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Published in Agron. J. 96:692-699 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA

WASTE MANAGEMENT

Effects of Application of a By-Product of the Two-Step Olive Oil Mill Process on Maize Yield

M. Tejada*,a and J. L. Gonzalezb

a Departamento de Cristalografía, Mineralogía y Química Agrícola, EUITA Universidad de Sevilla, Crta de Utrera, km 1, E-41013, Sevilla, Spain
b Departamento de Química Agrícola y Edafología, Universidad de Córdoba, Campus de Rabanales, Edificio C-3, Crta N-IV-a, km 396, E-14014 Córdoba, Spain

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

Received for publication February 19, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This study presents an account of soil quality parameters and maize (Zea mays L. cv. Tundra) yields as influenced by the application of a by-product of two-step olive oil mill process (BOM). Such information is desirable for finding out the suitability of renewable energy resources such as by-products of different industries as alternatives to synthetic fertilizers and amendments. For this purpose, the main objective of this work was to study in the field the effect of incorporating BOM on soil properties (chemical, physical, and biological) in the period between two maize crops. The second objective was to study the effect of BOM on the productivity and quality of maize crop and to evaluate the utility of the BOM for maize. A by-product of two-step olive oil mill process was applied at 0, 10, 20, 30, and 40 t ha–1 rates, respectively, on a maize crop in Lora del Río (Andalusia, Spain) for 2 yr. The results indicated that BOM has a great soil amendment potential due to its organic matter and nutrient content. The application of BOM to the soil caused an increase in soil chemical, physical, and biological properties. Mineralization of organic matter produced higher contents of NO–3–N in soil and increased NO–3–N uptake by plants. Yield parameters of the second experimental season were better than those of the first experimental season due to the residual effect of the organic matter after application in the first season. In fact, application of the BOM gave a significant grain gross protein content of about 18 and 20% for each experimental season, a significant grain soluble carbohydrate content of about 25% for both experimental seasons, a significant number of grains per corncob of about 17 and 21% for each experimental season, and a significant maize yield of about 16 and 18% for each experimental season over the control.

Abbreviations: BOM, by-product of a two-step olive oil mill process


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
SOIL FERTILITY is a dynamic concept influenced by climate and cultural practices (Ayoub, 1999). Nowadays, mineral fertilizers are the major factor in the maintenance of soil fertility. However, the massive use of mineral fertilizers and some bad cultivation practices, such as burning of stubble, have greatly reduced the organic matter content in soils. This directly influences the physical, chemical, and biological properties and the risk of degradation of soils. The main consequence of the above noted agronomic practices could be the mineralization of organic matter and desertification of soil (Tejada et al., 2001).

For this reason, issues of agricultural sustainability and environmental hazard minimization should be addressed simultaneously. Recycling of organic residues along with judicious use of mineral fertilizers can mitigate environmental hazards resulting from intensive agriculture. The application of organic sources of nutrients, such as animal manure (Haynes and Naidu, 1998), crop residues (De Neve and Hofman, 2000; Trinsoutrot et al., 2000), sewage sludge (Brendecke et al., 1993; Fließbach et al., 1994; Albiach et al., 2001), city refuse (Giusquiani et al., 1995; Eriksen et al., 1999), compost (Epstein et al., 1976; Gonzalez et al., 1992; Chen et al., 1996; Sikora and Enkiri, 1999; Tejada and Gonzalez, 2003b), by-products with higher organic matter content (Gemtos and Lellis, 1997; Duran, 2000; Salgado, 2000; Madejon et al., 2001; Tejada and Gonzalez, 2001, 2003a; Tejada et al., 2001), etc., to soil is a current environmental and agricultural practice for maintaining soil organic matter, reclaiming degraded soils and supplying plant nutrients. In this respect, BOMs, especially those obtained after the second centrifugation, are of great agricultural interest due mainly to their organic matter content (Tejada et al., 2001; Tejada and Gonzalez, 2003a, 2003b).

Under field conditions, the decomposition of BOM is complex and is mediated by soil microorganisms and controlled by numerous factors such as availability of C and N, chemical nature of the BOM, contact between soil and by-product, and soil and weather factors. Application of BOM may lead to immobilization of soil mineral N and can cause N deficiencies in plants and depress crop yield. Combining BOM with sufficient N fertilizer to meet crop requirements is an appealing alternative that (i) utilizes by-products at rates lower than those of fertilizers and (ii) reduces the amount of N inorganic fertilizer applied to soils (Sikora and Enkiri, 1999; Tejada and Gonzalez, 2003a, 2003b).

The effective use of BOM for soil application requires information on the net impact on soil N mineralization and immobilization. The first objective of this work was to study the effect of incorporating BOM on physical, chemical, and biological properties of soil over two cropping seasons. The second objective was to study the effect of BOM on productivity and quality of a maize crop (cv. Tundra) and to evaluate the utility of this by-product for maize.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Site and Climatic Conditions
The study was conducted from March 1998 to September 1999 in Lora del Rio (Andalusia, Spain). The experimental soil was a Typic Xerofluvent. The general properties of this soil (0–25 cm) are listed in Table 1.


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  		Table 1. Main soil characteristics (data are the means of five samples).

 
Listed in Table 2 are the climatic characteristics of the study area. Precipitation was variable throughout the study time. The total annual rainfall was 438 and 301 mm for 1998 and 1999, respectively. The average mean air temperature was 18.7 and 19.1°C for 1998 and 1999, respectively. These values are typical of Mediterranean climate.


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  		Table 2. Characteristic climate (means) of the study area.

 
Properties of the By-Product of a Two-Step Olive Oil Mill Process
The general properties of BOM obtained for second centrifugation are listed in Table 3. The BOM was analyzed according to MAPA (1986) protocols. The methodology for obtaining BOM is described in detail elsewhere (Gomez, 2000). In summary, the BOM obtained from the first centrifugation in the two-step process is subjected to a second centrifugation to extract residual oil. The results suggest that the BOM of the second centrifugation is the most suitable in regard to soil permeability, seed germination, and P contents (Gomez, 2000).


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  		Table 3. Average properties of the by-product obtained after the second centrifugation in the two-step olive oil extraction process (oven-dry basis).{dagger}

 
Experimental Layout and Treatments
The experimental layout was a split plot in a randomized complete block design with a total amount of 16 plots. Each plot measured 10 by 6 m. Five treatments were used (four replicates per treatment): (i) Treatment A0, incorporation of 250 kg N ha–1 (as NH4NO3), 80 kg P ha–1 [as (NH4)H2PO4], and 120 kg K ha–1 (as K2SO4), which is the common practice in the area, serving as the control plot; (ii) Treatment A1, fertilized with mineral fertilizers of Treatment A0 plus 10 t ha–1 of BOM (fresh material); (iii) Treatment A2, fertilized with mineral fertilizers of Treatment A0 plus 20 t ha–1 of BOM (fresh material); (iv) Treatment A3, fertilized with mineral fertilizers of Treatment A0 plus 30 t ha–1 of BOM (fresh material); and (v) Treatment A4, fertilized with mineral fertilizers of Treatment A0 plus 40 t ha–1 of BOM (fresh material).

The mineral fertilizers were incorporated on 11 Mar. 1998 and 14 Mar. 1999, respectively, to a 25-cm depth. The BOM was surface-broadcast on 12 Mar. 1998 and 15 Mar. 1999, respectively, and incorporated to a 25-cm depth by chisel plowing and disking the day after application.

Maize (cv. Tundra) was chosen as the test crop and used at a rate 100000 plants ha–1 in 75-cm interrow spacing, which is common practice in the area. The sowing date is 15 Mar. 1998 and 18 Mar. 1999, respectively. These experiments were designed to evaluate maize yield parameters in relation to mineralization of soil organic C in the by-product–amended soils. Crop yield (kg ha–1) and number of grains per corncob were determined on samples collected in each plot on 30 Sept. 1998 and 29 Sept. 1999, respectively.

Table 4 is a listing of the irrigation plan performed during each experimental season and for all treatments (common practice in the area). Irrigation was performed by sprinklers.


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  		Table 4. Irrigation plan carried out for each experimental season.

 
Soil Sampling, Plant Sampling, and Analytical Determinations
Soil samples (0–25 cm) were collected from each plot with a gauge auger (30-mm diam.) at three stages during the two maize growth cycles on the following dates: (i) when maize was 30 cm high (17 Apr. 1998 and 18 Apr. 1999, respectively), (ii) at tasseling (30 July 1998 and 29 July 1999, respectively), and (iii) at harvest (30 Sept. 1998 and 29 Sept. 1999, respectively). Soil samples were also collected between successive crops, on 19 Nov. 1998 and 30 Feb. 1999, respectively.

Soil samples were either immediately oven-dried at 32°C or frozen at –10°C and oven-dried at a later date. After drying, soil samples were ground to pass a 2-mm sieve and stored in sealed polyethylene bags for laboratory analysis in a cool, dry place until chemical analysis. Soil NO–3–N was extracted with 2 M KCl (250 mL) on an orbital shaker for 2h. The suspension was filtered and stored at –15°C until analysis. The concentration of NO–3–N in the extracts was determined by the colorimetric method by Barnes and Tolkard (1951) and Bremner (1965). Soil organic C was determined by oxidizing organic matter in soil samples with K2Cr2O7 in very strong sulfuric acid for 30 min and measuring the concentration of Cr3+ formed (Sims and Haby, 1971).

Structural stability test was determined by the Hénin and Monnier method (1956). The aggregate size fraction <2 mm was used. The proportions (%, w/w) of stable Ag, Aga, and Agb aggregates (corresponding to untreated, alcohol-treated, and benzene-treated aggregates, respectively) were retained on a sieve of 0.2-mm mesh. The instability index, Is, was obtained using the equation

where % <20 µmmax 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 fraction 0.2–2 mm) forming part of the stable aggregates.

Soil bulk density was determined by using core method. Metal cores of 6.1-cm length and 7.6-cm diameter were used for collecting soil core samples at 6- to 16.1-cm soil depth. The soil was weighted and dried at 105°C for 48 h, and bulk density was determined by the ratio between soil dry weight and the ring volume, according the official methods of the Spanish Ministry of Agriculture (MAPA, 1986).

Cation exchange capacity and exchangeable cations (Ca, Mg, Na, and K) were determined at the end of each experimental season by saturating with 1 M ammonium acetate at pH 7, according the official methods of MAPA (1986). Extracted Ca and Mg were determined by atomic absorption spectrophotometry and extracted Na and K by atomic emission spectrophotometry.

Triplicates of plant samples were collected from each plot at three growth stages during the two maize growth cycles: (i) when maize was 30 cm high (17 Apr. 1998 and 18 Apr. 1999, respectively), (ii) at tasseling (30 July 1998 and 29 July 1999, respectively), and (iii) at harvest (30 Sept. 1998 and 29 Sept. 1999, respectively), by selecting the whole plant for the first date and spike leave in the other two (Tejada et al., 1992). The lyophilized samples were assayed for N (Kjeldahl method) and, after digestion (MAPA, 1986), for P (Guitian and Carballas, 1976), K (by atomic emission spectrophotometer), and Ca, Mg, Fe, Mn, Cu, and Zn (by atomic absorption spectrophotometer).

Chlorophylls and total carotenoids in the lyophilized leaf samples were measured by extraction with methanol and quantified by the Lichtenthaler (1987) method. Leaf soluble carbohydrate contents were measured using the anthrone method (Yemm and Willis, 1954). About 50-g samples were collected from each plot. Dried leaf samples were extracted in 5 cm3 80% (v/v) ethanol (30 min, 30°C). The extract was centrifuged (10 min, 2650 x g), and the pellet was extracted again with ethanol. After centrifugation, chlorophyll was removed from the combined supernatants by chloroform extraction. The samples were analyzed colorimetrically for soluble carbohydrates using the anthrone method.

Grain mineral composition was characterized by analyzing N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn by techniques described previously. Grain gross protein was determined according the official methods of the MAPA (1986). This parameter is obtained when multiplying the grain N content, determined by the Kjeldahl method, by a factor of transformation of the N in protein (6.25). Also, grain soluble carbohydrate contents were characterized by techniques previously mentioned.

Soil Microbial Activity
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 = 2.64EC, where EC = (organic C in K2SO4 from fumigated soil) – (organic C in K2SO4 from unfumigated soil). Soil microbial biomass was determined at the end of both experimental seasons.

Statistical Analysis
The results obtained were analyzed by ANOVA using the Statgraphics v. 5.0 software package (Statistical Graphics Corp., 1991), considering the treatment as the independent variable. The means were separated by Tukey's test, with a significance level of P < 0.05 throughout the study.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Soil Microbial Analysis
Data listed in Table 5 show the changes in the soil microbial biomass in the soil for all treatments. The supply of readily metabolizable C in the organic by-product is likely to have been the most influential factor contributing to the biomass C increases. In this respect, and according to Bending et al. (2000), Blagodatsky et al. (2000), De Neve and Hofman (2000), Schaffers (2000), Trinsoutrot et al. (2000), and Tejada and Gonzalez (2003a)( 2003b), soil microbial biomass responds rapidly, in terms of activity, to additions of readily available C.


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  		Table 5. Soil microbial biomass as affected by different treatments.{dagger}

 
For the same authors, the application of organic wastes decreased soil microbial biomass. In this respect, 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 t ha–1 yr–1 of sewage sludges. These authors indicated that the presence of high amounts of heavy metals (Cd, Cr, Hg, Pb, etc.) in this by-product may counterbalance the positive effects of organic matter in soil microbial biomass. The BOM analyses (Table 3) indicate very low concentrations of Cd, Cr, Hg, and Pb.

Soil Structural Stability, Bulk Density, and Exchangeable Cations in Soils
Data listed in Table 6 show an increase of the structural stability of the soil with an increase of the rates of the BOM applied. These results are in accord with those of Tisdall and Oades (1982), Benito and Díaz-Fierros (1989)(1992), Chenu et al. (2000), Puget et al. (2000), and Tejada and Gonzalez (2003b), who found that a good soil structure depended on the content and nature of organic matter, which promotes flocculation of clay minerals, the essential condition for the aggregation of soil particles. Specifically, organic matter as a source of C and energy for microorganisms is supposed to increase the aggregate stability. Structural stability was still higher in the second experimental season, affecting mainly the macroaggregates of the soil (Chaney and Swift, 1984; Robertson et al., 1991; Angers, 1992). In this respect, macroaggregation is very sensitive to changes in land use and cultivation practices (Chaney and Swift, 1984; Robertson et al., 1991; Angers, 1992), whereas microaggregation is much less so (Besnard et al., 1996). Such changes in stable aggregation have generally been correlated with tillage changes and have been monitored over several years (Tisdall and Oades, 1982) but with changes in organic matter fractions in short-term studies (Baldock and Kay, 1987; Robertson et al., 1991; Angers et al., 1993). Our results confirm that BOM stabilized the macroaggregates and that the information of stable macroaggregates is strongly linked to soil organic matter dynamics, as suggested earlier by Monnier (1965), Chenu et al. (2000), and Puget et al. (2000).


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  		Table 6. Soil structural stability (log 10.Is) as affected by added amendments during two experimental seasons.{dagger}

 
In addition, bulk density decreased and soil aeration increased because of the increase in soil porosity with the structural stability. This increase was especially evident for high doses of BOM and for the second experimental season (Table 7).


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  		Table 7. Soil bulk density as affected by added amendments during two experimental seasons.

 
The results for soil cation exchange capacity and exchangeable cations (Ca, Mg, Na, and K) in soils are listed in Table 8. For the two experimental seasons, A4 produced the highest values of these parameters, followed by A3, A2, and A1. This was due to a higher supply of organic matter in the soil. A0 had the lowest values because no BOM was applied. These results are in accordance with those of Tejada and Gonzalez (2003b) when they applied a compost originating from crushed cotton gin residues to soil and Duran (2000) and Tejada and Gonzalez (2001) when they applied beet vinasse to soil. This increase in exchangeable cations is of great importance because they increase the soil nutritious reserves.


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  		Table 8. Soil cation exchange capacity (CEC) and exchangeable cations (Ca2+, Mg2+, Na+, and K+) as affected by added amendments during two experimental seasons.

 
Carbon and Nitrate Nitrogen Evolution in Soils
In the first experimental season (17 Apr. 1998 to 30 Sept. 1998), A4 produced the highest values of organic C, followed by A3, A2, and A1 (Table 9). This is due to a higher supply of organic matter to the soil. A0 yielded the lowest values of organic C because no BOM was applied. The A4 treatment gave the highest contents of NO–3–N in soil followed by A3, A2, A1, and A0 (Table 10) because of a higher mineralization of organic N in the plots where higher amounts of organic matter were applied. Nitrate N contents in soils increased gradually during the first experimental season, mainly due to mineralization of organic matter.


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  		Table 9. Changes in organic C contents during two experimental seasons.

 

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  		Table 10. Changes in NO–3–N contents during two experimental seasons.

 
On 19 Nov. 1998 and 30 Feb. 1999, the organic C contents in soils decreased. This may be due to mineralization of organic matter.

For the second experimental season (18 Apr. 1999 to 28 Sept. 1999), highest values of organic C and NO–3–N in soils for A4 were observed again, followed by A3, A2, and A1, respectively. These results indicate that the BOM has significant amendment potential because of its organic matter content. The application of the BOM to the soil resulted in an increase in NO–3–N contents in soils and an increase in NO–3–N uptake by plants (Table 11) similar to results reported by Tejada et al. (2001) and Tejada and Gonzalez (2003b).


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  		Table 11. Leaf mineral nutrient content during two maize growth cycles (on a dry matter basis).

 
Leaf Mineral Nutrient Content of the Maize Growth Cycle
Data listed in Table 11 show the dynamics of the leaf mineral contents during the maize growth cycle, expressed on a dry matter basis. Treatment A4 showed the highest leaf average N, P, and K levels for both experimental seasons with an increase of the rates of BOM applied and with the greatest difference when maize was 30 cm high. These values tended to decrease until harvest. This may be due to mineralization of organic matter, changes in portion of the plant sampled, and growth stage of the plant. This mineralization led to an increase in the soil N contents and an increase of N, P, and K uptake by plants.

For both experimental seasons, leaf N and P levels decreased gradually along the maize growth cycle because of N transfers from leaves to corncob and grains for protein synthesis. The higher K content will exert a beneficial effect on the maize produced on these plots as this element has a positive influence on the transfers of carbohydrates to the corncob (Tejada et al., 1992) and improves the yield by a more efficient grain filling. The values obtained for the different stages considered suggest a correct N, P, and K nutrition of the maize crop (Tejada et al., 1992).

Leaf Pigments and Soluble Carbohydrates Analysis
The statistical analysis indicated significant differences of leaf pigments and soluble carbohydrate contents with respect to fertilizer treatments (Table 12). The highest values of chlorophyll a and b, carotenoids, and soluble carbohydrate contents were obtained in the fertilized plots fertilized with BOM, mainly where there was a higher supply of BOM, similar to Sladky (1967), Fortun et al. (1985), and Gamiz et al. (1998). Leaf pigments and soluble carbohydrate contents decreased gradually along the maize growth cycle.


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  		Table 12. Leaf pigments and soluble carbohydrate contents.

 
Chemical Analysis of the Grains, Grain Soluble Carbohydrates, Protein Content, and Crop Yield Parameters
Data listed in Table 13 show the chemical analysis of the grains from the different treatments. The most significant differences were found in N and P. For these macronutrients, the highest values were observed with the A4 treatment. The P levels were lower and the N levels higher than the values previously reported (Tejada et al., 1992). The K, Ca, and Mg levels did not show any significant differences with the fertilizer treatments, and their values were lower than the values reported by Salgado (2000) for the same maize variety. These values are higher in the A4 treatment. With respect to the analyzed micronutrients, the most significant differences were observed in Fe and Zn. For these micronutrients, the highest values were observed with A4 treatment. With respect to grains soluble carbohydrate contents, the higher values were observed in the plots fertilized with a higher dose of BOM. In fact, application of the BOM gave a significant increase in grain soluble carbohydrate contents of about 25% for both experimental seasons. This may be due to transfers of soluble carbohydrates from leaves to grains, coinciding with Rajcan et al. (1999) and Rajcan and Tollenaar (1999).


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  		Table 13. Chemical analysis of the grains.

 
Data listed in Table 14 indicate the grain gross protein content and crop yield parameters for the different treatments. The highest gross protein content was in the A4 treatment while the lowest corresponded to the A0 treatment. The values were higher than those reported by Tejada et al. (1992) for the same maize variety fertilized with BOM applied to the soil. The fertilizer treatments increased the number of grains per corncob, with BOM applied comparing A0 to A1, A2, A3, and A4. Finally, maize yield increased significantly from A0 to A1, A2, A3, and A4, and A4 was significantly higher than A1. Grain gross protein and yield parameters of the second experimental season were better than those of the first experimental season due to the residual effect of the organic matter after application in the first season. Application of the BOM gave a significant grain gross protein content of about 18 and 20% for each experimental season, a significant number of grains per corncob of about 17 and 21% for each experimental season, and a significant maize yield of about 16 and 18% for each experimental season.


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  		Table 14. Grain gross protein content and crop yield parameters.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The results obtained in this study indicated that the BOM, especially that obtained after the second centrifugation in the two-step process, have great amendment potential due mainly to its organic matter and nutrient content. The application of BOM to the soil resulted in an increase in soil microbial activity, structural stability, porosity, cation exchange capacity, and exchangeable cations (Ca2+, Mg2+, Na+, and K+). Mineralization of the organic matter produced higher concentrations of NO–3–N in soil and increased NO–3–N uptake by plants. Due to enhanced NO–3–N uptake by plants, better maize yield parameters were obtained. Finally, the yield parameters of the second experimental season were better than those of the first experimental season due to the residual effect of added BOM. In fact, application of the BOM gave a significant grain gross protein content of about 18 and 20% for each experimental season, a significant grain soluble carbohydrate content of about 25% for both experimental seasons, a significant number of grains per corncob of about 17 and 21% for each experimental season, and a significant maize yield of about 16 and 18% for each experimental season.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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