الفهرس 
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Abstract
SUMMARY AND CONCLUSION
This investigation was conducted to evaluate stability and maturity of composted rice straw (RS) and olive pomace (OP) to extract humic substances and determine their characteristics. As well as, to assess the impact of humification degree of these composted materials on metal loading capacity of extracted humic acids with Fe, Mn and Zn. In addition, the humic acids loaded with micronutrients were applied in two pot experiments and two field experiments to assess the impact of the concerned humic acids on soil fertility, growth, and productivity of plant grown on newly reclaimed soils.
For this purpose, a composting experiment was carried out to evaluate the stability and maturity of three compost piles i.e. pile A (60% RS+10% OP+10% tomato hallum+10% banana residues+10% farmyard manure), pile B (50% RS+20% OP+10% tomato hallum+10% banana residues+10% farmyard manure) and pile C (40% RS+30% OP+10% tomato hallum+10% banana residues+10% farmyard manure). The mature piles i.e. A, B and C as well as compost D (cotton stalks and rice straw, farmyard manure) as comparative sample were used for extraction and purification of humic substances to determine characteristics of humic and fulvic acids (total acidity, carboxylic groups and phenolic groups, elemental analysis and IR absorption).
Laboratory study was performed to determine loading capacity of the extracted humic acids with Fe, Mn and Zn at different pH values (4, 5 and 6).
Pot experiments were carried out using sandy and calcareous soil samples were taken from Ismailia and Nubaria Agric. Res. Stations, Egypt, respectively to investigate the impact of humic acids extracted from different composts and the loaded metal on nutrients availability and uptake by maize grown on newly reclaimed soils. Both experiments were laid out in a factorial complete randomized design with three replicates. The studied factors included humic acids sources (HA-b, HA-c and HA-d) and the loaded metal (without metal loaded, Fe, Mn and Zn). All treatments applied as a soil application at a rate of 1g/kg soil.
Field experiments were established at Ismailia and Nubaria Agric. Res. Stations, Egypt during summer season 2016 to assess the impact of humic acids sources, rates and the loaded micronutrients on soil fertility, growth and productivity of maize grown on newly reclaimed soils. The experiments were conducted in split split plot design with three replicates. The plot area was 10.5 m2 (3m x 3.5m). The main plots were devoted to humic acids loaded with and without micronurients. The sub plots were devoted to humic acids sources i.e. HA-b, HA-c and HA-d. The sub-sub plots were assigned for humic acids at rates of 0.75, 1.5 and 3 g/L. All treatments applied as a foliar spray and a soil drench at the rate of 600L/fed in two intervals i.e. 30 and 50 days from planting.
The obtained results could be summarized as the following:
Physical and chemical characteristics of three compost piles during composting process
- In all compost piles, a slight increase in temperature occurred through the first 2-3 days of composting and then gradually increased at 30 days of composting to reach the maximum temperature value (60.63oC) for pile C, whereas the corresponding value (52.32oC) was recorded for pile A. Then, the temperature gradually declined by progressing decomposition and dropped to reach near the ambient temperature (cooling stage) until the 90th day of composting.
- The bulk density of three compost piles gradually increased during the composting process. The highest value of bulk density (440.0 kg m-3) achieved for compost C.
- The pH values at the final of composting process reached to 8.60, 8.31 and 7.95 for piles A, B and C, respectively.
- Electrical conductivity (EC) showed gradually increased during the composting process and reached 8.13, 7.79 and 7.68 dS/m for piles A, B and C respectively, at the end of the composting period.
- Total organic carbon (TOC) declined from 47.59, 43.45 and 41.66% at the first 15 days of composting to 35.28, 27.00 and 25.00% at the end of composting for the compost piles A, B and C, respectively.
- Total nitrogen content showed slight increases in all compost piles during initial stages of the composting process up to 45 days, and then markedly augmented from the 60th till the 90th day of composting. Where, the highest values of total nitrogen were obtained for pile C.
- The values of C/N ratios of all composted piles significantly decreased with composting progress. The values of C/N ratios narrowed from67.38, 54.31, and 43.39 at the first 15 days of composting to 35.64, 25.23 and 18.80 at the end of composting for the compost piles A, B and C, respectively.
- Regarding to ammonical-N and nitrate-N, the concentration of NH4+–N diminished from 354.90, 427.50 and 487 mg/kg to 58.50, 45.60 and 63.85 mg/kg for piles A, B and C, respectively. On the other hand, NO3-–N was intensified gradually to reach the highest values (113.75, 194.13 and 232.24 mg/kg) at the end of composting process for piles A, B and C, respectively.
- The NH4+/NO3- ratio significantly decreased during composting process and reached 0.51, 0.23 and 0.27 in the later stage.
- Total phosphorus and potassium content markedly increased during the composting period up-to 90th days. Where, the highest values of Total phosphorus (0.61, 0.74 and 0.78%) and potassium (1.12, 1.15 and 1.23%) were obtained for piles A, B and C, respectively in final compost.
Maturity and stability indices of three compost piles during composting process
- Total extractable carbon (TEC) declined gradually during different stages of composting. Where, the final TEC concentrations were 17.15, 18.63 and 19.24% for piles A, B and C, respectively.
- The values of humification parameters (HI, HD, and HR) increased with composting progress for all the compost piles. Where, the HI values increased from 9.33, 10.67 and 17.59% to 18.14, 32.44 and 40.84% at 90 days of composting for compost piles A, B and C, respectively. HD and HR values significantly affected by the type of compost piles and compost period. Hence, the greatest values of HD and HR were obtained for pile C (30%OP), followed by pile B(20%OP).
- Extinction co-efficient) E4/E6 ratios (are found to decreases over time through the composting process for all compost pile. The highest decline of E4/E6 ratios was 2.87, 2.54 and 2.21 at the maturity stage for piles A, B and C, respectively.
- CO2 evolution rate declined at initial values from 28.57, 26.18 and 24.47 to 2.18, 1.89 and 1.75 mg CO2.C/g organic carbon/day at the end of the composting process )at 90th day) for piles A, B and C, respectively.
- After 90 days of the composting process, the highest values of germination index (92.22 and 95.39%) were achieved for pile C for cress and barley seeds, respectively.
Characteristics of extracted humic and fulvic acids
Total acidity
The total acidity in humic acids ranged from 275 to 350 mmol/100 g, while, the total acidity in fulvic acids varied from 446 to 561 mmol/100 g. in this respect, the highest values of total acidity were obtained by FA-c and HA-c followed by FA-d and HA-d.
Carboxyl (COOH) and Phenolic-OH groups
The values of COOH of fulvic acids were ranging from 241 to 324 mmol/100g on the contrast of humic acids varied from 141 to 200 mmol/100 g. The highest values of COOH and phenolic-OH were obtained for FA-c and HA-c.
Elementary analysis
The carbon, nitrogen, and sulfur contents were higher in humic acids than those of fulvic acids. While, fulvic acids contained higher amounts of hydrogen and oxygen than humic acids. Whereas, the maximum values of carbon and nitrogen occurred with HA-c and FA-c. Conversely, the minimum values of oxygen and hydrogen as well as H/C, O/C and C/N atomic ratios were realized for HA-c and FA-c. On the other hand, HA-b and FA-d have the highest content of sulfur.
Infrared Spectroscopy (FT-IR)
Fourier-Transform Infrared (FT-IR) spectra of the humic acids isolated from the three compost samples exhibited similar bands with different intensity distribution as the the following: (1) the strong broad band at 3432 cm-1 assigned to H bonded OH group of carboxylates, phenol, alcohols and NH groups; (2) the aliphatic bands C-H, at 2930-2928 cm-1 which is more intense in humic acids derived from HA-d and HA-c than in HA-b; (3) an absorption at 1714 cm-1 corresponding to C=O stretching of COOH appear at all the spectra of humic acids except HA-d;(4) The band at 1660-1630 cm-1 characterizing the C=O stretching of amide groups were more intense in the HA-d and HA-c;(5) The peak at 1460–1440 cm-1 was caused by aliphatic C–H bending of CH2 or CH3 groups which was found in HA-a and HA-c only; (6) A peak at 1050-1034 cm-1 (C–O stretching of Polysaccharides) was found in HA-a and HA-d.
Regarding to the spectra of fulvic acids, some peaks occurring in humic acids disappeared in fulvic acids. The FT-IR spectra of fulvic acids are less aromatic, aliphatic structure than humic acids. The bands at 2927 cm-1 occurring only in FA-d which attributed to aliphatic structures. A peak at 1628-1632 cm-1 is ascribed to C=O of amide groups has a high intensity in FA-c and FA-d and a medium intensity in the spectra corresponding to FA-b and FA-c. The band at 1401-1405 cm-1 is assigned to phenolic OH, COO was intense in FA-a and FA-d.
Loading capacity of extracted humic acids with Fe, Mn and Zn
- The loading capacity of Fe2+ reached to optimum values at pH 5 for all humic acids. Whereas, the highest amount of Fe2+ (79.2 mg/g) loaded by HA-c followed by HA-d at pH 5.
- In the case of Mn2+, loading capacity of the studied humic acids by Mn2+ was very low at pH 4 and 5. However, it markedly built up at pH 6. Whereas, the greatest amounts of Mn2+ loaded onto humic acids are 98.8 and 77.7 mg/g for HA-c and HA-d, respectively at pH 6.
- In the case of Zn2+, the maximum loading capacity of Zn2+ took the following descending order: HA-c (174.01 mg/g) > HA-d (161.1 mg/g) > HA- b (151.0 mg/g) > HA-a (126.0 mg/g) at pH 6.
Pot experiments
Impact of humic acids and the loaded metal on nutrients availability
- Available macronutrients (N, P and K) significantly affected by humic acids and the loaded metal in both sandy and calcareous soils. Thus, the addition of HA-c (1g/Kg soil) was more pronounced for increasing soil availability of N, P and K in sandy and calcareous soils. Also, the same results were obtained as result of applying HA-c loaded by Mn.
- HA-c gave more pronounced values of available Fe (4.60 and 5.10 mg kg-1) than adding HA-b (4.06 and 4.28 mg kg-1) in sandy and calcareous soil, respectively. Additionally, available Fe significantly intensified from 4.36 and 4.84 mg/kg through adding unloaded humic acids to 5.80 and 6.18 mg/kg due to applied humic acids loaded by Fe in sandy and calcareous soils, respectively.
- Applied HA-c resulted in 7.0% and 14.87% increases in available Mn over HA-b in sandy and calcareous soil, respectively. Also, available Mn augmented from 2.18 and 2.36 to 2.72 and 4.29 due to adding humic acids loaded by Mn in sandy and calcareous soils, respectively.
- Humic acids and the loaded metal significantly increased available Zn. Hence, the maximum values of available Zn (1.80 and 2.87 mgkg-1) were recorded for HA-c which was higher than HA-d (1.69 and 2.52 mgkg-1) in sandy and calcareous soils, respectively. The humic acids loaded by Zn achieved more pronounced values of available Zn as compared with others obtained from unloaded.
Impact of humic acids and the loaded metal on maize seedlings.
- The highly significant increment of shoot fresh and dry weight was achieved for applying HA-c, while the minimum one was realized for applying HA-b. Similarly, the addition of humic acids loaded by Fe gave the same obtained results as compared to unloaded humic acids in both sandy and calcareous soils.
- More pronounced increases in macronutrients concentrations (N, P and K) and uptake of shoots were recorded as result of adding HA-c as compared to HA-b in both sandy and calcareous soils. Also, humic acids loaded with Fe heighten N, P and K concentrations and uptake of shoots versus unloaded humic acids.
- The maximum values of micronutrients concentrations (Fe, Mn and Zn) and of uptake were obtained by applying HA-c. On the other hand, humic acids loaded with Fe augmented Fe concentration by 32.86 and 31.19% in shoots versus unloaded humic acids in sandy and calcareous soils, respectively. Whereas, Mn concentration exceeded by 68.44 and 67.66% in shoots as a result of adding humic acids loaded with Mn over those unloaded in sandy and calcareous soils, respectively. While, applying humic acids loaded with Zn heightened Zn concentration in shoots with 96.46 and 82.14% versus unloaded humic acids in sandy and calcareous soil, respectively. On the other hand, micronutrients uptake by maize shoots gave a similar trend of micronutrients concentrations.
Field experiments
Impact of humic acids sources, rates and the loaded micronutrients on nutrients availability
- Available N, P and K at 60 DAP significantly affected by humic acids sources, rates and the loaded micronutrients in both Ismalia and Nubaria soils. Where, application of humic acids loaded with micronutrients significantly exceeded available N, P and K. Regarding humic acids sources, HA-c extracted from compost C achieved the maximum values of available N, P and K. Similarly, increasing the application rate of humic acids from 0.75 up to 3g/L significantly exceeded available N, P and K in both Ismailia and Nubaria soils. Furthermore, the available N, P and K in soil gave less pronounced values at harvesting stage than at 60 DAP in both Ismalia and Nubaria soils.
- There were significant increments of soil available Fe, Mn and Zn as a result of applying humic acids loaded with micronutrients over those obtained for unloaded humic acids at 60 DAP in both Ismalia and Nubaria soils. Moreover, applied HA-c at the rate of 3 g/L significantly maximized available Fe, Mn and Zn versus applied HA-b at the rate of 0.75 g/L at 60 DAP in both Ismalia and Nubaria soils. At harvesting stage, applied humic acids loaded with micronutrients and/or HA-c at a rate of 3g/L individually gave less pronounced values of soil available Fe, Mn and Zn over those obtained at 60 DAP in both Ismalia and Nubaria soils.
Impact of humic acids sources, rates and the loaded micronutrients on maize
- The greatest values of plant height, shoot fresh and dry weight were obtained as a result of applying humic acids loaded with micronutrients or HA-c. Similarly, the high rate of humic acids (3 g/L) caused a significant increment of these parameters.
- Macronutrients (N, P and K) concentrations and uptake shoots at 60 DAP were not significantly influenced by applying humic acids loaded with macronutrients. However, the highly significant increment of N, P and K concentrations and uptake of maize shoots were realized for applying either HA-c or humic acids at a rate of 3 g/L in both Ismalia and Nubaria soils. In this respect, a significant increment was found for N, P and K concentrations and uptake of maize grains due to the application of humic acids loaded with macronutrients, HA-c and the rate of 3 g/L individually in both Ismalia and Nubaria soils.
- The micronutrients concentrations and uptake of maize shoots (at 60 DAP) as well as maize grains significantly affected by the application of humic acids sources, rates and the loaded micronutrients. Where, plants receiving humic acids loaded with micronutrients achieved more pronounced values of Fe, Mn and Zn concentrations and uptake over those receiving unloaded humic acids in both Ismalia and Nubaria soils. Similarly, a significant increment of Fe, Mn and Zn concentrations and uptake of maize shoots and grains were obtained by applying humic acids sources which could be arranged as the following descending order: HA-c > HA-d > HA-b. Also, the concerned micronutrients concentrations and uptake of maize shoots and grains significantly exceeded when the rate of applied humic acids was increased from 0.75 g/L to 3 g/L.
- The highest significant values of ear weight, ear grains weight, and 100-grains weight occurred as result of adding humic acids with loaded micronutrients, HA-c as well as the high rate of humic acids (3 g/L) individually.
- Applied humic acids with loaded micronutrients maximized maize grain yield (13.44 and 36.56 Ardab/fed) in both Ismailia and Nubaria soils, respectively. Also, the addition of HA-c gave the higher significant increment of maize grain yield (15.61 and 39.22 Ardab/fed) as compared to HA-b (9.66 and 29.74 Ardab/fed) in Ismailia and Nubaria soils, respectively. Moreover, maize grain yield markedly exceeded from 10.48 and 30.80 Ardab/fed to 14.46 and 37.43 Ardab/fed when the humic acids rate raising from 0.75 to 3g/L in both soils, respectively. Concerning the effect of interaction, applying HA-c at a rate of 3g/L proved highly significant increment of maize grain yield in both Ismalia and Nubaria soils.
- The best values of stover yield were obtained due to applying humic acids with loaded micronutrients as compare to unloaded humic. Similarly, the maximum stover yield (3.54 and 7.25 ton/fed) were produced for HA-c. However, the minimum stover yield (2.21 and 5.77 ton/fed) was obtained due to applied HA-b in Ismailia and Nubaria soils, respectively. On the other hand, stover yield significantly increased from 2.62 and 6.17 to 3.14 and 6.75 ton/fed in Ismailia and Nubaria soils, respectively when raising the application rate of humic acids from 0.75g/L to 3 g/L.
Conclusion
from the aforementioned results, it could be concluded that recycling rice straw with olive pomace by composting is considered as one of the environment-friendly methods could solve the disposal problem of these wastes. It is possible to biodegradable phytotoxic compounds present in olive pomace and produces more stable and mature compost could be used as fertilizer for sustainable agricultural practices. Furthermore, increasing olive pomace ratio up to 30% of pile composition may be increased humification degree of final compost product which reflects on the extracted humic acids content of carboxylic and phenolic groups. Consequently, the loading capacity of the extracted humic acids by Fe2+, Mn2+, and Zn2+ markedly enhanced.
Moreover, the optimum values of loading capacity of the studied humic acids with Fe2+ were realized at pH 5. However, the highest values of loading capacity of humic acids by Mn2+ and Zn2+ were achieved at pH 6. In this respect, HA-c extracted from compost C realized more pronounced values of loading capacity by Fe2+ (79.2 mg/g), Mn2+ (98.8 mg/g), and Zn2+(174.0 mg/g). Therefore increasing loading capacity of the studied humic acids could be enhanced soil nutrient availability which reflected on nutrient content and uptake of maize grown in newly reclaimed soils
We can recommend that applied HA-c extracted from compost C (40% rice straw+30% olive pomace+10% tomato hallum+10% banana residues+10% farmyard manure) loaded with micronutrients at a rate of 3g/l as a foliar spray and a soil drench increasing macro and micronutrients availability in the newly reclaimed soils. Consequently, maize growth, nutrients concentration and productivity could be maximized