SJA_42_1_454-464

Introduction

The Physical and mechanical disintegration of soil is important in explaining the degree to which soil degradation such as the reduction in organic matter, structural strength, among others will occur (Dahham et al., 2025). As a result, soil physical degradation induces changes in different properties (bulk density, porosity, penetration resistance, infiltration rate and hydraulic conductivity) which affect water processes and root growth (Nguyen and Tran, 2020). A great deal of research in agriculture and environmental soil science has been devoted to improving infiltration, aggregate stability (AS), and water holding capacity (WHC). (Zhang et al., 2021) revealed that parent material and interactive effects of soil-forming factors have a considerable impact on the soil attributes and behavior under different management regimes. It is well documented that parent material has a significant effect on soil physical property and hence, on soil texture (Aljibury et al., 2021).

Gypsiferrous soils are widely Iraq, occupying extensive areas in the western, central (Jassim, 2019). Therefore, the soils of the study sites are considered gypsum and constitute approximately 12% of the soil area of Iraq (Ismaeel et al., 2025). Kim et al. (2022) compared the hydro-physical properties of gypseous (50 - 92%) and non-gypseous soils under various soil conditions and found that the nongypseous soils exhibited a more defined microstructure and retained more water at near saturation conditions than did the gypseous soils.

Organic matter, derived from plant and animal residues, is a rich source of nutrients required for plant growth and soil protection from erosion. It plays a major role in improving soil structure, aggregate stability, and water retention due to its decomposition products (Mahmoud et al., 2025). Predicting the overall impact of soil organic matter on productivity is complex due to its multiple effects that depend on seasonal conditions and soil type, particularly soil texture.

To assess the relation between organic matter of soil and functionality, it was estimated that a 10-1500 kPa increase in plant-available water for sandy soils occurs due to an increase in organic carbon content (compared with clay particles). However, such improvement is usually confined to the plough layer (5-10 cm), and thus, the overall enhancemen t of the soil water-holding capacity will be very limited (Zhou et al., 2021). The role of soil organic matter for the maintenance of aggregate stability differs with textural class and is more import in sandy soils than in clayey soils, where cation balance plays a lead role (Ali and Kamal, 2025). In general, a SOC of between 2 and 2.5% is required in order to maintain good aggregate stability, which falls rapidly below 1.2–1.5% (Chen et al., 2023).

Maize (Zea mays L.) is a major field crop and plays crucial roles in food security, feed manufacturing and bio-industry worldwide. It is an important starch, oil and ethanol crop with high yield and wide adaptability to different climates. Furthermore, its growing also helps improve soil fertility in sustainable agricultural practices (Abbas et al., 2023; Ranum et al., 2014). Saturated hydraulic conductivity (Ks), the soil’s water transmission capacity under saturated conditions- is a key indicator for assessing water transport and serves as a critical parameter in irrigation and drainage design as well as in salinity management for agricultural soils (Fattah and Shihab, 2023).

This study aims to investigate the impact of different application rates of organic Sources on important soil properties (bulk density, aggregate stability and saturated hydraulic conductivity). The incidence of gypsiferous soils in Iraq where gypsic horizons have low natural stability and water retention is poor justifies this study. A knowledge of these factors would aid the design of sustainable soil management systems underpinned with sound science to improve crop yield and water use in dry farming or semiarid conditions.

Materials and Methods

This study was conducted in agricultural fields. Sheep, poultry and cow manure were collected from different farms. This organic waste was allowed to ferment for 60 days, adding water occasionally to keep the moisture content with a 1% urea dosage being added in order to improve microbial degradation. The organic waste was mixed to maintain its homogeneity and speed up its decomposition.

Soils samples were taken from three different agricultural locations with 5, 10, and 25% concentrations of gypsum. The accumulated soil samples were transferred to 25 kg perforated plastic containers, and organic materials were mixed well as per treatments prescribed. The experiment consisted of two replications for each treatment. The organic residue was added at the concentrations of 1%, 2%, and 3% (w/w) to soil dry weight. A total of 72 experimental units (pots) were arranged under a controlled wooden shelter.

After mixing residues with the soil, each pot was re-moistened and homogenized. The soil was then rested for one week under moderately humid conditions. Methods of analysis included electrical conductivity (EC) and pH of the water extracted from the soil and measurement of organic matter contents (Tables 1 and 2). Core sample method was used for bulk density determination. Due to the high gypsum content, soil texture analysis was omitted to avoid unreliable particle-size distribution results.

Maize (Zea mays L.) was sown in all experimental units three seeds per anvil after the preparation period. After emergence, each plant was thinned to the ground so that only one per anvil remained after thinning for even spacing.Plants were watered as needed and monitored throughout the growth period. Data on plant growth parameters were collected in parallel with soil property measurements to compare the effects of different types and levels of organic residues in gypsum soils on maize growth and yield. Aggregate stability: The percentage of soil aggregate stability was measured using a 250-micron sieve, according to the method proposed by Hillel (1980), with the percentage calculated according to the following equation:

Mean weight diameter (MWD):

Soil samples were taken and sieved so that their particles were confined between two sieves with apertures of 4 and 9 mm. 25 grams of the sample was placed on a set of sieves with aperture diameters of (0.25, 0.5, 1.0, 2.36, and 4.75) mm after being moistened by capillary action for 6 minutes. The sieving process was carried out using a Youker (Kemper, 1965) sieve at 30 rpm for 6 minutes. The contents of each sieve were transferred and oven-dried. The weight of the soil was then recorded. The mean weight diameter (MWD) was calculated according to the equation proposed by Youker and Mcguiness (1956):

Wi = Mass of aggregates as a percentage of the total weight of the sample (without units).

Xi = Average diameter of those aggregates (mm).

Experimental design and statistical analysis:

The experiment was conducted according to a Randomized Complete Block Design (RCBD) with a factorial arrangement involving two factors:

(١) Type of organic residue (three levels: poultry, sheep, and cow manure), and

(٢) Application rate (three levels: 1%, 2%, and 3% based on soil dry weight).

Each treatment combination was replicated twice, giving a total of 18 treatments × 2 replications = 36 experimental units per gypsum level, and 108 units in total across the three gypsum soils (5%, 10%, and 25%).

All data collected on soil physical properties (aggregate stability, bulk density, water-holding capacity, saturated hydraulic conductivity).

Table 1: Physical and chemical analyses of the studied soils

Gypsum % properties	C55%	C10 10%	C25 25%	Unit
Bulk density	1.34	1.38	1.44	mg.cm-3
particle density	2.71	2.72	2.72	mg.cm-3
Ec	2.89	3.3	4.06	ds.m-1
PH	7.52	7.8	8.19	-
Total Porosity	51	49	47	%
Organic matter	1.18	0.94	0.8	%

Table 2: Chemical analyses of organic waste

Characteristic	Unit	Type of Waste
Characteristic	Unit	Cattle manure	Poultry manure	Sheep manure
EC	ds.m-1	20.3	11.65	22.32
PH	-	7.68	6.74	7.53
Phosphorus	gm.Kg-1	7.31	6.98	7.73
Nitrogen		13.98	16.42	12.6
Potassium		7.2	21. 72	15.43
Carbon		243.1	213.9	256.5
Organic matter		439.4	493.9	460.5
C/N Ratio	-	17.38	13.02	20.19
CEC	Cmol.kg-1	110	103	96

Results and Discussion

From Table 3, it is clear that the percentage of moisture in the studied soils at different moisture tension levels shows an increase in the amount of water held in the soil at different tension values due to the addition of various amounts of organic waste. This

Table 3: Effect of adding organic waste on the soil water retention curve.

Retention Curv Organic waste (gm)		water available	١٥٠٠ Kpa	٣٣ Kpa	water available	١٥٠٠ Kpa	٣٣ Kpa	water available	١٥٠٠ Kpa	٣٣ Kpa
Retention Curv Organic waste (gm)		G25			G10			G5
Poultry manure	0	12.14			13.17			25.59
	20	1٢.٤1	12.٥6	2٤.97	13.16	13.15	26.31	13.33	13.44	26.77
	40	1٢.٧٣	1٢.٧٢	2٥.٤5	13.31	13.43	26.74	13.43	13.62	27.05
	60	13.١8	1٣.٤1	26.٥9	13.43	13.77	27.20	13.74	13.91	27.65
Sheep manure	20	13.17	12.60	25.77	13.41	12.70	26.11	13.5	13.23	26.73
	40	13.28	12.89	26.17	13.71	12.99	26.70	13.55	13.40	26.95
	60	13.36	13.24	26.60	13.66	13.35	27.01	13.76	13.77	27.53
Cattle manure	20	12.71	12.62	25.33	13.13	13.07	26.20	13.52	13.20	26.72
	40	13.00	12.87	25.87	13.27	13.37	26.64	13.٥٥	13.38	2٦.٩٣
	60	13.25	13.09	26.34	13.32	13.55	26.87	13.٦٦	13.٨6	27.٢٢

increase is attributed to the enhanced surface area of soil particles resulting from the higher organic matter content, which improved the soil’s capacity to retain more water at tension levels of 0.3 and 15 bars. The type and quantity of animal waste added to each of the different gypsum study soils affect the percentage of available water held between 3.1 and 15 bars.

Table 3 shows that adding organic waste of different sources to the gypsum soil contributed to increasing moisture retention at field capacity and the permanent wilting point. Poultry manure also outperformed other wastes, reaching, for example, (27.65, 27.33, and 27.22) for the G5 gypsum soil at the 60-gram addition level for poultry, sheep, and Cattle manure, respectively. Similarly, the available water had its highest value when Poultry manure was added at the 60-gram addition level for all study soils, reaching (13.74, 13.43, and 13.18), respectively. This improvement is mainly attributed to the colloidal properties of organic materials, which can absorb 10 to 100 times more water than mineral particles. As a result, soils treated with organic residues retain more available water for plant use. Another reason for the resulting increase in water-holding capacity is the modification of the soil’s physical properties by organic additives, such as bulk density, porosity, and permeability. It has been shown that organic additives increase the proportion of water-storing pores (0.5-50 µm) and water-transmitting pores (50-500 µm). This increases the soil’s ability to retain water and facilitates its movement within the soil profile (Hamid et al., 2025).

Table 4: Moisture content (PW) of soil after adding animal waste in different rates

Type of organic waste (gm)		C25 25%	C10 10%	C5 5%
Poultry manure	0	44.65	44.87	٤٥.٩٠
	20	48.56	50.12	52.128
	40	49.22	51.16	52.63
	60	50.32	51.73	53.50
Sheep manure	20	47.43	46.16	48.86
	40	47.96	47.82	49.32
	60	48.12	48.36	49.90
Cattle manure	20	45.04	45.16	46.22
	40	45.72	46.03	46.90
	60	46.35	46.76	48.32

From Table (4), it is clear that the moisture content value increases when organic waste is added to the soil, especially Poultry manure, which outperformed the rest of the waste, reaching 53.50 at a gypsum percentage of 5% and an addition level of 60 grams. Moisture content consistently increased with higher addition levels for all types of organic wastes. The reason for the increase in the soil moisture content with the increase in the addition levels of animal organic waste may be due to the colloidal nature of the added organic waste, which can absorb larger quantities of water than the soil minerals absorb, in addition to its effect in improving the physical properties of the soil (Sisouvanh et al., 2021), who indicated an increase in the moisture content of sandy soil with the increase in the levels of organic waste, and they attributed the reason to the role of organic matter, which improves the physical properties of the soil. Mohammed et al. (2019) also found that organic waste increases the moisture content of the soil as a result of improving the soil properties by binding individual soil particles and giving them stable soil aggregates, thus increasing the soil’s ability to retain moisture, due to its having an area of high superficiality.

Table 5: Soil aggregate stability % after adding animal waste in different rates

Gypsum% organic waste (gm)		C2525%	C1010%	C55%
Poultry manure	0	28.07	27.86	27.٦٤
	20	34.60	35.77	35.90
	40	36.85	38.54	39.80
	60	39.31	42.59	43.26
Sheep manure	20	34.45	35.24	35,79
	40	36.17	36.91	37.12
	60	38.76	39.12	40.44
Cattle manure	20	34.22	35.27	35.47
	40	36.60	36.87	37.11
	60	39.87	39.49	40.33

From Table (5) and Figure 1, it is clear that the stability values of the aggregates increased when adding organic waste to the soil, especially Poultry manure, which outperformed the rest of the waste, as it reached (43.26) at a gypsum ratio of 5%, (42.59) at a gypsum ratio of 10%, and (39.31) at a gypsum ratio of 25% and an addition level of (60) grams, after its value before addition was (28.07). Aggregate stability increased proportionally with higher organic residue levels due to the formation of stable aggregates resistant to water dispersion, resulting from improved cohesion between soil particles (Hamid, 2025a; Wang et al., 2023).

From Table 6 and Figure 2, it is clear that the weighted diameter values increased when adding organic waste to the soil, especially Poultry manure, which outperformed the rest of the waste, as it reached (0.75) mm at a gypsum ratio of 5%, (0.67) mm at a gypsum ratio of 10%, (0.55) mm at a gypsum ratio of 25% and an addition level of (60) g, after its value before addition was (0.37) mm. We note an increase

Table 6: Average weighted diameter (mm) after adding animal waste in different rate

Gypsum % organic waste (gm)		C2525%	C1010%	C55%
Poultry manure	0	0.37	0.38	0.38
	20	0.47	0.50	0.52
	40	0.50	0.59	0.66
	60	0.55	0.67	0.75
Sheep manure	20	0.44	0.50	0.58
	40	0.49	0.55	0.63
	60	0.54	0.61	0.71
Cattle manure	20	0.41	0.47	0.55
	40	0.48	0.52	0.60
	60	0.52	0.59	0.68

in the stability values of the aggregates when the addition levels increase for all types of organic waste. The reason for the increase in the stability of the aggregates and the weighted diameter rate when adding organic waste is attributed to the role of organic matter in forming adhesive materials when they decompose due to microbial activity, and the release of organic acids that help increase the stability of the aggregates. The soil content of organic matter has an effect in increasing the concentrations of some organic compounds such as Fulvic acid and polysaccharides, which play an important role along with the ions with positive charges Ca+2 and Mg+2, which Together, they contribute to increasing the stability of the aggregates and thus increasing the weighted diameter rate (Hamid, 2025b; Abed and Kareem, 2025).

Table 7: Saturated hydraulic conductivity (cm h-1) of soils after adding animal waste at different rates.

Gypsum % organic waste (gm)		C2525%	C1010%	C55%
Poultry manure	0	3.66	4.02	4.54
	20	4.05	4.72	4.85
	40	4.80	5.25	5.15
	60	5.11	5.80	6.71
Sheep manure	0	4.19	4.35	4.64
	20	4.69	4.90	5.09
	40	5.1	5.28	5.74
Cattle manure	60	3.8	4.17	4.60
	0	4.45	4.64	4.94
	20	5.08	5.2	5.33

Table 7 and Figure 3 shows that the type and level of animal waste addition affected the hydraulic conductivity values compared to soils not treated with animal waste, where its value was (4.54) cm/h-1 and increased to (6.71) cm/h-1 in soil with 5% gypsum and the highest percentage of Poultry manure addition. This increase may be due to the increase in the number of small water-bearing pores resulting from improving the soil structure, in addition to the organic matter resulting from the decomposition of the added organic waste, which has a great capacity to hold water (Demir and Demir, 2019). We also note a decrease in the hydraulic conductivity values with the increase of gypsum. This is due to the fact that the presence of gypsum reduces the hydraulic conductivity, as the role of gypsum with fine particles appears, as these fine particles work to fill and close the spaces between them, which affects the saturated hydraulic conductivity (Jafaar et al., 2022).

Table 8: Bulk density (Mg cm-3) of soil after adding animal waste at different rates

Gypsum % organic waste (gm)		C2525%	C1010%	C55%
Poultry manure	0	1.44	1.38	1.34
	20	1.40	1.36	1.32
	40	1.39	1.34	1.30
	60	1.37	1.32	1.29
Sheep manure	20	1.42	1.37	1.31
	40	1.40	1.32	1.28
	60	1.37	1.31	1.29
Cattle manure	20	1.43	1.37	1.33
	40	1.42	1.35	1.31
	60	1.40	1.33	1.29

From the apparent density values in Table 8 and Figure 4, it is clear that there was a continuous decrease with increasing levels of organic waste addition. The addition level and type of animal waste also affected the apparent density values, as we note that the lowest value of apparent density was at a gypsum percentage of 5% and an addition level of 60 grams of Poultry manure (1.24) g/cm3. Poultry manure at the addition level of 60 g outperformed all gypsum levels. This is due to the degradation product of added organic waste material increasing the organic matter content of soils. This enhancement of soil structure results in a decrease in density and an increase in porosity (Zhao et al., 2021). It was found from the measured data that apparent densities reduced moderately by an average of around 5% with inclusion of organic waste, and reduction noticeably increased as the quantity of waste added increased (Hundi et al., 2025). The bulk density also decreased significantly with increase in the levels of organic waste addition, which implies improved soil porosity. It is noteworthy that the water of irrigation also infiltrated more rapidly as higher amounts of organic wastes are added.This is attributed to the improvement of soil structure and increased interstitial pores resulting from the decomposition of added organic waste, as well as to the increased percentage of residual organic matter in the soil, which has a low bulk density compared to mineral matter (Fernandes et al., 2020).

Table 9: Total porosity (%) of soil after adding animal waste at different rates

Gypsum % organic waste (gm)		C2525%	C1010%	C55%
Poultry manure	20	47.2	49.1	50.2
	40	47.6	49.9	51.00
	60	48.4	51.00	51.4
Sheep manure	20	46.5	48.7	50.6
	40	47.2	49.9	51.7
	60	48.4	51.4	52.5
Cattle manure	20	46.1	48.00	49.9
	40	46.5	48.4	50.6
	60	47.2	49.1	51.4

Table 9 and Figure 5 shows that the total porosity of the studied soils showed an increase in its values in the soils treated with different levels of different organic matter compared to the untreated soils. The Poultry

manure outperformed the rest of the wastes in its effect on increasing the porosity values, as it reached (54.3, 51.5, and 50%) for the addition levels of 20, 40, and 60 poultry, respectively, and at a gypsum level of 5%. The reason is that the addition of animal waste led to a decrease in the percentage of rapidly draining pores and an increase in the percentage of slowly draining pores and water-bearing pores in the soil, as a result of the increase in the amount of organic matter in this soil through the added amounts of organic waste, and the decrease in the percentage of rapidly draining pores usually increases with the increase in the levels of waste addition. The pores between soil particles are of the small type, pores Micro, while between soil aggregates they are of larger dimensions and of the type pores Macro. The presence of organic matter in the soil allows fine soil particles to combine with organic parts to form larger soil masses that contain pores of larger diameters between them. This supports the fact that organic amendments do not only lead to an increase in porosity, and this is in agreement (Baiamonte et al., 2019).

Conclusions and Recommendations

It is concluded from the current study that the addition of organic waste, especially poultry manure, improves the physical properties of gypseous soils with different gypsum contents. This improvement includes higher capacity for water holding, lower bulk density, better soil aggregate stability, and better saturated hydraulic conductivity of water. More importantly, the increase in SOC, TN, and POC increased with the increase of organic waste inputs, in which poultry manure > sheep manure > cow manure. In light of these results, it can be suggested that organic waste, in particular poultry manures, could be used as efficient soil conditioners of gypsum soils and optimal application rates defined with respect to improve physical properties, increase soil moisture retention, and promote crop growth (especially maize), especially within arid and semi-arid zones. Furthermore, the integration of these organic amendments into sustainable soil management practices is highly recommended to enhance the productivity and long-term fertility of gypsiferous soils.

Novelty Statement

The article is distinguished by its focus on addressing a real soil problem using natural, sustainable, and environmentally friendly materials.

Generative AI or AI assisted technology statement

The author declares that no genrative AI was used in the creation of this manuscript.

Conflict of interest

The authors have no conflict of interest.

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