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Abstract 93 5. S U H H A R Y This work was conducted to evaluate the effects due to organic manuring on the availablility of soil P. To substantiate these effects, the following trials and analyses were carried out. 1- Compost preparation experiment: Organic residues of soybean and rice straw as well as cotton stalks (3 sources) were compos ted to distinct C/N ratios namely, 49, 33, 17 and .10 to ·1 beside the raw materials (5 C/N ratios). 2- Huatc acid preparation: The tested 15 organic materials, composted to different degrees, were subj ected to humic acid extraction in order c to be used as a tool for explaining the results. In this respect, humus extraction was run through 0.5 N NaOH and was purified using water electrodialysis until complete free of Cl • Isola ted pur i f i ed humic aci ds were ident if ied through elementary analysis for C, H, N, Sand 0 as well as infrared analysis. 94 3- Soil aanuring experiment: Soil samples obtained from three different locations namely, Moshtohor (clay), El-Dair (sandy) and El-Nobaria (calcareous) were treated with the different organic sources (15 samples). The soils were treated with these residues at a rate of 5 s residues/lOO g soil. This the laboratory conditions for 6 experiment lasted under months where subsamples were removed after 7, 30, 60 and 180 days from experiment starting. These subsamples were subjected to organic, inorganic, total and available P determinations. The obtained data of P forms were also subjected to statistical analysis. The obtained results could be briefly summarized as follows: A) Properties of isolated humic acids: 1- Total carbon content of humic acids amounted to about 44.32, 47.31 and 41.29% for humic acids derived from soybean straw, rice straw and cotton stalks, respectively. 2- The ~orresponding average values of total nitrogen were 4.79, 2.84 and 2.21%. respectively. 3- The C/N rat t os of humic acid samples are fluctuating between 6.30: 1 and 40: 1. 95 4- The highest C/N ratios were observed in humic acid samples derived from both rice straw and cotton stalkst whereas the lowest ones were obtained from humic acid prepared from soybean straw~ 5- The infrared absorption by humic acids showed the following trends: i) Absorption -1· at 3409-3300 em (due to frequency H bending of OH) reached its maximum with humic acid derived from soybean straw whereas the lowest one was obtained from humic acid prepared from rice straw ii) At 1620-1600 -1 em (due to frequency of aromatic C;C and H-bonded C==O)t maximum absorption was observed with soybean and the lowest value was due to cotton stalks H.A. iii) At 1590~1517 cm-1 (due to frequency of C;C), maximum absorption was observed with soybean H.A. and the lowest values was due to cotton stalks H.A. iv) At 1400-1390 cm-1 (due to frequency of O-H bending)t maximum absorption was observed wi th rice straw H.A. and the lowest value was due to cotton stalks H.A. ------------- ----------------- -~-_._-.----- 96 v) At 1280-1200 -1 em (due to frequency of C-O stretching and OH bend Lng ) I maximum a bsor pt ion was observe d wi t h cotton stalks H. A. and the lowest. value was due to rice straw H.A. However, it was observed that infrared absorption by H.A. derived from soybean straw residues at 3409- 3300 and 1620-1600 -1 cm tended to be inc r eased as the C/N of the residues ~as closer. B) Effects due to organic source: 1- Organic P fraction: Treating the soils with different organic residues led to: 1- In general the organic P content was approximately doubled in Mosh tohor clay and El-Dair sandy soils, meanwhi Le it was increased to more than 5 times in El-Nobaria calcareous soil as a results c of treating so i 1s wi,th or ganic manures. 2- It was proved that the highest inducing effect due to or ganic res id ues application resulted from so ybean st raw, rice straw and rice straw or cot ton stalks residues for calcareous, sandy and clay soils, respectively. 11- Inorganic P fraction: The hi ghest figures obtained f or this P frac t ion wer e yielded wi th application of soybean or rice straw residues ----_.~---_. ------------------------------ -- 97 in case of EI-Nobaria calcareous soil and EI-Dair sandy soil or soybean straw in case of Moshtohor clay soil. 111- Soil available P fraction: The compost derived from soybean straw significantly affected the level of soil P availability in a I I the tested soils if compared with the other two sources. c) Effect of elM ratio: 1- Organic P fraction: The level of organic P was significantly induced with the use of residues having C/N ratio of 17: 1 in El-Nobaria and EI-Dair soils and residues of wider ratios (raw. and 49:1) in case of Moshtohor soil. 11- Inorganic P fraction: The raw applied residues were more calcareous soils. The organic residues efficient with of C/N ratio amounting to (17-33:1) or·· (10-33:1) were more efficient for the sandy soil(El-Dair)and clay soil(Moshtohor),respec~- ively. ~--- -~----~~-~ ------~~---- ---_._- ---- 98 111- Soil available P fraction: The soil content of available P (in all the tested soils) increased progressively as the C/N ratio of the added residues became closer and closer and thus the C/N ratio of 10:1 yielded the highest inducing effect on soil content of available P. D) Effect of contact period: 1- Organic P fraction: The organic P fraction occurrence in the soils was significantly increased with increasing the period of soil con tac t wi t h the different organic residues from 7 to 30 days. 11- Inorganic P fraction: The soil content of inorganic P was initially decreased with increasing the interaction or contact period from 7 to 30 days. thereafter this fraction was gradually increased as the contact period was prolonged upto 60 and 180 days. respectively. 111- Soil available P fraction: The soi 1 con ten t of available P was inc reased wi th inc reasi ng the can tac t period from 7 to 30 days. dec reased after 60 days and increased again with time to reach its maximum values after 180 days of interaction. _._-_ .. _------------ 99 E- Combined effect of organic source and C/K ratio: 1- Soybean residues: 1- The highest level of organic P was observed with residues of C/N ratio amounting to 49: it 57: 1 (Raw) in EI-Nobaria, El~Dair and Moshtohor soils, respectively, while the minimum values were observed with residues having C/N ratios of (raw), 33:1 and 57:1 (raw) for calcareous., sandy and clay soils, respectively. 2- The inorganic P fraction, occurred at maximum levels with application of soybean residues having C/N . r at Lo s of 57:1 (raw) and 10:1 for El-Nobaria, Ei-Dair and MoshtoRor soil, respectively, while the minimum values were· observed wit h soy be an res idue s havi n gel N rat i0 s 0 f: -10:1, 57: 1 (r a-w) and 33:1 for the aforementioned _soils, respectively. 11- Rice str~w residues: 1- The maximum values of soil organic P fraction were achieved with application of rice straw residues having C/N ratios of 17:1 and 97.5:1 (raw) for EI-Nobaria and Moshtohor soils, respectively, but no significant differences could be detected in El-Dair sandy soil, while the minimum occurrence of organic P fraction in soils was observed with rice straw residues having c/N ratios of 49: 1, 97.5t1 (raw) and 17:1 for El-Nobaria, El-Dair and Moshtohor soils, respectively. .~--------------------_._--_._.----- 100 2- The maximum values of soil inorganic P fraction were achieved with rice straw residues having elN ratiosof 33:1, 17:1 and 17:1 for El-Nobaria. EI-Dair and Moshtohor soils, respectively, while the minimum values were recorded with ric est raw res i due s ha v in gel N rat i OS 0 f 97. 5 : 1 ( raw), 49: 1 and 97.5:1 (raw) for the aforementioned soils, respectively. c 111- Cotton stalks residues: 1- The maximum values of organic P due to addition of cotton stalks residues were achieved when their elN ratios were 49:1-17:1, 17:1-10:1 and 49:1 for EI-Nobaria, EI-Dair and Moshtohor soils, respectively, but the minimum occurrence was observed with cotton stalks residues having elN ratios of 96:1 (raw), 33:1 and 33: 1 for the aforementioned soils, respectively. 2- The inorganic P fraction, occurred at maximum leve 15 with application of cotton stalks residues having elN ratios of 96:1 (raw), 33:1 and 33:1 for El-Nobaria, El-Dair and Moshtohor soils, respectively. but the minimum values were ac cur e d wit h res i 4 ue 5 ha vin gel N rat i as o f 17 : 1. 17 : 1 and 10:1. respectively. lY- Soil aYailable P: Gradual and consistent increase in the soil available P was obtained as the elN ratio of added residues became 102 10:1 in when their C/N ratio amounted to EI-Nobaria and E1-Dair soils. 17: 1 and residues respectively, while the corresponding value in case of Moshtohor soil was achieved with the raw residues. 2- The highest values of inorganic P were recorded after 180 days from treating the soils with the different organic residues when their C/N ratio was 17:1 in case of El-Dair soil and 33:1 in case of both El-Nobaria and Moshtohor soils. 3- Available P content of all the investigated soils reached its highest value at C/N ratio of 10:1 and after 180 days of interaction. |