively (Fig. 2). The treatment with larger level of sulphur (600 kg/ha) and a smaller salinity
N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
°
Fig. 3. Eect of sulphur inoculated with Thiobacillus and gypsum on exchangeable magnesium and calcium in saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
level (0.2 dS/m) presented the lowest level of exchangeable sodium in the soil 0:13 cmolc =kg. The lowest level of exchangeable potassium in soil was also observed when sulphur was employed. This showed the eect of Thiobacillus in the formation of H2 SO4 and consequently the displacement of potassium by the dissociated hydrogen ion. When a salinity level of 8.2 dS/m was applied, a greater concentration of potassium was accumulated. 3.4. Exchangeable calcium and magnesium Sulphur inoculated with Thiobacillus reduced soil exchangeable calcium, primarily when supplied at a level equivalent to 1200 kg/ha (Fig. 3). The higher values of exchangeable calcium obtained with the application of the two levels of gypsum were justi®ed by the fact that this ameliorant is an important source of calcium and the cations liberated to the soil solution are susceptible to leaching. Similar results were obtained by Moolman (1989) when evaluating the eects of gypsum for amendment of sodicity in soils of the Brazilian semiarid region.
57
The levels of water salinity used in this study, generally, did not in¯uence soil exchangeable calcium although a signi®cant interaction between water salinity and the soil correctives was observed P < 0:05. When the higher level of sulphur (600 kg/ha) inoculated with Thiobacillus was applied, soil calcium content decreased. This suggests that sulphuric acid formed from higher levels of sulphur not only removed sodium from the soil complex but also calcium, and both can be percolated from soil by leaching. These results are compatible with Rowell (1985) and Ferreyra and Coelho (1986), who concluded that washing the soil pro®le with a mixture of salts reduces the soil sodicity. Ayars et al. (1993) observed that the salts dissolved in the irrigation water increased the contents of magnesium, sulphate, borax and chlorine but maintained the levels of potassium and calcium in the soil after 4 years of irrigation. The eect of the treatments on the exchangeable magnesium in the soil was similar to calcium (Fig. 3). The smallest concentrations of exchangeable magnesium in the soil were observed when sulphur was applied diering signi®cantly in the treatment control and gypsum application P < 0:05. In relation to saline water addition, the content of magnesium in the soil was not signi®cantly aected P > 0:05. There was an observed interaction between water salinity and the treatments with sulphur, resulting in an increased magnesium content in the soil for the highest levels of water salinity and higher sulphur levels. 3.5. Electrical conductivity The results of EC of the soil saturation extract in the ®nal of the experiment yielded statistical dierences between the tree legumes leucena and mimosa P < 0:05. We observed that the levels of salinity in the irrigation water provided a signi®cant increase of EC of the soil for all the treatments (Table 3). The results are in agreement with Miyamoto et al. (1986), Mass et al. (1988), Homan et al. (1989) and Holanda et al. (1998). The smallest values of EC in the saturation extract were obtained when sulphur inoculated with Thiobacillus was applied, resulting in levels below the limit for classi®cation as saline soil (4 dS/m), in reference to Richards (1954). The treatment with larger salinity water Sal3 re¯ects the occurrence of sodium and other cations leached during the process of soil amendment. Comparing the values of EC in the soil saturation extract after growing leucena and mimosa tree legumes a signi®cant interaction could be observed between plants and chemical correctives. When sulphur inoculated with Thiobacillus was applied to leucena the values of EC were smaller compared to mimosa. In the treatment with gypsum the EC relationship with the growing legumes was inverted and lower values are observed in mimosa tree legume.
58
N.P. Stamford et al. / Bioresource Technology 81 (2002) 53±59
Table 3 Soil electrical conductivity (dS/m) determined at the end of the experiment Soil ameliorant
Leucena
Mimosa
Sal1 (0.2)
Sal2 (6.1)
Sal3 (8.2)
Sal1 (0.2)
Sal2 (6.1)
Sal3 (8.2)
No addition (control) Gypsum 600 Gypsum 1200 Sulphur 300 Sulphur 600
4.9aC 4.8aC 4.6abC 4.2bB 2.1cC
7.6aB 6.6bB 7.6aB 5.9cA 2.9dB
8.4aA 8.7aA 8.5aA 5.4bA 3.7cA
5.2aB 4.7bC 4.6bB 4.8bC 2.8cC
7.8aA 6.1bA 6.0bA 7.7aB 4.1cB
7.7bA 6.5cA 6.7cA 8.5aA 4.9dA
Within topics, values followed by dierent letters are signi®cantly dierent at P 0:05, using the Tukey test. Upper case letters compare data in rows and lower case letters compare data in columns.
3.6. Plant dry matter weight The production of dry matter of leucena and mimosa in the treatments with sulphur inoculated with Thiobacillus and irrigation and using dierent levels of saline water is presented in Fig. 4. There was a dierential response between mimosa and leucena in relationship to the application of chemical correctives and water salinity. Dry matter of mimosa was reduced as the conductivity of the irrigation water increased in the treatments without gypsum and was strongly reduced when gypsum was applied, independent of the irrigation water's EC.
Application of sulphur with Thiobacillus at the lowest level increased dry matter production. Leucena dry matter was not aected by the application of gypsum and by sulphur with Thiobacillus at the lowest level (300 kg/ha) and was independent of the water salinity. Sulphur applied at the highest level (600 kg/ha) reduced plant dry matter signi®cantly, independently of the water salinity. This suggested that mimosa is more susceptible to the salinity than leucena, but more tolerant to soil acidity. The same rate of tolerance was described by Stamford et al. (1997) in an acid soil of the rain forest, when growing mimosa was inoculated with ecient strains of Bradyrhizobium and fertilised with soluble phosphate. These factors should be taken into account for legume selection in acid soils or irrigated with saline water. We can conclude that irrigation with saline water can increase the content of exchangeable cations and soil pH. Sulphur inoculated with Thiobacillus is more ecient than gypsum in the displacement of sodium and other cations from the soil complex to leaching solution. Leucena and mimosa tree legumes respond dierently to salinity levels and soil ameliorants with leucena being more tolerant to salinity and mimosa more resistant to the acidity promoted by sulphur inoculated with Thiobacillus. Acknowledgements We are indebted to Conselho Nacional de desenvolvimento Cientõ®co e Tecnol ogico (CNPq) for the ®nancial support and the research fellowship conceded. References
Fig. 4. Eect of sulphur inoculated with Thiobacillus and gypsum on mimosa and leucena dry matter yield grown in a saline sodic soil using water with dierent ECs. Values followed by dierent letters are signi®cantly dierent at P 0:05, using Tukey test.
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