Glycine betaine application improved seed cotton yield and economic returns under deficit irrigation

1 Introduction

Low profitability, high energy use, greenhouse gas emissions due to intensive use of fertilizers and tillage practices, drought, salinity, floods, pest infestation, and evolution of herbicide and pesticide resistance are threatening cotton production around the world (Mollaee et al., 2019). Global climate changes characterized by gradual rise in temperatures and adverse regional consequences of temperature and precipitation alterations are further aggravating the difficulties in cotton production (Li et al., 2024). Precipitation plays a crucial role in growth and maturation of cotton plants. Inadequate precipitation-mediated drought is considered a significant abiotic stress, significantly curtailing cotton yield (Guo et al., 2024). Climate projections have revealed that Türkiye is expected to significantly affect from global warming (Demircan et al., 2017) and recent reports suggested that the country is warming at a higher rate than the rest of the world (Zittis et al., 2022). Hence, effective exploitation of available water resources is inevitable for sustainable cotton production. Elevated temperature and reduced precipitation are the expected consequences of climate change in Türkiye, which would reduce the available water resources. Hence, there is a dire need to conserve and efficiently utilize available water. Cotton production in the southeastern Anatolia region requires 700–800 mm water by drip irrigation method. Although the region receives ∼450 mm rainfall during the whole year, only 2 % of this (∼10–12 mm) is received during the cotton growing season. Therefore, irrigation becomes inevitable for cotton production.

Harran plain in Türkiye is the major cotton cultivation region producing 25 % of the country’s total production (Çullu et al., 2022). The development of major irrigation project [Southeastern Anatolia Project (GAP)] in 1995 has increased the cotton cultivation in the region due to surplus irrigation water supply (Aydogdu et al., 2018). Cotton crop requires higher amount of water (700–800 mm water by drip irrigation method), particularly in Harran plain (Cetin, 2020); however, altered precipitation regimes (no or minimum rainfall during the cotton growing season) could lower water availability in the region (Demircan et al., 2017). Nevertheless, the number of irrigations required for successful crop production will increase due to the extreme temperature, causing excessive use of underground and surface water resources (Hussain et al., 2018). Therefore, agronomic practices aimed at improving irrigation water use efficiency would be required to sustain cotton production in the Harran plain.

Irrigation practices exert significant impacts on the soil microbial activities and subsequently emission of greenhouse gases such as CO₂, N₂O and CH₄ (Sapkota et al., 2020). Increased emission of these gases could decrease available water resources because of global warming. Different irrigation systems exhibit significant variation in the emission of greenhouse gases (Wu et al., 2014) and deficit irrigation is known to lower the emission of these gases (Gultekin et al., 2023). Nevertheless, greenhouse gas emissions of soils under different tillage systems increased after the irrigation as compared to pre-irrigation (Calderón and Jackson, 2002). The increased emission after irrigation is associated with an increased soil moisture content and an improvement in soil physical quality and biological activity. Deficit irrigation is a viable alternative to full irrigation for lowering greenhouse gas emissions (Martínez-Nicolás et al., 2019). Reducing irrigation quantity to a certain extent did not alter the yield of pomegranate (Martínez-Nicolás et al., 2019). Nevertheless, combination of deficit irrigation and osmolytes could provide comparable yield to full irrigation (Ünlü et al., 2011). Moreover, deficit irrigation significantly reduces the emission of greenhouse gases (Hou et al., 2019). Therefore, combination of deficit irrigation and osmolytes could prove a viable alternative to sustain cotton yield and lower greenhouse gas emissions.

Osmolytes such as salicylic acid, ascorbic acid, and glycine betaine are exogenously applied to plant leaves under deficit irrigation. Several earlier studies have indicated that application of salicylic acid, ascorbic acid, and glycine betaine improved cotton productivity under deficit irrigation practices (Arekhi et al., 2023; Mahdi et al., 2020). These substances stimulate defensive response against biotic and abiotic stresses (Mehta and Vyas, 2023). Glycine betaine is used as foliar spray and mixed with irrigation water to improve the negative effects of water stress and increase crop yield (Hussain et al., 2008). These osmolytes improve cotton productivity under water deficit by multiple mechanisms, including maintaining water balance, protecting cellular structures, and enhancing photosynthesis and growth under water deficit conditions. However, the impact of these substances on CO₂ emissions in cotton crop under water deficit conditions remains elusive.

The objective of this study was to investigate the impact of osmolyte treatments and deficit irrigation on seed cotton yield, CO₂ emissions, and economic returns of cotton crop. The practice of deficit irrigation was believed to have the potential to decrease both crop productivity and CO₂ emissions. It was hypothesized that providing osmolytes during deficit irrigation will help decrease crop loss and CO₂ emissions.

2 Materials and methods

2.1

2.1 Experimental site and soil properties

The study was carried out in the research fields of the Harran University, Şanlıurfa, Türkiye during cotton growing season of 2021. Soil pH of experimental site was 7.92, and the organic matter content was 1.12 % (Ramazanoglu, 2019). Some soil properties are given in Table 1.

Table 1 Physical and chemical properties of experimental site.

Depth (cm)	pH	Organicmatter (%)	Lime(%)	Plant Nutrients (mg kg−1)
				P	K	Mg	Fe	Zn	Cu	Mn
0–30	7.92	1.12	29.6	4.70	180	303	3.46	0.72	4.64	0.44

The average monthly temperature during the cotton growing season was 28.7 °C, total precipitation was 31.2 kg m⁻², and relative humidity was 31.2 %. The long-term average monthly temperature was 26.2 °C, total precipitation was 91.1 kg m⁻², and relative humidity was 38.3 %. The cotton-growing season was drier compared to the long-term climate data of the study area (Fig. 1).

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Fig. 1

Weather data of the experimental site during cotton growing seasons and long-term climatic conditions of the region.

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3 Results

3.1

3.1 Effect of osmolytes and deficit irrigation on daily CO₂-C emission (mg CO₂-C m⁻² h⁻¹)

The individual and interactive effects of irrigation levels and osmolytes significantly (p < 0.01) altered CO₂-C emission. The lowest (1.55) and the highest (1.94) carbon emission were recorded for 50 % deficit (I₅₀) and 100 % irrigation (I₁₀₀) treatments, respectively. Similarly, the lowest (1.52) and the highest (2.19) carbon emission were noted for salicylic acid and glycine betaine application, respectively. Regarding interactions, the lowest (1.13) and the highest (2.42 mg) carbon emission ess recorded for I₅₀ × salicylic acid and I₁₀₀ × salicylic acid interactions, respectively.

The lowest CO₂-C emission from individual and interactive effects of different irrigation levels and osmolyte applications was measured in the 18th week (Fig. 2). The individual and interactive effects of different irrigation levels and osmolyte applications significantly (p < 0.01) affected CO₂-C emission from soil. The lowest (10.91) and the highest (12.73) carbon emission was recorded for I₅₀ and I₇₅ irrigation treatments, respectively. Likewise, the lowest (11.56) and the highest (11.85) emission were observed for control and glycine betaine application, respectively. Regarding interactive effect, I50 × salicylic acid and I75 × salicylic acid resulted in the lowest (10.04) and the highest (13.61) carbon emission, respectively.

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Fig. 2

Relationship between osmolytes application with CO₂-C emission under different irrigation.

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3.2

3.2 Effects of deficit irrigation and osmolyte application on cumulative CO₂-C emission

The highest (90.10 ± 0.06 mg kg⁻¹ soil) and the lowest (80.59 ± 0.45 mg kg⁻¹ soil) total CO₂-C emission in I₅₀ × osmolytes’ interaction was recorded for I₅₀ × control and I₅₀ × glycine betaine application, respectively. Similarly, I₇₅ × osmolytes’ interaction indicated that the highest (85.27 ± 0.22 mg kg⁻¹ soil) and the lowest (82.89 ± 0.07 mg kg⁻¹ soil) total CO₂-C emission was recorded for I₇₅ × salicylic acid treatment, and I₇₅ × glycine betaine treatments, respectively. The decrease in CO₂-C emission for I₇₅ × glycine betaine application was 1.7 % compared to the I₇₅ × control treatment. The CO₂-C emission in all other osmolyte treatments increased compared to the control except glycine betaine. Likewise, I₁₀₀ × osmolytes’ interaction indicated that the highest (89.89 ± 0.45 mg kg⁻¹ soil) and the lowest (85.68 ± 0.39 mg kg⁻¹ soil) total CO₂-C emission was observed for I₁₀₀ × glycine betaine, and I₁₀₀ × salicylic acid application, respectively. The I₁₀₀ × glycine betaine application caused a 4.8 % increase in CO₂-C emissions compared to control. The CO₂-C emission in all I₁₀₀ × osmolytes’ interactions except salicylic acid application increased compared to the control (Fig. 3).

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Fig. 3

The CO₂-C (mg m⁻² h⁻²) emission from the cotton-cultivated soil under different osmolyte applications and deficit irrigation treatments.

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3.3

3.3 Effect of deficit irrigation and osmolytes application on cotton yield

Seed cotton yield was significantly (p < 0.01) affected by the individual and interactive effects of different irrigation levels and osmolytes. The I₅₀ and I₁₀₀ irrigation treatments resulted in the lowest (3800 kg ha⁻¹), and the highest (4746 kg ha⁻¹) seed cotton yields, respectively. Similarly, no application of osmolytes and glycine betaine application resulted in the lowest (4097 kg ha⁻¹) and the highest (4545 kg ha⁻¹) seed cotton yield, respectively. Regarding interactions, I50 × control and I100 × glycine betaine resulted in the lowest (3530 kg ha⁻¹) and the highest (5050 kg ha⁻¹) seed cotton yield, respectively (Fig. 4).

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Fig. 4

The effect of osmolytes application on cotton yield (kg ha⁻¹) under different deficit irrigation treatments.

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4 Discussion

The CO₂ emissions from cotton planted in a semi-arid region were investigated in the current study. The lowest and the highest carbon emission was noted for I₅₀ and I₁₀₀ irrigation treatments, respectively. The CO₂-C emission from the soil is closely related to the soil properties (microorganism, C, N, etc.), topography, environmental conditions (irrigation, fertilization), and plant root respiration. Insufficient water in soils causes significant disruptions in the carbon and nutrient cycles. Water constraint is the main factor affecting the physiological properties of soil microorganisms. Therefore, the amount of CO₂-C emission increased with the increase in the amount of irrigation water. The application of irrigation water increased the C emission from the soil. The CO₂-C emission rate increased at the beginning of cotton growth period and then decreased. Microorganism activity in soils is higher under drip irrigation conditions. The increase in carbon mineralization increases microbial activity and respiration, thus increasing CO₂-C emission from the soil. The emission of greenhouse gases is significantly influenced by irrigation techniques (Sapkota et al., 2020). Increased release of these gases may lead to a reduction in accessible water resources due to the effects of global warming. Various irrigation systems differ significantly in their greenhouse gas emissions (Wu et al., 2014). It is well-established that deficit irrigation reduces the emission of these gases (Gultekin et al., 2023). The higher irrigation rates (I₁₀₀ and I₇₅) increase activities of the soil microorganisms, as well as the breakdown of organic matter and CO₂ release (Kumar et al., 2016) The results of the current study are in agreement with the findings of Scheer et al. (2013) who studied the effects of deficit irrigation on CO₂-C emissions. The lower water application decreased the CO₂-C emission. Kumar et al. (2016) reported less CO₂-C emission in the low irrigation level in eastern India than in the higher irrigation level. The root respiration is largely dependent on the photosynthetic rate transported from the above-ground part of the plant; therefore, soil CO₂-C emission may be significantly correlated with plant production (Kakumanu et al., 2019).

The lowest mean carbon emission was noted for salicylic acid and the highest was recorded for glycine betaine application. The lowest carbon emission in irrigation × osmolyte application was recorded for I₅₀ × salicylic acid, whereas the highest emission was recorded I₁₀₀ × salicylic acid application. The high CO₂-C emission in glycine betaine applications may be associated with the high plant activity since glycine betaine is a simple and flexible amino acid readily used by the plants (Hernandez-Leon and Valenzuela-Soto, 2023). However, the uptake of salicylic acid is difficult because it has a crystalline structure and is less soluble in water (Kawashima et al., 2011). Therefore, the utilization rate of salicylic acid by the plants is low, and thus, its activity on the plants is low. Low plant root activity and low respiration can result in low CO₂ production. Photosynthesis rate decreases as the CO₂ concentration in the leaves decreases with the closure of the stomata (Lawlor, 2002). The decrease in photosynthesis rate with the closure of stomata (Farrant, 2000) and lowered use of atmospheric CO₂ by the plants is a disadvantage for global warming. The plants constrain CO₂ fixation under insufficient soil water by closing its stomata to prevent water loss (Flexas, 2002).

The production of crops remains unaffected when the amount of irrigation is reduced to a certain degree (Martínez-Nicolás et al., 2019). Nonetheless, the use of deficit irrigation combined with osmolytes has the potential to achieve a yield similar to that of full irrigation(Ünlü et al., 2011). In addition, deficit irrigation has been found to substantially decrease the release of greenhouse gases(Hou et al., 2019). Thus, the utilization of deficit irrigation and osmolytes may present a feasible option to maintain cotton productivity. The CO₂ needed in photosynthesis increases the emission of greenhouse gases that cause an increase in atmospheric temperature. Therefore, different osmolytes were applied to help cotton plants perform their normal life functions under deficit irrigation. The application of all osmolytes improved cotton yield under deficit irrigation. Ascorbic acid proved the most effective in improving cotton yield even under severe deficit. Ascorbic acid can improve cotton output under water deficit conditions by minimizing oxidative injury, conserving photosynthetic ability, and stimulating growth and yield factors (Mekki et al., 2015). Hence the improvement in seed cotton yield by the application of ascorbic acid is owed to these mechanisms.

The C, CO₂ and soluble mineral substances increase rapidly in dry soil compared to moist soil. Therefore, deficit irrigation causes more CO₂-C emissions in wetting and drying soils (Kakumanu et al., 2019). The application of osmolytes causes an increase or decrease in CO₂-C, when a dry soil is wetted (Warren, 2016). Similar results were obtained in the present study. The response of emission factor to osmolyte + deficit irrigation applications was positive. The EFs values were lower than the default values stated in the IPCC. The results can be attributed to the low organic carbon content of the experimental site (Wang et al., 2016). Cayuela et al. (2017) reported the EFs value as 0.005 (0.5 %) in a study on fertilizer management, crop management and water management in warm climate zone and stated that this was far below the default value. In another study using mineral fertilizer applications, the EF values were calculated as 0.0107 and 0.006 (1.07 % and 0.6 %), which were different from the default values (Mazzetto et al., 2020). In the near future, the products can only be exported or imported considering the amount of water (green, blue, gray) used in the production and CO₂ emission values (emission value per product).

5 Conclusion

It is concluded that application of glycine betaine can be used to improve seed cotton yield and economic returns under I₁₀₀ and I₇₅ irrigation treatments. Nevertheless, ascorbic acid proved most effective in improving yield and economic returns under I₅₀ irrigation treatment. The carbon emission was higher under full irrigation compared to deficit irrigation and glycine betaine proved helpful in reducing CO₂-C emission under deficit irrigation compared to normal irrigation. Therefore, glycine betaine can be used to improve yield and economic returns of cotton and lower CO₂-C emission under deficit irrigation.

CRediT authorship contribution statement

Emrah Ramazanoglu: Writing – review & editing, Writing – original draft, Visualization, Software, Investigation, Formal analysis, Data curation. Nimet Kılınçoğlu: Writing – review & editing, Methodology, Investigation, Formal analysis, Data curation. Vedat Beyyavas: Writing – review & editing, Writing – original draft, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization. Cevher İlhan Cevheri: Writing – review & editing, Visualization, Methodology, Investigation, Formal analysis, Conceptualization. Erdal Sakin: Writing – review & editing, Validation, Methodology, Conceptualization. Ahmet Çelik: Writing – review & editing, Validation, Methodology, Investigation, Data curation, Conceptualization.