Early Sowing Combined with Adequate Potassium and Sulfur Fertilization: Promoting Beta vulgaris (L.) Yield, Yield Quality, and K- and S-Use Efficiency in a Dry Saline Environment

: Field trials for two seasons (2018/2019 and 2019/2020) were conducted to investigate the influence of the addition of three levels of potassium (K) (K 1 = 60, K 2 = 120, and K 3 = 180 kg K 2 O ha −1 ) and/or sulfur (S) (S 1 = 175, S 2 = 350, and S 3 = 525 kg CaSO 4 ha −1 ) to the soil, as well as the sowing date (the 1st of September, D 1 ; or the 1st of October, D 2 ) on the potential improvement of physiology, growth, and yield, as well as the quality characteristics of sugar beet yield under soil salinity conditions. With three replicates specified for each treatment, each trial was planned according to a split-split plot in a randomized complete block design. The results revealed that early sowing (D 1 ) led to significant improvements in all traits of plant physiology and growth, in addition to root, top, and biological yields and their quality, gross and pure sugar, and K- and S-use efficiencies based on root yield (R-KUE and R-SUE). The K 3 level (180 kg K 2 O ha −1 ) positively affected the traits of plant physiology, growth, yield and quality, and R-SUE, and reduced the attributes of impurities, impurity index, and R-KUE. Additionally, the S 3 level (525 kg CaSO 4 ha −1 ) affirmatively affected plant physiology, growth, yield and quality traits, and R-KUE, and decreased impurity traits, impurity index, and R-SUE. The interaction of D 1 × K 3 × S 3 maximized the yield of roots (104–105 ton ha −1 ) and pure sugar (21–22 ton ha −1 ). Path coefficient analysis showed that root yield and pure sugar content had positive direct effects with 0.62 and 0.65, and 0.38 and 0.38 in both studied seasons, respectively, on pure sugar yield. Significant ( p ≤ 0.01) pos itive correlations were found between pure sugar yield and root yield (r = 0.966 ** and 0.958 **). The study results rec-ommend the use of the integrative D 1 × K 3 × S 3 treatment for sugar beet to obtain maximum yields and qualities under salt stress (e.g., 8.96 dS m −1 ) in dry environments.


Introduction
During the period of growth to maturity, plants face many environmental stresses, including salinity, especially in arid and semiarid environments in most parts of the world, including Egypt, where soil salinity increases annually; therefore, these adverse conditions cause a major ecological problem and restrict the performance of plants [1][2][3][4][5]. Salinity is the biggest enemy for plants because, as harmful environmental stress, it causes another harmful stress, "osmotic stress", which is the lack of water [6,7].
Soil salinity is associated with many factors that destroy the productivity of different crop plants such as low fertility, poor structure, and water restrictions or "osmotic stress" in many parts of the world [8,9]. These destructive factors cause changes in plant me-However, research work discussing the investigation of potential improvements with early sowing date in combination with K and/or S applied as soil supplementation has not yet been investigated with sugar beet plants growing in saline soil located in semi-arid environments. Therefore, the current study hypothesized that an early sowing date (the 1st of September compared to the 1st of October) in combination with K (60, 120, or 180 kg K2O ha −1 ) and/or S (175, 350, or 525 kg CaSO4 ha −1 ) applied as soil supplementations may mitigate the osmotic stress and ionic imbalance induced by salinity through the positive influences on morpho-physiological traits, yield components, and yield quality, as well as K-and S-use efficiency (based on root yield) in sugar beet grown under soil salinity (ECe = 8.96 dS m −1 ) conditions over two seasons in an arid environment.

Field Trials Details
Two consecutive field experiments, at two different locations on the same site, were carried out for the 2018/2019 and 2019/2020 winter seasons at an experimental station (29°17' N, 30°53' E, Southeast Fayoum) located at the Faculty of Agriculture experimental farm, Fayoum University. Each experiment was arranged in a split-split plot (three factors-sowing dates, potassium fertilization, and sulfur fertilization-were applied in main plots, subplots, and sub-subplots, respectively) in a randomized complete block design (RCBD), and each experimental treatment was repeated three times. The size of the basic experimental unit was 10.5 m 2 , consisting of 5 rows of 3.5 m in length and 60 cm in width (i.e., row spacing).
The experimental region is climatically classified as semi-arid [36] on the aridity scale. Pre-season physicochemical characteristics [37] of the 0-50 cm soil depth from the 2018/19 and 2019/20 seasons are presented in Table 1. The experimental soil samples were classified as sandy loam [38] by the USDA Soil Taxonomy. Soil samples were air-dried and sieved through a 2-mm sieve. Approximately 300 g of soil for ECe measurement was dried, ground, passed through a 10-mesh screen, and saturated with distilled water for 24 h. The pH values of soil samples were measured in saturated soil-water paste using a Bekman pH meter (model Elico, LI120-UK) [37]. Several milliliters of soil-water paste were extracted through a Whitman No. 1 paper filter in Buchner funnel with a vacuum system. The electrical conductivity (EC 25 °C) of the soil-paste extracts was determined using a calibrated, temperature-compensating, digital readout conductivity instrument (model 3200, YSI, Inc., Yellow Springs, OH, USA) [37]. Healthy seeds of sugar beet (var. BTS 301 multigerm, Germany; Moderately Tolerant to Salt) were obtained from the Sugar Crops Research Institute, Egyptian Agricultural Research Center, and the seeds were sown on the 1st of September and October in each of the first and second seasons. After sterilization with 1% (v/v) sodium hypochlorite, 2-4 sugar beet seeds were sown in each hill 20 cm apart. Thirty days after planting (DAS) (4-6 leaf stage), the seedlings were thinned to one per hill to reach approximately 83,000 plants ha −1 .
During seedbed preparation, phosphorus (P) at a rate of 120 kg P2O5 ha −1 as calcium superphosphate (15.5% P2O5) was applied to the soil. Nitrogen (N) was applied at 240 kg N ha −1 as ammonium nitrate (33.5% N) in three equal doses; the first dose was applied directly after thinning, and the second and third doses were added immediately before the second and third irrigation, respectively. To apply K that was chosen as an experimental factor, it was applied at three levels (K1 = 60, K2 = 120, and K3 = 180 kg K2O ha −1 ) as potassium sulfate (48% K2O). To equalize S amount for all treatments related to K treatments, elemental S was used for this purpose, as well as regarding the S treatments using CaSO4. The K levels were arranged in subplots, and each K level was divided into two equal doses-the first dose was applied upon sowing and the second dose after thinning. To apply sulfur (S) that was chosen as another experimental factor, it was applied at three levels (S1 = 175, S2 = 350, and S3 = 525 kg CaSO4 ha −1 ) as calcium polysulfide (CaSO4, 30% S). The S levels were arranged in sub-sub plots, and each S level was divided into two equal doses applied at 45 and 70 DAS. Thus, nine treatments were maintained (i.e., K1S1, K1S2, K1S3, K2S1, K2S2, K2S3, K3S1, K3S2, K3S3) on two sowing dates (early and late sowing) in two years. Table 2 shows the values of thermal units during the trial period in two growing seasons (obtained from the Fayoum meteorological station). The number of days was computed from the date of sowing to the date of harvest. Growing degree days (GDD) were computed by total daily mean values of temperatures minus the temperature base value of 3 °C [39]. GDD values were computed for sugar beet using the following equation:

Environmental Growing Conditions
All other cultural practices for the cultivation of sugar beet such as weed control and irrigation were carried out as recommended by the Egyptian Ministry of Agriculture and Land Reclamation.

Sampling
For all determinations, sampling was done twice from all sub-sub plots in the two seasons. At 90 days after sowing (DAS), the first sample was taken to assess vegetative growth traits according to the sowing date. The sample was composed of five fully-expanded upper leaves taken from four sugar beet plants randomly selected to measure both the chlorophyll concentration (SPAD values) and the chlorophyll fluorescence (Fv/Fm) as physiological parameters. The second sample was taken at 210 DAS (harvest stage) from all sub-sub plots in both seasons to evaluate the yield and quality traits according to the sowing date. Each sample consisted of six randomly selected plants, which they were completely removed after irrigation of the soil to facilitate obtaining the plant with the whole root. The plants were then cleaned with tap water and separated into roots and tops to estimate their morphological characteristics. Sugar beet plants from all rows were then collected in each sub-sub plot, plus the six previously sampled plants that were all used to measure yield traits.

Morpho-Physiological and Yield Attributes
At 90 DAS, the selected samples were subjected to measure SPAD values (the chlorophyll concentration) using a chlorophyll meter (SPAD-502, Plus Konica Minolta, Inc., Tokyo, Japan). To obtain accurate SPAD values, each measurement was performed on both the second and third leaves and the mean of the two readings was recorded for each replicate. The Fv/Fm (chlorophyll fluorescence) was recorded by using (Handy PEA, Hansatech Instruments Ltd., Kings Lynn, UK), as described in [40], while the PI (performance index) was measured as described in [41]. At harvest (210 DAS) in both seasons, the sampled plants were separated into roots and tops to estimate the following traits: root length and diameter (cm) were measured using a meter scale, while root fresh weight and top fresh weight (kg plant −1 ) were measured using a digital balance. Leaf area index (LAI) was measured using the following equation [42]: where leaf area per plant was measured using a leaf disc method [42], and plant ground area was assessed by multiplying the distance among plants (20 cm) by row width (60 cm).

Yield Traits
Sugar beet plants from all rows of each sub-sub-plot were weighed, in addition to weighing six plants that were previously sampled and then converted to root yield (Mg ha −1 ) and top yield (Mg ha −1 ), along with biological yield (Mg ha −1 ), which was computed by adding the root yield to the top yield (Mg ha −1 ). Gross sugar yield (Mg ha −1 ) was calculated by multiplying the root yield by the gross sugar (%). Pure sugar yield (Mg ha −1 ) was computed by multiplying the root yield by the pure sugar (%). Harvest index (HI) was computed as follows: The K-use efficiency was computed based on root yield (R-KUE as kg root per kg K) and the S-use efficiency was also computed based on root yield (R-SUE as kg root per kg S) by dividing the root yield using K and S rates, respectively.

Statistical Analysis
The data obtained were statistically analyzed by the technique of analysis of variance (ANOVA) for the split-split plot arranged in randomized complete blocks design using MSTAT-C (MI, USA). Fixed factors were sowing dates, potassium, and sulfur fertilization, while replications were the random factor. Duncan's Multiple Range Test was practiced at 5% and 1% levels of probability to test the differences between treatment means. Correlations and regressions were implemented by IBM SSPS Statistical 21st ed.

Results
The use of the highest levels of both potassium (K) fertilizer and sulfur (S) fertilizer combined with early sowing on the 1st of September provided temperatures and nutrition suitable for the growth of sugar beet plants to overcome the conditions of salinity in soil located in a semi-arid environment and secure adequate yields of high quality.

Effect of Sowing Dates on Sugar Beet Physiological, Growth and Yield Traits
The data listed in Tables 3-5

Effect of Potassium Fertilization on Sugar Beet Physiological, Growth and Yield Traits
Potassium (K) levels had significant (p ≤ 0.01) variations for Fv/Fm, PI, SPAD, root length and diameter, root and top fresh weight plant −1 , LAI, and for all juice quality traits (impurity index, loss sugar content, purity percentage, α-amino N, alkalinity index, and pure sugar content) in both seasons under soil salinity conditions (ECe = 8.96 dS m −1 ) as presented in Tables 3-5. The data in Tables 5 and 6 report that K levels had significant (p ≤ 0.01) positive effects on all yield traits, but had no significant effects on harvest index in both two seasons. The highest K level (K3 = 180 K2O ha −1 ) outperformed the other two K levels (K1 = 60 K2O ha −1 and K2 = 120 K2O ha −1 ) and increased Fv/Fm by 4.94% and 2.41% in the first season, and by 3.66% and 2.41% in the second season compared to K1 and K2, respectively. K3 also increased PI by 68.13% and 28.07% in the first season, and by 72.41% and 25.00% in the second season compared to K1 and K2, respectively. Furthermore, K3 increased SPAD values by 17.49% and 7.95% in the first season, and by 15.43% and 9.29% in the second season compared to K1 and K2, respectively. The highest K level (K3 = 180 kg K2O ha −1 ) exceeded the other two levels of K (K1 = 60 kg K2O ha −1 and K2 = 120 kg K2O ha −1 ) for the above growth traits. K3 increased root length by 18

Effect of Sulfur Fertilization on Sugar Beet Physiological, Growth and yield Traits
The data in Tables 3-5 show significant (p ≤ 0.01) differences among the levels of sulfur (S) for sugar beet plant Fv/Fm in the first season, and PI, SPAD, growth traits (root length and diameter, root and top fresh weight plant −1 , and LAI), and juice quality (gross sugar content, impurity index, loss sugar content, purity percentage, Na + , K + , α-amino N, and pure sugar content) in both seasons, but this was not true for alkalinity index in the 2019/2020 season. The data in Tables 5 and 6 show that the applied level of S3 resulted in a significant increase in the yields of sugar beet. The responses of these traits to S were gradually increased by increasing the applied S level. The highest S level (S3 = 525 kg CaSO4 ha −1 ) was associated with increases in Fv/Fm of 2.44% in the first season, in PI of 20.07% and 18.20%, in SPAD of 11.39% and 9.91%, in root length of 11.23% and 9.15%, in root diameter of 19.83% and 15.32%, in root fresh weight plant −1 of 19.42% and 17.19%, in top fresh weight plant −1 of 29.49% and 28.92%, and in LAI of 37.80% and 38.81% in the first and second seasons, respectively, compared with the lowest level (S1 = 175 kg CaSO4 ha −1 ). The S2 level (350 kg CaSO4 ha −1 ) increased gross sugar content by 2.49% and 2.99%, and pure sugar content by 2.23% and 1.18% in the first and second seasons, respectively, compared to the S1 level (175 kg CaSO4 ha −1 ). The S3 level (525 kg CaSO4 ha −1 ) increased purity (%) by 0.79% and 2.06% in both the 2018/19 and 2019/20 seasons, respectively, and alkalinity index by 46.90% in the first season compared to the S1 level. On the other hand, the S1 level collected the highest Na + content (1.81 and 2.04), K + content (4.21 and 4.22), α-amino N content (1.57 and 1.62), impurity index (1.53 and 1.66), and loss sugar (2.33% and 2.59%) in the first and second seasons, respectively. It significantly (p ≤ 0.01) increased root, top, biological, gross, and pure sugar yields by 8.34% and 9.60%, 18.58% and 14.92%, 10.88% and 10.87%, 11.77% and 13.82%, 11.61% and 12.00%, and 6.49% and 9.52% in the first and second growing seasons, respectively, compared to S1. On the other hand, S3 significantly (p ≤ 0.01) decreased R-SUE by 64.29% and 62.50% in the first and second seasons, respectively, and harvest index by 2.60% in the first season compared to S1.

Effect of the Different Two-Way Interactions of the Three Factors Studied
For the effect of the different two-way interactions of the three factors studied (Table  S1) (20.25 and 19.97 Mg ha −1 ), and pure sugar yield (18.37 and 17.94 Mg ha −1 ). However, the lowest R-KUE (1.26 and 1.56 kg root per kg K) was obtained with the interaction of D1 × S3, and the maximum R-SUE (0.45 and 0.43 kg root per kg S) was produced with the interaction of D3 × S1 in the first and second growing seasons, respectively, compared to the other two-way interactions.

Effect of the Different Three-Way Interactions of the Three Factors Studied
Concerning the effect of the applied three-way interactions, Tables 3 and 4

The Direct and Indirect, Stepwise Regression, and Correlation Analyses
The data in Table 7 Table 8, correlation and regression data analysis between pure sugar yield and each of pure sugar content, root dimensions, root fresh weight, root yield, LAI, and SPAD values were calculated to concentrate on the relationship of the efficacious sugar beet traits interest. Highly significant (p ≤ 0.01) positive correlations were found between pure sugar yield and root yield (r = 0.966 ** and 0.958 **) and between the dependent variable and each of pure sugar content (r = 0.909 ** and 0.866 **), root length (r = 0.907 ** and 0.944 **), and SPAD values (r = 0.820 ** and 0.983 **). Furthermore, highly significant positive correlations (r = 0.921 ** and 0.937 **, r = 0.869 ** and 920 ** and r = 0.876 ** and 0.925 **) were observed between root yield and each of root length, root diameter, and root fresh weight in the first and second seasons, respectively. The stepwise regression in Table 9 shows the significant (p ≤ 0.01) contribution of three traits (i.e., root yield, pure sugar content, and LAI) to the variations in pure sugar yield.

Discussion
In the present study, in addition to soil salinity (ECe = 8.96 dS m −1 ; Table 1), its potassium (K + ) content is 39.124 mg kg −1 soil, making it K + -poor soil. Additionally, saline soils often suffer from a deficiency of nutrients, including S [27], so the soil examined in this study is deficient in S. Therefore, it was necessary to supply the tested saline soil with sufficient amounts of K + (to antagonize the harmful Na + ion) and S in favor of sugar beet plants to be able to take their nutritional requirements to be robust and thus be able to resist/tolerate the soil salinity conditions. In addition to the nutritional factor, the key climatic factor affecting sugar beet productivity is temperature. For sugar beet plants to obtain sufficient thermal units throughout their growing season, it has been estimated the seasonal growing period of sugar beet plants to be approximately 200 days [45]. Thus, the sowing date of sugar beet has a great influence on the plant development and productivity through the adequate accumulation of thermal units, especially from the emergence stage until sugar beet plants reach the harvest stage [45]. Therefore, the date of sowing beets should have been early on the 1st of September to meet the required growth period for the plants to be supplied with the required thermal units, which would be reflected in the best growth and high yield with high quality under the tested salty soil conditions.
For the above reasons, the saline soil examined in this study was provided with three levels of K (K1 = 60, K2 = 120, and K3 = 180 kg K2O ha −1 ) and/or S (S1 = 175, S2 = 350, and S3 = 525 kg CaSO4 ha −1 ), along with early sugar beet sowing on the 1st of September to provide all somewhat better environmental conditions for seed germination and seedling/plant growth until harvest to obtain the preferable yield with high quality for sugar beet plants grown under the adverse conditions of soil salinity.
The increased values recorded for Fv/Fm and PI (photosynthetic efficiency), along with SPAD (chlorophyll concentration) (Table 3) (Table 2). This finding allows for optimal early emergence, plant development, and leaf surface area, especially in the early stage of sugar beet plants. These increases in chlorophyll concentration and photosynthetic efficiency with K and S applications (especially the highest levels) [3,27] along with the early sowing date enabled plants to photosynthesize for more assimilates to obtain the highest root yield with high quality (Tables 3-6) under salt stress conditions. The increase in root dimensions, root and top fresh weight, and LAI may be due to the exposure of sugar beet plants to some favorable environmental conditions prevalent during the late growth stage and may be due to the increase in chlorophyll concentration and photosynthetic efficiency (Fv/Fm, PI, and SPAD), which resulted from the early sowing date employing accumulate higher thermal units for efficient photosynthesis increase leaf surface area to improve plant growth and increase the root weight of sugar beet [46].
The early sowing date (the 1st of September) also resulted in a marked increase in juice quality traits compared to the late sowing (the 1st of October) (Tables 4-6). These improvements in juice quality characteristics can be attributed to the appropriate climatic conditions, particularly the light and temperature required for the plant to perform well concerning the effective photosynthesis process [47]. This investigation reported a posi-tive response of the photosynthesis process to the effective temperature with sufficient light, water (with increasing the osmolyte K + by K application), and nutrients (acidification of growing medium with increasing S by S application) in favor of adequate chlorophyll concentration and photosynthetic efficiency (Table 3) for efficient production with high quality of sugar beet plants. The early sowing date resulted in a marked increase in gross and pure sugar contents, purity percentage, and alkalinity index, while it resulted in a marked decrease in impurities (e.g., Na + , K + , and α-amino N), impurity index, and loss sugar percentage (Tables 4 and 5). Some reports indicated that the early sowing of sugar beet markedly increases the sugar content, purity percentage, and pure sugar content [11,13]. Moreover, it was reported a positive correlation between climatic factors and sugar beet giving yield quality traits [48]. These findings can be attributed to that early sowing enables sugar beet plants to collect maximum energy for storing sugars in tubers. Besides, early sowing is likely to result in more possibilities for more favorable plant growth. These results are confirmed by those in [13,46,49]. Furthermore, the root, top, biological, gross sugar, and pure sugar yields, as well as R-KUE and R-SUE were markedly increased with the early sowing. These results can be attributed to better climatic conditions conferring higher chlorophyll concentration and photosynthetic efficiency (Fv/Fm, PI, and SPAD) that encouraged increased leaf surface area, root dimensions, root and top fresh weights, and gross and pure sugar contents, which reflected in the increased root, top, and biological yields, thus increasing the pure sugar yield. These results are confirmed by those in [13,46,49].
Merwad et al. [26] reported that increased salt tolerance in sugar beet plants has been correlated with increased K + availability in plant tissues. Salt damage in plants can be prevented by increasing the K + content due to its beneficial roles, directly as a protective osmoprotectant and indirectly by being used in antioxidation [50]. The beneficial effects of fertilization with K + , especially the highest level (180 kg K2O ha −1 ), of sugar beet plants growing under salt stress are related to its key roles in photosynthesis, protein synthesis, photosynthates translocation, control of ionic balance, and water availability [21]. Some investigations have confirmed, under salt stress, the importance of applying K + alone or in combinations in improving enzymatic activities, causing increased nutrient mobilization in the plant and translocation of photo-assimilates to active growing organs in the plant system to improve plant growth and high-quality production, all due to the improved chlorophyll concentration and photosynthetic efficiency (Fv/Fm, PI, and SPAD) [26,51,52]. Sufficient K + supply to saline soil (ECe = 8.96 dS m −1 ) increases chlorophyll concentration (SPAD value) and leaf photosynthetic carbon, and thus also enhances light reaction routes (PSI and PSII) [53], which are strongly reflected in the increased growth and high-quality productivity for sugar beet plants. In this study, although applying K + to the examined salty soil increased the gross and pure sugar contents, quality percentage, and alkalinity index in the tubers of sugar beet, it markedly decreased impurities such as Na + , K + , α-amino N, impurity index, and loss sugar content, which may be attributed to the major role of K + in stimulating starch synthetase enzymes and the accumulation of carbohydrates that transfer from leaves to developing tubers of sugar beet, thus improving biochemical traits [54]. The major role of K + in inducing enzymatic activity and photosynthesis process is correlated to the synthesis of sucrose and the carrying of photosynthesized sucrose to phloem to raise sugar's level [55]. Mehrandish et al. [21] illustrated that applying K + increases recoverable sugar and reduces impurity traits. Moreover, increasing top and biological yields associate with increasing Fv/Fm, PI, SPAD value, top fresh weight, and leaf area index. These results confirm the results of this study. Table 6 shows that gross (root yield multiplied by gross sugar content) and pure sugar (root yield multiplied by pure sugar content) yields increased due to using K + for salty soil can be explained by the fact that K + plays a major role in enhancing all plant morpho-physiology, root yield, and gross and pure sugar contents, thus increasing gross and pure sugar yields of sugar beet plants. Additionally, the highest value of R-KUE was obtained using the highest K + that can be attributed to the highest K + level was associated with the highest increase in root yield. Furthermore, the highest R-SUE was obtained when sugar beet plants received 525 kg CaSO4 ha −1 to give the highest root yield.
The inclusion of S in the plant's stress defense system increases plant tolerance to stresses, including salinity [27], and thus the application of S to saline soil alone or in combinations increased chlorophyll concentration and photosynthetic efficiency (Fv/Fm, PI, and SPAD values), which were reflected in the increased performance of sugar beet plants under salt stress (Tables 3-6). A report [27] indicates that applying S to salt-stressed plants increases glutathione pool (a compound containing S), which may lead to increased photosynthesis efficiency due to the critical role of S in photosynthesis functions and the improvement of the leaf chlorophyll concentration, thus increasing plant growth and yield characteristics. In this study, a gradual increase in S level from 175 to 525 kg CaSO4 ha −1 to salt-stressed sugar beet plants resulted in a gradual increase in chlorophyll concentration and photosynthetic efficiency (Fv/Fm, PI, and SPAD values), which were reflected in increased plant growth and yield characteristics with high quality. These positive results can also be attributed to that adding S to the soil may be enhanced soil properties and fertility in favor of the growing plants [27], causing an increase in the photosynthetic area in sugar beet plants that it gives maximum returns. Additionally, the impurity traits (Na, K, and α-amino N), impurity index, and loss sugar content were decreased by applying S, especially the highest level, thus increasing the gross and pure sugar content with high purity and quality percentages, and alkalinity index, while non-sugars decreased in salt-stressed sugar beet plants (Tables 4 and 5). The increase in yield traits and their quality can be illustrated based on the increases in growth traits, which in turn were achieved through increased chlorophyll concentration and photosynthesis efficiency, all due to the beneficial effects of S applied alone or in combinations (Tables 3-6).
Fertilizing strategy of saline soils (ECe = 8.96 dS m −1 ) is very important to bring the nutrients into balance status in favor of growing plants. Applying K + up to 180 kg K2O ha −1 with S application to these defective soils up to 525 kg CaSO4 ha −1 can help, as effective agronomical practice, these defective soils to become highly productive due to overcoming the effects of high salinity and encouraging increased salt tolerance in sugar beet to improve its productivity and industrial traits by increasing K-and S-use efficiency under dry environmental conditions. Finally, various environmental foes, including the foes studied in this work, have negative impacts on plant growth. These negative impacts may exceed the natural tolerance capacity of stressed plants. In this case, the components of the stressed plant's defense system do not meet the requirements of adequate defense, and therefore the external use of auxiliary substances such as nutrients and other beneficial strategies helps the plants to increase the efficiency of their antioxidant defenses; thus, plants can perform efficiently under adverse conditions of environmental foes [3,4,8,[56][57][58][59].

Conclusions
This work was conducted to shed light on the potential positive effects of potassium and sulfur applied to saline soil (ECe = 8.96 dS m −1 ) to stimulate salt tolerance by promoting growth, pure sugar yield, and juice quality, as well as K-and S-use efficiency of sugar beet with two sowing dates in semi-arid regions. Early sowing date (the 1st of September) increased responses of morpho-physiological trait responses (root dimensions and weight; top fresh weight; Fv/Fm; PI; SPAD; LAI; juice quality; productivity; root, top, biological, gross, and pure sugar yields; and the alkalinity index; as well as Kand S-use efficiency) to soil fertilization with potassium (especially at a level of 180 kg K2O ha −1 ) and sulfur (especially at a level of 525 kg CaSO4 ha −1 ) under salt stress conditions. The application of potassium and sulfur induced salt tolerance in sugar beet plants by enhancing growth indices and sugar quality traits while reducing impurity traits (Na, K, and α-amino N), loss sugar content, and impurity index. Path coefficient analysis data showed that root yield, pure sugar content, SPAD, and LAI in sugar beet had positive direct effects with 0.62 and 0.65, 0.38 and 0.38, 0.01 and 0.0041, and 0.05 and 0.05 path coefficients, in the first and second seasons, respectively, on pure sugar yield. Highly significant (p ≤ 0.01) positive correlations were found between pure sugar yield and root yield (r = 0.966 ** and 0.958 **), and between the dependent variable and each of pure sugar content (r = 0.909 ** and 0.866 **), root length (r = 0.907 ** and 0.944 **), and SPAD value (r = 0.820 ** and 0.983 **). Stepwise regression data showed that three traits (i.e., root yield, pure sugar (%), and LAI) contributed significantly (p ≤ 0.001) to the variations in pure sugar yield. Soil application with potassium and sulfur with the above-mentioned doses can be assisted to correct their reductions in the saline soils to reduce salt stress effects on sugar beet plants. The results of our study will open new research prospects for fertilization strategy, one of the important factors for overcoming different abiotic stresses, especially salinity in climate change scenarios.

Supplementary
Materials: The following are available online at www.mdpi.com/2073-4395/11/4/806/s1, Table S1: Photosynthetic efficiency (Fv/Fm, PI(%) , and SPAD values), and root length (cm) of sugar beet as affected by the interactions of sowing date (D), potassium (K) and sulphur (S), during two growing seasons (Mean ± SE) under soil salinity (ECe = 8.96 dS m − 1 ) conditions, Table S2: Root diameter, root fresh weight, and top fresh weight of sugar beet as affected by the interactions of sowing date (D), potassium (K) and sulphur (S), during two growing seasons (Mean ± SE) under soil salinity (ECe = 8.96 dS m − 1 ) conditions, Table S3: Leaf area index (LAI), biological yield, harvest index, and purity content of sugar beet as affected by the interactions of sowing date (D), potassium (K) and sulphur (S), during two growing seasons (Mean ± SE) under soil salinity (ECe = 8.96 dS m − 1 ) conditions, Table S4 Figure S17: R-KUE (kg root kg K -1 ) and R-SUE (kg root kg S -1 ) of sugar beet as affected by the interactions of sowing dates (d) and sulphure (S), in 2019/2020 season (Mean ± SE) under soil salinity (ECe = 8.96 dS m − 1 ) conditions, Figure S18: R-KUE (kg root kg K -1 ) and R-SUE (kg root kg S -1 ) of sugar beet as affected by the interactions of potassium (K) and sulphur (S), in 2018/2019 season (Mean ± SE) under soil salinity (ECe = 8.96 dS m − 1 ) conditions, Figure S19: R-KUE (kg root kg K -1 ) and R-SUE (kg root kg S -1 ) of sugar beet as affected by the interactions of potassium (K) and sulphur (S), in 2019/2020 season (Mean ± SE) under soil salinity (ECe = 8.96 dS m − 1 ) conditions, Figure