الفهرس 
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Abstract
The present investigation aims to study the effect of the soil application of K-humate and foliar spray of proline, as well as Zn and Si nanoparticles, to overcome the salinity stress on wheat (Triticum aestivum L.) plants grown on saline sandy soils. Two field experiments were conducted at the experimental farm of Soil, Water and Environmental Research Institute, West of Minia, Minia Governorate, during two successive winter seasons (2019/2020 and 2020/2021). The soil was sandy, has a pH of 7.98, SOM of 1.88 g kg‒1, and ECe of 11.09 dS m‒1. The experiments were laid out in a split-plot within a randomized complete block design (RCBD) with three replicates for each treatment. The soil application of K-humate (KH) was assigned to the main plots, and the foliar spraying of proline as well as Si and Zn nanoparticles were assigned to the sub-plots. The observations on growth, yield, yield attributes, crude protein, and nutrient use efficiency (NUE) of wheat plants, as well as some soil chemical properties and nutrient availability (N, P, and K), were recorded during the two seasons under study and were subjected to chemical and statistical analysis.
The results presented and discussed in the preceding chapter can be summarized as follows:
The growth parameters of wheat plants
Plant height: The obtained results revealed that a significant effect of adding K-humate to the saline sandy soil at the rate of 10, and 20 kg ha−1 was observed on the plant height of wheat at all the crop growth stages. At the highest rate of K-humate (20 kg ha−1), the plant height of wheat at 45 and 90 days and at harvest increased by 6, 6, and 4%, respectively, in the first season. While, in the second season, the plant height of wheat at 45 and 90 days and at harvest increased by 6, 5, and 5%, respectively, as compared with the control. Concerning the foliar spraying of proline, Si-NPs, and Zn-NPs, the foliar spraying significantly affected the plant height of wheat at all the crop growth stages. The foliar spraying of proline, Si-NPs, and Zn-NPs significantly increased the plant height of wheat at 45 and 90 days and at harvest in the first season by 8, 4, and 3%, respectively, compared with the control. However, the foliar spraying of proline, Si-NPs, and Zn-NPs significantly increased the plant height of wheat at 45 and 90 days and at harvest in the second season by 11, 9, and 7%, respectively, compared with the control. The interaction between the soil application of K-humate and the foliar spray of proline, Si-NPs, and Zn-NPs significantly affected the plant height of wheat at 45 and 90 days and at harvest in both seasons. The soil addition of 20 kg ha−1 K-humate along with the foliar application of proline, Si-NPs, and Zn-NPs had the highest values of plant height. Maximum plant heights of wheat recorded at 45 and 90 days and at harvest were 52.33, 87.67, and 103.33 cm, respectively, in the first season, but, in the second season, they were 51.00, 86.00, and 105.67 cm, respectively.
Number of tillers/m2: Data showed that the number of tillers/m2 of wheat significantly and gradually increased with increasing the rate of K-humate from 0 to 20 kg ha−1 and the maximum increase was observed at the highest rate of K-humate (20 kg ha−1) in both seasons under study. Regarding the foliar spraying of proline, Si-NPs, and Zn-NPs, the foliar spraying significantly affected the number of tillers/m2 of wheat. The foliar spraying of proline, Si-NPs, and Zn-NPs significantly increased the number of tillers/m2 of wheat at harvest by 17 and 27%, in both seasons, respectively, as compared with the control. The interaction between the soil application of K-humate and the foliar spray of proline, Si-NPs, and Zn-NPs significantly affected the number of tillers/m2 of wheat at harvest in both seasons. Among the applied treatments, the soil addition of 20 kg ha−1 K-humate along with the foliar application of proline, Si-NPs, and Zn-NPs resulted in significantly higher numbers of tillers/m2 of wheat (449.00 and 480.67) in both seasons.
Leaf-chlorophyll (using a SPAD meter): The soil amendment with K-humate as well as the foliar spray of proline, Si-NPs, and Zn-NPs had a significant impact on leaf-chlorophyll. When K-humate was increased from 0 to 20 kg ha−1, there was a significant and gradual increase in the leaf-chlorophyll. In comparison to the control treatment, the highest rate of K-humate (20 kg ha−1) enhanced leaf-chlorophyll by 7 and 9%, respectively, in the two seasons under study. Concerning the foliar spray of proline, Si-NPs, and Zn-NPs, when compared to the control, the foliar spray of proline, Si-NPs, and Zn-NPs significantly increased leaf chlorophyll in wheat plants by 7 and 6%, respectively, in both seasons. The interaction between the soil applications of K-humate and the foliar spraying of proline, Si-NPs, and Zn-NPs had a significant impact on wheat leaf-chlorophyll content. The maximum values of leaf-chlorophyll content in both seasons (51.77 and 50.21, respectively) were found in the soil-applied 20 kg ha−1 K-humate along with a foliar spray of proline.
Proline content in the leaves of wheat plant (mmol g‒1 dry weight): The proline content was significantly affected by the soil application of K-humate as well as the foliar spraying of proline, Si-NPs, and Zn-NPs. There was a significant and gradual decrease in the proline content when K-humate was increased from 0 to 20 kg ha−1. In comparison to the control treatment, the highest rate of K-humate (20 kg ha−1) declined the proline content by 7 and 13%, respectively, in the two seasons under study. Relating to the foliar spray of proline, Si-NPs, and Zn-NPs, when compared to the control, the foliar spray of proline, Si-NPs, and Zn-NPs significantly increased proline content in wheat plants by 30 and 52%, respectively, in both seasons. The proline content of wheat was significantly impacted by the interaction between soil applications of K-humate and foliar spraying of proline, Si-NPs, and Zn-NPs. The maximum values of proline content in both seasons (5.663 and 6.976 mmol g‒1 DWt., respectively) were recorded in the soil-applied 20 kg ha−1 K-humate combined with the foliar spray of proline, Si-NPs, and Zn-NPs.
Sodium (Na+) content in the leaves of wheat plant: The addition of K-humate to the soil as well as foliar spraying of proline, Si-NPs, and Zn-NPs had a significant impact on the Na content of wheat plant. The Na content decreased significantly and gradually as the K-humate rate was increased from 0 to 20 kg ha−1. In comparison to the control treatment, the highest rate of K-humate (20 kg ha−1) decreased Na content in wheat leaves by 7 and 9%, respectively, in both seasons under study. Concerning the foliar spray of proline, Si-NPs, and Zn-NPs, when compared to the control, the foliar spray of proline, Si-NPs, and Zn-NPs significantly decreased the Na content in the leaves of wheat plant by 9 and 13% in the first and second seasons, respectively. The Na+ content in the leaves of wheat was significantly impacted by the interaction between the soil applications of K-humate and the foliar spraying of proline, Si-NPs, and Zn-NPs. The highest values of Na content in wheat leaves in both seasons (5.329 and 5.994 g kg‒1, respectively) were observed in the control treatment (without K-humate along with water spraying). Whereas the lowest value of Na content (4.412 g kg‒1) in the first season was recorded in the soil-applied 20 kg ha−1 K-humate combined with Si nanoparticle foliar spray, while, in the second season, the soil-applied 20 kg ha−1 K-humate combined with the foliar spray of proline, Si-NPs, and Zn-NPs gave the lowest value of Na content (4.513 g kg‒1) in the leaves of wheat.
K+/Na+ ratio in the leaves of wheat plant: The soil application of K-humate had a significant impact on the K+/Na+ ratio. When K-humate was increased from 0 to 20 kg ha−1, the K+/Na+ ratio increased significantly and gradually. In comparison to the control treatment, the highest rate of K-humate (20 kg ha−1) increased the K+/Na+ ratio by 21 and 21%, respectively, in the two seasons under study. When compared to the control, the foliar spray of proline, Si-NPs, and Zn-NPs significantly increased the K+/Na+ ratio in wheat plants by 25 and 30%, respectively, in both seasons. The interaction between the soil applications of K-humate and the foliar spraying of proline, Si-NPs, and Zn-NPs significantly impacted the K+/Na+ ratio in wheat plants. The maximum values of the K+/Na+ ratio in both seasons (7.582 and 7.451, respectively) were recorded in the soil-applied 20 kg ha−1 K-humate combined with the foliar spray of proline, Si-NPs, and Zn-NPs.
Nitrogen, phosphorus, and potassium content in leaves of wheat plant: The data obtained indicated that the nutrients content, i.e., N, P, and K (g kg‒1), in wheat plants at the booting stage were significantly affected and increased by increasing the soil application rate of K-humate from 0 to 20 kg ha−1. The highest N content (33.603 and 34.800 g kg‒1), P content (4.267 and 4.564 g kg‒1), and K content (31.510 and 31.151 g kg‒1) in both seasons were obtained by adding 20 kg K-humate ha‒1. According to the results obtained, the foliar spray of proline, Si-NPs, and Zn-NPs had positive and significant effects on nutrient content, including N, P, and K in wheat plants at the booting stage. The highest N, P, and K contents in the first season (34.253, 4.343, and 31.691 g kg‒1, respectively) and in the second season (34.991, 4.559 and 31.021 g kg‒1, respectively), were observed in the foliar spray of proline, Si-NPs, and Zn-NPs, except, the highest N content in the second season was found in the foliar spray of Si-NPs and Zn-NPs. The interaction of the soil K-humate application and the foliar spraying of proline, Si-NPs, and Zn-NPs had a significant effect on N, P, and K content in the leaves of wheat plants at the booting stage. The highest N, P, and K contents in the first season were 35.182, 4.765, and 33.889 g kg‒1, respectively, while in the second season they were 35.821, 4.895, and 33.622 g kg‒1, respectively, in 20 kg K humate ha‒1 combined with the foliar sprays of proline, Si-NPs, and Zn-NPs treatment.
Silicon and zinc content in leaves of wheat plant: A significant effect of adding K-humate to the soil at a rate of 10 and 20 kg ha−1 was observed on the Si and Zn content in the leaves of wheat plants at the booting stage. The highest Si content (5.915 and 6.188 g kg‒1), Zn content (44.067 and 40.533 mg kg‒1) were obtained by adding 20 kg K-humate ha−1 in the two seasons, respectively. Concerning the foliar spraying of proline, Si-NPs, and Zn-NPs, the foliar spraying significantly affected the Si and Zn content in the leaves of wheat plants at the booting stage. Among the foliar spray treatments, the foliar spray of proline, Si-NPs, and Zn-NPs resulted in significantly higher Si contents (6.673 and 6.776 g kg−1) in both seasons. While the foliar spraying of proline and nanoparticles of Si and Zn resulted in significantly higher Zn contents (45.789 and 41.711 mg kg−1) in both seasons. The interaction between the soil application of K-humate and the foliar spray of proline, Si-NPs, and Zn-NPs significantly affected the Si and Zn content in the leaves of wheat plant in both seasons. Among the different treatments, the soil addition of 20 kg ha−1 K-humate along with the foliar application of proline, Si-NPs, and Zn-NPs gave the highest values of Si content (8.090 and 8.288 g kg−1) and Zn content (51.233 and 48.367 mg kg−1) in both seasons.
Yield and yield components of wheat plants
Number of spikes/m2, number of spikelet’s/spike, and spike length (cm) of wheat: The obtained results indicated a significant and gradual increase in the number of spikes/m2 and spike length (cm) of wheat by increasing the K-humate rate from 0 to 20 kg ha−1, while the number of spikelet’s/spike was not significant. The highest rate of K-humate (20 kg ha−1) gave the maximum number of spikes/m2 (368.39 and 392.28) and spike length (14.75 and 14.92 cm) in both seasons, respectively. According to the obtained results, the foliar spray of proline, Si-NPs, and Zn-NPs had positive and significant effects on the number of spikes/m2, number of spikelet’s/spike, and spike length of wheat plant. The foliar spray of proline, Si-NPs, and Zn-NPs gave the highest number of spikes/m2 (386.33 and 380.56), number of spikelet’s/spike (24.14 and 25.02), and spike length (14.98 and 14.82 cm) in both seasons. In the current investigation, the results showed that the interaction between the soil application of K-humate and the foliar spray of proline and nanoparticles of Si and Zn significantly affected the number of spikes/m2 and spike length of wheat plants, whereas the interaction did not significantly affect the number of spikelet’s/spike. The highest values of number of spikes/m2 (424.33 and 453.33) and spike length (15.30 and 15.37 cm) in both seasons were recorded in 20 kg K-humate ha−1 along with foliar sprays of proline, Si-NPs, and Zn-NPs.
1000-grain weight (g) and harvest index (%) of wheat: Data given in the current investigation indicated that there is a significant and gradual increase in the 1000-grain weight (g) and a significant and gradual decrease in harvest index (%) of wheat plants by the soil addition of K-humate (10 and 20 kg ha‒1) in the two seasons. The highest 1000-grain weights (43.70 and 46.66 g) were obtained by adding 20 kg K-humate ha‒1 in both seasons. Whereas the highest values of the harvest index (37.41 and 36.92%) in both seasons were recorded in the control treatment (without K-humate). The foliar spraying of proline, Si-NPs, and Zn-NPs had positive and significant effects on 1000-grain weight (g) and harvest index (%) of wheat plants in both seasons, except, the harvest index of wheat plants in the first season didn’t reach significance. The highest 1000-grain weights (44.33 and 47.03 g) in both seasons were observed in the foliar sprays of proline, Si-NPs, and Zn-NPs, but the highest harvest index (37.46%) in the second season was found in the control treatment (water spraying). The results obtained reveal that there is a significant and gradual increase in the 1000-grain weight (g) and harvest index (%) of wheat plants due to the interaction between the soil application of K-humate and the foliar spray of proline and nanoparticles of Si and Zn during the two seasons under study, except, the increase in harvest index in the second season didn’t reach significance. The highest 1000-grain weights (45.28 and 47.45 g) in both seasons were recorded in 20 kg of K-humate ha‒1 combined with foliar sprays of proline, Si-NPs, and Zn-NPs. However, the highest harvest index (38.84%) in the first season was observed in foliar sprays of Zn-NPs without K-humate treatment.
Biological, grain, and straw yields (t ha‒1) of wheat: The results indicated that a significant and gradual increase in the biological, grain, and straw yields (t ha‒1) of wheat plants was found by increasing K-humate rates from 0 to 20 kg ha‒1 in both seasons under study. Consequently, the highest biological yields (14.20 and 14.04 t ha‒1), grain yields (4.76 and 4.78 t ha‒1), and straw yields (9.44 and 9.26 t ha‒1), were observed when applying 20 kg K-humate ha‒1. The results also revealed a significant improvement in the biological, grain, and straw yields (t ha‒1) of wheat plants due to the foliar spray of proline, Si-NPs, and Zn-NPs during the two seasons of the study. Whereas the highest biological yields (13.32 and 13.43 t ha‒1), grain yields (4.61 and 4.78 t ha‒1), and straw yields (8.71 and 8.65 t ha‒1), in both seasons were obtained in the foliar sprays of proline, Si-NPs, and Zn-NPs. The interaction between the soil application of K-humate and the foliar spray of proline and nanoparticles of Si and Zn led to significantly augmented biological, grain, and straw yields (t ha‒1) of wheat plants. Moreover, it was found that the soil addition of K-humate at a rate of 20 kg ha‒1 combined with foliar sprays of proline, Si-NPs, and Zn-NPs gave the highest biological yields (15.44 and 15.60 t ha‒1), grain yields (5.28 and 5.38 t ha‒1), and straw yields (10.16 and 10.22 t ha‒1), in the two seasons, respectively.
Crude protein in grains
Crude protein in grains of wheat plant: The data show that increasing K-humate rates from 10 to 20 kg ha−1 significantly increased the crude protein (%) in wheat plant grains compared to the control in both seasons. The soil-applied K-humate at the highest rate (20 kg ha−1) gave the highest values of crude protein in grains (12.058 and 13.261%), and furthermore, significantly increased the crude protein in grains by 8 and 18% in the two seasons, respectively. The foliar spray of proline, Si-NPs, and Zn-NPs had positive and significant effects on the crude protein of wheat plant grains during the two seasons under study. The foliar sprays of proline, Si-NPs, and Zn-NPs significantly increased the crude protein by 13 and 14% over the control in both seasons. The crude protein in wheat grains ranged between 10.894 and 12.350% in the first season, but in the second season, it ranged between 11.431 and 13.068%. The highest values of the crude protein were observed in the foliar sprays of proline, Si-NPs, and Zn-NPs. The results demonstrate that the foliar spraying of proline, Si-NPs, and Zn-NPs improved the protein content of wheat grains under saline conditions. In the current investigation, the results indicate that the interaction between soil application of K-humate and foliar spray of proline, Si-NPs, and Zn-NPs significantly affected the crude protein in the grain of wheat plant during the two seasons. The maximum values of crude protein in both seasons (12.787 and 13.970%, respectively) were recorded in the soil-applied 20 kg ha−1 K-humate combined with the foliar spray of proline, Si-NPs, and Zn-NPs. The results show that the combination of K-humate soil application and foliar spraying of proline, Si-NPs, and Zn-NPs enhanced the protein content of wheat grains under saline conditions.
Nutrient use efficiency (NUE) of wheat plants
Nutrient use efficiency (AEN, P, and K kg kg–1 of nutrient applied): The results show that the interaction between the soil application of K-humate and the foliar spray of proline, Si-NPs, and Zn-NPs significantly affected the agronomic efficiency of N, P, and K (AEN, P, and K kg kg–1 of nutrient applied) in both seasons under study. Among the different treatments, the soil-applied 20 kg K-humate ha‒1 combined with the foliar spray of proline + Si-NPs + Zn-NPs recorded maximum use efficiency as AEN (8.02 and 7.99 kg kg–1 of nutrient applied), AEP (26.73 and 26.64 kg kg–1 of nutrient applied), and REK (16.70 and 16.64 kg kg–1 of nutrient applied) in both seasons, respectively. In the current investigation, the highest N, P, and K agronomic efficiency (kg kg–1 of nutrient applied) of wheat plants was recorded in the soil-applied treatment of 20 kg K-humate ha‒1 combined with the foliar sprays of proline, Si-NPs, and Zn-NPs.
Soil characterization
The soil chemical properties: Concerning the soil chemical properties, K-humate significantly improved the studied soil characteristics. The soil addition of K-humate at the highest rate (20 kg ha−1) produced a considerable increase in the soil organic matter (SOM) by 10.9 and 11.2% as compared with the control in both seasons, respectively. The addition of 20 kg ha−1 of K-humate significantly decreased the soil pH from 8.26 and 8.21 to 8.09 and 8.12 in both seasons, respectively.
The nutrients availability: The soil applications of K-humate improved the availability of N, P, and K in the soil. The availability of N, P, and K significantly increased as the rate of K-humate increased from 0 to 20 kg ha−1. At the highest rate of K-humate (20 kg ha−1), the available N, P, and K increased by 41.4, 63.5, and 23.8%, respectively, in the first season as compared with the control, whereas in the second season the available N, P, and K increased by 34.6, 70.1, and 18.3%, respectively, as compared with the control. Potassium humate addition to the saline soil enhanced the availability of N, P, and K.
Based on the findings of this study, it could be concluded that the soil application of K-humate and the exogenous application of proline improved the effectiveness of Si-NPs and Zn-NPs in minimizing the adverse effects of salt stress. It is not recommended to only apply silicon and zinc nanoparticles via foliar spraying; an integrated parenteral management plan that depends on the addition of organic amendments to the saline sandy soils is also required. The combined application of potassium humate and foliar spray of proline, as well as Si and Zn nanoparticles, can be employed as a suitable strategy for increasing wheat yield under saline conditions and enhancing salt resistance. So, it could be recommended that:
It is recommended to add 20 kg ha−1 of potassium humate with irrigation water to wheat grown in sandy soils that suffer from soil salinity problems at 15 and 30 days after planting.
Under salinity conditions in sandy soils, the addition of potassium humate is not sufficient and the foliar sprays of 50 mM proline as well as 2 mM Si and Zn nanoparticles at 30 and 45 days from planting is required.