Agronomic use of solarization technology on soil fertility and pest management in dryland agriculture

Abstract

Crop production in dryland agriculture is challenged by weed infestation, and soil borne diseases which are sever in poorly fertile and moisture deficit soils where pathogen spores and weed seeds endure and persist for several years. There is little knowledge and organized information about the impact of solarization technology on soil fertility, beneficial soil microorganisms, greenhouse gas emission and its economic feasibility in dryland agriculture. This paper aimed to review the role of soil solarization as pest control mechanisms, its effect on soil biota and soil fertility in dryland. Data and information were gathered, synthesized and paraphrased from relevant and peer reviewed published papers. Studies showed that soil solarization increases the total population of soil microorganisms by 477 (no.g⁻¹soil) and improves soil fertility by 16%, reduce weed infestations and soil borne diseases by 90 and 80% respectively in drylands, thereby it gives a yield advantage of 17.42 t ha⁻¹ than unsalaried soil. Solarization is economically profitable and gives a return investment of 56% per year. It is more sounding with prior irrigation and biodegradable plastic films during hot seasons of dryland areas. This technology is safe, affordable, effective and sustainable crop protection and soil fertility enhancing strategy.

PUBLIC INTEREST STATEMENT

Crop production in dryland is challenged by moisture deficiency, weed and soil born disease infestation, and degraded and poor soil fertility. In response, farmers are forced to apply extensively harmful, high-priced and unsustainable chemical fertilizers, herbicides and pesticides. Therefore, there is a demand for sustainable and sounding technology that manages soil, weed and soil born disease together at the same time. As the result, adopting alternative management technologies like soil solarization which enables safe and sustainable crop protection with minimum or no use of chemical fertilizer, pesticides and herbicides. Solarization would be a promising technology to promote beneficial soil microorganisms kills soil borne pathogens and depletes soil weed seed bank effectively and sustainably thereby improves crop yields significantly.

Keywords:

• Agronomy
• dryland agriculture
• pest management
• solarization
• soil fertility

REVIEWING EDITOR:

• Manuel Tejada, Universidad de Sevilla, Spain

SUBJECTS:

• Soil Sciences; Soil Conservation Technology; Microbiology

1. Introduction

Soil is a fundamental medium for food production and will remain so in future. Besides, it is the home of all plant species, several beneficial microorganisms responsible for recycling and making nutrients available for plants, and harmful microorganisms that causes diseases (Kanaan et al., 2018). Crop production in dryland agriculture is severely challenged by moisture deficiency, poor soil fertility, soil borne diseases, and weed infestation, especially parasite weeds (Cohen et al., 2019; Wolie et al., 2023). The dynamics of weed seeds and pathogen spores in the soil determines the distribution, density, and infestation of weeds and soil borne diseases (Kumar et al., 2023). Moreover, poor soil fertility aggravates the infestation and damaging effects of weeds and soil borne diseases (Safdar et al., 2021). Weeds compute for nutrient, moisture, and light with crops, and being vectors for soil-borne diseases which could result a significant yield loss. Due to weeds, soil born disease, and poor soil fertility status, about 71, 65, and 100% respectively crop yields could be reduced (Mihajlovic et al., 2017; Panth et al., 2020). Management of soil borne pathogens and weed soil seed bank is challenging and causes substantial damage to arable land productivity. This is due to they can endure and persist for several years by developing structures (microsclerotia, sclerotia, chlamydospores or oospores) (Gebretsadkan et al., 2020), and stay dormant for centuries predominantly in fragile dryland farmlands (Mihajlovic et al., 2017; Panth et al., 2020).

Management of soil borne pathogens, soil fertility, and weed infestation become challenging in drylands, and farmers are applying doses of agrochemicals (synthetic fertilizers, pesticides, and herbicides) which overheads their economy, kills beneficial soil microorganisms and declines natural soil fertility, pollutes the environment (water and air), makes the agricultural system dependency on these chemicals (Wolie, 2023). By 2030, the agricultural sector will expected to reduce chemical fertilizers and pesticides by 20, and 50%, respectively and expand and promote organic farming by 25% (European Commission, 2023). Therefore, sustainable, economically feasible, environmental friendly, socially accepted and effective soil fertility, weed and diseases management strategies are in demand.

Soil solarization is a practice of trapping solar energy using locally available materials (plastics, crop residues, and manures) used to cover the soil. This rises soil temperature depletes weed soil seed bank and facilitate organic matter decomposition (Bahadur et al., 2015; Gill et al., 2017). In drylands where resources are scarce, solarization with crop residues may not be an option for small holder farmers due to low biomass production and tradeoffs with livestock (Wolie et al., 2023). Besides, the required maximum temperature to kill pathogens and weed seeds may not be achieved by solarization with residue mulches. As safe, affordable, effective and sustainable crop protection strategy, soil solarization with plastic mulches has suggested to control weeds, soil borne diseases and improve soil moisture and fertility in drylands (Gebretsadkan et al., 2020; Tewodros et al., 2016; Wolie et al., 2023). It is a promising technology to transform crop protection from environmental polluting to environmental sounding sector (Wolie et al., 2023), and more effective for small scale farmers and commercially in areas of tropical and subtropical regions.

There is little knowledge and unorganized information in the literature about the impact of soil solarization on soil fertility, beneficial soil microorganisms, greenhouse gas emission and economic feasibility in dryland agriculture (Jagtap et al., 2022; Rokunuzzaman et al., 2016; Sompouviset et al., 2023). As a result, its wide-scale adoption is poor. This work is expected to bridge these unaddressed gaps in the existing literatures by providing organized and updated information about its application, impact on soil biodiversity, soil fertility and environment. The objective of this paper is to review the role of soil solarization as pest control mechanisms, its effect on soil biota and soil fertility in drylands.

2. Review methodology

This synthesize review type has organized various updated works of soil solarization. Firstly, priority was given for scientifically peer reviewed, relevance, and recently published works in drylands which were searched & collected using the terms (solarization, plastic mulching, dryland, temperature and soil borne pathogens, weed seed bank depletion and economic feasibility) as searching engines. Secondly, after critically understanding the findings, relevant data and information were collected, paraphrased and synthesized. Thirdly, for convenience of discussion and to keep consistency throughout the paper, the collected data from various literatures were converted into same measurement units, interpreted and discussed without losing the main concepts and meanings of the original findings as indicated by Wolie (2023). To enhance clarity about the adopted methodology a flowchart was added as described by Cumpston et al. (2023) (Figure 1). Finally, all the sources of information are cited and properly referenced.

Figure 1. Synthesize literature review methodology flow chart (Cumpston et al., 2023).

3. Discussions

3.1. Concepts and principles in applying soil solarization in dryland agriculture

Soil solarization is applied to moist soils that are evenly tilled, labeled, and after irrigation to field capacity (Wolie et al., 2023). Plots must then be covered with polythene sheeting or other covering material and anchored to the ground by burying the edges in the ditch around the treated area (Jagtap et al., 2022). Visible solar radiation and short-wave infrared radiation are responsible for heating the soil through the mulch. Radiation from the earth (terrestrial radiation) is normally in the form of far-infrared radiation, which cannot pass through covering plastic (Cohen et al., 2019). This traps solar radiation inside to heat the upper layers of the soil surface for up to 2 to 8 weeks, depending on soil type and moisture conditions, color of plastic used, seasons of the year and agro-climatic conditions (Gill et al., 2017; Mihajlovic et al., 2017; Wolie et al., 2023) (Table 1). Therefore, this technology is more effective in hot seasons, as well as in tropical and subtropical agro-climatic regions of dryland areas.

Table 1. Plastic color, durations (weeks), and depth (cm) of soil solarization on soil temperature scales (⁰C).

Treatments	Cover type	Duration	Depth	Temperature	Reference
Solarized	BPEP	6	10, 20, 30	56, 52, 46	Abd-Elgawad et al. (2019)
Unsolarizd		–	10, 20, 30	41, 38, 34
Solarized	WPEP	4	0, 10, 20	30, 34, 33	Mullaimaran et al. (2022)
Unsolarizd		4	0, 10, 20	36, 33, 25
Solarized	BPEP	6	10, 20	46, 43	Di Mola et al. (2021)
Unsolarizd		–	10, 20	40, 41
Solarized	BPEP	2	5, 10, 15	47, 43, 40	Dwivedi and Dwivedi (2020)
		3	5, 10, 15	49, 46, 42
		4	5, 10, 15	54, 51, 48
Unsolarizd	–	–	5, 10, 15	38, 34, 29
Solarized	WPEP	3	10, 15	51, 54	Wolie et al. (2023)
Unsolarizd	–		10, 15	38, 42
Solarized	WPEP	4	5, 10	45, 35	Jagtap et al. (2022)
		6	5, 10	48, 40
		8	5, 10	53, 48
Unsolarizd	–	–	5, 10	35, 29
Solarized	WPEP	3	10	37	Safdar et al. (2021)
		6	10	41
		9	10	41
		12	10	52
Unsolarizd	–	4	10	25
Solarized	BPEP	3	5, 10, 20	39, 41, 41	Shutt et al. (2021)
		5	5, 10, 20	41, 42, 42
		7	5, 10, 20	33, 33, 33
Unsolarizd	–	–	10	19

Dash (-) indicates no data recorded or not applied treatment.

WPEP: white polyethylene plastic sheet; BPEP: black polyethylene plastic sheet.

The longer the soil is heated, the better and more thoroughly all soil borne pathogen pests and weed seeds are controlled and leading to changes in the chemical, physical, and biological properties of the soil (Gill et al., 2017). The damaging effect of high temperatures is attributed to metabolic and structural changes in the cells of soil organisms and weed seeds, which become irreversible with increasing temperature (Birthisel et al., 2019). Polyethylene plastics reduce heat convection and evaporation of water from the soil (Golzardi et al., 2015). The formation of water droplets on the inner surface of the polyethylene film also significantly reduces the transmittance of long-wave infrared radiation, which leads to better heating due to an increased greenhouse effect (Gebretsadkan et al., 2020).

3.2. Soil solarization on soil temperature, moisture and soil fertility

3.2.1. Solarization on soil temperature

Covering the upper part of the soil with plastic mulching significantly increases the soil temperature (Table 1). The degree of temperature increment in the solarized soil depends on several factors. Mainly the climate, types of covering materials, the season when solarization is used duration of solarization, depth at which plastic is buried, color and thickness of the plastic, and moisture status of soil to be solarized (Shinde et al., 2023; Tewodros et al., 2016).

Soil solarization is effective in hot tropical regions and/or seasons with the highest temperature records. The longer the duration, the higher the soil temperature records because the soil absorbs more solar energy (Di Mola et al., 2021). Also, if the plastic is buried deeper, there is a greater chance of solar radiation penetrating the lower part of the soil. Black polyethylene plastic film absorbs 11 °C temperature over white and other types of plastic films (Mullaimaran et al., 2022; Shinde et al., 2023) (Table 1). Because this type of plastic is dark and not shiny, the back-reflected solar radiation is slower compared to white plastics.

Prior irrigation enhances effectiveness of soil solarization, because water has a high specific heat capacity. Depending on the above conditions, the average soil temperature in solarized soil ranges between 35–55 °C which rises soil temperature by 20°C over unsolarized soil (Abd-Elgawad et al., 2019; Wolie et al., 2023). This increment in soil temperature is about 50% from the non-solarized soil (Table 1). Soil temperature decreases by 1.5 °C for every 10 cm of depth (Abd-Elgawad et al., 2019; Jagtap et al., 2022). Therefore, in order to reach the incoming solar radiation down to the deepest layer of the soil, a longer solarization period is required. Different soil types can react differently to solar radiation (Birthisel et al., 2019). It is more effective on sandy soils. This is may be due to sandy soil has more pore spaces and wider airflow, which absorbs more solar energy faster than clay and silt soils (Sofi et al., 2014).

3.2.2 Soil solarization improves soil fertility and productivity

Processes of soil nutrient and water uptake, and life of soil microorganisms depend on soil temperature. Besides, it facilitates and promotes the rate of decomposition of crop residues and decay of weed seeds stored in the soil (Al-Solaimani et al., 2015). Utilizing soil solarization in agricultural fields could greatly improve contents of N, P, K, Zn and other essential elements on the soil (Al-Solaimani et al., 2015) (Table 2). Because solarization promotes the transient production of biotoxins that increases the availability of plant nutrients, and can positively change the physical, chemical, and biological properties of the soil (Al-Shammary et al., 2020). This improves soil porosity, facilitates root penetration, enables easier access to water and nutrients to plant roots, promotes organic matter breakdown, mineralization and nutrient availability by more than 25% (Figure 2) thereby promotes crop growth and productivity (Safdar et al., 2021).

Figure 2. Role of soil solarization on improving the percentage of soil fertility, total population of soil microbiology and crop yields, and reducing diseases and weed seed bank depletion (Abd-Elgawad et al., 2019; Dwivedi and Dwivedi, 2020; Meena et al., 2019; Safdar et al., 2021).

Table 2. Effect of soil solarization on Soil pH, EC organic matter and carbon (%), and soil NPK contents in (mgkg⁻¹⁾.

Treatments	PH	EC	P	K	N	Om	OC	NH4	Na	Ca	Mg	Reference
Solarized	7.8	5.4	50	70	14	–	–	–	–	–	–	Al-Solaimani et al (2015)
Unsolarizd	7.6	5.1	20	62	12	–	–	–	–	–	–
Solarized	7.8	0.8	20	390	45	1.6	–	12.5	15500	–	–	Bhardwaj et al. (2023)
Unsolarizd	7.3	0.4	20.5	193	27	2.2	–	5.2	7600	–	–
Solarized	7.7	–	–	–	–	2.7	1.57	–	–	–	–	Gebretsadkan et al. (2020)
Unsolarizd	7.5		–	–	–	2.6	1.6	–	–	–	–
Solarized	7.2	1.4	–	–	–	15.1	1.45	–	–	–	–	Golzardi et al. (2015)
Unsolarizd	7	1.1	–	–	–	12.7	1.17	–	–	–	–
Solarized	7.8	1.5	70	99.8	12	–	–	–	–	--	–	Hamooh (2014)
)Unsolarizd	7.7	1.7	10	55.9	6	–	–	–	–	–	–
Solarized	7.8	3.14	28	70	151	–	–	–	–	–	–	Neamatallah (2018)
Unsolarizd	7.8	2.26	18	56	104	–	–	–	–	–	–
Solarized	7.6	3.4	142	642	1.6	–	–	–	13800	23700	4100	Al-Shammary et al. (2020)
Unsolarizd	7.2	3.8	135	623	1.43	–	–	–	–	–	–
Solarized	–	–	9.6	166	71	1.12	–	–	–		–	Shutt et al. (2021)
Unsolarizd	–	–	7.4	124	47	0.92	–	–	–	–	–
Solarized	7.3	0.1	21	202	362	2.7	1.5	–	–	11800	2000	Sofi et al. (2014)
Unsolarizd	7.1	0.03	15	153	195	2.6	1.6	–	–	11300	900

P: Phosphorus; K: potassium; N: nitrogen; OM: organic matter; OC: organic carbon; EC: electric conductivity (desm^-1), Dash (-) indicates no data recorded.

Soil solarization for about 12 weeks duration improves soil N, P, and K content, increases N-NO₃ and N-NH₄ concentrations and soil organic matter, cation exchange capacity, and carbon content under tropical conditions (Birthisel et al., 2019; Safdar et al., 2021; Zhang et al., 2023) (Tables 1 and 2). Lower soil temperature leads to nutrient interaction called the chelation effect in which some essential plant nutrients become bound to soil particles and unavailable to crops (Safdar et al., 2021). This may result to a reduction in hydraulic conductivity and active nutrient transport. Rising soil temperature increases soil chemical reactions (e.g. cation exchange capacity) (Al-Shammary et al., 2020). Therefore, increasing soil temperature through solarization can release the chelated nutrient and make it available to plants (Zhang et al., 2023). Thus, solarization could alter soil chemistry and improves the availability of nutrients to crops.

Soil solarization improves soil texture in addition to N, P, K and other nutrients important for plant growth and development (Birthisel et al., 2019). It helps to conserve limited dryland soil moisture by 5.48% and increases cation exchange capacity (Abd-Elgawad et al., 2019; Mitidieri et al., 2021). This improves soil structure, increases the availability of essential plant nutrients, promotes nutrient absorption, and reduces soil acidity (Golzardi et al., 2015). This is attributed to the rapid conversion of organic matter and the associated release of soluble substances into the soil at higher temperature (Golzardi et al., 2015; Sofi et al., 2014), which increases the soluble electrical conductivity index (EC) of the soil after solarization (Table 2). Soil solarization kills and decomposes a large population of soil pathogens in to organic fertilizer. This helps to reduce the need for fertilizer dose and enhances plant growth (Hamooh, 2014). Besides, it may minimize the harmful effects of soil biochemical activities by mineralization of organic matter and increasing soil organic carbon by about 2 kg m⁻² (Table 2). This could improve soil health and fertility through reducing the need for expensive, harmful and short term efficacy of chemical fertilizers (Di Mola et al., 2021). Therefore, soil solarization is a sounding technology to improve essential nutrient availability and soil fertility that can enhance crop performance.

3.4. Soil solarization on soil biodiversity and beneficial microorganisms

Soil is home to numerous complex microorganisms that can influence soil biological, physical and chemical properties (Balakrishna et al., 2015). Soil biological properties play an indispensable role in soil and plant productivity (De los Santos et al., 2021).

Increased temperature during solarization may slightly reduce the diversity of some microorganisms (growth-promoting and pathogen-antagonistic bacteria and fungi), but they can quickly adapt to soil temperature, especially hemophilic, thermo tolerant and actinomycetes (Kanaan et al., 2018). These soil biota survive under solar radiation (45 ⁰C) while other pathogens could be killed (Table 3). This is due to the restriction of evaporated moisture and released CO₂ by inhaled plants and microorganisms, which led to heating of the microclimate under the polyethylene film (Di Mola et al., 2021). Although there is sufficient oxygen in the soil, the induced temperature suffocates and breaks down the mesosphere organs of thermophilic microorganisms (Rokunuzzaman et al., 2016).

Table 3. Soil solarization on population dynamics of soil microbiology (no.g^-1 soils).

Treatment	TMO	Fungi	AMF	Fusarium spp	Actomycete	Bacteria spp.	Nematode spp.	Reference
Solarized	310	4.49	1576	–	–	–	–	Balakrishna et al. (2015)
Unsolarizd	142	2.68	434	–	–	–	–
Solarized	276	96	–	–	84	96	–	Di Mola et al. (2021)
Unsolarizd	262	88	–	–	84	90	–
Solarized	85	–	–	–	–	16	69	Dwivedi and Dwivedi (2020)
Unsolarizd	27	–	–	–	–	12	15
Solarized	7000	–	–	–	–	–	7000	Gebretsadkan et al. (2020)
Unsolarizd	2735	–	–	–	–	–	2735
Solarized	48	32812	–	–	38	–	10	Hamooh and Alsolaimani, (2014); Ney et al. (2019)
Unsolarizd	100	7211	–	–	50	–	50
Solarized	284.6	16.6	–	–	268	–	–	Sharat et al. (2018)
Unsolarizd	132.6	12.6	–	–	120	–	–
Solarized	531.33	–	–	528	–	–	3.33	Shutt et al. (2021)
Unsolarizd	1275.33	–	–	1270	–	–	5.33
Solarized	14.86	4.8	–	4.4	4.4	5.66	152	Sofi et al. (2014)
Unsolarizd	53.58	25.6	–	3.6	3.6	20.78	5650

AMF: Arbuscular microrrhiza fungi; TMO: total number of soil microorganisms.

Dash (-) indicates no data recorded.

Beneficial microorganisms such as Rhizobium bacteria (fixes atmospheric nitrogen), Earthworms (facilitates the breakdown of organic matter and improves soil fertility), and mycorrhizal fungi (symbiotic relationships with crop plants that aid in nutrient uptake and plant growth) are highly sensitive to higher levels of temperature (Bhardwaj et al., 2023; Zhang et al., 2023), but their number in the soil increases by 80% after the solarization process and becomes more resistant to the pathogens than unsolarized soils (Zhang et al., 2023) (Figure 2; Table 3). In addition, the beneficial fungal, bacterial, and actinomycete populations are reported to increase after 12 weeks of solarization (Gebretsadkan et al., 2020; Sofi et al., 2014) (Figure 2). Similarly, 8 weeks solarization period increases soil microbial biomass and reduces the antagonistic effect on beneficial microorganisms such as Bacillus spp., actinomycetes, and fluorescent pseudomonads (Balakrishna et al., 2015). Solarization increased the number and percentage of root nodules and colonization of mycorrhizal fungal in beans (Kader et al., 2020). Pathogen-hostile and growth-promoting bacteria and fungi survive, adapt, and repopulate quickly on the solarized soil (Balakrishna et al., 2015). Although detailed information is lacking, it is generally believed that earthworms hideaway deeper into the ground to escape the heat (Di Mola et al., 2021).

3.5. Soil solarization on soil borne diseases management

Soil borne pathogens are responsible directly for reducing crop yields and quality deterioration, and indirectly more money is needed for buying pesticides which has negative impact on soil biodiversity (Wolie, 2023).

The heat generated by soil solarization, alters the microbial population in the soil and eliminates the harmful pathogens including soil fungi (Fusarium oxysporum, Rhizoctonia solani, and Phytophthora cinnamomi), bacteria (Pseudomonas, Solanacearum-Solanacearum-Tonanaellum-Tonanaartansie-Scabies), and nematodes (Cricibactera, MeloidaNesie, Atylenchus penetrants) (Bhardwaj et al., 2023; Jagtap et al., 2022; Rokunuzzaman et al., 2016). The population of fungal pathogens decreased by 25% after 30 days of solarization (Dwivedi and Dwivedi, 2020) (Tables 3 and 5). This is due to the increasing humidity and volatile compounds that are toxic to many pathogens (Sofi et al., 2014). Fungal pathogens are sensitive to higher soil temperature and other antagonists (Jagtap et al., 2022; Thakur & Raj, 2023).

Table 5. Effect of soil solarization on numbers of pathogen population (g^-1 of soil), disease infestation and management (%).

Treatments	Durations	Crop type	Diseases (pathogen) type	Diseases parameters			Reference
				Pop. No	Infestation	DME
Solarized	3, 6, 9	Strawberry	Nematode	–	69, 84, 87	90	Abd-Elgawad et al. (2019)
Unsolarizd	–	Strawberry	Nematode	–	10	–
Solarized	4	All type	Fusarium oxysporum	498	–	40.64	Bhardwaj et al. (2023)
Unsolarizd	–	All type	Fusarium oxysporum	839	–	–
Solarized	4	Artichoke	Verticilium wilt	–	34	33	Guerrero et al. (2019)
Unsolarizd	4	Artichoke	Verticilium wilt	–	67	33
Solarized	6	Tomato	Nematodes	14.61	0	100	Mullaimaran et al. (2022)
	–	Melon	Nematodes	–	0	100
Unsolarizd	–	Tomato	Nematodes	20.37	100	–
	–	Melon	Nematodes	–	100	–
Solarized	2, 3, 4	Guava	Fusarium wilt	–	40, 38, 42	60, 62, 58	Dwivedi and Dwivedi (2020)
Unsolarizd	–	Guava	Fusarium wilt	–	46	54
Solorized	4	Cabbage	Fungi	17387	–	62.7	Neamatallah (2018)
Unsolarizd	–	Cabbage	Fungi	46631	–	–
Solarized	4	Onion	Blight bacteria	–	50	5.66	Sharat et al. (2018)
Unsolarizd	–	Onion	Blight bacteria	–	53	–
Solorized	4	egg plant	Root knot	3.2	–	39.6	Shutt et al. (2021)
Unsolarizd	–	Egg plant	Rootknot	5.3	–	–
Solarized	4,5	Egg plant	Nematode	3.5, 16	–	30.1
Unsolarizd	–	Egg plant	Nematode	5.01	–	–

Pop. No. = numbers of pathogen populations, DME = diseases management of efficacy of solarization (%).

The negative sign (-) indicated increment of soil seed bank from the previous season, dash (-) indicates no data recorded.

Solarization for 3, 6 and 9 weeks reduce soil borne diseases incidence and severity by more than 50% (Abd-Elgawad et al., 2019; Gebretsadkan et al., 2020) (Figure 2; Table 5). Similarly, Nematode population reduced with increased time of solarization by up to 37- 100% (Mullaimaran et al., 2022), and stem rot disease by 83.02% compared to unsolarized plots (Rubayet et al., 2017). After 6 weeks of solarization, the population density of Verticillium dahliae decreased from 1,600 to 300 CFU g⁻¹/soils, and reduced its incidence by 70% (Fatemy, 2019; Guerrero et al., 2019). Therefore, soil solarization controls a wide range of soil-borne pathogens including fungi, bacteria and nematodes (Gebretsadkan et al., 2020). Thus, soil solarization is similar with biological control agents to eliminate soil borne disease.

3.6. Soil solarization on weed density and weed soil seed bank management

Soil seed bank is a source of weeds for the next seasons and have an allure that allows them to sense the soil environment to either go dormant or become active for germination (Schwartz-Lazaro and Copes, 2019).

Solarization has abroad spectrum to kill and deplete the seed reserves of diverse invasive weed species (Kisekka et al., 2023). Raised temperature above certain threshold (>54⁰C), and humidity due to soil solarization are the main factors behind the thermal death of seeds during solarization (Cohen et al., 2019; Jagtap et al., 2022). Irrigation before solarization increases the efficiency in depleting weed soil seed bank by 78% at greater depth (Wolie et al., 2023). This is due to moisture initiates the buried seeds to germinate, and reduces soil seed bank through interrupting longevity and dormancy, sunburn of sprouted weeds, and reduces seed germinability (Schwartz-Lazaro and Copes, 2019).

The broader efficacy of soil solarization has been demonstrated on several invasive and parasite weed species, including broomrape (Wolie et al., 2023; Golzardi et al., 2015; Mauro et al., 2015) (Table 4). About 82% of the weed species density was killed by 7 weeks of solarization (Kanellou, et al., 2023), and it has decreased the viability Acacia saligna seeds by 100% which was intentionally buried (Cohen et al., 2019). It reduces general weed infestation by 64% (Safdar et al., 2021). Successful control of weeds such as bluegrass, Ageratum spp., Amaranthus spp., barnyard grass, cogongrass, common purslane, Digitaria spp., Portulaca spp., redroot pigweed, Setaria spp., broomrape, and many others has been achieved using soil solarization (Gill et al., 2017; Kisekka et al., 2023) (Figure 2).

Table 4. Effect of soil solarization on weed density (m^-2), biomass (gm^-2) and soil seed bank depletion (%).

Treatments	Duration (weeks)	Crop	Weed type	Weed density	Biomass	Seed bank depletion	Reference
Solarized	–	All type	All type	–	–	95.5	Pereira et al. (2023)
Unsolarizd	–	All type	All type	–	–	−7.59
Solarized	4	Onion	All type	85	–	90	Gill et al. (2017); Setyowati et al. (2017)
Unsolarizd	–	Onion	All type	166	90	10
Solarized	4, 6, 8	Mooth	Acacia saligna	–	1.5,0.5,0.025	80,40 & 40	Cohen et al. (2019); Jagtap et al. (2022)
Unsolarizd	–	Mooth	Acacia saligna	–	2.6	−10
Solarized	3	Tomato	Orbanche	1.67	11.67	78	Wolie et al. (2023)
Unsolarizd	–	Tomato	Orbanche spp.	37.3	32.33	−10
Solarized	2, 3, 4, 6, 8	Tomato	Orbanche spp.	41, 46, 35, 12, 26	–	21,37,53, 68, 84	Golzardi et al. (2015)
Unsolarizd		Tomato	Orbanche spp.	114.5		−32
Solarized	3, 6, 9	Carrot	All type	861, 553, 314	245, 195, 127		Muthumanickam and Anburani (2019)
Unsolarizd		Carrot	All type	1057	316	–
Solarized	1, 2, 3	Tomato	Orbanche spp.	–	–	97.7	Mauro et al. (2015)
Unsolarizd	–	Tomato	Orbanche spp.	–	–	−2.2
Solarized	2, 3, 4	Cumin	All type	37,24,16	8,6,3	90
Unsolarizd	–	Cumin	All type	55	21	−10	Meena et al. (2019)

Application of a single cycle wet solarization reduces broomrape seedbank by 56% (Fatemy, 2019), 72.95% (Wolie et al., 2023) and 98% (Hamooh, 2014; Mauro et al., 2015) over unsolarized plots, respectively. Findings from dryland environments indicated that soil solarization reduces weed density by 90% in potato (Salvador & Bañoc, 2020), 50% in carrot; 80% in tomato (Kumar et al., 2023) and 90% in lettuce over unsolarized soil (Zhang et al., 2023). This significant reduction of weed density may be due to maximum temperature attained during solarization decayed weed seed bank and killed germinating seedlings.

3.7. Is soil solarization really economically feasible to improve crop productivity?

Soil Solarization with transparent plastic film enhances crop yield significantly. Studies show that vegetable biomass weight and yield improved by 30%, and 53% (Al-Shammary et al., 2020). It increases yield of potato by 121.67% (Rubayet et al., 2017), orange trees 58% (Abouziena, and Haggag, 2016), tomato 76.83, 90%, 133 to 258% (Al-Shammary et al., 2020; Nicole and Christian, 2017; Wolie et al., 2023), lettuce 32.1% (Mullaimaran et al., 2022), strawberry 115.4% (Abd-Elgawad et al., 2019), cabbage 26.9%, 90%, (Neamatallah, 2018), eggplant 79.1%, 65.56% (Hamooh, 2014; Hamooh and Alsolaimani, 2014), onion 26.4% (Gebretsadkan et al., 2020), pepper 21.2.% (Zayed et al., 2013), cucumber 133 to 258% (Fatemy, 2019), fababean and chick Pea 200–300%, dry bean 43.2%, field Beans 331%, lentils 441%, peas 92% (Kader et al., 2020), corn 276.7, wheat 82.1% (Zhang et al., 2020), sesame 33.6% (Safdar et al., 2021) over unsolarized plots (Table 6). This yield improvement may be due to the sequential application of soil solarization eliminates weeds, and diseases infestation and improves soil fertility (Safdar et al., 2021).

Table 6. Effect of soil solarization on crop yield (t.ha) and economic profitability (US$) over unsolarized plots.

Crop type	Solarized	Unsolarizd	Advantage	Country	SP kg^-1	EA ha^-1	Reference
Strawberry	14	6.5	7.5	Egypt	0.032	240	Abd-Elgawad et al. (2019)
Lettuce	21.4	11.6	9.8	Saudi Arabia	0.68	6664	Al-Solaimani et al. (2015)
Cucumber	82.8	57.3	25.5	Iran	0.27	6885	Fatemy (2019)
Artickoke	53.23	45.74	7.49	Spain	6.69	50108.1	Guerrero et al. (2019)
Strawberry	68.035	55.75	12.28	Spain	1.06	1484	De los Santos et al. (2021)
Lettuce	46.9	35.5	11.4	Italy	1.06	12084	Öz (2023)
Tomato	31.17	8.07	23.1	Ethiopia	0.018	415.8	Wolie et al. (2023)
Onion	10.6	7.8	2.8	Ethiopia	0.018	50.4	Gebretsadkan et al. (2020)
Cabbage	1.144	0.904	0.24	Saudi Arabia	0.27	64.8	Hamooh and Alsolaimani (2014)
Eggplant	9.5	5.7	3.8	Saudi Arabia	0.27	1026	Hamooh and Alsolaimani (2014)
Soya bean	3.7	2.1	1.6	Japan	0.057	91.2	Kader et al. (2020)
Okra	4.5	2.8	1.7	China	1.2	2040	Jagtap et al. (2022)
Tomato	47.06	36.73	10.33	India	0.012	123.96	Kumar et al. (2023)
Cabbage	19.9	14.3	5.6	India	0.3	1680	Kumar et al. (2023)
Cauliflower	25.02	18.58	6.44	India	0.27	1738.8	Kumar et al. (2023)
Chili	19.71	16.79	2.92	India	0.27	788.4	Kumar et al. (2023)
Cabbage	87	80	7	China	1.6	10560	Zhang et al. (2023)
Sesame	1.68	1.18	0.5	Iran	0.024	12	Madandoust and Ranjbar (2017)
Cumin	1.79	1.24	0.55	India	0.12	66	Meena et al. (2019)
Kale	8.1	5	3.1	Georgia	5.95	18445	Ney et al. (2019)
Chill	46.38	11.46	34.92	Indonesia	0.065	2269.8	Purnamasari and Dianawati (2022)
Sesame	0.57	0.43	0.08	Pakistan	0.35	28	Safdar et al. (2021)
Tomato	31.2	8.06	23.14	Ethiopia	0.018	416.52	Wolie et al. (2023)
Onion	29.07	23.33	5.74	United States	4	22960	Sharat et al. (2018)
Eggplant	19	11	8	Nigeria	0.013	104	Shutt et al. (2021)
Pepper	71.4	58.9	12.5	Egypt	0.032	400	Zayed et al. (2013)
Tomato	3.4	1.6	1.8	Ethiopia	0.018	32.4	Tewodros et al. (2016)
Average	46.81	29.07	17.42		0.913	5363.91

SP: Selling price (US$ kg^-1); EA: economic advantage over unsolarized plots (US$ ha^-1).

Economic viability of soil solarization is determined by the cost of plastic, the labor required to install and remove plastic, positive residual effect, and the price of crop yields (Wolie et al., 2023). The use of solarization has reported as the most economically viable and sustainable option for small-scale farmers (Gill et al., 2017). It is profitable by 11,798.48 $ ha⁻¹ over unsolarized plots and investing one dollar gives a return of 6.6$ profit (Wolie et al., 2023). Besides, a cost benefit ratio of 1.79 has reported in the application of soil solarization to control disease and weeds on cumin productivity (Meena et al., 2019). This indicates that investing one dollar for the application of solarization to control diseases and weeds provides about 1.79 $ of return. It would yield a return investment of about 56% per year (Maraveas, 2020) and represents a beneficial management measure to increase soil productivity and these results encourage future commercial application of this environmentally sound technique.

3.8. Impact of soil solarization on environment and climate

Soil solarization has supposed to impose several positive and negative effects on the environment and climate. It accelerates the turnover and degradation of organic matter, and its disposal through incineration, creates excessive toxic greenhouse gas emissions, and higher environmental pollution (Maraveas, 2020). It can directly affect soil respiration and alter CO₂ by altering soil surface properties and influencing the soil microenvironment (soil temperature, humidity, porosity, and ventilation) (Pereira et al., 2023). Studies indicated the temperature gradients created during soil solarization could result in a shift in soil micro biota, although these impacts have not yet been well quantified (Fernández-Bayo et al., 2019).

Soil solarization reduces soil surface evaporation and increase soil water content in the root zone and this induces more active nitrifying microorganisms until the next harvest at 45.5⁰C, and this promotes CH₄ production and emissions (Ihara et al., 2014). During solarazation, the population of anaerobic microorganisms begins to increase, they consume the carbon in the organic compounds and oxygen in the soil, resulting in a significant rise in temperature and release of carbon dioxide and water, but aerobic microorganisms stop multiplying, and then formation of organic acids ammonium, and nitrous acid takes place (Díaz-Hernández et al., 2017). Higher concentration of greenhouse gases could be emitted from soil which could aggravate global warming and climate change (Pereira et al., 2023).

The amount of polyethylene plastic films used for solarization has been estimated to be about 1.8 million tones (Mormile et al., 2017). Therefore, their proper disposal and recycling is vital to reduce environmental footprint (Wolie, 2023). Because these plastic sheets are hydrophobic, this may aggravate runoff rate and accelerates soil erosion (Dong et al., 2022; Nan et al., 2016). These polyethylene plastic sheets are often disposed in a landfill, in the ground and these approaches can cause adverse environmental impacts (Di Mola et al., 2021). Especially low-density polyethylene films have great impact on the environment as they take around 100 years to decompose (Van Schothorst, 2021). This may impose a negative impact on climate and health. Besides, their disposal demands labor, special equipment, and cost.

The value of solarization in terms of its disposal and environmental impact initiates the development of biodegradable plastics which are safe to the environment and climate (Dong et al., 2022). So as environmentally safe technique, exploring biodegradable films should be considered in agronomic application of solarization (Mormile et al., 2017). During and after the application of solarization, care should be taken not to throw the plastic anywhere and should be removed during night to reduce greenhouse gas emission from covered surfaces (Di Mola et al., 2021; Dong et al., 2022).

4. Conclusion

Soil solarization which significantly increases soil temperature has a broader efficacy in improving moisture deficiency, depletes weed seed bank and infestation, control soil borne diseases and enhances soil nutrient contents which are the major challenges in dryland agriculture sustainably and effectively. Besides, it has a positive impact on beneficial soil microorganisms to improve soil fertility, and nutrient availability thereby increase crop yields by more than 50% and being the most economically viable and sustainable option for small-scale farmers. It is more successful in sandy and moist soils, hottest season, dark cover type and long duration. However, its mismanagement may aggravate greenhouse gas emission and environmental pollution. Therefore, application of biodegradable plastic films with prior irrigation makes solarization safe, effective, and economical. Application of sequential soil solarization in small scale farmers could substitute the use of pesticides, herbicides and chemical fertilizers thereby reducing their adverse impacts on the environments and economics. It is a sustainable and environmentally sound solution which is similar with biological control agents to eliminate weeds and diseases infestation and improves soil fertility.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Wolie Gebremicheal Gebreegziher

Wolie Gebremicheal Gebreegziher is a lecturer and researcher at department of dryland crop and Horticultural science, college of dryland agriculture and natural resources, Mekelle University working since the last 7 years ago. He has been working in agronomic application of soil solarization, soilless culture technology and exploitation of genetic diversity for climate change adaptation and food security in drylands. He is interested in dealing with new agricultural technologies which could help to use land and other farm inputs efficiently, improve yield, reduce climate and pest related risks so as to transform dryland agriculture.