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Article

Recycling Olive Mill Wastewater to Calcareous Soil: Effect of Preplanning Application Period on Phytotoxicity, Corn Growth, and Nutrient Uptake

by
Yousef N. Y. Hasan
1,
Ibrahim Ahmed
1,
Fahad N. Al-Barakah
1,
Jeff J. Schoenau
2 and
Khaled D. Alotaibi
1,*
1
Department of Soil Science, College of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia
2
Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(4), 1369; https://doi.org/10.3390/su17041369
Submission received: 11 December 2024 / Revised: 2 February 2025 / Accepted: 4 February 2025 / Published: 7 February 2025
Browse Figures
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Abstract

:
This study investigated the effects of applying olive mill wastewater (OMWW) at different periods prior to corn (Zea mays) sowing on germination rate (GR), growth, and soil nutrient availability in calcareous soil. The OMWW was applied at rates of 0, 20, 40, and 60 m3 ha−1 and was allowed to remain in soil for zero, one, two, three, or four months before sowing corn seeds. Immediate planting after OMWW application significantly reduced the GR, with rates of 83%, 75%, and 63% at 20, 40, and 60 m3 ha−1, respectively. Germination improved when corn was sown one month after OMWW application, with a GR of 92% at both 20 and 40 m3 ha−1 and 79% at 60 m3 ha−1. The GR increased to 96% for the 40 and 60 m3 ha−1 rates when OMWW was applied two months before planting. The adverse impact on GR disappeared when OMWW was in the soil for three months before sowing, providing a GR similar to the unamended control. Corn dry matter yield also improved when OMWW was applied two to three months before planting. The phytotoxic effects of OMWW, due to its high polyphenol content, diminished over time due to rapid degradation in calcareous soils. Soil available N and P were highest, and plant N, P, and K content increased, when OMWW was applied two months prior to planting. Soil pH decreased from 7.8 to 7.2 at 60 m3 ha−1 of OMWW at planting time. Results suggest that OMWW can enhance soil quality and corn growth if applied one to two months before planting to avoid possible negative impact on germination. This work bridges the gap between waste management and sustainable agriculture, offering practical guidelines for OMWW utilization.

1. Introduction

Olive cultivation has received great attention since ancient times, with cultivated areas expanding to over 10 million hectares globally. In 2021, global olive oil production exceeded 3 million tons [1]. This growth is driven by the nutritional benefits of olive oil, which is rich in minerals, vitamins, and antioxidants, enhancing its economic value.
The olive oil industry generates significant amounts of liquid waste known as olive mill wastewater (OMWW). The extraction process requires large quantities of water, with approximately 50 L of OMWW per 100 kg of olives [2]. OMWW is acidic, with high electrical conductivity and biological and chemical oxygen demand, and contains high levels of phenolic compounds, nutrients, organic matter, fats, and oils [3]. Its chemical composition varies based on factors such as olive variety, fruit maturity, climatic conditions, and extraction methods [4,5,6,7].
Disposing of OMWW poses a significant challenge due to environmental concerns, including soil, water, and air pollution [8]. Its complex composition and slow decomposition, due to high concentrations of phenolic compounds and organic acids, make treatment difficult and expensive [9,10]. Common disposal methods include evaporation in ponds, which can contaminate air, water, and soil [11]. Recycling OMWW by applying it to agricultural soils has been studied, but results on its impact on plants and soils are inconsistent [12,13,14,15]. The effects of OMWW on crop growth and yield depend on soil type, crop type, and OMWW composition and application rate [12,16,17,18,19,20,21,22,23,24,25,26]. Some studies reported temporary phytotoxic effects of OMWW that disappear after a few months [13,27,28].
In Saudi Arabia, particularly the Al-Jouf region, olive cultivation for oil production has expanded significantly, with olive oil output reaching over 10,000 tons in 2021 [29]. The cultivated area in northern Saudi Arabia reached 32,000 ha in 2022 [30]. The resulting OMWW is currently disposed of in open ponds for evaporation. To date, there are no reported attempts to test its potential for recycling by land application to the arid soils of Saudi Arabia. Saudi soils are typically low in organic matter and nutrients, with a sandy texture and high calcium carbonate content.
There is a lack of systematic evaluation of different pre-plant application periods of OMWW on crop growth and nutrient availability under the conditions of highly calcareous soil. Specifically, this study examines the effects of different OMWW pre-planting application periods on corn (Zea mays) germination, growth, and nutrient availability. By addressing the phytotoxicity concerns associated with OMWW application and identifying optimal timing for its use, this research provides valuable insights into its potential as a sustainable soil amendment in arid regions.
The aim of this study was to evaluate the impact of applying OMWW at various rates (0, 20, 40, and 60 m3/ha) and five pre-planting periods (zero, one, two, three, and four months) on corn germination rate, growth, and nutrient availability in calcareous soil. The findings of this research study will help determine whether OMWW can be effectively utilized to enhance soil fertility and crop productivity while mitigating the environmental challenges associated with its disposal.
Recycling OMWW directly to soil can be a viable option for its utilization and can promote environmental and agricultural sustainability. This option can also promote sustainable cultivation of olive crop and improve arid soil productivity.

2. Materials and Methods

2.1. Collection and Characterization of OMWW

A bulk sample of OMWW was collected from a three-phase olive oil mill located in Al-Jouf governorate, northern Saudi Arabia. The sample was freshly obtained immediately after the extraction of olive oil and brought to the laboratory. A subsample sample was taken and sent to an external laboratory for essential characteristic analysis using the methods described in ‘Standard Methods for the Examination of Water and Wastewater’ [31]. The analyzed parameters included pH; EC; dry matter; organic matter; total phenols; total N, P, K; and NH4-N, NO3-N, and Na.

2.2. Chemicals and Instruments Used

Several analytical grade reagents were used in this study, including 30% hydrogen peroxide, sodium hydroxide, hydrophilic acid, ascorbic acid, ammonium molybdate, ammonium acetate, potassium chloride, boric acid and Folin and Ciocateu’s phenol reagent. These reagents were purchased from different sources (Scharlab S.L., Barcelona, Spain; AppliChem GmbH, Darmstadt, Germany; Lobachemi, Mumbai, India). The instruments used in this study included inductively coupled plasma optical emission spectrometry (ICP-OES; PerkinElmer Optima 4300 DV, Waltham, MA, USA), flame photometer (Environmental and Scientific Instruments Co., Haryana, India), spectrophotometer ((9100UV-Vis, Palintest, Gateshead, UK), and Kjeldahl (KjeltecTM 9, FOSS, Hilleroed, Denmark)).

2.3. Experimental Setup

A bulk soil sample was collected from an uncultivated site at the Agricultural Experiments and Research Station of the College of Agriculture and Food Sciences, King Saud University, located 50 km south of Riyadh (24°25′ N, 46°34′ E). The soil was air-dried, thoroughly mixed, and sieved to pass through a 2 mm mesh. It was then analyzed for its basic characteristics. The soil has a pH of 8.01, EC of 0.40 dS m−1, 0.03% OM, and it is highly calcareous with CaCO3 content of 33%. Soil pH and EC were determined in a suspension of soil and distilled water at a ratio of 1:2.5. The basic soil characteristics were determined following the methods described in [32].
The experimental treatments included five pre-plant application periods of OMWW and four rates of application. The experiment was conducted in a greenhouse located at Faculty of Food and Agriculture Science, King Saud University.

Methods and Procedure

The following (Table 1) outlines the experimental procedures conducted in this study to investigate the effects of OMWW application on corn growth in calcareous soil.

2.4. Statistical Analysis

Prior to statistical analysis, data homogeneity was checked using the Shapiro–Wilk test, which revealed that data were normally distributed. Then, the effects of the pre-planting period of OMWW application, rate of OMWW, and their interaction on corn and soil variables were determined using the two-way ANOVA [36]. Treatment means were separated at p < 0.05 for comparisons using the SNK test. Data analysis was carried out using CoStat software package [37]. The data of each dependent variable was reported as the mean ± standard error. Statistical analysis outputs are included in the figures.

3. Results

3.1. Physicochemical Characterization of OMWW

The analysis of OMWW showed that this liquid material is characterized by low pH, high EC, and high content of COD, BOD5, total solids, TSS, TDS, and K, in addition to a high concentration of phenols (Table 2). It contains a significant amount of total N and total P, with about 4% of the total N comprised of immediately plant-available ammonium.

3.2. Effects on Corn Seed Germination Rate

The GR of corn seeds recorded seven days after sowing was significantly affected by the pre-planting application period of OMWW (Figure 1). The effects were pronounced in the first two periods (zero and one month); however, the magnitude of OMWW impact on the GR was largely dependent on the application rate (Figure 1). The negative impact on the GR and the rate effect decreased with the pre-planting time period following OMWW application. The immediate seeding after OMWW application resulted in a significant reduction in the GR, and this negative impact increased with increasing the rate of application in which the GR was 83, 75, and 63% at the application rates 20, 40, and 60 m3 ha−1, respectively. The GR improved when corn was seeded one month after OMWW application, where the GR was 92, 92, and 79% at the rate of 20, 40, and 60 m3 ha−1, respectively. The GR in 40 and 60 m3 ha−1 treatments increased to 96% when OMWW application preceded corn seeding by two months. The adverse impact on the GR disappeared when OMWW was applied three months before sowing, where all the rates of OMWW provided a GR that was similar to the control (Figure 1).

3.3. Corn Plant Response

The OMWW pre-planting application time period, rate of application, and their interaction had a significant effect on the dry biomass yield of corn (Figure 2). The yield of corn sown immediately after OMWW application was slightly reduced compared to the control. After remaining in soil for one month, the OMWW showed no negative impact and the yield was similar to the control. A positive impact of OMWW on corn yield started to appear when the interval between application of OMWW and seeding was two months or longer, as shown in Figure 2, in which the corn yield was higher than the untreated control (Figure 2). At the 3-month pre-planting application period, the OMWW applied at 40 and 60 m3 ha−1 provided the highest yield, 13.6 g, compared to the control, representing an approximately 42% increase over the control (Figure 2). The OMWW continued to show a significant impact on dry biomass yield after four months of its application.
Plant height was also significantly affected by OMWW pre-planting application time period, rate of application, and their interaction (Figure 3). This effect followed a similar pattern to that observed with biomass yield, especially at the pre-planting application time periods of two, three, and four months, but height was not as greatly impacted as dry matter yield. The greatest effect on plant height was found at the pre-planting application time period of three months, with the highest corn plants at the rate of 40 and 60 m3 ha−1 (average of 74 cm).
From the effects on yield observed averaged across the rate of application (Figure 4), it appears that a net negative effect on the yield of OMWW was present when applied one month in advance of seeding and persisted long enough to curtail responses to the nutrients contained in the OMWW for three months before planting, at which time the highest corn yield (12.19 g) was obtained compared to the other time periods (Figure 4a). A decrease in positive response after four months compared to three may reflect some loss of nutrients over the longest pre-plant interval time. The clear and significant effects of OMWW residence time started after two months (10.77 g), reaching the maximum after three months (12.19 g) and decreasing after four months (10.78 g). A similar pattern was also observed with plant height response, where the highest value was observed at the pre-planting application time period of three months (68.15 cm) followed by two months (64.10 cm) (Figure 4b).

3.4. Effects on Plant Nutrient Content

The OMWW pre-planting application time period, rate of application, and their interaction had a significant effect on plant N content (Figure 5a). The N content was lower in all the rates of OMWW application when corn was sown immediately after OMWW application (zero residence time) compared to the untreated control (Figure 5a). The N content in plant began to increase with OMWW application from two months until reaching the pre-planting period of three months where it was the highest at the rate of 60 m3 ha−1 (1.8%), followed by 40 m3 ha−1 (1.5%). A decrease in %N at the low rate of application in the one-month pre-plant interval may be explained by growth dilution, while the general trend for increasing % N in plants with increasing rate in the later months reflects the effect of the OMWW on enhancing N availability. The plant P content was also affected by the OMWW pre-planting application time period and rate of application (Figure 5b). The effect of OMWW on P content started after the pre-planting time of one month and continued until the end of the study, and it was evident at the rates of 40 and 60 m3 ha−1, with a P content of 371 and 378 mg kg−1, respectively. The plant K content was significantly affected by OMWW pre-planting time period, rate of application, and their interaction (Figure 5c). It ranged from 1.5 to 3.7%, with the greatest content being observed at the pre-plant interval periods of one and two months (Figure 5c). At those pre-planting time periods, the three rates of OMWW application resulted in significantly higher concentrations of plant K, ranging from 2.7 to 3.7%, compared to the control at 1.7% (Figure 5b).
The comparison of the pre-planting application time period averaged across the rate of application clearly showed that plant nutrient content tended to be highest when the OMWW was added to soil two or three months in advance of seeding (Figure 6a–c), reflecting a large effect of the addition on enhancing nutrient availability, uptake, and growth at those times The three month period provided the highest plant N content (1.4%) (Figure 6a), whereas the highest contents of plant P (362 mg kg−1) and K (2.9%) were found in OMWW treatments applied to soil two months ahead of planting the corn (Figure 6b,c).

3.5. Effects on Residual Soil Available Nutrients

Soil content of available N measured after 6 weeks of corn growth decreased with increasing the OMWW rate when OMWW was applied and immediately followed by planting, with all the rates being significantly lower than the control treatment (Figure 7a). This may reflect some initial immobilization of available N induced by the OMWW. None of the treatments provided a significant enhancement in residual available N at the time period of one month, but the rate of 40 and 60 m3 ha−1 showed significantly higher available N left in the soil at the pre-planting application time periods of two, three, and four months, ranging from 60 to 64 mg kg-1 (Figure 7a), suggesting some mineralization enhancement from the OMWW. The same was also observed in the case of the soil content of available P, where the pre-planting application time periods of two, three, and four months significantly increased P content, especially at the rate of 40 and 60 m3 ha−1 (Figure 7b). The residual available K in soil after harvest decreased with increased OMWW residence time in soil before planting and was the highest in higher application rates at the time periods of zero, one, and two months (Figure 7c). This could be due to some K fixation in these soils.
The effect of pre-planting time period averaged across the rate of application on residual soil nutrient content after harvest varied according to the nutrient (Figure 8a–c). The available N was the highest at the time periods of two and three months (average of 62 mg kg−1) (Figure 8a). It was 51, 59, 62, 62 and 60 mg kg−1 in the pre-planting application time periods of 0, 1, 2, 3, and 4 months, respectively. The available P content in soil was higher in time periods of 2, 3, and 4 months prior to seeding (average of 52.4 mg kg−1), all of which are significantly higher than that observed in the immediate planting after application time period (33.4 mg kg−1) (Figure 8b). In contrast, available soil K was the highest at the time period of one month (282 mg kg−1) and decreased with increasing the residence time period, with the values of 227, 198, and 186 mg kg−1 at 2, 3, and 4 months, respectively (Figure 8c).

3.6. Effects on Soil pH and EC

The lowest soil pH was observed when OMWW was applied immediately before planting and when OMWW was applied one month or two months before planting (Figure 9a); pH was lower compared to three month interval, with the greatest decrease (pH 7.2) at the high rate of 60 m3 ha−1 compared to the control (pH 7.9) in the first pre-planting application period. The acidifying effect of the OMWW amendment appears to decrease as the time period in the soil is extended. Averaged across the application rates, soil pH was significantly affected by OMWW pre-planting application time period (Figure 9a). Soil EC (salinity) was generally low and was slightly decreased with increasing the residence time period of the OMWW in soil, ranging from 0.36 to 0.46 dS m−1 (Figure 9b).

4. Discussion

This study reveals the significant impact of OMWW application timing and rate on crop performance, nutrient availability, and soil properties, emphasizing the potential for OMWW as a soil amendment in arid, nutrient-poor soils.
Previous studies evaluating the direct application of OMWW to soil have shown contrasting effects, with reports of phytotoxic effects, positive effects on plant growth and yield, or no significant effect at all [16,18,19,20]. These variable outcomes are attributed to several factors, such as soil type, composition of OMWW, rate of application, and plant species [12,17,21,23,24,26]. The current study demonstrates that OMWW’s effects on corn germination rate (GR) and growth are highly dependent on the timing of application before planting. A significant reduction in the GR was observed when corn seeds were sown immediately after OMWW application, particularly at the highest rate (60 m3 ha−1), where the GR dropped to 63%. This initial reduction indicates phytotoxic effects, likely caused by the high concentration of polyphenols in OMWW, consistent with earlier studies [13,38]. These effects were mitigated when a pre-planting interval of two months was allowed, with the GR improving to 96% at higher OMWW rates (40 and 60 m3 ha−1). By the third month, all OMWW treatments produced GRs comparable to the control. This recovery aligns with findings that polyphenols degrade within 2 to 3 months in calcareous soils due to microbial activity and the high buffering capacity of these soils [27,39,40]. While other studies suggest recovery from phytotoxic effects can take 40 to 60 days [13,28,41], some report up to 180 days [27], highlighting the variability influenced by soil conditions.
The recovery and subsequent enhancement in plant biomass yield and nutrient uptake in this study underline OMWW’s potential as a nutrient-rich amendment. Corn biomass yield increased significantly after a two-month pre-planting interval, with the highest yield observed after three months, representing a 42% increase over the control. Enhanced plant concentrations of N, P, and K further support the role of OMWW in promoting nutrient availability and uptake. These results are consistent with studies showing OMWW’s positive impact on soil fertility through organic matter mineralization and microbial stimulation [24,42,43].
The observed increase in soil available N, P, and K with OMWW application, particularly at 40 and 60 m3 ha−1 rates, aligns with findings from similar studies [24,26,44,45]. These findings indicate a high fertilizing potential of OMWW, especially in arid soils that are poor in their content of nutrients and organic matter. The decrease in soil residual available K with increasing residence time of OMWW is interesting and may reflect some fixation of K in unavailable forms in minerals.
Additionally, the temporary acidifying effect of OMWW on soil pH, most pronounced at the highest application rate, aligns with prior observations of organic acids lowering pH before being neutralized by calcareous soils’ buffering capacity [22,46,47,48]. The short-term decrease in soil pH observed in this study (up to two months) is consistent with the persistence of these effects reported in earlier research (42 to 90 days) [46,47,48]. Finally, soil electrical conductivity (EC) exhibited minor fluctuations. A slight increase was observed immediately after OMWW application at higher rates (60 m3 ha−1), likely due to the soluble salts in OMWW. However, this effect diminished after two months, possibly due to nutrient uptake by plants and leaching of excess salts [43]. Overall, these findings suggest that OMWW, when applied judiciously, can serve as a valuable and economically viable soil amendment in arid and nutrient-poor soils. By effectively utilizing a waste product that would otherwise pose an environmental challenge, OMWW application can offer a cost-effective solution for improving soil fertility and crop productivity. However, careful management of application timing and rates is crucial to mitigate initial phytotoxic effects and maximize nutrient availability. Further research into long-term impacts, repeated applications, and the development of cost-effective treatment methods for OMWW to minimize phytotoxicity is warranted to fully assess its potential for sustainable and economically sound soil management

5. Conclusions

The results of the current study suggest a high potential of using OMWW as a sustainable soil amendment under arid soil conditions. Applying OMWW to calcareous soil negatively impacts germination and yield if seeding occurs immediately but shows recovery within two to three months after application. Allowing OMWW to remain in calcareous soil for a few months before planting is necessary to eliminate its phytotoxic effects and to optimize its benefits to for plant and soil. The OMWW increased plant content of N, P, and K when allowing two to three months to elapse between application and seeding, and a similar trend was observed with post-harvest residual soil content of available N, P, and K. A temporary decrease in soil pH was observed up to the period of two months following application. The soil used in this study is highly calcareous, and its high content of calcium carbonate increases its buffering capacity that counters the persistence of soil pH reduction. Further long-term field studies are recommended to confirm these findings.

Author Contributions

Methodology, Y.N.Y.H.; Investigation, Y.N.Y.H., I.A., F.N.A.-B. and K.D.A.; Writing—original draft, Y.N.Y.H.; Writing—review & editing, I.A., F.N.A.-B., J.J.S. and K.D.A.; Supervision, F.N.A.-B. and K.D.A.; Funding acquisition, K.D.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Researchers Supporting Project number (RSPD2025R633), King Saud University, Riyadh, Saudi Arabia.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

The Researchers Supporting Project at King Saud University, Saudi Arabia, is greatly acknowledged for funding this research through the project number (RSPD2025R633).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Effects of pre-planting application period of OMWW on corn seed germination rate (GR). The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letters among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
Figure 1. Effects of pre-planting application period of OMWW on corn seed germination rate (GR). The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letters among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
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Figure 2. Effects of pre-planting application period of OMWW on corn dry matter yield. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
Figure 2. Effects of pre-planting application period of OMWW on corn dry matter yield. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
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Figure 3. Effects of pre-planting application period of OMWW on corn plant height. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
Figure 3. Effects of pre-planting application period of OMWW on corn plant height. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
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Figure 4. Effects of pre-planting application period of OMWW, averaged across the four rates of application on corn dry matter yield (a) and plant height (b). Bars sharing the same letter among the residence time of OMWW in soil are not significantly different (p > 0.05).
Figure 4. Effects of pre-planting application period of OMWW, averaged across the four rates of application on corn dry matter yield (a) and plant height (b). Bars sharing the same letter among the residence time of OMWW in soil are not significantly different (p > 0.05).
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Figure 5. Effects of pre-planting application period of OMWW on plant N (a), P (b), and K (c) content. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
Figure 5. Effects of pre-planting application period of OMWW on plant N (a), P (b), and K (c) content. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
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Figure 6. Effects of pre-planting application period of OMWW, averaged across the four rates of application on plant N (a), P (b), and K (c) content. Bars sharing the same letter among the residence time of OMWW in soil are not significantly different (p > 0.05).
Figure 6. Effects of pre-planting application period of OMWW, averaged across the four rates of application on plant N (a), P (b), and K (c) content. Bars sharing the same letter among the residence time of OMWW in soil are not significantly different (p > 0.05).
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Figure 7. Soil available nutrients: N (a), P (b), and K (c) after plant removal, as affected by residence time of (OMWW) in soil. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
Figure 7. Soil available nutrients: N (a), P (b), and K (c) after plant removal, as affected by residence time of (OMWW) in soil. The OMWW was applied at four rates: 0 (control), 20, 40, and 60 m3 ha−1. Bars sharing the same letter among the rates of OMWW at a given residence time are not significantly different (p > 0.05). Error bars represent the standard error of the treatment mean (n = 4).
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Figure 8. Soil available nutrients: N (a), P (b), and K (c), averaged across the four rates of application after plant harvest as affected by residence time of OMWW in soil before planting. Bars sharing the same letter among the residence times of OMWW in soil are not significantly different (p > 0.05).
Figure 8. Soil available nutrients: N (a), P (b), and K (c), averaged across the four rates of application after plant harvest as affected by residence time of OMWW in soil before planting. Bars sharing the same letter among the residence times of OMWW in soil are not significantly different (p > 0.05).
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Figure 9. Soil pH (a) and soil EC (b), averaged across the four rates of application after plant harvest as affected by residence time of OMWW in soil before planting. Bars sharing the same letter among the residence time of OMWW in soil are not significantly different (p > 0.05).
Figure 9. Soil pH (a) and soil EC (b), averaged across the four rates of application after plant harvest as affected by residence time of OMWW in soil before planting. Bars sharing the same letter among the residence time of OMWW in soil are not significantly different (p > 0.05).
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Table 1. Experimental procedures used in this study.
Table 1. Experimental procedures used in this study.
Procedures Description
Soil PreparationBulk soil samples were collected, air-dried, mixed, sieved to pass through 2 mm mesh and analyzed for basic characteristics (pH, EC, OM, CaCO3 content).
Pot Preparation2.5 kg of soil was weighed into each pot, and OMWW was applied at 0 (control), 20, 40, and 60 m3 ha−1 to soil surface at the same time. The initial soil moisture was adjusted using tap water.
Seed SowingSix corn seeds per pot were sown and thinned to three plants per pot after 10 days.
Soil Moisture MaintenanceSoil moisture was maintained at 80% of field capacity during the entire study period.
FertilizationNitrogen and phosphorus fertilizers were applied to all pots, including the control, at a rate equivalent to 300 kg N ha−1 and 200 kg P ha−1
Corn GrowthCorn (Zea mays) was grown for six weeks, and then plant height was measured, aboveground biomass was harvested, and the biomass was dried at 70 °C for dry matter yield determination. Nutrient content such as N, P, and K in plant samples were determined using methods in [33]. The Kjeldahl method was used to determine N [34], the P was measured calorimetrically [35], and K was analyzed using a flame photometer.
Soil AnalysisComposite soil samples were collected from each pot after harvesting, and then soils were air-dried, sieved, and analyzed for pH, FC, and available N, P, and K following the laboratory procedures described in [32].
Table 2. Physicochemical characteristics of the OMWW used in the current study.
Table 2. Physicochemical characteristics of the OMWW used in the current study.
Characteristics Value
pH4.47 ± 0.06
EC dS/m14.2 ± 0.10
COD g/L108 ± 2.62
BOD5 g/L414 ± 1.54
Phenols mg/L5370 ± 3.21
FOG mg/L799 ± 0.43
TSS mg/L2800 ± 1.41
TS%6.34 ± 0.05
TVS%64.4 ± 0.11
TDS mg/L44600 ± 5.31
Total N mg/L845 ± 0.05
NH4-N mg/L32.5 ± 0.04
Nitrate-N mg/L<1.13
Total P mg/L515 ± 0.07
K mg/L3690 ± 2.56
Na mg/L69.4 ± 0.06
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MDPI and ACS Style

Hasan, Y.N.Y.; Ahmed, I.; Al-Barakah, F.N.; Schoenau, J.J.; Alotaibi, K.D. Recycling Olive Mill Wastewater to Calcareous Soil: Effect of Preplanning Application Period on Phytotoxicity, Corn Growth, and Nutrient Uptake. Sustainability 2025, 17, 1369. https://doi.org/10.3390/su17041369

AMA Style

Hasan YNY, Ahmed I, Al-Barakah FN, Schoenau JJ, Alotaibi KD. Recycling Olive Mill Wastewater to Calcareous Soil: Effect of Preplanning Application Period on Phytotoxicity, Corn Growth, and Nutrient Uptake. Sustainability. 2025; 17(4):1369. https://doi.org/10.3390/su17041369

Chicago/Turabian Style

Hasan, Yousef N. Y., Ibrahim Ahmed, Fahad N. Al-Barakah, Jeff J. Schoenau, and Khaled D. Alotaibi. 2025. "Recycling Olive Mill Wastewater to Calcareous Soil: Effect of Preplanning Application Period on Phytotoxicity, Corn Growth, and Nutrient Uptake" Sustainability 17, no. 4: 1369. https://doi.org/10.3390/su17041369

APA Style

Hasan, Y. N. Y., Ahmed, I., Al-Barakah, F. N., Schoenau, J. J., & Alotaibi, K. D. (2025). Recycling Olive Mill Wastewater to Calcareous Soil: Effect of Preplanning Application Period on Phytotoxicity, Corn Growth, and Nutrient Uptake. Sustainability, 17(4), 1369. https://doi.org/10.3390/su17041369

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