Introduction

Salinity stress is one of the most critical environmental constraints to global agriculture, increasingly threatening crop yields in arid and semi-arid regions. This challenge has significant implications for food security, particularly under climate change scenarios. According to the Food and Agriculture Organization (FAO), nearly 50% of the world’s arable land could be affected by salinization by 2050, posing a serious threat to global food supply1,2,3. The problem is especially acute in semi-arid Mediterranean areas, such as Morocco, where climatic conditions and irrigation practices exacerbate soil degradation through salt accumulation4. With the progressive decline in freshwater availability, many agricultural regions rely on saline water irrigation to sustain crop production5,6. While this strategy alleviates water scarcity, it also generates agronomic challenges: salt accumulation, particularly sodium (Na⁺) and chloride (Cl⁻), in the root zone disrupts osmotic balance, reduces nutrient uptake, and negatively affects crop performance7,8,9,10. Repeated use of saline water, particularly without proper management, accelerates salinization, alters soil pH, increases electrical conductivity (EC), and deteriorates soil physical properties such as porosity and water retention capacity11,12,13. These changes result in measurable soil and crop stress, ultimately reducing soil fertility and crop yields, and can render lands unproductive14,15,16.

Soil quality degradation is a major concern in Mediterranean agricultural systems, particularly in semi-arid regions where climatic conditions and irrigation practices intensify soil constraints17. Maintaining and enhancing soil fertility through eco-friendly management strategies is essential to sustain soil health and crop production, especially in cultivated silty-clay soils, which often suffer from low permeability, poor aeration, and nutrient imbalances that can be aggravated under saline irrigation18. These soils are characterized by high water retention, which benefits crop water absorption, but their low permeability may limit water infiltration and create conditions that restrict root respiration and nutrient uptake under excess irrigation19,20. Studies have shown that organic amendments, particularly green waste compost derived from plant residues, can improve soil structure, enhance water retention, increase nutrient availability, stimulate microbial activity, and mitigate the adverse effects of salinity21,22,23,24. Integrating these amendments supports root development, maintains ionic balance in the rhizosphere, and enhances plant tolerance to saline conditions, providing a sustainable approach for long-term crop production25.

Durum wheat (Triticum turgidum L. subsp. durum Desf.) is a key cereal crop widely cultivated across the Mediterranean basin, including Southern Europe, North Africa, and West Asia, and represents a strategic component of food security in Morocco26,27,28. Its cultivation is increasingly challenged by salinity stress, exacerbated by the reliance on marginal or saline water sources. Durum wheat is valued not only for its yield potential but also for its nutritional quality, contributing to staple foods such as flour, pasta, couscous, and semolina29,30. Salinity adversely affects agronomic, morpho-physiological, and biochemical traits of durum wheat, though the magnitude of these effects varies with genotype, duration of stress, and growth stage sensitivity31. Morphological symptoms include leaf chlorosis, reduced plant height, shortened peduncle length, diminished leaf area, and impaired root elongation, while physiological and biochemical disruptions compromise water uptake, photosynthetic efficiency, and osmolyte accumulation, ultimately reducing grain yield and biomass32,33. Understanding these specific plant responses is essential for developing effective soil and crop management strategies.

Sustainable options that reduce reliance on chemical inputs are critical to maintaining long-term agricultural productivity. Organic amendments, particularly green waste compost derived from plant residues, are recognized as effective strategies to improve soil fertility, enhance nutrient availability, stimulate microbial activity, and improve soil structure and water retention, thereby mitigating the negative effects of salinity stress34,35,36,37. Green waste compost can also support root development and maintain ionic balance in the rhizosphere, thereby addressing the physiological and agronomic challenges caused by salinity38. Recent studies further demonstrate that compost application can reduce sodium accumulation, enhance nutrient uptake, and improve physiological performance, ultimately sustaining growth and yield under saline irrigation39,40.

This study is motivated by the increasing salinization of irrigation water and the resulting decline in freshwater quality, which threaten crop productivity in arid and semi-arid regions. It specifically examines whether this type of compost can improve soil conditions and enhance the performance of durum wheat (cv. Faraj) under saline irrigation. This cultivar, noted for its drought adaptability, has a reported salinity tolerance threshold of 8 dS m⁻141,42, making it suitable for evaluating soil amendment strategies.

To enhance the robustness of the assessment, this study presents an integrated framework that combines graded doses of green waste compost with varying levels of saline irrigation. While the individual effects of compost on soil fertility and durum wheat performance under salinity are well documented, little is known about their interactive effects across different salinity levels. Therefore, this study aims to investigate whether compost application can improve soil physicochemical properties, enhance plant physiological responses, and sustain vegetative growth and yield of durum wheat (cv. Faraj) under saline conditions. We hypothesize that, compared with saline irrigation without amendment, the application of this organic amendment will improve soil fertility and nutrient availability, support plant physiological performance, and ultimately promote biomass accumulation and grain yield formation.

Materials and methods

Characterization of the experimental site and field sampling

The study was carried out under controlled greenhouse conditions at the Agronomic Research Station of INRA, affiliated with the Research Unit for Environment and Natural Resources Conservation (URECRN). This station is situated in the coastal zone of Rabat, Morocco (34°03′50″ N, 6°50′40″ W), at an altitude of around 70 meters. The local climate is Mediterranean with significant maritime influence, typified by warm, arid summers and mild, humid winters. A homogeneous clay soil was used for all experimental treatments. This soil was collected from the Témara region, approximately 30 km south of Rabat. This location was selected due to the high content of fine particles in the soil, which makes it particularly vulnerable to salinization processes, an important consideration for the objectives of this study. Soil sampling was performed using a manual auger to a depth of 40 cm, targeting the biologically active upper layer of the soil profile, which is most sensitive to surface degradation and salt accumulation. In addition, a composite soil sample was collected from the 0–20 cm depth, representing the most reactive zone in terms of physical, chemical, and biological properties (Fig. 1).

Fig. 1
figure 1

Geographical position of the experimental site and soil sampling point.

Full size image

Plant material and experimental design

Durum wheat seeds (Triticum turgidum L. var. durum, cv. “Faraj”) were used in this study. The seeds were provided by INRA and obtained from INRA’s Merchouch Experimental Station in Morocco. This variety was selected for its agronomic performance and tolerance to key abiotic and biotic stresses, as summarized in Table 1. Uniform plastic pots (10 kg capacity; approximately 30 cm height × 25 cm diameter) were filled with 6 kg of silty clay soil collected from the Témara region, chosen for its relevance to salinity-prone environments. A gravel drainage layer was installed at the base of each pot to prevent waterlogging and promote root zone aeration. Each pot covered a surface area of 0.04 m2 and was sown with 10 seeds. The experiment followed a completely randomized design (CRD), with a factorial combination of four salinity treatments: freshwater (I0: 0.2 dS m⁻1), 8 dS m⁻1 (I1), 12 dS m⁻1 (I2), and 16 dS m⁻1 (I3), and four compost amendment rates: 0 t ha⁻1 (C0, no compost), 15 t ha⁻1 (C1), 20 t ha⁻1 (C2), and 30 t ha⁻1 (C3) applied at the 0–10 cm soil depth. A total of 150 kg ha⁻1 of nitrogen was applied using ammonium sulfate (21% N) and ammonium nitrate (33% N). Each treatment combination was replicated three times, totaling 48 experimental units. Irrigation was carefully monitored, with each pot receiving 0.5 L of water per event, applied three times per week, to maintain consistent soil moisture, prevent salt leaching, and ensure optimal growth. Environmental conditions were maintained at 23 ± 2.5 °C and 61 ± 8% relative humidity.

Table 1 Principal agronomic attributes of the durum wheat variety Faraj.
Full size table

Soil physicochemical, granulometric, and compost characteristics

Soil characterization was performed prior to the experiment to establish baseline physicochemical properties. Soil S1 had a silty-clay texture, with a high clay content and moderate proportions of sand and silt. The pH was neutral to slightly alkaline, and electrical conductivity (EC) indicated low salinity. Key nutrient levels were within the typical range for this soil type. Detailed physicochemical properties and particle size distribution of the soil used in this study are summarized in Table 2.

Table 2 Soil granulometry and chemical properties.
Full size table

For the irrigation of the plants, we adhered to protocols based on Maas’s research43. Freshwater with low salinity (EC = 0.2 dS m⁻1) was used as the control treatment. In this irrigation water, Na⁺ and Cl⁻ were the dominant ions, followed by Mg2⁺, K⁺, Ca2⁺, CO₃2⁻, HCO₃⁻, and NO₃⁻. Saline solutions were prepared by dissolving commercial sodium chloride (NaCl) to achieve the desired EC levels (8, 12, and 16 dS m⁻1). The concentrations of major ions and other chemical properties of the irrigation water are summarized in Table 3.

Table 3 Chemical properties of the irrigation water.
Full size table

The compost used in this study was a commercially available green waste compost derived from plant residues. It was prepared through aerobic decomposition with controlled moisture (approximately 50–60 %), followed by a maturation phase of approximately 12–16 weeks until stable and humified. This duration is sufficient to ensure the compost is fully stabilized, humified, and suitable for plant application. Prior to treatment application, representative samples were collected and analyzed to determine the compost’s key physicochemical characteristics. The pH was measured in a 1:2 (w/v) aqueous suspension using a digital pH meter (Mettler Toledo Seven Easy-728 model). Electrical conductivity (EC) was measured on the same extract using a conductivity meter (Orion 162 model). Organic matter (OM) content was determined using the Walkley–Black method as described by44, while organic carbon (OC) was calculated based on a modified wet combustion method according to45. Total nitrogen (N) content was analyzed using the Kjeldahl method, and the carbon-to-nitrogen (C/N) ratio was derived from the OC and N contents to assess compost stability. Available phosphorus (P) and potassium (K) were estimated using the Egnér–Riehm method, following the procedure reported by46. The results of the physicochemical characterization of the compost are summarized in Table 4.

Table 4 Physicochemical characteristics of the vegetal compost used in the experiment.
Full size table

The moisture content (MC) of the compost was measured by saturating a known weight of oven-dried compost with distilled water, allowing it to drain under gravity, and weighing the remaining moist sample. MC was calculated using the following Eq. 141:

$$\rm{MC} = \frac{\rm{Wet weight}-\rm{Dry weigh }}{\rm{Dry weight}}\times100$$
(1)

Before analysis, soil samples were air-dried under ambient conditions, then homogenized and passed through a 2 mm sieve to eliminate coarse debris and large aggregates. The resulting <2 mm fraction was used for the assessment of pH, electrical conductivity (EC), cation exchange capacity (CEC), and exchangeable base cations. A finer subsample (<0.2 mm) was subsequently used for the determination of organic matter content, total nitrogen (N), and available phosphorus (P). Soil texture was analyzed by sedimentation following Stokes’ law, enabling the quantification of sand, silt, and clay fractions47. Soil pH was determined potentiometrically in a 1:2.5 (w/v) soil-to-distilled water suspension using a calibrated pH meter (Seven Easy-728, Mettler Toledo, USA)48. Electrical conductivity (EC) was assessed from the extract of a saturated soil paste prepared with 50 g of air-dried soil. After centrifugation at 2500 rpm to separate the supernatant, EC was measured using a conductivity meter (Orion 162, Thermo Scientific, USA)49.

Organic matter content was estimated using the Walkley–Black dichromate oxidation method. Total nitrogen content was determined according to the Kjeldahl method, involving digestion with concentrated sulfuric acid, followed by steam distillation and titration with standardized 0.1 N HCl50. Available phosphorus was extracted using 0.5 M sodium bicarbonate solution (pH 8.5) and quantified by spectrophotometry at 882 nm51. Exchangeable sodium (Na) and potassium (K) were extracted with 1 M ammonium acetate solution at pH 7 and analyzed by flame photometry using a Jenway PFP7 photometer48. Exchangeable calcium (Ca) and magnesium (Mg) were measured by atomic absorption spectrophotometry (NovAA 800 D, Analytik Jena, Germany) following complexometric titration with ethylenediaminetetraacetic acid (EDTA)49. Chloride (Cl⁻) concentration was determined colorimetrically by reacting chloride ions with silver nitrate (AgNO₃) and measuring the intensity of the precipitate formed.

Measurement of plant growth and chlorophyll fluorescence

Plant height was measured by positioning a graduated ruler vertically alongside each plant to ensure accurate readings. Measurements were taken from the base of the stem to the tip of the tallest leaf on three randomly selected plants per experimental unit, and the average value was calculated. The total number of leaves on these plants was manually counted at each developmental stage to assess leaf number. Chlorophyll fluorescence was assessed using the OS-30p+ fluorometer (Opti-Sciences, Inc., Hudson, NH, USA) to evaluate plant physiological responses under saline stress. Prior to measurement, leaves were dark-adapted for 30 minutes to stabilize fluorescence signals and obtain baseline readings, allowing re-oxidation of the electron transport chain and relaxation of transient non-photochemical quenching. Fluorescence parameters were recorded on randomly selected leaves according to the manufacturer’s guidelines to ensure reliability and reproducibility. Key parameters indicative of photosystem II (PSII) efficiency and salinity-induced stress effects on photosynthesis were derived from light pulse analysis. Measurement duration ranged from 10 to 20 seconds depending on leaf adaptation and light intensity. Recorded parameters included minimum fluorescence (Fo), maximum fluorescence (Fm), instantaneous fluorescence (Ft), variable fluorescence (Fv = Fm − Fo), and maximum quantum efficiency of PSII (Fv/Fm = (Fm − Fo)/Fm), a widely accepted indicator of plant vitality under stress conditions52,53.

Measurement of yield components and harvest procedures

At the end of the experiment, all treatments were carefully monitored to evaluate the yield components of the Faraj variety. After a total growth period of 154 days, ears were manually harvested at physiological maturity to minimize grain loss and ensure sample uniformity. Prior to grain extraction, detailed morphological measurements were conducted on each ear. Awn length was measured using a precision caliper from base to tip, while ear length was recorded from the base to the apex of the longest spike. The number of spikelets per ear was counted meticulously to accurately estimate floral density and ear development. Following these assessments, grains were extracted, cleaned to remove impurities, and dried at 105 °C for 45 minutes to standardize moisture content. Each ear was individually weighed, and a representative sample of 200 grains was taken for precise grain weight determination. Total grain count per ear was established using a digital grain counter to ensure accuracy and efficiency. Planting density was defined as the ratio of the total number of plants to the total surface area (Eq. 2):

$$\text{Planting density}=\frac{\text{Total number of plants}}{\text{Total surface area}}$$
(2)

Planting density was fixed at 250 plants m⁻2, corresponding to an experimental unit surface area of 0.04 m2 per container.

Statistical analysis

Data were subjected to two-way analysis of variance (ANOVA) to assess the effects of salinity and compost dose, with significance determined at p ≤ 0.05. When significant differences were detected, Duncan’s multiple range test was applied for post-hoc pairwise comparisons. To evaluate the combined influence of salinity (X₁) and compost doses (X₂) on plant yield parameters and soil physicochemical properties, multiple linear regression analyses were performed using the following model54:

$${\text{Y}}= \alpha +{\beta }_{1}{X}_{1}+{\beta }_{2}{X}_{2}+\epsilon$$
(3)

Where Y represents the dependent variable (yield or soil property), α is the intercept, β₁ and β₂ are the regression coefficients for salinity and compost dose, respectively, and ε is the residual error.

Furthermore, a two-dimensional Principal Component Analysis (PCA) was applied to eight selected variables (EC, Na, K, Ca, Pht, ChlF, GY, and NL) to guide organic management practices under salinity stress. This PCA captures the main physiological and agronomic variation while avoiding redundancy from strongly correlated variables. It revealed a clear separation of treatments according to compost doses and salinity levels, efficiently synthesizing the complexity of interactions and highlighting the treatment combinations most favorable for production. All statistical computations, including PCA, were performed using SPSS version 25, and graphs were generated using Origin 2025b (version 10.25, OriginLab Corporation, Northampton, MA, USA). Figure 2 illustrates the experimental design, including soil sampling for physicochemical analysis and the assessment of durum wheat growth, physiological traits, and yield components under varying compost and saline irrigation regimes.

Fig. 2
figure 2

Systems-based experimental approach to assess compost–soil interactions and the effects of saline irrigation on durum wheat growth, physiology, and yield components at different growth stages: PL (Planting), GR (Germination), SP (Seedling), TR (Tillering), JT (Jointing/Booting), HG (Heading), FG (Grain Filling), and MT (Maturity). (A) Schematic illustration of the experimental process; (B) Greenhouse setup arranged according to a completely randomized design (CRD) with varying salinity levels.

Full size image

Results

Impact of compost dose on soil chemical properties under saline irrigation

The chemical properties of the soil were significantly influenced by both salinity levels and compost application (Table 5). Duncan’s multiple range test (α = 0.05) revealed significant differences among compost rates within each salinity treatment. The highest compost rate (C3) consistently improved soil chemical quality across all salinity levels. Soil pH increased with rising salinity, reaching 8.55 at 16 dS m⁻1 under the control (C0), while compost application mitigated this effect, resulting in a pH of 7.40 under C3 at the same salinity, representing a reduction of 13.45%. Electrical conductivity (EC) naturally increased with salinity; however, compost application slightly moderated EC values at the intermediate salinity level (8 dS m⁻1), whereas at higher salinity levels (12 and 16 dS m⁻1) EC remained high. Organic matter (OM) content progressively increased with compost application, reaching 1.68% at 0.2 dS m⁻1 under C3, representing an increase of 26.32% relative to the control. Under high salinity (12 dS m⁻1), total nitrogen (N) increased by 18.57% under C3 compared to C0, while phosphorus (P) and potassium (K) increased by 19.05% and 24.39%, respectively. Calcium (Ca) and magnesium (Mg) showed increases of 20.00% and 20.85%, respectively, under the same conditions. Sodium (Na), which accumulated under saline irrigation, was significantly reduced by compost application. At 12 dS m⁻1, Na decreased from 4.90 mg kg⁻1 (C0) to 3.74 mg kg⁻1 (C3), corresponding to a reduction of 23.67%, indicating the effectiveness of compost in limiting Na accumulation in the soil.

Table 5 Duncan’s multiple range test (DMRT) for soil chemical parameters under varying salinity levels (0.2, 8, 12, and 16 dS m⁻1) and compost rates (C0 = no compost, C1 = 15 t ha⁻1, C2 = 20 t ha⁻1, C3 = 30 t ha⁻1).
Full size table

The ANOVA results revealed significant effects of salinity (Sa) and compost (C) on the chemical properties of the soil, with notable interactions between these two factors (Table 6). Salinity significantly influenced electrical conductivity (EC), nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg) (p ≤ 0.05), while compost had a highly significant effect on all chemical parameters (p ≤ 0.01), including pH. The interaction between salinity and compost was significant for all chemical properties (p ≤ 0.05), indicating that the effect of compost depended on the salinity level. Specifically, soil pH was significantly affected by compost (p < 0.05) and its interaction with salinity, but not by salinity alone. EC responded strongly to both salinity (p < 0.05) and compost (p < 0.01), with a significant interaction between the two factors. Organic matter (OM) and nitrogen (N) contents were significantly influenced by both factors, with compost exerting a more pronounced effect. Similarly, phosphorus (P), potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg) showed significant responses to salinity and compost, and all exhibited significant interactions between salinity and compost.

Table 6 Analysis of variance (ANOVA) of the effects of salinity (0.2, 8, 12, 16 dS m⁻1), compost rate (0, 15, 20, 30 t ha⁻1), and their interaction on soil physicochemical properties.
Full size table

Relationship between compost doses and chemical parameters

Significant linear regressions were observed between compost doses and the soil’s physicochemical parameters, with high determination coefficients (R2), indicating significant changes as compost doses increased from C0 to C3 (Fig. 3). Soil pH showed a negative relationship with increasing compost doses, with a determination coefficient of R2 = 0.9570 (Fig. 3a). In contrast, electrical conductivity (EC) also exhibited a negative trend, with R2 = 0.9020 (Fig. 3b). The organic matter (OM) percentage and nitrogen (N) percentage followed positive trends, with R2 values of 0.9870 and 0.9622, respectively (Fig. 3c,d). Phosphorus (P) also showed a positive relationship with compost doses, with an R2 of 0.9774 (Fig. 3e), while sodium (Na) demonstrated a negative correlation with an R2 of 0.9626 (Fig. 3f). Meanwhile, potassium (K), calcium (Ca), and magnesium (Mg) all displayed positive relationships with compost doses, with determination coefficients of 0.9623, 0.9620, and 0.9627, respectively (Fig. 3g,h,i).

Fig. 3
figure 3

Linear regressions of soil chemical parameters in response to compost application rates (C0 = no compost; C1 = 15; C2 = 20, and C3 = 30 t ha⁻1) under different salinity levels (0.2, 8, 12, and 16 dS m⁻1). Parameters: (a) pH; (b) electrical conductivity (EC); (c) organic matter (OM); (d) nitrogen (N); (e) phosphorus (P); (f) sodium (Na); (g) potassium (K); (h) calcium (Ca); (i) magnesium (Mg). Circles represent measured values at each compost rate; solid lines indicate the fitted linear regressions; error bars represent standard deviations (±SD, n = 3); R2 values are reported for each regression.

Full size image

Effect of compost application rates on growth parameters and photosynthetic efficiency

Salinity stress caused a marked reduction in plant height, with mean values decreasing progressively as irrigation salinity increased from I0 to I3 (Fig. 4). Under non-saline conditions (I0 = 0.2 dS m⁻1), durum wheat plants exhibited the greatest growth, with mean plant height increasing from 73.0 ± 0.5 cm in the untreated control (C0) to 80.0 ± 0.5 cm at the highest compost dose (C3). Compost application significantly enhanced plant height, and Duncan’s multiple range test (p ≤ 0.05) revealed significant differences among compost rates within this salinity level, confirming the positive contribution of compost to vegetative growth under optimal irrigation conditions. At moderate salinity (I1 = 8 dS m⁻1), plant height declined relative to I0, with mean values ranging from 66.0 ± 0.5 cm in C0 to 73.0 ± 0.5 cm in C3. Under higher salinity stress (I2 = 12 dS m⁻1), plant height was substantially reduced across all treatments, reaching 36.0 ± 0.5 cm in C0. However, compost application led to a significant improvement, with plant height increasing to 47.0 ± 0.5 cm at the highest compost dose (C3). At the highest salinity level (I3 = 16 dS m⁻1), plant growth was severely constrained, and mean plant height decreased to 25.0 ± 0.5 cm in the control treatment. Nevertheless, compost amendment significantly mitigated this reduction, with plant height reaching 37.0 ± 0.5 cm under C3.

Fig. 4
figure 4

Effect of compost application rates on plant height (Pht) of durum wheat grown under different salinity levels (I0 = 0.2 dS m⁻1, I1 = 8 dS m⁻1, I2 = 12 dS m⁻1, and I3 = 16 dS m⁻1) and compost application rates (C0 = 0 t ha⁻1, C1 = 15 t ha⁻1, C2 = 20 t ha⁻1, and C3 = 30 t ha⁻1). Bars represent mean values (n = 3). Different lowercase letters above bars indicate statistically significant differences among compost treatments within the same salinity level according to Duncan’s multiple range test (p < 0.05). For each parameter, means sharing the same letter are not statistically different.

Full size image

Salinity stress markedly reduced leaf number in durum wheat, with mean values progressively declining from I0 to I3. However, compost application significantly mitigated this effect across all salinity levels (Fig. 5).

Fig. 5
figure 5

Effect of compost application rates on leaf number (NL) of durum wheat grown under different salinity levels (I0 = 0.2 dS m⁻1, I1 = 8 dS m⁻1, I2 = 12 dS m⁻1, and I3 = 16 dS m⁻1) and compost application rates (C0 = 0 t ha⁻1, C1 = 15 t ha⁻1, C2 = 20 t ha⁻1, and C3 = 30 t ha⁻1). Bars represent mean values (n = 3). Different lowercase letters above bars indicate statistically significant differences among compost treatments within the same salinity level according to Duncan’s multiple range test (p < 0.05). Means sharing the same letter are not significantly different.

Full size image

Under non-saline conditions (I0 = 0.2 dS m⁻1), leaf number increased from 28.2 ± 0.8 leaves in the control (C0) to 64.7 ± 2.3 leaves under the highest compost dose (C3). At moderate salinity (I1 = 8 dS m⁻1), compost maintained a strong positive effect, with leaf number rising from 18.3 ± 0.6 to 42.1 ± 0.6 leaves. Under higher salinity (I2 = 12 dS m⁻1), compost application significantly improved leaf number from 12.4 ± 0.5 in the control to 27.6 ± 0.6 leaves under C3, while at severe salinity (I3 = 16 dS m⁻1), leaf number increased from 12.5 ± 0.5 to 18.5 ± 0.5 leaves. Duncan’s multiple range test confirmed significant differences between compost-treated plants and the control at each salinity level, highlighting the effectiveness of compost particularly at the highest dose (C3) in sustaining leaf development under saline irrigation.

Significant differences in chlorophyll fluorescence (Fv/Fm) were observed across salinity levels and compost application rates (Fig. 6).

Fig. 6
figure 6

Effect of compost application rates on chlorophyll fluorescence (Fv/Fm) of durum wheat under different salinity levels (I0 = 0.2 dS m⁻1, I1 = 8 dS m⁻1, I2 = 12 dS m⁻1, and I3 = 16 dS m⁻1). Compost application rates were C0 = 0 t ha⁻1, C1 = 15 t ha⁻1, C2 = 20 t ha⁻1, and C3 = 30 t ha⁻1. Bars represent mean values ± standard deviation (n = 3). Different lowercase letters indicate statistically significant differences among treatments according to Duncan’s multiple range test (p < 0.05).

Full size image

Under non-saline conditions (I0 = 0.2 dS m⁻1), Fv/Fm values were high across all treatments, ranging from 0.757 ± 0.017 in the control (C0) to 0.793 ± 0.010 under the highest compost dose (C3). Compost application slightly but significantly enhanced Fv/Fm, and Duncan’s multiple range test (p < 0.05) showed that C3 differed from the control, reflecting improved photochemical efficiency under optimal conditions. At moderate salinity (I1 = 8 dS m⁻1), Fv/Fm declined relative to I0; however, compost application maintained higher values, increasing from 0.747 ± 0.017 in C0 to 0.783 ± 0.010 in C3. Under higher salinity stress (I2 = 12 dS m⁻1), Fv/Fm values were further reduced, reaching 0.617 ± 0.017 in the control. Compost amendment significantly mitigated this decline, with Fv/Fm increasing up to 0.653 ± 0.010 under the highest compost dose (C3). At severe salinity (I3 = 16 dS m⁻1), chlorophyll fluorescence was strongly constrained, with the lowest value recorded in C0 (0.617 ± 0.017). Nevertheless, compost application remained effective, and C3 significantly increased Fv/Fm to 0.653 ± 0.010.

Impact of compost application on yield components under saline irrigation

The obtained data demonstrated that yield-related parameters grain yield (GY), 200-grain weight (200-GW), straw yield (SY), awn length (AWL), and spike length (SL) were significantly influenced by salinity (Sa), compost (C), and their interaction (Sa × C) (Table 6). Salinity significantly affected 200-GW, SY, AWL, and SL (p < 0.05), while its effect on GY was not significant (p > 0.05). Compost application had a highly significant effect on all parameters (p ≤ 0.01), and the interaction Sa × C also showed a significant influence, particularly on GY, 200-GW, SY, and SL.

According to Duncan’s test (Table 7), compost application significantly improved grain yield across all salinity levels, with a consistent increase from C0 to C3. Under low salinity (0.2 dS m⁻1), grain yield increased from 1.12 t ha⁻1 (C0) to 1.24 t ha⁻1 (C3), corresponding to an increase of 10.71%, indicating a positive response to compost application under non-stress conditions. At 8 dS m⁻1, grain yield rose from 0.80 t ha⁻1 (C0) to 0.89 t ha⁻1 (C3), representing an increase of 11.25%, demonstrating that compost partially alleviated the negative effects of moderate salinity. The beneficial effect of compost became more pronounced at 12 dS m⁻1, where grain yield increased from 0.38 t ha⁻1 (C0) to 0.50 t ha⁻1 (C3), corresponding to a gain of 31.58%, highlighting the greater relative efficiency of compost under higher salinity stress. Even under severe salinity (16 dS m⁻1), compost application maintained a positive effect, with grain yield increasing from 0.16 t ha⁻1 (C0) to 0.20 t ha⁻1 (C3), representing an improvement of 25.00%. Although absolute yield levels remained low under severe salinity, these results indicate that compost mitigated, but did not fully overcome, the adverse effects of high salt stress. For 200-grain weight, values remained high under non-saline conditions, while a marked decline was observed at 16 dS m⁻1 for the control (12.00 g). Compost application mitigated this reduction, with C3 reaching 13.50 g, indicating improved grain filling under saline conditions. Straw yield showed comparable values among compost treatments at 0.2 dS m⁻1, suggesting limited compost effects under non-stress conditions. At 8 dS m⁻1, C1 produced the highest straw yield, followed closely by C3. Under 16 dS m⁻1, straw yield increased slightly from 0.57 t ha⁻1 (C0) to 0.60 t ha⁻1 (C3), corresponding to a gain of 5.26%, indicating a modest but consistent positive response to compost. Compost application also enhanced awn length, particularly under low salinity, where C3 reached 19.10 cm, exceeding all other treatments. Similar trends were observed for spike length, with C3 attaining 7.22 cm at 0.2 dS m⁻1 and maintaining relatively higher values under 12 and 16 dS m⁻1, reflecting improved spike development in response to compost application.

Table 7 Analysis of variance (ANOVA) for the effects of salinity (Sa) and compost doses (C0 = no compost; C1 = 15; C2 = 20; C3 = 30 t ha⁻1) on durum wheat yield components.
Full size table

Correlation between compost application rates and yield components

The regression analysis demonstrated that increasing compost doses positively influenced all evaluated yield components of durum wheat (Fig. 7). Grain yield (GY) exhibited an exceptionally strong positive correlation with compost application (R2 = 0.994, Fig. 7a), indicating that higher compost rates consistently enhanced grain production. Similarly, 200-grain weight (200-GW) showed a strong correlation (R2 = 0.969, Fig. 7b), reflecting improved grain filling with increased compost. Straw yield (SY) also responded positively to compost, although the relationship was moderate (R2 = 0.677, Fig. 7c). Awn length (AWL) and spike length (SL) displayed moderately strong to strong positive correlations (R2 = 0.803, Fig. 7d, and R2 = 0.858, Fig. 7e, respectively), highlighting the beneficial effect of compost on spike morphology.

Fig. 7
figure 7

Linear regressions of durum wheat yield components in response to compost application rates (C0 = no compost; C1 = 15 t ha⁻1; C2 = 20 t ha⁻1; C3 = 30 t ha⁻1) under different salinity levels (0.2, 8, 12, and 16 dS m⁻1). Parameters: (a) grain yield (GY); (b) 200-grain weight (200-GW); (c) straw yield (SY); (d) awn length (AWL); and (e) spike length (SL). Circles represent measured values for each compost rate; solid lines indicate the fitted linear regressions; error bars represent standard deviations (± SD, n = 3). R2 values are shown for each regression.

Full size image

Heatmap and hierarchical clustering of soil and plant responses under different compost rates and salinity treatments

The plant and soil responses are represented through a heatmap with hierarchical clustering based on the response patterns of all measured parameters across different compost and salinity treatments, revealing the relationships between soil properties, plant growth, and yield components (Fig. 8).

Fig. 8
figure 8

Circular heatmap and hierarchical clustering of soil and plant parameters based on normalized data. The columns around the circle represent the different treatments combining four compost application rates (C0–C3) and four salinity levels (I0–I3). The measured parameters, arranged radially, include EC, K, OM, Mg, Ca, P, Na, 200-GW, GY, SL, and AWL. A color gradient from brown (lower values) to green (higher values) illustrates the relative response patterns of each parameter under the applied treatments.

Full size image

Certain soil chemical parameters, such as EC, K, OM, and Mg, clustered together, indicating that these variables may be collectively influenced by soil chemical and physical properties. Notably, the co-clustering of EC and organic matter suggests a close relationship between ion availability and soil organic content. Conversely, plant growth and yield parameters, including 200-GW, GY, SL, and AWL, exhibited distinct response patterns under specific treatments, suggesting that certain doses or combinations of compost and salinity significantly affect plant morphological development. In terms of nutritional and physiological responses, moderate levels of elements such as Ca, P, and Na were associated with improved overall plant performance. The color gradient in the heatmap (from green to brown) reflects relative levels of each parameter, with higher values observed for K and OM and lower values for Ca and P. Overall, these results indicate that groups of parameters respond coherently to the applied treatments. The observed clusters provide insight into potential interactions between soil chemistry, plant nutrition, and growth, highlighting key factors that may play a central role in maintaining plant health and productivity.

Principal component analysis of soil and plant parameters under different compost and salinity treatments

The results of the PCA biplot are illustrated in the biplot (Fig. 9), which integrates both the scores of the treatments and the loadings of the variables.

Fig. 9
figure 9

PCA biplot of soil and plant parameters under different compost (C0–C3) and salinity (I0–I3) treatments: (Pht) plant height; (NL) number of leaves; (GY) grain yield; (ChlF) chlorophyll fluorescence; (EC) electrical conductivity; (Na) sodium; (K) potassium; and (Ca) calcium.

Full size image

The first two principal components (PC1 = 87.19%, PC2 = 10.72%) together account for 97.91% of the total variance, indicating that these axes effectively capture the major patterns induced by compost and salinity treatments. PC1 primarily discriminates treatments according to compost levels. High compost doses (C2 and C3) are positioned on the positive side of PC1, while low doses (C0 and C1) occupy the negative side. Variables related to growth and yield, including plant height (Pht), number of leaves (NL), grain yield (GY), and chlorophyll fluorescence (ChlF), exhibit strong positive loadings along this axis, suggesting that increased compost application enhances these traits. PC2 mainly separates treatments based on salinity levels. Higher salinity treatments (I2, I3) are located toward the upper region of PC2, particularly when combined with higher compost doses (C2–I3, C3–I3), and are associated with elevated soil salinity indicators (EC, Na). Lower salinity treatments (I0, I1) cluster in the lower region of PC2, corresponding to conditions more favorable for plant growth. Although PC2 accounts for a smaller proportion of the variance than PC1, it is crucial for capturing the effects of salinity that are not represented along PC1. The directions of the vectors reveal correlations among variables. Growth and yield parameters (Pht, NL, GY, ChlF) are positively intercorrelated and inversely related to salinity-associated soil parameters (EC, Na), indicating the mitigating effect of compost on salt stress. Additionally, soil nutrients such as K and Ca align with higher compost treatments, reflecting improved nutrient availability and uptake.

Discussion

The current study clearly indicated that the application of compost significantly improved the chemical properties of saline soils. Increasing compost doses enhanced SOM, TN, P, K, Ca, and Mg, while simultaneously regulating pH and EC. Improvement of CEC and nutrient retention may be due to increased SOM, enhanced microbial activity, and stabilization of soil structure, which supports better nutrient availability under saline conditions. Similar effects have been reported in previous studies, where organic amendments such as compost and biochar increased SOM, CEC, and nutrient availability while mitigating the adverse impacts of salinity55,56.

Application of compost at increasing doses (15–30 t ha⁻1) in this study improved soil chemical dynamics under saline conditions. Higher compost rates contributed to a slight acidification, likely due to enhanced microbial activity, organic acid production, and ongoing nitrification57,58. Similar findings were reported by Zaghloul et al.59 and Chtouki et al.60, who highlighted the beneficial effects of organic amendments and nutrient management on soil fertility and plant performance under abiotic stress conditions. Total nitrogen (TN) was also enhanced, likely through accelerated mineralization of organic nitrogen and stimulation of nitrogen-fixing and nitrifying microorganisms, increasing plant-available N36,61. These mechanisms collectively indicate that compost application improves nutrient availability and mitigates the chemical stress of salinity on soil and plant growth. In addition to TN, compost application significantly influenced the availability of other essential nutrients, particularly phosphorus (P), calcium (Ca), and magnesium (Mg), which are critical for plant growth and metabolism. The breakdown of organic matter releases humic substances, including fulvic and humic acids, which enhance the conversion of phosphates into plant-available forms62. This effect has been reported during the composting of manure enriched with rock phosphate, where increases in available P were linked to improved microbial activity and enhanced P solubilization efficiency63. Other studies have confirmed that the transformation of organic matter promotes the release of mobile phosphorus in soil layers rich in humic and fulvic acids, whose structural properties can significantly influence nutrient dynamics64. Moreover, humic substances derived from compost improve soil physicochemical properties and stimulate microbial activity, further contributing to P mobilization65. Similarly, compost application increased the availability of Ca and Mg, essential for plant metabolism and cell structure, consistent with findings in degraded soils where compost use enhanced both element availability and plant nutritional status35,66.

Irrigation with saline water markedly constrained the vegetative growth of durum wheat, particularly reducing plant height and leaf number at higher salinity levels. These limitations are primarily driven by osmotic stress, which restricts water uptake, lowers turgor pressure, and inhibits cell elongation, while salinity-induced hormonal imbalances and nutrient deficiencies further restrict shoot and leaf development. Plants perceive salt stress at the cell wall level and activate complex signaling pathways to maintain cellular homeostasis, regulate osmotic balance, and mitigate oxidative stress, highlighting the combined effect of water deficit and ionic toxicity on vegetative growth67,68,69. The application of vegetal compost effectively mitigated these adverse effects, promoting taller plants and increased leaf development across vegetative stages. This response is likely attributable to the combined enhancement of soil fertility, nutrient availability (N, P, Ca, Mg), water-holding capacity, and microbial activity, which collectively improve root development and nutrient uptake under saline conditions. Beyond general growth promotion, co-composted biochar and farmyard manure have been reported to enhance plant height and alleviate oxidative stress under drought or contaminated conditions70,71, suggesting that organic amendments not only supply nutrients but also buffer plants against environmental stresses. Chtouki et al.72 demonstrated that the co-application of phosphate rock with compost significantly enhanced plant growth, root nodulation, and nutrient uptake under stress conditions, highlighting the potential of biologically-based phosphorus amendments in improving crop performance. Similarly, Loudari et al.73 reported that appropriate phosphorus fertilization improved shoot and root biomass, root morphology, and chlorophyll content in durum wheat under salt stress, indicating that optimized P management can mitigate the adverse effects of salinity on plant growth. Overall, these findings support the use of integrated phosphorus and organic amendment strategies to enhance plant resilience and productivity under abiotic stress conditions. These results further underline how compost-based amendments create a favorable rhizosphere environment that improves nutrient acquisition, supports cellular processes, and enhances stress resilience. Chlorophyll fluorescence (Fv/Fm) measurements indicate that compost stabilizes photosystem II activity and chloroplast integrity under saline irrigation, maintaining photochemical efficiency and light energy conversion. These physiological benefits likely contribute to the observed increases in plant height and leaf number, illustrating the integrated effect of soil amelioration on both vegetative growth and photosynthetic resilience74,75,76.

Compost amendment markedly improved wheat yield components under moderate salinity, with the highest dose (C3) showing the greatest effectiveness. Grain yield increased by 11.6 % at low salinity (0.2 dS m⁻1) and by 31.6 % at 8 dS m⁻1 compared to the control, while the 200-grain weight remained high, indicating sustained grain development under saline stress. These improvements can be attributed to enhanced soil structure, nutrient availability, and microbial activity, which together mitigate salinity-induced stress and support plant growth35,77. By improving osmotic balance and nutrient uptake, compost stabilizes reproductive growth and yield traits, while modulating physiological responses that maintain cellular homeostasis78,79. Importantly, these findings reinforce the role of organic amendments as a sustainable strategy for improving wheat productivity in saline soils. Nonetheless, large-scale adoption requires evaluation of compost availability, economic feasibility, and long-term effects on soil microbial health. Future studies should integrate agronomic, environmental, and economic assessments to optimize compost use and strengthen its contribution to sustainable cereal production systems25,80.

Conclusion

The findings demonstrated that the use of green waste compost, particularly at 30 t ha⁻1, had considerable beneficial effects on soil quality and the growth performance of durum wheat under saline irrigation. Compost application enhanced soil chemical properties and supported better plant development, confirming its effectiveness as an organic amendment. However, its efficiency declined at the highest salinity level, indicating that vegetal compost alone cannot fully mitigate severe salt stress. Since this study was conducted under controlled greenhouse conditions, field-scale trials are required to validate these results under variable environmental conditions. Future research should explore the combined use of vegetal compost with salt-tolerant durum wheat varieties and complementary soil management strategies to improve crop resilience and ensure sustainable production in saline soils.