Effects of oil mill wastes on surface soil properties, runoff and soil losses in traditional olive groves in southern Spain

Catena 85 (2011) 187–193

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Catena j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c a t e n a

Effects of oil mill wastes on surface soil properties, runoff and soil losses in traditional olive groves in southern Spain B. Lozano-García a,⁎, L. Parras-Alcántara a, M. del Toro Carrillo de Albornoz b a b

Dpto. de Química Agrícola y Edafología, Universidad de Córdoba, Campus Rabanales, Edificio Marie Curie, 3a planta, 14071, Córdoba, Spain Dpto. de Edafología y Química Agrícola, E.T.S.I.A. Ctra. De Utrera, km 1, 41013, Sevilla, Spain

a r t i c l e

i n f o

Article history: Received 24 September 2010 Received in revised form 20 January 2011 Accepted 27 January 2011 Keywords: “Alperujo” Oil mill waste Runoff Soil losses Rainfall simulator

a b s t r a c t In Spain, agriculture triggers soil degradation and erosion processes. New strategies have to be developed to reduce soil losses and recover or maintain soil functionality in order to achieve a sustainable agriculture. This experiment was designed to evaluate the effect of two olive mill wastes (olive leaves and “alperujo”) on soil properties and soil erosion in a rain fed olive grove in SE Spain. After three years experiment, oil mill wastes application significantly improved physical and chemical properties of the studied soil with respect to control. The organic matter content, bulk density and porosity were increased, which confirmed the interactions of these properties. Available water capacity increased with olive leaves but decreased when applied “alperujo”. With respect to erosion, after simulated rainfall experiments it was found that the oil mill wastes contributed to increase the roughness and the interception of raindrops, delaying runoff generation and enhancing the infiltration of rainwater. Treatment with oil mill wastes contributed to a reduction in runoff generation and soil losses compared to bare soil, especially when applied olive leaves. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Olive oil production worldwide estimated to be about 2.8 106 Mg per year (IOOC, 2009). Within the EU, the main producer is Spain with an average production of 0.9 106 Mg per year, reaching 1.4 106 Mg in the 2003–2004 campaign (AAO, 2010). There are approximately 750 106 productive olive trees in the world (IOOC, 2004), of which 215 106 are in Spain (De Hidalgo, 2008). Proper management and utilization of olive mill wastes is becoming more urgent due to the expansion of this industry and an increasing awareness of environmental protection (Pfeffer, 1992). Spain, Italy and Greece, three Mediterranean countries, involved in solving the olive mill wastes problem, have made many studies regarding the possible ways of cleaning and recycling olive mill wastes (Tomati and Galli, 1992; Cardelli and Benítez, 1998; Colodrero et al., 1998 and Benítez et al., 2000). Annually, Spain generates 5.89 106 Mg “alperujo” (waste from the current procedure for olive oil extraction in two stages) and 0.367 106 Mg olive leaves (olive leaves dragged along with the olives at harvest and separated in the initial cleaning process at the mill) (Moreno, 2009). Several advantages were reported for proper uses of olive mill wastes, using them as a source for plant nutrients and a supply of organic matter to improve soil fertility (Melgar et al., 2000; Sainz et al., 2000; Alburquerque et al., 2006 and Altieri and Esposito, 2008).

⁎ Corresponding author. Tel.: +34 957211092; fax: +34 957212146. E-mail address: [email protected] (B. Lozano-García). 0341-8162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2011.01.017

On the other hand, the disadvantages may be represented by the polluting load and accumulation of high mineral elements and organic phytotoxic compounds (Aqeel and Hameed, 2007). Soil erosion is a major problem in the Mediterranean region due to its arid conditions, storm intensity and rainfall concentration, which are factors that contribute largely to agricultural land degradation (López-Bermúdez and Albadalejo, 1990 and Lal, 1999). On average, in Spain, it lost 23 Mg ha− 1 of soil per year, contributing to desertification and loss of agricultural production (Fernández, 2008). López (1990) estimated an annual average of soil erosion in olive groves in 80 Mg ha− 1. Therefore it is necessary to replace the annually lost of organic matter to support agriculture in areas that already are low in organic matter (Fernández, 2008). This is why soil erosion control strategies are largely being applied to agricultural land. Catch crops, no-tillage or reduced tillage, chipped pruned branches, straw mulch, geotextiles and weed control by herbicides (or no-tillage techniques) are some of the land management currently being applied on experimental farms to reduce the usually high erosion rates on rain fed agricultural land in eastern Spain (García-Orenes et al., 2009). New soil management practices will not only affect the erosion processes, but also the soil properties. Several studies show that agricultural management has an important influence on chemical, physical and biological parameters (García et al., 1997; Caravaca et al., 2002 and Marinari et al., 2006), as microbial populations and activities are fundamental for maintaining soil quality by mediating the processes of organic matter turnover and nutrient cycling (Doran and Parkin, 1994).

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Fig. 1. Images of the three plots, from left to right: control plot, “alperujo” plot, olive leaves plot.

Differently from other land uses, cultivated soils show low organic matter contents (Masciandaro et al., 1998). Intensive soil use throughout history has led to the depletion in soil quality, leading in turn to low yields because of the consequent reduced organic matter (Reicosky et al., 1995). Celiki (1987) observed that Mediterranean cultivated soils present lower saturated hydraulic conductivities than forest soils. He found that cultivation degrades soil physical properties, and makes soils more susceptible to erosion processes. Furthermore, olive trees are usually grown in areas where water is scarce. The trees explore substantial soil volumes during their long lifetime, and depend on the soil water storage capacity to avoid water stress. The timing of water deficits has important effects on productivity. Although several soil management strategies may be applied to olive tree cultivation, the most widely used method is mechanical tillage. Recent findings, however, suggest that only an enhanced rate of water filtration would technically warrant interest in mechanical tillage (Hernández et al., 2005). There is strong evidence, especially for soils of low soil water storage capacity such as the present study, that water-saving production techniques are important requirements under drought conditions for the crop to reach its yield potential, particularly if the frequency and duration of droughts increase or soil and groundwater reserves decrease. Within this approach and in line with resource-soil

and water conservation concepts, the use of crop residues is quickly gaining popularity. Mulching protects soil from rainfall-induced erosion by reducing the raindrop impact. A partial covering of mulch residue on the soil can strongly affect runoff dynamics, and reduce the runoff amount (Rees et al., 2002 and Findeling et al., 2003). Blavet et al. (2009) have reported a significant reduction of soil loss when plant residues were left on the soil. They found that vineyards mulched with straw or with rock fragment cover were protected against runoff, and soil erosion. The addition of organic plant residues to crop soils also helps to improve soil water storage capacity because it improves soil structure. The addition of crop residues to cultivated soils helps to improve soil quality and productivity through its favorable effects on soil properties (Lal and Stewart, 1995 and Mulumba and Lal, 2008). The application of crop residue mulches to cultivated soils increases the organic matter content (Havlin et al., 1990; Duiker and Lal, 1999 and Saroa and Lal, 2003). Mulumba and Lal (2008) reported positive effects on soil porosity, available water content, soil aggregation, and bulk density after the application of wheat straw mulch. The objectives of this work are [1] to compare the effects of two oil mill wastes (“alperujo” and olive leaves) on the decrease of soil erosion and improving the physical and chemical properties of soil; [2] to recycle oil mill wastes apply them to the soil and convert them

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was 236 Mg ha− 1 of olive leaves and the treatment applied in the third plot was 270 Mg ha− 1 of “alperujo” (Fig. 1). 2.3. Soil sampling and analysis Five soil samples in each plot were taken in 2002, before the treatments, to determine soil type. Later, in 2005, five soil samples per plot were collected to analyze the behavior of soil after three year of treatment application. Each sample was dried at laboratory room temperature (25 °C) at a constant weight and sieved (2 mm) to eliminate coarse soil particles. Soil acidity (pH) was measured in an aqueous soil extract in de-ionized water (1:2.5 soil:water). Soil organic matter was determined by the Walkley–Black method (Walkley and Black, 1934). Prior to determining the particle size distribution, samples were treated with H2O2 (6%) to remove organic matter. The proportion of particles with a diameter above 2 mm was determined by wet sieving and particles b2 mm were classified according to USDA (2004). Water content at 1500 kPa (wilting point) and 33 kPa (field capacity) was determined using a pressuremembrane extraction apparatus (Richards, 1941). The available water capacity was calculated as the difference in moisture retention between 33 and 1500 kPa suctions, expressed on a volumetric basis. Bulk density was measured by the core method (Blake and Hartge, 1986), using cores 3 cm in diameter, 10 cm in length, and 70.65 cm3 in volume. Total porosity (TP) was calculated from the bulk density (BD) values and the measured particle density (PD) as TP = 1 − BD/PD.

Fig. 2. Shape and dimensions of LUW rainfall minisimulator.

2.4. Rainfall simulation experiments into by-products, in this way, it solves a problem of management in the oil mills. Rainfall simulation experiments were conducted in order to quantify erosion and determine the available water capacity. 2. Materials and methods 2.1. Study area A rain fed olive grove located in Torredelcampo-Jaén (37º 50′ N; 3º 52′ W, 441 m. a. s. l.) was selected as an example of a typical olive grove of southern Spain (Mediterranean area). The parent material is Miocene marl and marlaceous lime, the soil is a Cambisol (FAO, 1998) and the land management is conventional tillage (with disc harrow 25 cm). The climate is typical Mediterranean with 3–5 months of summer drought, usually from late June to September and moderately wet cool winters. According to the nearby weather station in Torredelcampo (Jaén), the annual average temperature is 17 °C, with a maximum air temperature of 40.6 °C in August and a minimum air temperature of −5.2 °C (January). The annual average precipitation is 645.7 mm, and monthly rainfall ranges from 4.7 mm (July) to 87 mm (February). 2.2. Experimental plots An olive farm with conventional tillage practices has been selected for the study. The farm was oriented N–NW, the slope was 2–4% and the flat side, slightly convex. In January 2002 three large plots (each of them 10000 m2; 100 m × 100 m) were established on the farm. The first plot, was the control plot, the difference between the second and the third plots was due to the application of oil mill wastes (olive leaves and “alperujo”). The treatment applied in the second plot

The erosion study was based on simulations of rain with a LUW minisimulator (Eijkelkamp) (Fig. 2) where the velocity and energy of the raindrop was constant. The water in the tank falls on a rectangular area (625 cm2), with a rainfall intensity of 240 mm h− 1. We used this type of rainfall simulator because it was small, handy and easy to transport, allowing its use in field and laboratory reproduction if necessary. Using a rainfall simulator to quantify erosion allowed it to be fully standardized (simulation surface, rainfall amount and speed). Comparing the results obtained in a given plot with those of any other plot the same simulation conditions were always repeated (Kamphorst, 1987). The simulations have been carried out in order to highlight differences in the phenomena of runoff and soil losses in the three plots considered. In each plot five rainfall simulations were conducted in different places. Runoff was collected in all simulations and we measured sediment concentration, after coarse organic residues were removed. Finally, soil loss rates were calculated from sediment concentrations in collected runoff. Also at the beginning and end of each simulation the volumetric soil moisture with a TDR probe (Time Domain Reflectrometry) was determined. The model used in this study was ML2× with a dataloger HH2 moisture meter (Delta-T Devices) and rain simulations have been made to reach field capacity. 2.5. Statistical analysis Data analysis included correlations, multiple regression, and ANOVA tests. Assumptions of normality and homogeneity of variances were tested using the Shapiro-Wilk and Brown-Forsyth tests,

Table 1 Physical and chemical soil properties (0–10 cm) in 2002 before the experiments. Sand (%)

Silt (%)

Clay (%)

pH

O.M. (%)

Bulk density (Mgcm− 3) Macroporosity (%) Microporosity (%) pF 33 kPa pF 1500 kPa AWC

Control 12.1 ± 1.9 45.4 ± 4.0 42.5 ± 2.5 8.4 ± 0.2 1.53 ± 0.2 1.36 ± 0.01 “Alperujo” 11.6 ± 1.5 46.0 ± 2.0 42.4 ± 1.5 8.3 ± 0.2 1.50 ± 0.2 1.32 ± 0.02 Olive leaves 11.8 ± 1.2 45.2 ± 2.3 43.0 ± 2.3 8.4 ± 0.2 1.51 ± 0.2 1.34 ± 0.01

49.3 ± 1.9 49.1 ± 2.1 49.0 ± 1.8

50.7 ± 2.2 50.9 ± 2.0 51.0 ± 2.1

33 ± 2.2 32 ± 2.1 33 ± 1.8

20.5 ± 1.6 20.7 ± 1.4 20.6 ± 1.7

12.5 ± 1.3 12 ± 1.1 13 ± 1.4

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Table 2 Soil properties (0–10 cm) after the experiments. Values with different letters within the columns are statistically different according to Kruskal-Wallis test.

Control “Alperujo” Olive leaves Kruskal–Wallis, p

O.M. (%)

Bulk density (Mgm− 3)

Macroporosity (%)

Microporosity (%)

pF 33 kPa

pF 1500 kPa

AWC

1.53 ± 0.2 a 3.2 ± 0.3 a 14.4 ± 2.2 b 0.0001

1.37 ± 0.01 c 1.26 ± 0.01 b 0.49 ± 0.01 a 0.0001

53,5 ± 3.1 a 73,4 ± 3.4 b 95.9 ± 1.9 c 0.0001

46.5 ± 2.2 c 26.6 ± 1.6 b 4.1 ± 1.0 a 0.0001

32 ± 2.3 a 31.7 ± 2.0 a 45.4 ± 2.0 b 0.0001

20.7 ± 1.8 a 23.4 ± 1.5 a 31.7 ± 1.9 b 0.0001

11.3 ± 1.6 ab 8.3 ± 1.2 a 13.7 ± 1.6 b 0.0092

respectively. Since most of the variables did not satisfy these assumptions, alternative non-parametric tests were used for comparing multiple independent groups of samples (Kruskal–Wallis ANOVA). When ANOVA null hypothesis was rejected, pos-hoc pair wise comparisons were performed to investigate differences between means (Bonferroni test). All computations were made using SPSS Statistics 17.0. 3. Results 3.1. Soil properties Table 1 shows texture, soil acidity (pH), OM content, bulk density, porosity, water content at 1500 kPa (wilting point) and 33 kPa (field capacity) and the available water capacity (AWC) before the experiment in February 2002. No significant differences were observed for plots before the treatment (Table 1). Data of OM, bulk density, macroporosity and microporosity and available water capacity in the different plots after treatment with oil mill wastes can be seen as compared in Table 2. OM content increased after the application of different oil mill wastes (Kruskal–Wallis p = 0.0001, Table 2). In the “alperujo” plot the increase was moderate (from 1.50% to 3.2%) while the increase was higher in the olive leaves plot (from 1.51% to 14.4%). Bulk density decreased with treatments at the same time varying the percentage distribution of macroporosity and microporosity (p = 0.0001, for the two cases, Table 2). The control plot bulk density was 1.37 Mg m− 3 and the porosity distribution was: 53.5% macroporosity and 46.5% microporosity. In the “alperujo” plot the bulk density decreased until 1.26 Mg m− 3. Also the microporosity decreased (26.6%) and the macroporosity increased (73.4%). In the olive leaves plot the trend was the same but the variations were much greater. Bulk density decreased from 1.34 Mg m− 3 to 0.49 Mg m− 3, macroporosity increased from 49.0% to 95.9%, and the microporosity decreased from 51.0% to 4.1%. Significant differences were observed for water content at 1500 kPa and 33 kPa between the olive leaves plot, the control plot and “alperujo” plot. With respect to the wilting point (1500 kPa) (p = 0.0001, Table 2) in “alperujo” plot it increased from 20.7% in initial state to 23.4% and in the olive leaves plot it increased from 20.6 to 31.7%. However, the field capacity (33 kPa) (p = 0.0001, Table 2) increased when the waste was olive leaves (from 33% to 45.4%), but

decreased when “alperujo” (31.7%) was applied. Therefore the available water capacity (p = 0.0092, Table 2) increased when the oil mill waste used was olive leaves, but decreased when “alperujo” was applied. 3.2. Runoff initiation The runoff generation is a key point in soil erosion processes as it determines the time and volume of water running off the soil surface, and controls soil detachment rates and sediment transport. The initial soil moisture (p = 0.0001, Table 3) is important, but not decisive in the beginning of the runoff that will occur after an episode of rain. Before the start of the simulations the soil moisture was 7.4% in the control plot, 13.8% in the “alperujo” plot and 14.5% in the olive leaves plot (Table 3). The beginning of the runoff was very different in the three plots (p = 0.0001, Table 3). In the control plot runoff began when the rainfall applied was only 12 mm, in the plot with application of “alperujo” 56 mm were needed, whereas in the olive leaves plot 156 mm were necessary. 3.3. Water losses Average total runoff (p = 0.0014, Table 3) collected from the 0.0625 m2 was very low from the olive leaves plot (0.275 10− 3 m3), low from the “alperujo” plot (1.320 10− 3 m3) and high from the control plot (3.320 10− 3 m3). Runoff coefficients (p = 0.0001, Table 3) show that the control plot lost 55.3% of the rain to runoff; while for the “alperujo” plot it was 14.7% and for the olive leaves plot it was 2.8% (Table 3). 3.4. Soil losses Sediment concentration in runoff (p = 0.0008, Table 3) provides information on the soil's susceptibility to erosion (erodibility). The control plot soil had the greatest sediment concentrations, with a mean value of 36.3 kg m− 3. The “alperujo” plot soil had mean sediment concentration values of 3.6 kg m− 3 (Table 3). For the olive leaves plot soil there was no sediment. Mean soil losses (p = 0.0001, Table 3) for each of the plots indicated that the control plot with conventional tillage contributed the greatest amounts (55.06 Mg ha− 1 h− 1); while the “alperujo” plot reduced erosion levels to 2.16 Mg ha− 1 h− 1. The olive leaves plot had not soil loss (Table 3).

Table 3 Mean values of soil and water losses for the three plots from the rainfall simulation. Values with different letters within the columns are statistically different according to KruskalWallis test. NS: not significant.

Control “Alperujo” Olive leaves Kruskal–Wallis,p

Initial volumetric soil moisture (%)

Increased moisture

Simulated rainfall at runoff initiation (mm)

Total runoff (m3)

Runoff coefficient (%)

Sediment conc. (kg m− 3)

Soil loss (Mg ha− 1 h− 1)

7.4 ± 0.1 a 13.8 ± 0.1 b 14.5 ± 0.1 c 0.0001

36.8 ± 0.9 30.7 ± 0.8 40.5 ± 1.5 NS

12 ± 0.2 a 56 ± 0.3 b 156 ± 0.5 c 0.0001

3.320 10− 3 ± 0.5 b 1.320 10− 3 ± 0.4 a 0.275 10− 3 ± 0.1 a 0.0014

55.3 ± 0.5 a 14.7 ± 0.2 b 2.8 ± 0.2 c 0.0001

36.3 ± 1.2 b 3.6 ± 0.6 a 0±0 a 0.0008

55.06 ± 1.3 a 2.16 ± 0.4 b 0±0 c 0.0001

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4. Discussion 4.1. Changes on superficial soil properties The most dynamic soil position on agricultural land is the surface, where the treatments are applied and where soil erosion processes take place. After three years of different land management treatments some superficial soil properties have changed. The application of “alperujo” and olive leaves to soil produced a significant increase in soil organic matter content between 0 and 10 cm after 3 years of treatment with respect the control. Jordán et al. (2010) showed that organic matter content generally increased, although no benefit was found beyond 10 Mg ha− 1 year− 1 of crop residues applied to soil. Marinari et al. (2006) found significant increases of microbial biomass carbon content with organic management in farming systems in Italy, but did not find any significant differences in soil organic carbon content after 14 months. In contrast, Blanco-Canqui and Lal (2008) demonstrated that organic carbon content varies with soil depth, and in many cases, till or non-till systems do not induce significant differences through the soil profile. Bulk density and porosity were also improved with the application of oil mill wastes, which confirmed the interaction of these properties. This is in agreement with other studies. García-Orenes et al. (2009) found that straw mulch was able to significantly improve soil properties after a 16 month study period in a Mediterranean farming area. Other authors found that bulk density and porosity improved with mulch application, especially with certain quantities (Mulumba and Lal (2008) and Jordán et al. (2010)). Bulk density decreased with the “alperujo” and olive leaves application. “Alperujo” has a texture similar to the soil, however, olive leaves produce a mulching effect on soil. This effect caused the density decrease to be more pronounced. This is in agreement with Oliveira and Merwin (2001), who found that bulk density was lower and soil porosity greater under mulch than under other groundcover management practices, and Ghuman and Sur (2001), who studied the effect of mulching on soil properties and yields of rain fed maize and wheat in a sub-humid subtropical climate demonstrated that mulching decreased bulk density in compacted soils particularly in non tillage systems which can be ascribed to higher soil carbon content and biotic activity. In contrast, increased bulk density has been observed after mulching respect to conventional tilling by Bottenberg et al. (1999), showing even more negative consequences in plant growth. Reduced or non tillage usually increases soil density which has been widely reported by many authors (Van Ouwerkerk and Boone, 1970; Pidgeon and Soane, 1977 and Singh and Malhi, 2006). Głąb and Kulig (2008) found that bulk density increased in the 10–20 cm soil layer after reduced tillage, although the bulk density from the upper soil layer (0–10 cm) decreased and reached a similar value as those obtained with conventional tillage. Other researchers have demonstrated that non tillage practices contribute to a decrease in bulk density in Mediterranean (Murillo et al., 2006) and other climatic areas of the world. Many authors have found comparable or increased bulk densities in the first centimeters of soil after short-term studies of reduced tillage in eastern Canada (Angers et al., 1997), and USA (Yang and Wander, 1999; Puget and Lal, 2005 and Al-Kaisi et al., 2005). However long term studies, have shown that bulk density under reduced tillage was comparable or lower than under conventional tilling. Tebrügge and Düring (1999) reported that bulk density generally increased under non tillage, but decreased at the surface (0–3 cm). They explained it as a direct consequence of the mulch layer on top of non-tilled soils that provide organic matter and food for soil fauna, which loosens surface soil through burrowing activities. Other authors have reported no significant differences between different tillage practices. Deen and Kataki (2003) compared the results from long term conventional

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tilling and conservation tillage practices, and reported that different management practices had no significant influence on soil bulk density at different soil layers between 0 and 60 cm. Also, Dolan et al. (2006) found that soil bulk density did not vary among tillage treatments in the 0–5 cm soil layer. Besides, the duration of experiments, and the diversity of results may be due to differences in management practices, soil type and the type of mulch material used (Mulumba and Lal, 2008). The porosity distribution was also improved after the application of oil mill wastes. Macroporosity increased, while the microporosity decreased. Soil porosity is especially important to crop development since it helps to renew soil atmosphere and enhance root growth. The improved root growth makes it possible for the plant to absorb soil water and nutrients from the subsoil. Hoffmann and Jungk (1995) found that soil compaction inhibits root growth after oxygen deficiency and mechanical soil resistance. Increased porosity due to mulch application was also reported by many other authors. Głąb and Kulig (2008) observed that fodder radish mulching increased soil porosity in compacted soil under reduced tillage and temperate climate in Poland; Oliveira and Merwin (2001) studied the effect of a 15 cm shredded hardwood bark and found that soil porosity increased more under mulch than other management systems. 4.2. Soil water properties under different oil mill wastes We examined the effect of the oil mill wastes on water availability. The effect of water availability on the growth and production of olive trees was described by Michelakis (1995). “Alperujo” and olive leaves altered the properties of soil water, but their behaviors were totally different. Available water capacity increased respect to the control plot in 21% under olive leaves treatment while the water capacity decreased in 26% under “alperujo” treatment. “Alperujo” applied to the soil increased the hydrophobicity of the soil due to residual oil. This causes a decrease in water retention (Niaounakis and Halvadakis, 2006). High available water capacities have been reported under high mulching rates and non tillage by Duiker and Lal (1999) and Mahboubi et al. (1993). However, Hernández et al. (2005), did not find improvement in the amount of available water, except in one area of subterranean clover for different covers studied in olive groves. Anyway, contradictory data have been reported by Głąb and Kulig (2008), who found no effect in available water content after applying mulch and different tillage systems. 4.3. Runoff and erosional response under different oil mill wastes The runoff and erosional response of soils depend largely on the oil mill waste applied during the experiments. The highest soil erosion losses were observed in the control plot. The control plot, despite having lower initial moisture is the main contributor to the generation of runoff. In the “alperujo” the runoff initiation was delayed and the soil losses were lower compared to the control plot. Therefore the erosive rate after the implementation of “alperujo” was reduced. In the olive leaves plot the delay in the runoff initiation was much greater than in the “alperujo” one and there was no soil loss. It is often assumed that soil resistance to erosion is closely related to soil quality. Several studies show that agricultural management has an important influence on chemical, physical and biological parameters (García et al., 1997; Caravaca et al., 2002; Marinari et al., 2006 and Altieri and Esposito, 2008) as microbial populations are fundamental for maintaining soil quality by mediating the processes of organic matter turnover and nutrient cycling (Doran and Parkin, 1994). This paper compared how soil erosion and soil quality evolved on rainfed Mediterranean olive orchards. Different studies (Francia Martínez et al., 2006; García et al., 2006a, b) showed that soil management alters the soil susceptibility to erosion in

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olive groves, but most of them are based on different methods of tillage and the application of cover crops. Our results show that soil treatment with oil mill wastes contributes to a decrease in runoff generation and soil loss compared to the control plot. Oil mill waste application originated a mulch layer which contributed to increasing the roughness and the interception of raindrops, which delayed runoff generation. The delay of runoff flow enhanced the infiltration of rain water. This is in agreement with other findings reported by several authors. Puustinen et al. (2005) found that mulching contributes to decreasing runoff flow and enhancing infiltration. Lal et al. (1980) reported that saturated conductivity was significantly increased after mulch application in a tropical Alfisol. Prasad and Power (1991) observed that mulching can increase saturated conductivity because of higher activity of soil microorganisms. Francia Martínez et al. (2006) found that the combination of non tillage plus barley strip cover reduced runoff, erosion and nutrient losses. Other authors have found that runoff flow and infiltration may be affected by the mulching rate in a different way (Jin et al., 2009). García-Orenes et al. (2009) observed that time to ponding was delayed after straw mulching treatment respect to other types of management, as systemic herbicide or plowing. They found that no runoff was initiated after 55 mm h− 1 simulated rainfall after treatment under just 2.5 Mg ha− 1 year− 1. 5. Conclusions A three year experiment demonstrated that the application of oil mill wastes to rain fed olive grove soil with traditional techniques improved physical and chemical properties of the soil surface. So it is possible to use mill waste to improve soil properties. Soil water properties improve when olive leaves are applied, however, they get worse when “alperujo” is applied. The runoff and erosional response of soils depend largely on the oil mill waste applied. Both produced improvement of these properties, but the olive leaves reduce soil erosion more efficiently. Of the two products used the olive leaves are recommended because they reduce runoff and further erosion, improving the chemical soil properties and increasing the amount of water available.

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