Introduction

Mulching is an agronomic practice involving the application of a protective layer, known as mulch, to the soil surface. This layer can be made from organic materials (such as unincorporated plant residues or imported materials like straw), or inorganic materials (including plastic films, geotextiles, gravel, and crushed stones). It results in beneficial changes to the soil environment, namely improvements in physical conditions, chemical composition, and biological activities, as reviewed by Acharya et al. (2005). In terms of physical conditions, mulching significantly influences the soil moisture regime by controlling soil surface evaporation, changing soil temperature, facilitating nighttime water condensation due to temperature fluctuation, controlling soil erosion and, for non-plastic mulches, improving water infiltration, and enhancing soil water retention. As a result, mulching is often adopted in water-scarce regions for crop production, both in rainfed and irrigated areas, owing to its potential to enhance water use efficiency and save water (Pereira et al. 2009).

The benefits of organic mulches in soil water conservation are well-established, making mulching a fundamental component of Conservation Agriculture (Basch et al. 2012; Kassam et al. 2013; Jovanovic et al. 2020). Organic mulches act as a barrier to runoff and intercept raindrops, protecting the soil from splashing, particle detachment, and clogging of surface soil pores, thereby contributing to the minimization of soil erosion (Prosdocimi et al. 2016). They enhance the macroporosity of soil structural aggregates, leading to improved water infiltration and increased soil storage capacity (Blanco-Canqui and Lal 2007; Kahlon et al. 2013). Moreover, they reduce non-beneficial water consumption by plants through decreased exposure of the soil surface to solar radiation, increased resistance to water vapor loss to the atmosphere, and the expansion of the relatively non-turbulent air zone above the soil surface, thus altering the boundary layer conditions at the soil-air interface (Acharya et al. 2005). However, the effectiveness of organic mulches much depends on the thickness and composition of the mulch (Bond and Willis 1969; Acharya et al. 2005). A thicker mulch layer produces more significant effects, and a higher carbon-to-nitrogen (C:N) ratio results in longer-lasting effects. Furthermore, rainfall interception may prevent water from infiltrating the soil surface, which may be relevant in rainfed areas where precipitation is scarce. Still, Cook et al. (2006) concluded that canopy and mulch modified the soil water balance by adversely affecting soil water content beneath thicker application but increase in soil water was much greater. Those conclusions are not enough to consider that soil water was detrimentally affected. Montenegro et al. (2013) observed that the rainfall interception by mulch was much smaller than soil water increase. Therefore, the advantages of organic mulch far outweigh these limitations.

Plastic mulches, made primarily of thin sheets of polyethylene or similar materials, are the most used inorganic mulch materials (Kasirajan and Ngouajio 2012). These sheets are typically laid over the soil surface, especially along the plant rows, with holes cut into them at plant spacings to allow the plants to emerge. The effectiveness of plastic mulch largely depends on the color of the material, which can be mainly transparent, white, or black. The color significantly impacts albedo, influencing the mulch’s energy-radiating properties and affecting soil temperature in different ways (Acharya et al. 2005). This creates a microclimate around the plant by modifying the radiation budget of the surface, thus the energy balance, contributing to increased crop yields. The physical properties of soils are hardly affected since the soil may still be regularly disturbed by tillage, but changes in the soil moisture regime are evident as the plastic film acts as a barrier, preventing soil water evaporation and increasing soil moisture availability in the root zone (Kasirajan and Ngouajio 2012; Somanathan et al. 2022). The barrier evidently contributes to rainfall interception. However, as noted by Zheng et al. (2018), this effect does not overcome the positive impacts of plastic films on soil moisture conservation.

While organic and inorganic mulches have a significant impact on soil evaporation, particularly during the early stages of crop development when the plant’s canopy is still small, only partially covering the ground, there is still limited understanding of the influence of different types of mulches on the crop coefficient (Kc). The single Kc represents averaged soil evaporation and crop transpiration from a cropped surface for typical frequencies of wetting (Allen et al. 1998, 2005b; Pereira et al. 2020). Kc is defined as the ratio between crop evapotranspiration (ETc) and reference evapotranspiration (ETo), calculated using either the FAO Penman-Monteith equation (Allen et al. 1998) or the ASCE-PM equation (Allen et al. 2005a), and it provides for an integration of the effects of key characteristics (crop height, albedo, canopy resistance, and exposed soil surface to evaporation) that differentiate a specific crop from reference grass. Therefore, since mulching can significantly reduce soil evaporation compared to what is determined under standard, best growing conditions, Kc values available in the literature (Pereira et al. 2021a, b, 2023a, b; Rallo et al. 2021) may not be useful for mulched crops if effects of mulch on Kc values are not known.

Similar reasoning applies when considering the concept of the dual Kc coefficient, that comprises the basal crop coefficient (Kcb) representing crop transpiration, and the evaporation coefficient (Ke) representing soil evaporation (Allen et al. 1998, 2005b). The Ke can be significantly influenced by factors such as the thickness of the organic mulch layer in the case of organic mulches or, in the case of plastic mulches, by the fraction of the ground surface that can contribute to evaporation through the vent holes in the plastic cover and the fraction of the surface that remains wet and is not covered by the mulch. The Kcb is not expected to be affected by mulch, yet the Kcb value includes a residual diffusive evaporation component supplied by soil water beneath the dry surface and from soil water beneath dense vegetation (Allen et al. 1998). Furthermore, the increased water availability resulting from reduced soil evaporation may lead to greater crop transpiration, particularly in crops grown under non-optimal management.

Allen et al. (1998) proposed a set of general guidelines to modify the tabulated Kc (and Kcb) values for different crop stages based on the type of mulch, soil coverage, and the quantity of organic mulch applied. However, compared with present conditions, information at that time was rather limited. Therefore, those guidelines, while informative, are often deemed overly generic for practical applications (Odhiambo and Irmak 2012). Hence, the objective of this study is to review the existing literature regarding studies that compare mulching vs. no-mulching management to gain a deeper understanding of the impacts of mulching on crop coefficients.

Materials and methods

The review aimed at collecting data on the effects of mulching on actual crop coefficients (Kc act), soil evaporation (Es), and actual crop evapotranspiration (ETc act) of field, vegetable, and trees and vine crops. A total of 58 studies were selected (a much larger number of papers report on using mulch but do not allow comparing appropriately with no-mulch conditions). The search was performed using journals data repositories (Elsevier, Wiley, Springer, CSIRO publishing, Scielo), Google Scholar as well as using the reference lists of selected articles. Keywords included terms such as mulch, mulching, surface mulch, mulch versus no mulch, organic mulching, plastic film, crop coefficients, soil evaporation, and crop evapotranspiration. Various languages were used for the search (English, Portuguese, Spanish, French, Italian, and German). No restrictions regarding studies’ location or year of publication were considered. Only full articles were reviewed. The criteria used for selecting the papers from which data was collected followed similar reviews on Kc and ET data (Pereira et al. 2021a, b, 2023a, b; Rallo et al. 2021) and included the following:

  1. (a)

    The papers should be of good or acceptable quality, regardless of the journal in which they were published.

  2. (b)

    The field and computation methods should be comprehensively described and easily understandable for any interested reader. They should reference consistent methodologies for calculating Es and ETc act, preferably in accordance with Allen et al. (2011).

  3. (c)

    The studies should compare the effects of mulching on Kc act, Es, and/or ETc act data obtained in well-defined treatment plots. A control treatment should consider bare soil conditions.

  4. (d)

    The type of mulch should be well identified. In the case of organic mulching, the amount of material should be provided. In the case of inorganic mulching, the characteristics of the material used should be preferable given, as well as the faction of surface mulched.

  5. (e)

    For Kc data, the FAO56 Penman Monteith (PM) equation (Allen et al. 1998) or the ASCE-PM equation (Allen et al. 2005a) should be used to compute reference evapotranspiration (ETo).

  6. (f)

    The Kc data should adhere to the physical constraints of the surface energy balance process. The latent heat flux (𝜆E), representing the energy available for the evaporation process and derived from the net radiation flux (Rn) minus soil heat flux (G) and sensible heat flux (H), shows upper limits for Kc values of 1.2 in sub-humid regions and 1.2–1.4 in arid regions (both referenced to grass). Values exceeding these limits may result from errors in ET measurement, weather data used for ETo calculation, or data processing procedures (Allen et al. 2011; Pereira et al. 2021a), and related papers were therefore not considered.

  7. (g)

    In studies comparing various irrigation treatments, only data from the fully irrigated plots were taken into consideration.

  8. (h)

    When not explicitly reported in the text, data for Kc act, Es, and ETc act were extracted from tables and graphics.

The majority of field research methods followed a soil–water balance (SWB) approach based on observations of the soil water content (SWC) using soil sampling or various types of sensors, the eddy covariance system, and weighing and drainage lysimeters for measuring ET fluxes. Mini or micro lysimeters were also commonly used to measure soil evaporation. Less frequently, the Bowen ratio energy balance was used for measuring ET, and sap flow techniques for assessment of crop transpiration. Most of these field methods, along with their accuracy analyses, are comprehensively described by Allen et al. (2011). Models were not commonly employed in the analysis of mulching effects on Kc and ET data. The SIMDualKc (Rosa et al. 2012; Pereira et al. 2020) and Aquacrop (Vanuytrecht et al. 2014) models were the few exceptions.

Kc values were collected and categorized into three groups: early stages (Kc early), mid-season (Kc mid), and late and end season (Kc late). Conversions were inevitably made for studies reporting data for crop phenological stages. The early stages corresponded to the traditional initial and crop development stages as defined in Allen et al. (1998), therefore extending from sowing (for field crops), planting (for vegetable crops), or bud burst (for trees and vines) until the time before the plant’s canopy reaches its maximum coverage. During these early stages, the soil surface remained fully or partially exposed, soil evaporation rates were at their maximum, and the effect of mulching was expectably more significant. The definition of initial crop stage (Allen et al. 1998) could not be adopted because it was not followed by many authors. The mid-season was defined as in Allen et al. (1998), corresponding to the period with maximum ET and maximum canopy coverage. The late and end season included all Kc data measured during crop senescence, not just when the crop was fully matured and ready for harvest as the Kc value for the end season (Kc end) in Allen et al. (1998) implies. For each study, Kc data from different seasons was averaged to have a single value for each crop stage.

Likewise, Es and ETc act data were collected and sorted into the same three stage groups as the Kc data, when possible, or presented as seasonal values when no distinction was presented. Those values from various seasons and treatments were subjected to averaging. Since data was available either in cumulative terms for a specific crop stage or as daily averages, it was processed in relative terms, indicating the percentage increase or decrease of Es and ETc act in the mulching treatment compared to control bare soil plots.

Results and discussion

Results from literature review

Effects of mulching on soil evaporation

Table 1 presents the average relative variation (expressed in percentage values) in soil evaporation reported in studies comparing the effectiveness of mulch treatments to no mulch. While soil evaporation is the primary component of the soil water balance influenced by mulching, it is notable that there is a very limited number of available studies addressing this issue, primarily focused on field crops such as wheat, maize, sorghum, cotton, and potato. Predominantly, the organic materials used for mulching included wheat, maize, oat, and rice straws, with amount of straw ranging from 1.0 to 18.0 tonnes/ha, and surface soil coverage varying from 67 to 100%. The significant variation in crop residue rates was first reported by Adams et al. (1976), wherein they examined the effects of different residue rates (ranging from 1.0 to 10.0 tonnes/ha) on soil evaporation in a sorghum field irrigated by sprinklers. Klocke et al. (2009) considered the highest residue rates, averaging 15.0 to 18.0 tonnes/ha, in their study aimed at measuring soil evaporation from bare soil and soil covered with either corn stover or standing wheat stubble beneath the canopy of maize. No other study applied such high rates. Plastic film was the predominant inorganic mulching material used, typically positioned along the crop rows and covering 60–80% of the soil surface. An exception to this practice was found in the study by Zhang et al. (2018a), where they applied subsoil mulching by burying the plastic film 0.1 m deep. Unfortunately, not all studies offered a thorough characterization of the plastic film used, with many not indicating plastic color and thickness.

All studies documented a decrease in soil evaporation at various stages of crop growth due to mulching. The influence of soil mulching on soil evaporation was naturally more prominent in the earlier stages of crop growth, when the crop’s canopy was still small, and the energy available at the soil surface for soil evaporation was at its maximum. During these early stages, the differences in cumulative values observed between mulch and no-mulch treatments ranged from 4 to 53 mm, with an average of 25 mm across the different studies. In the mid-season and late-season stages, these differences were narrower, ranging from 1 to 33 mm (with an average of 14 mm) and from 1 to 25 mm (with an average of 7 mm), respectively. Still, there was always a decrease of soil evaporation rates in mulch treatments compared to no-mulch. In relative terms, the effect of mulching on soil evaporation during the different crop stages was less noted, as reductions of smaller absolute values can yield higher relative values. As a result, percentage reductions averaged 40% in the early crop stages, 35% in the mid-season, and 33% in the late season stage. Nevertheless, the seasonal data in Table 1 unambiguously demonstrate that mulching significantly contributes to decreasing soil evaporation, with percentage reductions ranging from 17% (Yan et al. 2018) to 79% (Tian et al. 2016) over the course of a full season. However, the extreme value of the range is quite uncommon as achieving complete efficiency in reducing soil evaporation during the late season stage, as reported in Tian et al. (2016), is rare especially when soil coverage is not total.

Despite the limited number of available studies, it is possible to observe in Table 1 that factors such as the crop residue rate and the type of material used for mulching significantly influenced the rate of soil evaporation reduction in agreement with Bond and Willis (1969). Adams et al. (1976) remains the most substantial study evaluating the impact of different crop residue rates on soil evaporation. Their findings indicated an average reduction ranging from 27 to 78% for oat straw rates varying from 1.0 to 10.0 tonnes/ha. Surprisingly, no subsequent studies were conducted anywhere in the world to corroborate those findings by extending them to different crops, climates, soils, and water management practices. The exception may be Yan et al. (2018), who examined various residue rates (4.5 and 9.0 tonnes/ha) and different soil coverage ratios (67% and 100%). Although the influence of residue rate on the reduction of soil evaporation was evident, the effect of soil coverage was not significant.

In terms of the type of mulch, Table 1 reveals that soil evaporation reductions averaged 30–35% in studies using straw mulch and 38–47% in studies using plastic mulching. Likely, it appears that plastic film is more effective in reducing soil evaporation rates. However, it is important to note that, based on the criteria outlined in Sect. 2, no study was found that compared the performance of these two types of mulch under the same conditions, thus it is not sure that plastic mulch is really superior and for which conditions this may occur. Furthermore, no study was found evaluating the impact of plastic color on soil evaporation, and the data from Table 1 is insufficient to draw any conclusive findings on this matter.

Table 1 Average variation (%) of soil evaporation (Es) in mulched plots compared to non-mulched plots
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Effects of mulching on crop coefficients

Table 2 presents the single Kc values observed during the early (Kc early), mid-season (Kc mid), and late-season (Kc late) crop stages in studies comparing the effectiveness of mulch treatments to no mulch. Data is available for various types of crops, including field crops (wheat, maize, sorghum, cotton, sugarcane, okra, and peanut), vegetables (squash, cucumber, tomato, onion, banana, and curcuma), as well as trees and vines (pear, apricot, and grapevine). More studies were available compared to those addressing soil evaporation, totaling 21 studies. Crop residues now further include sugarcane tops and leaves. Furthermore, a greater number of studies provide a more comprehensive characterization of the plastic films used.

The Kc values in Table 2 refer to the actual Kc (Kc act) as they reflect different crop and irrigation management practices. Therefore, the listed Kc act includes the coefficient Ks (Kc act= Kc Ks), which is defined for water and salinity stress, and may range from 0 to 1, with its maximum corresponding non-stress conditions. The use of the Ks coefficient under mulch conditions is widely reported in the literature (Liu et al. 2022a, b; Petry et al. 2023, 2024). However, in this review it was not possible to distinguish the stress component of the Kc act, either because many comparisons were held under full irrigation conditions (thus, Ks=1) or data was insufficient to evaluate the degree of crop stress.

In many studies, the reported Kc act values in Table 2 for non-mulch conditions seem to exhibit some degree of abiotic stress (most likely water stress) as they are substantially lower than the tabulated Kc values found in Allen et al. (1998) or the updates provided in Pereira et al. (2021a, b) for field and vegetable crops, and in Rallo et al. (2021) Pereira et al. (2023b) for trees and vines. In other studies, Kc values for non-mulched conditions are very close to those proposed in the above cited literature, suggesting better management of irrigation water in those experiments. These are, for example, the Kc mid values for winter wheat in the study by Wang et al. (2018), maize in Guo et al. (2020) and Shen et al. (2019), okra in Patil and Tiwari (2018), and onion in Igbadun and Oiganji (2012). When it comes to trees and vines, comparing Kc values is not as straightforward as it is for field crops and vegetables. This difficulty arises from the various factors known to influence crop evapotranspiration in orchard systems, including planting density, tree height, training system, canopy cover, irrigation method, and interrow management. Unfortunately, many of the reviewed studies did not provide sufficient information on these parameters for a more comprehensive comparison.

Mulching resulted in an overall reduction of the Kc values compared to those obtained under no-mulch conditions, as depicted in Table 3. The only exceptions were the Kc mid values for maize and cotton as reported by Zhang et al. (2018b); Han et al. (2019), respectively, and the Kc late values for onion provided by Igbadun and Oiganji (2012). These values were slightly higher under mulch treatments, albeit with minimal differences compared to the no-mulch treatments. A possible explanation for this phenomenon may be the increase of the transpiration component in response to the increase of water availability resulting from the reduction in soil evaporation. For all the rest, the Kc values under mulch directly translated the reduction of the soil evaporation component. The reduction in Kc values was typically more pronounced during the early crop stages, ranging from a 1.4% decrease in wheat, as reported by Wang et al. (2018), to a 43.5% reduction in curcuma, according to Santosh et al. (2021). The reduction in Kc early values was lower in organic mulch plots (averaging 22%) than in plastic film plots (averaging 26% reduction). More pronounced differences emerged when accounting for the color of the plastic. The black film showed an average reduction of 31%, while plots with white films exhibited a 30% reduction in Kc early. Transparent plastics were found to be relatively less effective in reducing Kc act values, demonstrating an average reduction of 18%. For the remaining crop stages, differences in terms of plastic materials compared to organic materials were less pronounced. Nevertheless, it should be noted that the discrepancies found in the plastic color was not evident when the comparison was conducted under the same conditions, as demonstrated by Hassan and Magdy (2014) in the case of squash and Yaghi et al. (2013) in the case of cucumber.

Table 2 Crop coefficients (Kc) in mulched plots compared to non-mulched plots
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Table 3 Average variation (%) of crop coefficients (Kc) in mulched plots compared to non-mulched plots
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Effects of mulching on actual evapotranspiration

Table 4 shows the average relative variation (expressed in percentage values) in actual crop evapotranspiration (ETc act) estimates reported in studies comparing the effectiveness of mulch treatments to no mulch. Undoubtedly, the ETc act was the parameter that received the most extensive evaluation in that comparison, involving a total of 52 different studies. The available data comprises estimates for a wide range of crops, including field crops (wheat, barley, maize, cotton, sugarcane, potato, okra, and peanut), vegetables (squash, cucumber, cabbage, tomato, bean, onion, rapeseed, chard, curcuma, strawberry, and watermelon), as well as trees and vines (pear, apricot, jujube, and grapevine). The organic materials used as mulch include maize, wheat, and rice straws, sugarcane residues, Egyptian clover, weeds residues, and vines pruning. Plastic films used were black, white, and transparent. 14 studies directly compared the effect of organic and inorganic materials (e.g., Li et al. 2013; Zhang et al. 2011; Prajapati and Subbaiah 2019) on ETc act. Likewise, 10 studies compared the impact of plastic colors (e.g., Hassan and Magdy 2014; Yaghi et al. 2013; Igbadun and Oiganji 2012; El-Naggar et al. 2018) on ETc act.

Consistent with Es and the Kc analysis, ETc act values exhibited a more pronounced reduction during the earlier crop stages due to decreased soil evaporation when comparing the results from mulch-treated plots with those from non-mulch plots. In the crop earlier stages, the reduction of ETc act due to mulching averaged 23% in all plots, with organic mulch plots exhibiting lower decrease (17%) than plastic film plots (27%). No significative differences were found relative to the effectiveness of plastic color in this context since ETc act average reductions ranged from 27% in white film mulched plots to 29% in black film mulched plots. This is primarily due to conflicting reports in the literature, as Hassan and Magdy (2014) and Yaghi et al. (2013) presented more favorable results for plots with transparent plastic, while Igbadun and Oiganji (2012) reported a more efficient effect with black films.

A reduction in ETc act values was also observed during the mid-season and late stages, although to a lesser extent when compared to the earlier crop stages. Consequently, seasonal reductions in ETc act values were more moderate, averaging 13% across all mulching plots, 11% in organic mulching plots, and 15% in plastic mulching plots. The color of the plastic film had no apparent effect on ETc act, except in the case of transparent films.

Several authors (e.g., Zhang et al. 2011, 2018a; Li et al. 2013; Shen et al. 2019; Chen et al. 2019; Wang et al. 2023) presented findings that contradict the general dynamics described above. They reported higher ETc act estimates for the mid-season and, less frequently, for the late-season in mulch plots compared to no-mulch plots. These studies primarily pertain to rainfed or irrigated wheat or maize systems, and as explained in these studies, the increased water availability resulting from the reduction of soil evaporation was subsequently used in the transpiration process. This conclusion appears reasonable, especially when considering that the Kc values reported in some of these studies were notably lower than the standard values for wheat and, particularly, maize grown under pristine conditions. While differences in seasonal ETc act values between mulch and no-mulch plots were very small for most cases, there are others where those differences were large (e.g., Chang et al., 2020; Wang et al., 2023). Reasons for this are unclear.

Table 4 Average reductions (%) of actual crop evapotranspiration (ETc act) in mulched plots compared to non-mulched plots
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Effect of mulch on crop evapotranspiration

Based on the literature reviewed in the previous sections, Table 5 summarizes the average effects of mulch materials on Es, Kc act, and ETc act values reported during the early, mid-season, and late-season crop stages. For each parameter and type of mulching material, a range of values is established, determined by the first and third quartiles of the data collected in the literature review. The intervals provided for different materials often overlap in many cases due to the various, and at times contradictory, effects reported in the literature. In certain instances, the available data is too limited for the intended purpose. Nevertheless, as referred above, the impact of mulching is particularly notable in the early crop stages when the soil is not fully covered, as compared to the other stages. This was to be expected as the energy available for soil evaporation is likely at its maximum during the early crop stages, when plant’s canopy is still small. Plastic films are more effective in reducing Es, Kc act, and ETc act, especially during the early crop stages when compared to organic materials. However, this effect diminishes during the rest of the season. In terms of color, black plastic films seem also more effective during the early crop stages compared to other colored plastics, particularly for the Kc act. However, the impact of plastic color remains subjected to some uncertainty due to contradictory studies assessing it under similar conditions. The effect of plastic color also diminishes during the rest of the season.

Table 6 further revises the general guidelines proposed by Allen et al. (1998) for expected reductions of Kc values based on the available information. The guidelines are given as range values and consider different crops, crop stages, and the preferred material used for mulching. For the case of organic mulching, it is still not possible to include the effects of residue rates in the guidelines due to lack of information. Selecting the values to use from the proposed ranges should be made with care as they represent approximative average effects related to the crop-soil conditions that determine the non-mulch Kc. Lower values of the ranges correspond to crop-soil conditions that refer to low non-mulch Kc act and to low soil cover and/or degraded mulch while the upper limits of the range concern non-mulch high Kc act, namely when influenced by local and/or regional advection and when the mulch largely covers the soil and its amount is large in case of organic mulch. Users are invited to develop their own guidelines based on those proposed herein.

Table 5 Approximate reductions (%) of soil evaporation (Es), crop coefficients (Kc) and actual crop evapotranspiration (ETc act) based on first and third quartiles of the data collected in literature reporting straw and plastic film mulch relative to no mulch
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Table 6 Approximate reductions (%) in Kc for various field and horticultural crops under nearly full plastic mulch and organic mulch relative to using no mulch when irrigation is by trickle irrigation
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Conclusions

This study systematically reviewed 58 research articles comparing mulching versus no-mulching management in various cropping systems. The primary aim was to deepen our understanding of the effects of this agronomic practice on soil evaporation (Es), crop coefficients (Kc), and actual crop evapotranspiration (ETc act). One crucial element stood out during the review, which was in many cases the insufficient description of mulching characteristics in the experiments. Authors, reviewers, and editors should pay closer attention to this issue, as crucial details were identified to be missing in numerous publications.

Nevertheless, it was possible to draw conclusions regarding the beneficial effects of mulching in reducing soil evaporation and crop coefficients, particularly during the early stages of crop development. Among various mulching techniques, plastic film, and specifically black plastic, emerged as the most efficient. However, it was observed that the differences in the efficacy of mulching materials tended to be similar over the course of the season. Despite this, there is still considerable uncertainty associated with the effectiveness of black plastic mulching compared to other colors, as data often presents contradictions, which are likely due to insufficiencies in field observations and data reporting.

The existing guidelines for estimating the impacts of mulching on Es, Kc, and ETc act during different crop stages were revised. These revisions were made by considering both the type of crop and the specific mulching material used. Unfortunately, in the case of organic mulching, incorporating the effect of residue rate into the guidelines remains challenging. Nevertheless, the guidelines provided in Tables 5 and 6 delineate the distinct effects of various mulching materials on crop evapotranspiration during different crop stages and should therefore be used as a reference for improving irrigation water management. However, it is crucial to refrain from saving water by surpassing the upper limits of the suggested ranges at the expense of inducing water stress in crops and compromising yields.