Comparative Impacts of Organic and Inorganic Fertilizers on the Restoration of Rangeland in the Semi-Arid Regions of Saudi Arabia

Abstract

Rangeland degradation in arid and semi-arid regions is a serious ecological challenge, damaging soil health and reducing plant growth. This study evaluated the comparative effects of Almarai organic and inorganic fertilizers on the growth performance of three native rangeland species across three semi-arid locations of Saudi Arabia, including Al-Tamiryyat (Al-Jouf), Al-Sahwa (Al-Madina), and Al-Fuhaihil (Thadiq), in a randomized complete block design. The study revealed that fertilization significantly influenced plant height and stem diameter, with organic fertilizers yielding superior results compared to inorganic treatments across most regions (p < 0.001). Specifically, plant height for Pl3 demonstrated a substantial increase of 71% and 159% under Almarai organic fertilization in the Al-Tamiryyat and Al-Fuhaihil regions, respectively, while inorganic fertilization yielded an improvement of 61% and 132% only in the Al-Tamiryyat and Al-Fuhaihil sites, respectively. Stem diameter also exhibited significant growth under both fertilizer types (p < 0.001), with the most significant increases observed in Pl1, particularly under organic amendment in Al-Tamiryyat (184%) and inorganic fertilizer in Al-Sahwa (151%). Conversely, the effect of fertilization on crown size ratio was minimal in Al-Tamiryyat and Al-Fuhaihil (p > 0.05) but was significantly improved in Al-Sahwa region (p < 0.001) under Almarai organic fertilization. Conclusively, results of current research suggest that organic fertilization is effective way of restoring rangelands in arid environments compared to inorganic amendments.

1. Introduction

Rangeland degradation and desertification are global issues, posing significant ecological and socioeconomic challenges in arid and semi-arid regions, particularly in the Middle East and North Africa (MENA) region [1]. Poor grazing practices, land degradation, desertification, and climate change result in an annual loss of approximately USD 9 billion in the MENA regions [2]. In Saudi Arabia, where 80% of the land is characterized as arid and semi-arid, it is under severe threat from over-grazing, vegetation decline, and desertification [3]. Besides this, it has been reported that around 80% of the country’s rangelands are vulnerable to land degradation, this degradation not only harms the native flora and fauna but also hinders the survival of livestock animals, which is another crucial component of the national economy [4,5]. Therefore, restoration of these rangelands has become an important part of Saudi Arabia’s National Environment Strategy and Vision 2030 initiatives.

Several fertilization strategies are being used to restore soil fertility and rangeland plants’ growth; however, the effectiveness of each fertilizer varies according to soil, plant, and climatic conditions. Inorganic fertilizers provide readily available nutrients (N, P, K) to plants, for instance adequate N supply boosts the plant’s vegetative growth, biomass accumulation, and nutritional quality in the shoot’s parts [6,7,8]. However, persistent application of such inorganic amendments often causes soil acidification, eutrophication, and nutrient imbalance [9,10]. Besides this, the higher cost of inorganic fertilizers also limits their application under such an extensive rangeland system [11]. Conversely, organic fertilizers usually originate from animal manure, compost, plant residues, or agricultural remains [12,13,14]. Application of these organic fertilizers is considered as a sustainable approach, which not only improves soil–plant nutrient content but also improves soil porosity, water holding capacity, cation exchange capacity, and subsequently encourages nutrient cycling [15,16,17,18]. Similarly, in arid and semi-arid conditions where organic matter is typically below 1%, organic fertilizers can improve soil fertility and subsequently lead to better plant growth [19,20]. However, the effectiveness of organic fertilization is varied according to feedstock type, climate conditions, and application rates [12,21,22].

Globally, various studies have demonstrated the role of organic fertilization in arid and semi-arid regions; however, the results of these findings remain inconsistent, varying based on region and fertilizer type [19,23,24,25,26]. For instance, in the temperate regions of America, the application of farmyard manure significantly increases plant aboveground biomass by up to 20% [27,28]. Meanwhile, in Chinese semi-arid tropical areas, the co-application of organic fertilization with chemical fertilization notably improved plant leaf area index, height, and chlorophyll content by approximately 42%, 26%, and 18%, respectively. However, limited studies have investigated the comparative effect of organic and inorganic fertilizers on rangeland shrub species. Specifically, in Saudi Arabia, previous studies focused on reseeding and grazing practices, but limited research emphasized the soil management and its link with the growth and production of rangeland [29]. Meanwhile, the selection of appropriate native rangeland species is another key concern because, under native climatic conditions, plants grow better and survive for a longer period of time. For instance, in the study by Sethi et al. [30] observed that inorganic fertilizer increased the growth of Acacia spp. Up to 21%, whilst farmyard manure did not substantially improve the growth attributes. In another experiment, farmyard manure, when combined with compost, significantly increased the root biomass of Haloxylon salicornicum by 37% in the North region of Saudi Arabia [31]; however, the potential of these organic amendments on multiple sites and under diverse rangeland species remains unexplored. Furthermore, Saudi Arabia’s Vision 2030-driven Saudi Green Initiative aims to rehabilitate vast areas of degraded rangelands by planting billions of trees and restoring tens of millions of hectares of land. By identifying the comparative effectiveness of organic versus inorganic fertilizers on key native shrubs, the findings of this study will offer practical guidance to enhance vegetation recovery, soil fertility, and ecosystem resilience in degraded rangelands. Therefore, the current study aimed to investigate the impact of organic and inorganic fertilizers on the growth (plant height, stem diameter, and crown size ratio) of Traganum nudatum, Atriplex spp., and Salsola spp. under three semi-arid regions of Saudi Arabia. Subsequently, this study not only advances the scientific understanding of rangeland restoration in arid environments but also aligns with and directly contributes to the Kingdom’s Vision 2030 and National Environment Strategy goals of sustainable land management and desertification control.

2. Materials and Methods

2.1. Site Description and Plant Selection

The field experiments were performed at three distinct semi-arid sites across Saudi Arabia, including Al-Tamriyyat in the Al-Jouf region (31.33° N, 37.34° E), Al-Sahwa in the Al-Madina region (24.47° N, 39.61° E), and Al-Fuhaihil in the Thadiq region (25.28° N, 45.87° E). These regions generally receive limited rainfall and experience significant temperature fluctuations; basic soil characteristics of the regions are given in

Table 1. Soil basic physico-chemical characteristics of the experimental sites at the two depths D1 = 0–20 cm and D2 = 20–40 cm.

					Al-Tamiryyat (Al-Jouf)
Depth	Sand (%)	Silt (%)	Clay (%)	Texture	BD (g cm−3)	SMC (%)	CaCO3	pH	EC (dS m−1)	TOC (%)	OM (%)	N (mg kg−1)	P (mg kg−1)	K (mg kg−1)
D1	77.5	6.7	15.8	Sandy Loam	1.75	0.95	15	7.65	0.13	0.28	0.48	16.80	0.75	150.0
D2	73.5	8.7	17.8	Sandy Loam		2.37	19.4	7.8	0.15	0.16	0.28	11.20	0.9	170.0
					Al-Sahwa (Al-Madina)
D1	80.6	3.3	16.1	Sandy Loam	1.63	1.8	7.0	7.9	0.13	0.38	0.65	19.0	0.15	183.0
D2	79.3	4.7	16.1	Sandy Loam		1.9	8.5	7.9	0.11	0.39	0.67	18.6	0.15	182.0
					Al-Fuhaihil (Thadiq)
D1	78.3	6.3	15.4	Sandy Loam	1.64	2.3	51.0	8.0	0.12	0.48	0.83	10.1	2.04	91.8
D2	79.8	4.5	15.6	Sandy Loam		2.0	54.2	8.0	0.12	0.42	0.72	12.9	2.26	69.6

.

Prior to the experimental setup, a comprehensive preliminary vegetation survey was undertaken at each location to assess the suitability of each native vegetation species for restoration and their growth dynamics. Moreover, a soil sample was also taken from each experimental site at a depth of 5 cm by covering a surface area of 15 × 15 cm; overall, 117 samples were collected from three experimental sites. Later, the collected soil samples were analyzed in the lab to determine their fertility and seed bank potential.

Additionally, selection of native vegetation species is based on criteria including their adaptability to local climatic and soil conditions, resistance to drought and salinity, palatability to livestock (with particular emphasis on camels and sheep), availability of seeds for propagation, economic feasibility for restoration, and ultimately the nutritional value (e.g., protein and carbohydrate content) of each vegetation type. After a thorough analysis of each factor, three vegetation species were selected for field trials at each experimental site. For instance, at the Al-Tamriyyat (Al-Jouf) site, selected species included Traganum nudatum (Aldamran), Atriplex leucoclada (Alrughal), and Salsola villosa (Al-Rutha). For Al-Sahwa (Al-Madina), the chosen species were Vachellia tortilis (Al-Samur), Lycium shawii (Al-Awsag), and Vachellia gerrardii (Talh), and in the Al-Fuhaihil (Thadiq) site, the selected species were Vachellia gerrardii (Talh), Haloxylon persicum (Al-Ghada), and Ziziphus nummularia (Sidir).

2.2. Experimental Design

The study was conducted using a Randomized Complete Block Design (RCBD) with a 3 × 2 factorial arrangement of treatments. In these field studies, a comparative interaction of vegetation species was checked with three different fertilization regimes, including (i) control (no fertilizer), (ii) Alamarai organic fertilizer, and (iii) inorganic fertilizer. Alamarai organic fertilizer is prepared from cow manure, with the basic nutrient composition of the fertilizer being 0.5%, 0.5%, and 0.5% of N, P₂O₅, and K₂O, respectively, as provided by the manufacturer. Each treatment combination was replicated three times, resulting in 27 experimental units per site. The plot area maintained up to 400 m² (20 m × 20 m) where 25 seedlings per plot were transplanted with an inter-plant spacing of 4m to provide optimum growth conditions for each selected shrub plant under semiarid conditions. The overall area of each experimental site was around 16,100 m^2, including all plots and pathways.

2.3. Seedling Preparation and Transplantation

Healthy seeds of selected plant species were initially germinated in controlled nursery conditions to provide optimal growth conditions. Once the seedlings reached the appropriate size for planting, the seedlings of each shrub plant were transferred to the respective treatment pits. Planting pits with a depth of 40 cm were manually excavated, and then fertilizers were applied to each pit according to the treatment plan. Organic fertilizer was applied at 3 kg per seedling, and inorganic fertilization was applied as 15 g of nitrogen (urea), 9 g of phosphorus, and 8 g of potassium per plant. Planting pits with a depth of 40 cm were manually excavated, and then fertilizers were applied to each pit according to the treatment plan. Organic fertilizer was applied at 3 kg per seedling, and inorganic fertilization was applied as 15 g of nitrogen (urea), 9 g of phosphorus, and 8 g of potassium per plant. Following fertilization, healthy and well-established seedlings were carefully transplanted into each pit of the respective plot, and subsequently, the seedlings were gently covered with the surrounding soil. After that, the soil was slightly compacted to maintain an optimal interaction between the roots and the soil. After transplantation, all seedlings were immediately irrigated to support root establishment under field conditions (as shown in Figure 1).

The adjusted Penman–Monteith equation was utilized to determine the reference evapotranspiration (ETo) using average climatic data for each area. Evapotranspiration (ETc) for each plant species was determined by multiplying the respective ETo by the plant factor (Kl) based on the equation ${ET}_c={ET}_O\times K_l$. The pasture plant factors were assessed from earlier studies to fall within the range of 0.3–0.5. Ultimately, the overall water needs (GWR) were determined as GWR = ETc/Ei, where Ei represents the efficiency of the irrigation system. The drip irrigation system’s efficiency was measured at 90%. Utilizing the described methodology, the irrigation water requirements for each plant species were determined in Al-Tamiryyat (Aldamran, 0.93 mm d⁻¹; Alrughal, 0.99 mm d⁻¹; and Al-Rutha, 1.13 mm d⁻¹), Al-Sahwa (Al-Samur, 1.11 mm d⁻¹; Al-Awsag, 1.48 mm d⁻¹; and Talih, 1.48 mm d⁻¹), and Al-Fuhaihil (Talih, 1.39 mm d⁻¹; Al-Ghada, 1.19 mm d⁻¹; and Sidir, 1.19 mm d⁻¹).

Emitters with a flow rate of 50 L h⁻¹ (High-flow emitters) were utilized. The irrigation quantity for the drip irrigation system was determined based on each plant, assuming a square area of 1 m² per plant. Using this premise, the irrigation water needs were determined from the computed ETc values for each plant species across the different regions. Each plant (1 m²) received a total quantity (over the entire experimental duration time) that differed based on the region and species of the plant. In Al-Tamiryat, plants Pl1, Pl2, and Pl3 were given 0.339, 0.361, and 0.412 m³, which correspond to 3395, 3614, and 4125 m³ ha⁻¹, respectively. In Al-Sahwa, plants Pl1, Pl2, and Pl3 received 0.405, 0.540, and 0.540 m³, which correspond to 4052, 5402, and 5402 m³ ha⁻¹, respectively. Ultimately, in Al-Fuhaihil, plants Pl1, Pl2, and Pl3 obtained 0.507, 0.434, and 0.434 m³, which correspond to 5074, 4344, and 4344 m³ ha⁻¹, respectively. In all study regions, irrigation water was applied daily. Based on the manufacturer’s discharge rate (50 L h⁻¹), emitters were operated for a time period that ranged between 31 and 49 minutes to deliver the required amount of irrigation water based on the specified amount of water requirement for each plant.

2.4. Growth Parameters Assessment

To evaluate plants’ response under applied conditions, three key plant vegetative parameters were analyzed. Plant height was measured from the base of the main stem to the tallest leaf or any shoot part by using a calibrated measuring tape. Stem diameter was measured from the root collar, approximately 2–4 cm above the soil, using a vernier caliper. Meanwhile, the crown size ratio was determined by crown width with plant height, where crown size was examined by measuring the two widest canopy points with a measuring tape. Overall, the data was collected 12 times, after every 30 days, ranging from 25 June 2024 to 27 June 2025. This sampling technique ensured the collection of data on the annual plant growth cycle under variable conditions, including seasons, temperature, rainfall, and photoperiod.

2.5. Statistical Analysis

The collected data were analyzed using Analysis of Variance (ANOVA) to evaluate the effects of fertilizer type, plant species, and their interactions over time. Significance levels were assessed at a threshold of p ≤ 0.05. Interaction effects, including Fertilizer × Species, Fertilizer × Time, and other relevant combinations, were also examined to evaluate their collective influence on plant growth. All statistical analyses were performed using SPSS software for Windows (version 18, SPSS Inc., Chicago, IL, USA).

3. Results

3.1. Effect of Soil Fertilization on Plant Height

The study revealed significant variation in plant height depending on fertilization type, plant height, and experimental site. For instance, in the Al-Tamiryyat (Al-Jouf) and Al-Fuhaihil (Thadiq) regions, the Analysis of Variance (ANOVA) showed that soil fertilization type (SA) had a statistically significant effect on plant height (p = 0.007), as shown in

Table 2. Analysis of variance (ANOVA) for the effect of soil amendment, plant type, and measurement period on plant height at Al-Tamiryyat (Al-Jouf), Al-Sahwa (Al-Madina), and Al-Fuhaihil (Thadiq) regions, respectively.

ANOVA of Plant Height at Al-Tamiryyat (Al-Jouf)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	733.095	366.548	5.052	0.007
Plant Type (PT)	2	1260.331	630.166	8.686	0.000
Time Period (P)	11	32,583.794	2962.163	40.828	0.000
SA × PT	4	854.733	213.683	2.945	0.021
SA × P	22	650.728	29.579	0.408	0.992
PT × P	22	4556.093	207.095	2.854	0.000
SA × PT × P	44	955.256	21.710	0.299	1.000
Residuals	216	15,671.144	72.552
ANOVA of Plant Height at Al-Sahwa (Al-Madina)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	4292.637	2146.319	5.502	0.005
Plant Type (PT)	2	51,240.430	25,620.215	65.672	0.000
Time Period (P)	11	86,443.058	7858.460	20.144	0.000
SA × PT	4	653.369	163.342	0.419	0.795
SA × P	22	1850.085	84.095	0.216	1.000
PT × P	22	4716.189	214.372	0.549	0.951
SA × PT × P	44	3619.454	82.260	0.211	1.000
Residuals	216	84,266.687	390.124
ANOVA of Plant Height at Al-Sahwa Al-Fuhaihil (Thadiq)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	733.095	366.548	5.052	0.007
Plant Type (PT)	2	1260.331	630.166	8.686	0.000
Time Period (P)	11	32,583.794	2962.163	40.828	0.000
SA × PT	4	854.733	213.683	2.945	0.021
SA × P	22	650.728	29.579	0.408	0.992
PT × P	22	4556.093	207.095	2.854	0.000
SA × PT × P	44	955.256	21.710	0.299	1.000
Residuals	216	15,671.144	72.552

. Similarly, organic fertilization produced more substantial results related to the improvement of plant height, compared to inorganic fertilization or the unamended control group. Plant species (PT) also indicated variation in height performance among the three selected species under organic amendment, followed by inorganic fertilization and control. Meanwhile, the effect of time (P) also significantly (p < 0.001) influenced the plant height as plant height increased over the passage of time. An interaction between fertilizer type and plant species (SA × PT) suggests that the response to fertilization varies depending on the shrub species type. For instance, Ziziphus nummularia (Pl3) exhibited consistently higher growth under inorganic treatment compared to organic amendment. Other interaction terms, including fertilizer × time (SA × P) and fertilizer × species × time (SA × PT × P), were not statistically significant (p = 0.992 and p = 1.000, respectively), implying that the effect of fertilizer on plant height was stable over time and not jointly influenced by species or timing.

However, a significant interaction between plant species and time (PT × P) (p < 0.001) was observed, indicating that species responded differently to temporal conditions. Overall, under both experimental sites, Pl3 showed a significant improvement in its height under both organic and inorganic fertilization conditions. Furthermore, Pl3 plant height improved around 71% and 159% in Al-Tamiryyat and Al-Fuhaihil regions, respectively, under organic fertilization; meanwhile, under inorganic fertilization, these increments were up to 61% and 132%, respectively, as shown in Figure 2.

Moreover, under Al-Sahwa (Al-Madina) conditions, soil fertilization also notably increased plant height (p < 0.005). Besides soil fertilization, the type of plant species also significantly (p < 0.001) improved the height of plants, indicating interspecific variability in growth response. Time also had a significant effect (p < 0.001), suggesting progressive growth over the measurement periods. Meanwhile, the interaction effects between fertilizer and plant type (SA × PT), fertilizer and time (SA × P), and plant type and time (PT × P) were all statistically non-significant (p > 0.79), indicating that the effect of fertilizer on plant height remained relatively consistent across species and over time. Besides this, the three-way interaction (SA × PT × P) was also non-significant (p = 1.000), showing that these combined amendments had no notable impact on the height of plants (Table 2). Overall, in this region, Pl1 showed the maximum increment in plant height under all applied conditions. For example, organic fertilization improved Pl1 height by 103%, followed by inorganic fertilization (66%) (Figure 2).

3.2. Effect of Fertilization on Stem Diameter

Plant stem diameter is greatly influenced by the application of organic and inorganic amendments. For instance, ANOVA results revealed a significant (p < 0.001) increment in plant stem diameter under the fertilizer-based treatments compared to the unamended control group in all three experimental regions. Moreover, the improvement in the diameter also varied (p < 0.001) according to species type (

Table 3. Analysis of variance (ANOVA) for the effect of soil amendment, plant type, and measurement period on stem diameter at Al-Tamiryyat (Al-Jouf), Al-Sahwa (Al-Madina), and Al-Fuhaihil (Thadiq) regions, respectively.

ANOVA of Stem Diameter at Al-Tamiryyat (Al-Jouf)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	142.095	71.047	8.220	0.000
Plant Type (PT)	2	1520.978	760.489	87.984	0.000
Time Period (P)	11	5883.332	534.848	61.878	0.000
SA × PT	4	238.747	59.687	6.905	0.000
SA × P	22	39.306	1.787	0.207	1.000
PT × P	22	510.047	23.184	2.682	0.000
SA × PT × P	44	87.297	1.984	0.230	1.000
Residuals	216	1867.002	8.644
ANOVA of Stem Diameter at Al-Sahwa (Al-Madina)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	101.060	50.530	6.418	0.002
Plant Type (PT)	2	366.117	183.059	23.251	0.000
Time Period (P)	11	1738.016	158.001	20.068	0.000
SA × PT	4	183.912	45.978	5.840	0.000
SA × P	22	91.356	4.153	0.527	0.961
PT × P	22	89.202	4.055	0.515	0.966
SA × PT × P	44	31.532	0.717	0.091	1.000
Residuals	216	1700.621	7.873
ANOVA of Stem Diameter at Al-Fuhaihil (Thadiq)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	142.095	71.047	8.220	0.000
Plant Type (PT)	2	1520.978	760.489	87.984	0.000
Time Period (P)	11	5883.332	534.848	61.878	0.000
SA × PT	4	238.747	59.687	6.905	0.000
SA × P	22	39.306	1.787	0.207	1.000
PT × P	22	510.047	23.184	2.682	0.000
SA × PT × P	44	87.297	1.984	0.230	1.000
Residuals	216	1867.002	8.644

). Similarly, measurement time also revealed a significant (p < 0.001) improvement in stem diameter throughout the experimental time of all shrub species in all specified sites. Moreover, a significant interaction between SA × PT (p < 0.001) suggests that shrub species showed variable responses under both kinds of fertilization approaches. Conversely, the interactions between SA × P and PT × P were not statistically significant (p = 0.961 and p = 0.966, respectively) in the Al-Sahwa and Al-Fuhaihil regions, indicating stable treatment responses over time and a consistent species response across the growth period. Meanwhile, in the Al-Tamiryyat experimental site, the interaction between plant species and time (PT × P) was significant (p < 0.001), indicating that species response can be varied according to the temporal factors. Besides this, the three-way interaction (SA × PT × P) was also found to be statistically insignificant (p = 1.000) under all experimental sites, indicating that the combination of fertilization, species, and time did not produce a compounded effect on stem diameter, as mentioned in Table 3.

Moreover, in the Al-Tamiryyat region, the maximum increment of stem diameter was observed in Pl1 (184%) under inorganic fertilization. Under organic fertilization, the same plant stem diameter growth increased by 171% from the first sampling period to the last, compared to the control group. Similarly, in the Al-Sahwa region, Pl1 also showed a significant improvement in stem diameter; however, at this experimental site, organic fertilization produced a more significant improvement (151%) compared to the inorganic fertilizer approach (101%), from the first sampling to the last. Moreover, at Al-Fuhaihil experimental site Pl2 showed great increment in stem diameter under organic fertilization regime (Figure 3).

3.3. Effect of Fertilization on Crown Size Ratio

Plant crown size ratio (CSR) at Al-Tamiryyat and Al-Fuhaihil regions did not significantly impact the CSR (p = 0.334), which indicates that the type of fertilizer, whether organic, inorganic, or control, did not produce any notable improvement in the CSR of all shrub species. However, in the Al-Sahwa site soil, amendment had a statistically significant effect on crown size ratio (p = 0.006), in which organic fertilizer generally resulted in higher crown size ratios compared to the inorganic or unamended control treatments. Additionally, plant species type showed a significant (p < 0.001) impact on CSR, which indicates that morphological characteristics and growth habits play a key role in determining the CSR. Similarly, the measurement period (P) showed a statistically significant effect (p < 0.001), indicating that the crown size ratio expanded consistently throughout the growing season. The interaction between PT × P was also significant (p = 0.007), suggesting that different species responded to seasonal or temporal changes at different rates at all experimental regions. However, no significant interaction was observed between SA × PT, nor between SA × P, or in the three-way interaction SA × PT × P (p > 0.1, across all regions), suggesting that the combined approach of fertilizer type, plant species, and time did not statistically significantly impact the CSR (

Table 4. Analysis of variance (ANOVA) for the effect of soil amendment, plant type, and measurement period on crown size ratio at Al-Tamiryyat (Al-Jouf), Al-Sahwa (Al-Madina), and Al-Fuhaihil (Thadiq) regions, respectively.

ANOVA of Crown Size Ratio at Al-Tamiryyat (Al-Jouf)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	5.134	2.567	1.103	0.334
Plant Type (PT)	2	118.167	59.083	25.380	0.000
Time Period (P)	11	614.617	55.874	24.001	0.000
SA × PT	4	1.926	0.482	0.207	0.934
SA × P	22	70.931	3.224	1.385	0.123
PT × P	22	102.293	4.650	1.997	0.007
SA × PT × P	44	38.059	0.865	0.372	1.000
Residuals	216	502.845	2.328
ANOVA of Crown Size Ratio at Al-Sahwa (Al-Madina)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	18.233	9.116	5.317	0.006
Plant Type (PT)	2	72.841	36.420	21.242	0.000
Time Period (P)	11	455.190	41.381	24.136	0.000
SA × PT	4	6.557	1.639	0.956	0.433
SA × P	22	13.148	0.598	0.349	0.997
PT × P	22	92.038	4.184	2.440	0.001
SA × PT × P	44	16.115	0.366	0.214	1.000
Residuals	216	370.335	1.715
ANOVA of Crown Size Ratio at Al-Sahwa Al-Fuhaihil (Thadiq)
Source of Variation	df	Sum of Squares	Mean Square	F-Value	p-Value
Soil Amendment (SA)	2	5.134	2.567	1.103	0.334
Plant Type (PT)	2	118.167	59.083	25.380	0.000
Time Period (P)	11	614.617	55.874	24.001	0.000
SA × PT	4	1.926	0.482	0.207	0.934
SA × P	22	70.931	3.224	1.385	0.123
PT × P	22	102.293	4.650	1.997	0.007
SA × PT × P	44	38.059	0.865	0.372	1.000
Residuals	216	502.845	2.328

).

Moreover, at the Al-Tamiryyat region, CSR remained steady from sampling 1 to 7, but at the 8th sampling time, these attributes increased remarkably until the 11th sampling. The maximum increment of CSR was observed in Pl1 under inorganic and organic fertilization, respectively. Meanwhile, in the Al-Sahwa region, this peak was observed from the 4th sampling day to the 7th, during which organic fertilization contributed the most to the improvement of CSR in Pl1 and Pl3. At Al-Fuhaihil experimental site, CSR showed a scattered response under the fertilization and plant types overall, from sampling day 2nd to the 7th sampling cycle. Pl2 showed a remarkable rise under both organic and inorganic fertilization, as shown in Figure 4.

4. Discussion

The application of Almarai organic fertilizer, which is composed of cow manure, resulted in a significant improvement of plant growth attributes and their physiology, specifically in the arid and semi-arid regions of Saudi Arabia. The results suggest that organic fertilization had a generally stronger and more consistent effect on early plant growth, particularly in terms of height and stem diameter or crown size ratio. Most of the species (Atriplex leucoclada, Salsola villosa, Traganum nudatum, Vachellia tortilis, Lycium shawii, Vachellia gerrardii, Ziziphus nummularia) tested in the field experiments of Al-Sahwa, Al-Fuhaihil, and Al-Tamriyyat showed great response under organic fertilization, compared to the inorganic amendments or unamended control group. Almarai fertilizer is a rich source of plant essential nutrients, including N (3%), P (1.6%), and K (2%), which play a crucial role in plant growth and production compared to inorganic synthetic fertilizers [8,16,32]. Moreover, the C:N ratio of this organic fertilizer also remains around 15:1, which minimizes the excessive release of these nutrients and ultimately prevents nutrient deficiency in the desert shrub species [14,33,34]. Such organic fertilizations also improve soil organic matter content up to 27% which subsequently elevates soil microporosity and water holding capacity [35]. Therefore, we noticed a significant rise in plant growth attributes, including stem thickness and shoot height, under organic amendments. This enhancement of soil water holding and water retention capacity in the regions where annual rainfall is below 100mm and temperature exceeds 50 °C plays a key role in the growth and survival of Vachellia tortilis and Ziziphus nummularia shrub species [36,37]. Besides this, the higher abundance of plant growth-promoting bacteria in the cow dung also increases soil nutrient cycling and minimizes the risk of pathogen attack which resulting in better plant growth, specifically increased plant height [38,39,40]. Moreover, application of cow dung-based fertilizer can regulate soil pH and reduce the salinity content of the Al-Madina region, where osmotic and antioxidant stresses decrease and shrub plants like Ziziphus nummularia and Lycium shawii result in better height and canopies [41].

Previous studies have reported that the application of cow manure at 50 t ha⁻¹ under calcareous soils of Thadiq can improve the plant height by over 400% compared to the unamended control group [42,43]. These results are in line with our findings, where we also observed a notable improvement in plant physiology growth under organic fertilization, compared to chemical fertilizers. This increment of soil height may be attributed to the rise in soil nutrient and organic matter content, which leads to better nutrient cycling and carbon content [44,45]. In another study, compost of cow manure increased the height of alfalfa plants up to 59% compared to the control group [46,47]. However, co-application of organic fertilizer with synthetic fertilization under arid regions may result in an effective strategy to boost drought-tolerant shrub cultivation by approximately 25% in the arid and semi-arid regions of Saudi Arabia [48]. The efficacy and potential of organic fertilization vary according to the soil type, application rates, and climatic conditions. For instance, in regions like Asir, Al-Sahwa, Al-Fuhaihil, and Al-Tamriyyat, soils are deficient in organic matter and nutrient content, and also the texture of these soils is calcareous and sandy [49,50]. The application of cow manure and other organic amendments in regions with limited rainfall and high temperatures may result in increased soil water retention ability, higher nutrient content, and enhanced carbon sequestration, ultimately supporting the growth of shrub species under such harsh climatic conditions [51,52]. Moreover, the composition of organic amendments also depends on the type of feedstock source. For instance, poultry manure is rich in N content and can boost the plant growth during its vegetative stage; however, in saline, calcareous, and sandy regions of Saudi Arabia, cow manure can be considered as an appropriate amendment in improving soil nutrient stock and reducing toxicity risks for the shrub species like Vachellia tortilis [53]. A study of Al-Jouf concluded that the application of vegetable waste compost, coupled with biochar, notably minimized the heavy metal stress in maize plants under Cr-contaminated conditions; however, these amendments had a limited effect on the plant height [54,55].

The improvement of plant stem diameter and crown size ratio in the current study may be attributed to the cell division and cell elongation process, which increased through the adequate nitrogen supply to plants [56,57]. Furthermore, elevated chlorophyll content and photosynthetic rate also increase stem girth and ultimately improve the gaseous exchange activity [58,59]. The application of organic fertilizers mineralizes nitrogen, converting it into a plant-available form. An adequate supply of nitrogen to the plants further boosts the turgor pressure, which encourages the cell expansion process, particularly in the stem of the plant under the harsh arid climatic conditions [60]. Moreover, an adequate supply of phosphorus from organic amendments enhances the root proliferation process, resulting in increased aboveground biomass, as stated by Jing et al. [61]. Similarly, potassium availability regulates osmotic balance, mitigating salinity stress prevalent in Al-Jouf’s saline-alkali terrains, thus maintaining turgor pressure for sustained growth [62,63]. Moreover, crown size mainly depends on leaf area expansion, branching pattern, and apical dominance, and the field application of farmyard manure can increase crown size up to 41% compared to the unamended control group [64,65]. Previous studies have indicated that the integrated application of cow manure along with 20 g mycorrhiza treatment substantially improved the oil palm plant height and stem diameter by around 24 and 32%, respectively, compared to the control [66,67]. Another study concluded that cow manure at 10 t ha⁻¹ significantly (p < 0.005) enhanced stem diameter, leaf area index, and plant height of water spinach against the control group [68]. Almarai organic fertilizer demonstrated significant improvements in the physiology of various shrub species; however, future research should be conducted to assess the long-term implications of such organic fertilizations on economic and environmental sustainability. Moreover, future studies should focus on desert reclamation through organic amendments by analyzing the cost/benefit ratio of each fertilization approach in the desert areas of Saudi Arabia.

5. Conclusions and Future Perspective

The findings of this study highlight the crucial role of organic fertilization in enhancing the early growth of native rangeland species in arid ecosystems. Across the three study sites, organic fertilizers consistently led to notable increases in plant height and stem diameter. In contrast, inorganic fertilizers provided some benefits in specific cases, such as stem thickening, but their effects were inconsistent and varied by plant species and site conditions. Moreover, Traganum nudatum showed a strong positive response to organic inputs, likely due to its adaptive rooting behavior and efficient nutrient uptake. Meanwhile, crown size ratio exhibited no strong correlation with fertilization treatments, indicating that canopy development is influenced more by genetic or environmental factors, such as seasonal rainfall or temperature, than by nutrient availability. These results demonstrate that applying organic fertilizer at transplanting is an effective management practice to boost seedling establishment and vigor in semi-arid rangelands. A single organic application was sufficient to sustain growth through the first growing season, simplifying field operations by avoiding the need for repeated fertilization. Moreover, organic inputs enhance soil health by increasing soil organic matter and promoting nutrient cycling, aligning with sustainable land management principles. Overall, such nature-based practices support Saudi Arabia’s Vision 2030 environmental goals by enhancing the re-establishment of native vegetation, promoting biodiversity conservation, and contributing to national targets (e.g., the Saudi Green Initiative) for expanding vegetation cover and rehabilitating degraded lands. However, future research should investigate the long-term effects of organic fertilizers on shrub survival and biomass beyond the one-year experimental duration by examining the physicochemical characteristics of both soil and plants. Further studies should also analyze the optimal composition and application rates of organic amendments for different native species to ensure the effectiveness and sustainability of applied amendments.