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Soil Biology & Biochemistry

Organic Amendment Based on Fresh and Composted Beet Vinasse

Influence on Soil Properties and Wheat Yield

^a Departamento de Cristalografía, Mineralogía y Química Agrícola, E.U.I.T.A. Universidad de Sevilla, Crta de Utrera km. 1, 41013 Sevilla, Spain
^b Departamento de Conservación de Suelos y Agua y Manejo de Residuos Orgánicos, Centro de Edafología y Biología Aplicada del Segura, CEBAS-CSIC, P.O. Box 4195, 30080 Murcia, Spain
^c Departamento de Química Agrícola y Edafología, Universidad de Córdoba, Campus de Rabanales, Edificio C-3, Crta N-IV-a, km. 396, 14014 Córdoba, Spain

^* Corresponding author (mtmoral{at}us.es)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Industry byproducts present an alternative to inorganic fertilizer use. Fresh and composted organic wastes (non-depotassified beet [Beta vulgaris L. subsp. Vulgaris] vinasse [BV]compost, BV, and a cotton gin crushed compost [CGCC], which was also included as structural agent in the first compost) were applied for 4 yr to a Typic Xerofluvent in dryland conditions near Sevilla (Guadalquivir Valley, Andalusia, Spain). The effect on the soil's physical properties, soil microbial biomass, and five soil enzymatic activities (dehydrogenase activity, protease activity, ß-glucosidase activity, arylsulfatase activity, and phosphatase activity) and the yield parameters of wheat (Triticum aestivum cv. Cajeme) were determined. Organic wastes were applied at 5, 7.5, and 10 Mg organic matter ha^–1 rates, respectively. The application of fresh BV had a detrimental impact on the soil's physical (structural stability, bulk density), chemical (exchangeable sodium percentage), and biological (microbial biomass, soil respiration, and enzymatic activities) properties and the wheat yield parameters, probably because high quantities of monovalent cations, such as Na, and fulvic acids were introduced into the soil by the vinasse, thus destabilizing its structure. However when non-depotassified BV was co-composted with a CGCC, the resulting compost had a positive effect on the physical, chemical, and biological properties of the soil. The application of fresh BV resulted in a significant decrease in wheat yield (30% after 4 yr when compared with composted BV.

Abbreviations: BV, beet vinasse • CGCC, crushed cotton gin compost • CV, compost obtained by mixing of CGCC and BV

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
IN THE LAST DECADE the application of wastes with a high organic matter content, such as animal manure (Haynes and Naidu, 1998), sewage sludge (Fließbach et al., 1994; Albiach et al., 2001), city refuse (Giusquiani et al., 1995; Eriksen et al., 1999), compost (Sikora and Enkiri, 1999; Tejada and Gonzalez, 2003a), crop residues (De Neve and Hofman, 2000; Trinsoutrot et al., 2000), and industrial byproducts (Madejon et al., 2001; Tejada and Gonzalez, 2003b, 2004), to soil has been performed in an effort to reclaim degraded soils, supply plant nutrients at a reduced cost and to maintain soil organic matter levels.

Organic byproducts originating from industrial processes represent an important source of nutrients, especially for organic farming. In this respect, BV, a final byproduct of the sugar industry, is a product of great agricultural interest, because of its organic matter content, N and K concentrations (Madejon et al., 2001). Sugar beet is processed to produce crystalline sugar, pulp and molasses, the last being fermented to produce alcohol. After removal of the alcohol by distillation the remaining material is known as vinasse. In SW Spain, the annual production is about 5 x 10³ Mg (Madejon et al., 2001).

Despite the nutrients contained in the vinasse, under dryland conditions this byproduct may negatively affect soil structure, nutrient uptake, and crop yield and quality (Alba, 2001; Tejada and Gonzalez, 2005), although other studies have indicated that such negative effects are not observed with irrigated maize (Tejada and Gonzalez, 2001). Some authors have suggested that the problems associated with fresh residues (such as BV) may be overcome by co-composting with solid agricultural wastes (Madejon et al., 1996; Madejon et al., 2001).

The objective of this field study was to evaluate the effects of using fresh non-depotassified BV, CGCC, and BV compost (using CGCC as a bulking agent), as soil amendments at different rates on some physical and chemical soil properties, soil microbial activity, and the yield of wheat grown in a semiarid Mediterranean agro-ecosystem.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Site and Properties of the Organic Wastes
The study was conducted from October 1999 to October 2003 near Sevilla (Guadalquivir Valley, Andalusia, Spain) on a Typic Xerofluvent with a 2% slope. The general properties of this soil (0–25 cm) are shown in Table 1.

The CV compost was obtained by submitting the CGCC-BV mixture to an aerobic digestion in heaps of approximately 2 by 1 by 0.5 m³, turning at intervals and controlling the temperature to be never above 60 to 65°C and the moisture (not lower than 40%) controlled by adding water when necessary. The temperature of 60 to 65°C was not exceeded to prevent possible alterations in the microflora and losses of NH₄⁺–N. The composting process was allowed to progress for 157 d, when the C/N ratio and the temperature had become constant.

The general properties of the organic wastes used are shown in Table 2. Organic matter content was determined by dry combustion method (MAPA, 1986). To determine humic and fulvic acids-C, BV were extracted with 0.1 M sodium pyrophosphate and 0.1 sodium hydroxide. The supernatant, was acidified to pH 2 with HCl and allowed to stand for 24 h at room temperature. To separate humic acids from fulvic acids, the solution was centrifuged and the precipitate containing humic acids was dissolved with sodium hydroxide (Yeomans and Bremner, 1988). The C content of humic acid and fulvic acids was determined by the method of Sims and Haby (1971). For BV, inorganic soluble P (PO₄H₂^– principally) were determined by Willians and Stewart method, described by Guitian and Carballas (1976). For CGCC and CV, inorganic soluble P were determined by Willians and Stewart method, described by Guitian and Carballas (1976) after nitric and perchloric acid digestion. For BV, K and Na were determined by atomic emission spectrometer, and Ca, Mg, Fe, Cu, Mn, Zn, Cd, Ni, Cr, and Hg were determined by atomic absorption spectrometer. For CGCC and CV, Ca, Mg, Fe, Cu, Mn, Zn, Cd, Pb, Ni, Cr and Hg were determined by atomic absorption spectrometer after nitric and perchloric acid digestion. Potassium and Na were determined by atomic emission spectrometer after nitric and perchloric acid digestion.

Beet Vinasse was mixed with 2000 L ha^–1 of water with the objective to decrease the density of the byproduct and to facilitate their handling in field. The organic wastes were surface applied on 15 Oct. 1999, 16 Oct. 2000, 17 Oct. 2001, and 15 Oct. 2002, respectively. The plots received surface broadcasted NH₄NO₃ fertilizer on 13 Oct. 1999, 14 Oct. 2000, 15 Oct. 2001, and 13 Oct. 2002, respectively. Organic wastes and NH₄NO₃ fertilizer were incorporated to a 25-cm depth by chisel plowing and disking the day after application.

Wheat was seeded at a rate of 150 kg ha^–1, which is the common practice in the area. The sowing dates were 7 Nov. 1999, 10 Nov. 2000, 10 Nov. 2001, and 11 Nov. 2002, respectively.

Soil Sampling and Analytical Determinations
Soil samples (0–25 cm) were collected from each plot over a period of 4 yr (2000–2003) with a gauge auger (30-mm diam.) (20 Apr. 2000, 15 Oct. 2000, 18 Apr. 2001, 16 Oct. 2001, 20 Apr. 2002, 14 Oct. 2002, 21 Apr. 2003 and 15 Oct. 2003).

After air drying, the soil samples were ground to pass a 2-mm sieve and stored in sealed polyethylene bags at 4°C until analysis.

Soil structural stability was determined by the Hénin and Monnier method (1956) and classified according to Baize criteria (1998). The aggregate-size fraction < 2 mm was used. The proportions (%, w/w) of stable Ag, Ag_a and Ag_b aggregates (corresponding to untreated, alcohol-treated, and benzene-treated aggregates, respectively) were calculated, and the instability index, Is, was obtained using the equation:

where (% < 20 µm) max indicates the largest proportion of suspended particles < 20 µm determined for the three samples treatments, and % CS is the largest proportion of coarse sand (the 0.2–2 mm fraction) forming part of the stable aggregates.

Soil bulk density was determined using the core method. Metal cores of 6.1-cm length and 7.6-cm diam. were used to collect soil-core samples at 6.1-cm depth. The soil was weighed and dried at 105°C for 48 h before determining bulk density as the ratio between soil dry weight and the ring volume, according to the official methods of the Spanish Ministry of Agriculture (MAPA, 1986).

The exchangeable sodium percentage (ESP) was also determined, using the formula:

where Na_x is the exchangeable sodium (cmol kg^–1) and CEC is the cation exchange capacity of the soil (cmol kg^–1). Exchangeable sodium (Na_x) was determined with 1 M ammonium acetate at pH 7 (Richards, 1954) and the cation exchange capacity was determined with 1 M ammonium chloride solution in ethanol/water (60:40 v/v) at pH 8.2 (Tucker, 1954). Extracted Na was determined by flame photometry.

Soil microbial biomass was determined using the CHCl₃ fumigation-extraction method (Vance et al., 1987). Samples of moist soil (10 g) were used, and K₂SO₄–extractable C was determined using dichromate digestion. Microbial biomass-C was calculated (Vance et al., 1987) using the equation: biomass C = 2.64E_C, where E_C = (organic-C in K₂SO₄ from fumigated soil) – (organic-C in K₂SO₄ from nonfumigated soil).

The levels of five enzymatic activities in the soil were measured: (1) dehydrogenase activity was measured by reduction of 2-p-iodo-3-nitrophenyl 5-phenyl tetrazolium chloride to iodonitrophenylformazan (Garcia et al., 1993), (2) protease activity (BBA protease) was measured using N--benzoyl-L-argininamide as substrate (Nannipieri et al., 1980), (3) ß-glucosidase activity using p-nitrophenyl- ß-D-glucopyranoside as substrate (Tabatabai, 1982), (4) arylsulfatase activity using p-nitrophenylsulphate as substrate (Tabatabai and Bremner, 1970), and (5) phosphatase activity using p-nitrophenyl phosphate disodium as substrate (Nannipieri et al., 1980).

In the laboratory, and in the samples at the end of the experiment (2003 season), soil respiration for all treatments was measured by incubation for 0, 3, 7, 15, 30, 45, 60, 90, and 120 d. Total C-CO₂ collected in the NaOH flasks was determined by the addition of an excess of 1.5 M BaCl₂ followed by titration with standardized HCl using a phenolphthalein indicator (Zibilske, 1994).

Crop Yield Parameters
The number of spikes m^–2, number of grains spike^–1 and crop yield (kg ha^–1) were determined on samples collected from each plot on 14 June 2000, 13 June 2001, 10 June 2002, and 11 June 2003, respectively.

Statistical Analysis
Analysis of variance (ANOVA) was performed using the Statgraphics v. 5.0 software package (Statistical Graphics Corporation, 1991). The means were separated by Tukey's test, considering a significance level of P < 0.05 throughout the study.

	RESULTS

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Structural Stability, Bulk Density, and Exchangable Sodium Percentage in Soils
Structural stability increased in soils amended with CGCC and CV but decreased in soils amended with high rates, Treatments 6 and 7, of BV (Table 3). Soil bulk density decreased in CGCC and CV amended soils during the experimental period but increased in BV amended soils (Table 4). Statistical analysis showed differences between the treatments at the end of experimental period, principally for Treatment 7. The soil without organic amendment (control soil) showed higher structural stability than the soil amended with fresh BV, but lower than the soil with CV.

Exchangeable sodium percentage increased significantly in BV-amended soils when compared with the CGCC and CV amended soils during the experimental period (Table 5). For CGCC and CV amended soils, ESP did not reach the critical sodicity value of around 15 mentioned by Richards (1954). However, for BV amended soils ESP had reached critical sodicity values (ESP = 15.1) at the end of the experimental period. The control soil presented the lowest ESP value of all treatments assayed.

	DISCUSSION

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Physical and Chemical Properties
The results obtained for CGCC and CV-amended soils (in which the organic matter increased the soil structural stability, especially at high organic waste rates and at the end of the experimental period) are similar to those of Chenu et al. (2000), Puget et al. (2000), and Tejada and Gonzalez (2003b, 2004) who found that a good soil structure depended on the content and nature of the organic matter added. Organic matter promotes flocculation of clay minerals, which is an essential condition for the aggregation of soil particles. In addition, bulk density is decreased as a result of the dilution of the denser soil mineral fraction and soil aeration increases because of the increase in soil porosity accompanying structural stability. This increase was especially evident for the high rates of CGCC and CV and at the end of the experimental period and was similar to the results of Kay and VandenBygaart (2002) and Tejada and Gonzalez (2003b, 2004).

The negative effect of vinasse on the soil structure may be due to its nature, since BV contains a high concentration of Na⁺ and fulvic acids (Tejada and Gonzalez, 2005). This interpretation would agree with Haynes and Naidu (1998) and Grahan et al. (2002), who also found that adding large quantities of organic manures to soils destroyed the soil structure presumably because of the high amounts of Na⁺ transported into the soil. Furthermore, ESP increased during the experimental period at the highest BV doses. According to Mamedov et al. (2002), this increase points to dispersibility and aggregate disintegration in these soils.

It is well known that the less oxidized, higher molecular weight humic matter is more important in the process of aggregate stabilization than the more oxidized humic substances of lower molecular weight. Chaney and Swift (1984) and Piccolo and Mbagwu (1990) suggested that the aggregate stability is significantly correlated with humic but not fulvic acid concentration, because the humic acids are directly involved in the clay-organic complex formation, whereas fulvic acids are not. Beet vinasse is a byproduct that has a low humic acid-C content and high fulvic acid-C concentrations. Fulvic acids are macromolecules with a lower polymerization index than humic acids. Hence, the applied organic matter may not have flocculated with clay minerals (essential condition for the aggregation of soil particles), for which reason thus aggregates formed under this treatment may not have been stable (Piccolo and Mbagwu, 1990; Porta et al., 1994). We assume that with the high doses of vinasse, not only the monovalent cations but also the fulvic acids were responsible for the degradation of the soil structure.

Microbial Activity in Amendment Soil
The supply of readily metabolizable C in the organic byproduct is likely to have been the most influential factor contributing to the biomass-C increases. In this respect and according to De Neve and Hofman (2000), Trinsoutrot et al. (2000), and Tejada and Gonzalez (2003a, 2003b, 2004), soil microbial biomass responds rapidly, in terms of activity, to additions of readily available C.

Our results indicated that an increase in soil microbial biomass lowered the soil instability index (log 10Is). Several studies have reported that soil microbial processes are directly and indirectly influenced by soil structure. The presence of small pores reduces accessibility of organic materials to decomposers, causing the physical protection of C and a reduction in N mineralization (Van Veen and Kuikman, 1990). The spatial distribution of microbes and soil mesofauna has been shown to be partially associated with the size distribution of aggregates (Jastrow and Miller, 1991).

Soil enzymes are biological catalysts of specific reactions and these reactions, in turn, depend on a variety of factors (Burns, 1978), such as the presence or absence of inhibitors, type of amendment, crop type, etc. Soil enzymes are good markers of soil fertility since they are involved in the cycling of the most important nutrients. The incorporation of organic amendments to soil influences soil enzymatic activities because the added material may contain intra- and extracellular enzymes and may also stimulate microbial activity in the soil (Goyal et al., 1993; Pascual et al., 1998). The development of microbial populations, which is favored by the root exudates of plants, may also be responsible for the dehydrogenase activity stimulation. The greater dehydrogenase activity noted at the high dosage suggests that the added compost did not include compounds which were toxic for this activity (Pascual et al., 1998). During each experimental season, dehydrogenase activity decreased. This may be due to microbial death because substrates were no longer available to sustain microbial biomass or to the fact that intracellular enzyme complexes were degraded by the microorganisms inhabiting amended soils (Pascual et al., 1998).

It is clear that N cycle functioning was improved in the soils treated with both composts assayed (CGCC and CV). The stimulation of protease activity BAA related with the N cycle suggests that the treatment used (compost) does not include compounds toxic for this activity, or that microbial growth and/or the addition of microbial cells or enzymes with the amendment counteract any inhibitory effect due to toxic compounds. The demand for N by both, plants and soil microorganisms, was probably responsible for the increase of this enzyme activity. Garcia et al. (1994) studied the influence of some toxic compounds contained in organic amendments, such as municipal solid wastes, on soil microbial activity in semiarid zones. These authors determined that the positive effect of the organic matter on biological soil quality counteracted the negative effect produced by these toxic compounds. Organic amendment by the composts studied had a positive effect on the activity of these enzymes, particularly when the amendment was at the high rate, probably due to the higher microbial biomass produced in response.

Soil arylsulfatase activity and soil phosphatase activity were higher in the CGCC amended soils than in CV amended soils. The demand for P by plants and soil microorganisms can be responsible for the stimulation of the synthesis of this enzyme (Garcia et al., 1994). In addition, the processes related to degradation of organic matter may be followed through hydrolases such as phosphatase. According to Rao and Tarafdar (1992), increases in phosphatase activity (as we have detected in the treated soils) indicate changes in the quantity and quality of soil phosphoryl substrates. The supply of readily metabolizable C in the organic byproduct is likely to have been the most influential factor contributing to the soil arylsulfatase activity and soil phosphatase activity increases.

For BV-amended soils, the effect on soil parameters is very different from compost amended soils: when fresh BV was added the soil microbial biomass, soil respiration, and soil enzymatic activities all decreased. For same authors, the application of organic wastes decreased soil microbial biomass. Brendecke et al. (1993), Fließbach et al. (1994), and Filip and Bielek (2002) reported a decrease of soil microbial biomass after a 10-yr application of 5 and 15 Mg ha^–1 yr of fresh organic matter (sewage sludges). These authors indicated that the presence of high quantities of heavy metals (Cd, Cr, Hg, Pb, etc.) in this byproduct may counterbalance the positive effects of organic matter in soil microbial biomass. The BV analyses indicated very low concentrations of Cd, Cr, Hg, and Pb; for this reason, the observed inhibition cannot be due to the heavy metal content. Perhaps this inhibition could have been caused by labile organic toxic compounds and/or an increase of the electrical conductivity in soil with the BV addition (Garcia and Hernandez, 1996). Composting process can eliminate toxic organic compounds by mineralization (Mena et al., 2003); in our case, CV compost reduced the electrical conductivity due to the dilution effect since this compost is made with a mixture with CGCC of low electrical conductivity.

Our data indicated that increasing the dose of BV to the soil, decreased the soil structural stability, soil microbial biomass and soil respiration, which increased the soil bulk density. According to Tate III (2002) oxygen concentration in soil can affect the metabolic status of the enzyme-producing cells. Disruption of soil aggregates negatively alters the oxygen diffusion rate from the atmosphere above the soil into the soil matrix as well as the rate of its consumption.

It is not easy to determine the reason for enzyme activity inhibition by BV addition; for example, phosphatase inhibition could be caused either by an excess of inorganic P (Nannipieri et al., 1990), or by heavy metals incorporated into the soil with the organic waste. However, in our case, the BV did not have a high quantity of neither P nor heavy metals. We think that this inhibition is probably due to the decrease in soil structural stability and the increase of salinity.

Wheat Yield Crop
Since soil enzymatic activities are responsible for important cycles such as C, N, P, and S, wheat yield parameters increased significantly when a higher dose of CGCC and CV was applied to the soil. These values are similar to the values reported by Gonzalez et al. (1992) for the same wheat variety fertilized with pig slurry compost in the Guadalquivir Valley (similar pedoclimatic conditions). Also, wheat yield parameters of the fourth experimental season were higher than those of the third, second, and first experimental seasons respectively, due to the residual effect of the organic matter of each organic waste after their application in the third, second, and first experimental seasons. Since the decrease in microbial diversity may reduce microbial functionality of soil and therefore decrease the N, P, and S available levels by plants, wheat yield parameters decreased significantly when a higher dose of BV were applied to the soil.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
The application of fresh BV at doses studied under dryland conditions caused a decrease in soil physical and biological properties and wheat yield, in spite of having a high organic matter content. Perhaps the increase in monovalent cations (Na and K), and labile organic matter (possible inhibitor compounds) are responsible for this behavior. However, when non depotassified BV was co-composted with solid agricultural wastes, an increase in soil physical and biological properties and wheat yield was obtained.

Received for publication August 17, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

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