Green waste-derived compost (GWC) alleviates drought stress and promotes sugar beet productivity and biofortification

ABSTRACT Green waste-derived compost (GWC) is a valuable soil amendment for improving soil organic matter and decreasing waste products and potential pollutants. The study was carried out to evaluate the effect of GWC application on the yield and quality of sugar beet under deficit irrigation conditions using different irrigation systems. A field experiment was conducted using the commercial sugar beet variety Gazelle in sandy soil. Two doses (0 and 14 t ha−1) of GWC were applied to the soil. Three water deficiency levels (60, 80 and 100% of the soil field capacity) under either drip and sprinkler irrigation systems were applied. The application of 14 ton ha−1 of GWC resulted in the highest root and recoverable sugar yields, especially under the well-irrigated conditions under drip irrigation. Sugar beet root biofortification and juice quality were also significantly improved under drip irrigation in response to the application of 14 ton ha−1 of GWC by increasing sucrose content, quality index (Qz)% and recoverable sugar (RS)%. The application of GWC under drip irrigation enhanced water use efficiency for root (WUERY) and recoverable sugar yields (WUERSY), in particular under drip irrigation and water deficit conditions (60% of the soil field capacity). The soil physicochemical properties were significantly improved in response to the application of GWC. GWC application promoted the yield and biofortification of sugar beet by improving the soil physiochemical properties, and nutrient mobilization and uptake. The application of GWC is essential for sustainable sugar beet production and efficient irrigation water use in sandy soils.


Introduction
Cultivation of sugar beet (Beta vulgaris, L.) in arid and semi-arid regions to replace or supplement cane sugar production is steadily increasing (Abou-Elwafa et al., 2020;Simova-Stoilova et al., 2016).The main advantage of sugar beet cultivation as a promising sugar crop in these areas is its ability to effectively grow and produce a high sugar content and yield in a short growing period.Besides, in addition to its ability to efficiently grow in the newly reclaimed soils which are common in these areas, sugar beet has a lower irrigation requirement (Abo-Elwafa et al., 2013;Abou-Elwafa et al., 2020;Balakrishnan & Selvakumar, 2009).
Drought stress is the most devastating abiotic stress that causes great crop losses worldwide.In light of global warming and climate changes, some geographical regions are expected to face frequent severe drought conditions.The development of agronomical practices to improve crop productivity by enabling plants to cope with deficit irrigation conditions is considered as an efficient and cost-effective strategy to overcome drought stress in low-value cropping systems (Abou-Elwafa, 2016;Abou-Elwafa & Shehzad, 2021;Simova-Stoilova et al., 2016).Therefore, significant efforts have been carried out to minimize the impacts of drought stress on the potential yield and quality of sugar beet (Abou-Elwafa et al., 2020).The occurrence of drought stress early in the growing season exhibits adverse effects on root growth and development of sugar beet.Meanwhile, when drought stress occurs during the late growth stages, the leaf area and the number of leaves, and thereby the photosynthetic capacity would be reduced.Furthermore, drought could adversely affect soil microorganisms leading to enhancing the susceptibility of crop plants to drought stress (Abou-Elwafa et al., 2020).Microorganisms could promote plant resistance to drought stress through several independent mechanisms, e.g.i) the production of polysaccharides that enhances soil structure and water-holding capacity, ii) the production of indole acetic acid (IAA), deaminase and proline that induce drought tolerance in crop plants, iii) enhancing water circulation through fungal mycelia, and iv) adverse impacts on microbial community structure and abundance, and thereby reducing nutrient availability (Milošević et al., 2012;Nguyen et al., 2018).Furthermore, drought stress would increase the concentrations of Na, K and α-amino-N, which adversely affect sugar recovery from the roots (Putnik-Delić et al., 2013).
Green waste-derived compost (GWC) is a concept for waste recycling and utilization that has recently become an essential approach for relieving urban green waste and improving urban polluted soil (Al-Dhumri et al., 2021;Bai et al., 2010;Jones et al., 2009;Vargas-Hernández et al., 2018).The reduction in the soil organic matter due to intensive cropping systems, and the increase in the water pollution caused by the elevated concentration of animal production has made the application of green waste-derived compost (GWC) a valuable approach for improving the soil organic matter while decreasing waste products and potential pollutants (Peigné & Girardin, 2004).GWC is known to have a high water-holding capacity and can supply water to plants over time, and thereby increasing the water retention of GWC-amended soils (Kranz et al., 2020).The application of GWC increases water availability to the plants and relieves the suppressant effect of irrigation deficit on plant productivity (Nguyen et al., 2012).
Beside its higher organic matter content, a major advantage of the application of GWC is a low pollutant and costs soil amendment (Aziablé & Kolédzi, 2018;Sánchez-Monedero et al., 2019).Furthermore, when mixed with the soil, GWC releases a large number of microorganisms into the soil and hence increases the soil microbes (Sánchez-Monedero et al., 2019).These microbes would have a significant impact on the decomposition of organic matter, and the accumulation and bioavailability of soil nutrients leading to an increase in agricultural productivity to ensure food security to a great extent (Ayilara et al., 2020;Tong et al., 2018).Additionally, the application of compost to the soil has been proven to reduce nitrogen losses, which is essential for sustainable agriculture (Ullah et al., 2020).Moreover, the GWC application helps in protecting the underground water from becoming polluted.
Considering the steadily rising demand for water from various fields and the expected water scarcity due to the adverse consequences of climate changes, various water demand management strategies have been implemented in agriculture to conserve water and enhance water use efficiency (Abou-Elwafa et al., 2020).Therefore, emphasis must be given to employing modern irrigation systems that are efficient in saving water and improving water use efficiency of crop plants such as drip and sprinkler irrigation.However, the acceptability of these systems relies on their success in terms of maximize the yield and biofortification with minimal water use.
The present study aims to i) evaluate the impact of green waste-derived compost (GWC) application on the yield and quality of sugar beet under different irrigation systems in sandy soils, and ii) evaluate the effect of GWC application on water-use efficiency and drought tolerance of sugar beet in sandy soils under drip and sprinkler irrigation systems.

Plant materials and experiments
A field experiment was conducted at the Nobaria Sugar Industry and Refining Company, El-Beheira, Egypt (lat 30° 38'N, long 30° 13' and alt 28 m asl) during the 2017/2018 and 2018/2019 growing seasons.A commercial sugar beet variety designated Gazelle was used in both growing seasons.Seeds were sown on September 23 and 27 and plants were harvested on April 10 and 13, in the first and second growing seasons, respectively.Seeds were hand sown at 15 cm spaces in a 15 m 2 plot consisting of 5 rows of 5 m in length, with 60 cm between rows.The green waste-derived compost (GWC) was applied as a soil amendment in two doses, i.e. 0 and 14 t ha −1 .GWC was applied to the soil surface before tillage and the incorporated into the soil in a different field in each growing season.The chemical analysis of the applied GWC is shown in Suppl.Table S1.Three levels of 60, 80 and 100% of the soil field capacity of either drip and sprinkler irrigation systems were applied.The application of N, P and K and other cultural practices were carried out according to the locally recommended practices for sugar beet production.In brief, superphosphate (15.5% P 2 O 5 ) was applied during soil bed preparation at a rate of 475 kg ha −1 .Nitrogen was applied at a rate of 250 kg ha −1 in the form of urea (46.5% N) in two equal doses, i.e. the first one after thinning (4-6 leaves-old plant), and the second one applied 4 weeks later.Potassium sulphate (50% K 2 O) was applied 4 weeks after sowing at a rate of 120 kg ha −1 .
A tri-replicate split-split plot design arranged in a randomized complete block design (RCBD) was used.The main plots were assigned to the two applied irrigation systems, i.e. drip and sprinkler irrigation.The deficit irrigation treatments were allocated to the supplot, whereas the sub-sub-plots were assigned to the application of GWC as a soil amendment.

Characterization of experimental soil and irrigation water
Composite representative samples were collected from the surface layer (0-30 cm) of the experimental soil for analyzing the physical and chemical properties before sowing.After harvest, soil samples were collected from each plot and chemical soil characteristics were analyzed.After airdrying and sieving, soil samples were ground and sieved using 2 mm sieves.The soil pH was estimated in a 1:2.5 of soil to deionized water suspension using a glass electrode (Jackson, 1973).A 1:2.5 of soil-to-water extract was implemented to measure the soil electrical conductivity (EC) using the EC meter (Hesse, 1998).The available nitrogen in the soil was extracted using 2.0 M potassium chloride and the micro-Kjeldahl method was employed to determine the nitrogen in the extract (Burt, 2004).A 0.5 M sodium bicarbonate solution was used to extract the available soil phosphorus at pH 8.5 and then the spectrophotometer set at a wavelength of 400 mµ was employed to measure phosphorus (Olsen, 1954).Extraction of the available soil potassium was performed according to the ammonium acetate procedure at pH 7.0.Potassium was then measured using flame photometry (Jackson, 1973).Estimation of the organic matter (OM) in the soil was performed using the Walkley -Black method (Jackson, 1973).The main physical and chemical soil properties are shown in Suppl.Table 2.
Irrigation water used in the experiment was pumped from a well.The chemical analysis of the irrigation water was performed according to the (AOAC, 1970) (Suppl.Table S3).Irrigation was performed by drip and sprinkler irrigation systems.The distance between the drippers was 20 cm.Sprinkler irrigation was applied with 4 and 5 m sprinkler spacing.Irrigation was applied based on measuring the soil field capacity using the undisturbed method essentially described by (Ali, 2010).Wellirrigated treatment was irrigated when the soil moisture reached 40% of the field capacity.Meanwhile, the drought-stressed treatments were irrigated when the soil moisture reached 24 and 32% of the soil field capacity (60 and 80% of the well-irrigated treatment).

Phenotypic evaluation
At harvest, roots from the three guarded rows of each plot were employed to determine root yield, and a representative root sample was used for analysis of juice quality at the Nobaria Sugar Industry and Refining Company laboratory.Sucrose% (Pol%), Na%, K%, αamino-N and quality index (Qz%) were measured using the Venema, Automation BV AnalyzerIIG-16-12-99, 9716JP/Groningen/Holland following the procedure used by Nobaria Sugar Company, as described by le-Docte (1927).Recoverable sugar (RS)% was calculated according to (Reinefield et al., 1974) as follows: Sugar recovery% Recoverable sugar yield (RSY) in tons per hectare was also estimated.
ii) The amount of irrigation water (AIW) was calculated using the following equation (Vermeirn & Gopling, 1984): where: IWA= the irrigation water applied (m 3 ), ETo = Reference evapotranspiration, Kc = crop coefficient (for sugar beet crop as reported by FAO, Allen et al. 1998), I= irrigation intervals (days), Ea= irrigation efficiency of the drip and sprinkler irrigation systems, and LR = leaching requirements.
The irrigation time for the drip irrigation system was estimated in advance by measuring the actual emitter discharges according to the following equation: (Jensen, 1980) where t = irrigation time (h), A = wetted area (m 2 ), and q = emitter discharge (L h −1 ).
The irrigation time for the sprinkler irrigation system was estimated according to the following equation: (Jensen, 1980) where AR= application rate (m 3 h −1 ) Jensen, 1980) where Q = sprinkler discharge (m 3 h −1 ), L l = distance between lateral (m) L s = distance between sprinkler (m).
iii) Water use efficiency (WUE) was calculated using the following formula according to (Jensen, 1980):

Statistical analysis
The Proc Mixed model in the SAS 130 package version 9.2 was implemented to carry out the analysis of variance (ANOVA) and Fisher's least significant difference (LSD) of significantly differed treatments.The SigmaPlot 14 Software (Systat Software, San Jose, CA, USA) was employed to perform correlation and linear regression analyses using three replicates.

Effect of GWC on beet root juice quality under deficit irrigation conditions
The application of GWC exhibited significant effects on beet root juice quality parameters, i.e. sucrose content, quality index (Qz%), recoverable sugar (RS)% and Na%, K % and α-amino-N% in the two growing seasons (Suppl. Table S5).The application of 14 ton ha −1 of GWC significantly improved beet root biofortification and juice quality by increasing sucrose content, Qz% and RS%.However, the impurities, i.e.Na%, K% and α-amino-N%, in the beet root juice were significantly increased in response to the application of GWC in both growing seasons (Tables 1 & 2; Suppl.Table S5).Irrigation systems significantly affect sucrose content, Qz%, RS%, Na%, K% and α-amino-N% in the two growing seasons (Suppl.Table S5).The Qz% and RS% were significantly increased under the drip irrigation system, whereas the Na%, K% and α-amino-N% were reduced in response to the employment of drip irrigation (Tables 1 & 2).All quality parameters including, sucrose, Qz%, RS%, Na%, K% and α-amino-N% differed significantly in response to deficit irrigation in the two growing seasons (Suppl.Table S5).
The juice quality and impurity parameters, i.e. sucrose%, RS%, Qz%, Na%, K% and α-amino-N%, were increased in the beet root juice in response to deficit irrigation leading to an overall considerable improvement in the juice quality and root biofortification.
The interaction between GWC application, irrigation systems and water deficit treatments revealed significant effects on all measured quality traits in both growing seasons (Suppl.Table S5).The highest values of sucrose%, Qz% and RS% (20.96 and 20.41%, 87.21 and 86.63%, and 17.99 and 16.87%, in the first and second growing seasons, respectively) resulted from the application of 14 ton ha −1 of GWC under drip irrigation conditions in combination with the 60% irrigation deficit treatment (Tables 1 & 2).Meanwhile, the lowest values of Na%, K% and αamino-N% resulted from the employment of sprinkler irrigation without GWC application under the wellirrigated treatment (100% irrigation treatment; Table 1).GWC-0; the control treatment (without GWC application), GWC-14; the application of 14 t ha −1 of GWC.LSD indicates significant differences (P≤0.05) between treatments in the same column.

Effect of GWC application on beet yields under deficit irrigation conditions
The application of the green waste-derived compost (GWC), irrigation systems and deficit irrigation conditions exhibited highly significant effects on water use efficiency (WUE), and root and recoverable sugar yields (Suppl.Table S5).The highest root and recoverable sugar yields resulted from the application of 14 ton ha −1 of GWC in the two growing seasons (Table 2).Deficit irrigation significantly reduced both root and sugar yields, and the highest values were produced from the 100% irrigation treatment in both growing seasons (Table 2).Moreover, the application of drip irrigation has significantly improved root and recoverable sugar yields in both growing seasons (Suppl.Table S5).
The interactions between GWC application, irrigation systems and deficit irrigation treatments exhibited significant and highly significant effects on root and recoverable sugar yields (Suppl.Table S5).The highest root and recoverable sugar yields (61.35, 10.77 and 62.66, 10.66 ton ha −1 , in the first and second growing seasons, respectively) resulted from the application of 14 ton ha −1 of GWC under drip irrigation conditions in combination with the wellirrigated conditions (100% treatment; Table 2).

Effect of GWC and irrigation systems on WUE under deficit irrigation
Water use efficiency calculated for either root yield (WUE RY ) or recoverable sugar yield (WUE RSY ) was significantly influenced by the application of the green wastederived compost (GWC), irrigation systems and deficit irrigation conditions (Suppl.Table S5).The application of GWC has significantly increased WUE.The highest WUE RY and WUE RSY values resulted from the application of 14 ton ha −1 of GWC in the two growing seasons (Table 3).WUE was significantly promoted in response to deficit irrigation, and the highest WUE RY and WUE RSY values were produced under the 60% deficit irrigation treatment in both growing seasons (Table 3).Furthermore, the employment of drip irrigation has significantly enhanced both WUE RY and WUE RSY in both growing seasons (Table 3).
WUE RY and WUE RSY were significantly affected by the interactions between GWC application, irrigation systems and deficit irrigation treatments in both growing seasons (Suppl.Table S5).The highest WUE RY and WUE RSY values (12.72 and 2.27 in the first growing season and 12.91 and 2.18 second growing season, respectively) resulted from the application of 14 ton ha −1 of GWC under drip irrigation conditions in combination with the 60% deficit irrigation treatment (Table 3).

Effect of GWC application on the soil chemical properties
The application of GWC significantly increased the available N, P and K in the soil.Similarly, GWC application significantly influenced the contents of calcium (Ca 2+ ), magnesium (Mg + ), sodium (Na + ), potassium (K + ), chlorine (Cl − ), bicarbonate (HCO 3 2- ) and sulfate (SO − 4 ) ions compared to the control treatment (Table 4).
The interaction between GWC application, irrigation systems and water deficit treatments exhibited significant effects on soluble cations, anions and some macronutrients in the soil after sugar beet harvest (Table 1).Except for chlorine (Cl − ), the highest values of all soluble cations and anions in the soil after sugar beet harvest were obtained from the application of GWC under drip irrigation conditions in combination with the 60% irrigation deficit treatment (Table 4).GWC-0; the control treatment (without GWC application), GWC-14; the application of 14 t ha −1 of GWC.LSD indicates significant differences (P ≤ 0.05) between treatments in the same column.

Correlation and regression analyses between GWC application and root quality parameters
Root yields revealed highly significant positive correlations with the recoverable sugar yields (RSY).Moreover, sucrose content exhibited highly significant positive correlations with the quality index and the recoverable sugar percentage (RS%).Meanwhile, the correlation coefficients between the quality index (Qz%) and either of Na%, K% and α-amino-N and were highly significantly negative (Table 5).The general linear model regression exhibited positive correlations between the soil Ca 2+ content and either of the Qz%, RS% and RSY across the two growing  seasons as fitted by the linear equation, with a coefficient of determination (R 2 ) ranging from 0.119-0.375(Figure 1).Meanwhile, the soil Na 2+ content exhibited negative correlations with Qz%, RS% and RSY across the two growing seasons as indicated by the linear equation, with a coefficient of determination (R 2 ) ranging from 0.526-0.836(Figure 1).

Discussion
In light of climate changes and global warming, steady population growth and diminishing sugarcane cultivated area, promoting sugar beet cultivation in arid and semi-arid regions is the only possible solution to overcome the gap between sugar production and consumption (Abo-Elwafa et al., 2006;Aljabri et al., 2021).This necessitates seeking the application of agronomical practices that would improve sugar beet productivity to cope with deficit irrigation conditions.
In the present study, the application of GWC significantly increased sugar content and RS% as well as impurity% which in turn reduced the root juice quality index (Qz%).The higher sucrose contents observed in response to the GWC application could be attributed to the elevated plant growth caused by GWC application which led to an increase in the photosynthetic capacities of the plants and the accumulation of more sucrose in the roots (Anli et al., 2020;Pedroza-Sandoval et al., 2017;Rady et al., 2016).Besides, it has been reported that GWC could accelerate the synthesis of photosynthetic pigments not only by supplying essential nutrients but also by changing the physical and chemical properties of the growth media, and hence reducing nutrient leaching and increasing plant water-use efficiency (Elhindi, 2012).Meanwhile, the increase in the RS% as a result of the application of GWC could be attributed to the increase in the sucrose%.The increased impurity and the reduced Qz% levels in response to the application of GWC might be due to the improved metal solubility, mobility and bioavailability in the soils which in the presence of low Ca 2+ content promotes the absorption of Na + , K + and α-amino nitrogen and therefore affected membrane permeability to control sodium absorption (Wakeel, 2013).This is obvious from the strong negative linear regressions between impurities content in the root juice and the RS% and RSY observed under the application of GWC (Figure 1).Besides, soil amendment materials would exhibit contradictory impacts on the mobilization and phytoavailability of elements depending on the type of the applied soil amendment and the element (Shaheen et al., 2017).The application of GWC promoted root yield in both growing seasons, which might be due to that GWC dramatically improves the soil's physical and chemical properties, such as the available N, P and K in the soil as well as all soluble cations and anions in the soil, and enhances the nutrient solubility and phytoavailability in the soil and thereby promoting sugar beet growth and yield (Businelli et al., 2009;Smolinska, 2015).The significant increase in the recoverable sugar yield resulting from the application of GWC is likely due to the high root yields produced from the application of GWC.
The significant improvement in the sugar beet water-use efficiency calculated for either root yield (WUE RY ) or recoverable sugar yield (WUE RSY ) in response to the application of GWC, in particular under irrigation deficit conditions suggests that GWC application has enhanced the water-holding capacity of the soil, and thereby promoted the ability of the plants to face irrigation deficit and to use the applied water more efficiently.The soil waterholding capacity is the most determinant factor for water-use efficiency (WUE) in agriculture.The application of GWC is a powerful approach to improves soil organic matter, which has been evidently proven to be the key responsible factor for water-holding capacity (Martínez-Blanco et al., 2013;Sayara et al., 2020).In large granules of soil such as sandy soils, compost serves as a sponge that holds water, therefore, application of compost to sandy soils is considered an ideal promising natural fertilizing approach to overcome the adverse consequences of climate change and water shortage, in particular in arid and semi-arid regions (Adugna, 2016;Garcia et al., 2017;Skuras & Psaltopoulos, 2012).The drastically elevated contents of soluble cations, anions and some macronutrients in the soil after harvest in response to the application of GWC is consistent with the role of compost application in the soil in increasing metal availability by the formation of soluble metal-organic complexes, and hence increasing the plant uptake efficiency (Businelli et al., 2009;Rady et al., 2016;Smolinska, 2015;Zheljazkov & Warman, 2004).

Conclusions
The application of green waste-derived compost (GWC) is essential for sustainable sugar beet production and efficient irrigation water use in sandy soils.

Figure 1 .
Figure 1.Response of beet root quality index (Qz%), recoverable sugar (RS%) and recoverable sugar yield (RSY) to soil Ca 2+ and Na + contents fitted by the linear-linear model over the 2017/2018 and 2018/2019 growing seasons.Black and blue dots denote data under the application of green waste-derived compost (GWC) and the control treatments, respectively.* and ** denote significant (P ≤ 0.05) and highly significant (P ≤ 0.01) regression, respectively.

Table 1 .
Effect of the application of green waste-derived compost (GWC) and water deficit on juice quality of the sugar beet variety Gazelle under drip and sprinkler irrigation systems in sandy soil in 2017/2018 and 2018/2019 growing seasons.

Table 2 .
Effect of the application of GWC and water deficit on root quality index (Qz%), recoverable sugar (RS%), root yield (RY) and recoverable sugar yield (RSY) under drip and sprinkler irrigation systems in sandy soil in 2017/2018 and 2018/2019 growing seasons.

Table 3 .
Effect of green waste-derived compost (GWC) on water use efficiency (WUE) for root yield (RY) and recoverable sugar yield (RSY) of sugar beet under three levels of water deficit under drip (D) and sprinkler (S) irrigation systems in sandy soil in 2017/2018 and 2018/2019 growing seasons.; the control treatment (without GWC application), GWC-14; the application of 14 t ha-1 of GWC.LSD indicates significant differences (P ≤ 0.05) between treatments in the same column.Different letters in the same column indicate significant differences (P ≤ 0.05) between treatments.

Table 4 .
Effect of the application of green waste-derived compost (GWC) and water deficit on the chemical properties of the experimental soils in the 2017/2018 and 2018/2019 growing seasons after harvest.

Table 5 .
Correlation and regression analyses between GWC application and root quality parameters.
PLANT PRODUCTION SCIENCE