الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
Abstract
SUMMARY
This study was carried out to explore the effect of some factors i.e. CaCO3, pH, organic matter (Humic acids) and clay mineral (Bentonite) on the availability and behavior of phosphorus in rhizosphere and nonrhizosphere zone as well as dry weight and P content of phaseolus plant grown on calcareous and noncalcareous sandy soils. The study involved three experiments, an incubation experiment, a split medium technique experiment and pots ones. The experiments were conducted at the faculty of agriculture, Ain Shams University.
5.1. Incubation experiment
The experiment was conducted using 50 g of acid washed sand as pure media that were placed in plastic bottles (100 ml), mixed with the used treatments plus solution of soluble P as KH2PO4 containing 16 mg.kg-1 of P and incubated at laboratory conditions for 4 weeks at room temperature- ̃25°C after adjusting the water content to 70% of field capacity and then adjusting the moisture content daily. The treatments were applied as follows:
Calcium carbonate (CaCO3) in the levels of 0 , 6 or 18%, Humic acid (H.A) in the levels of 0, 1 or 2%., Bentonite in the levels of 0, 20 or 40% and pH of the sand medium was adjusted to 7, 7.8 or 8.6.
Samples from the incubated materials were taken after one, tow, three and four weeks for evaluating NaHCO3 extractable P.
The obtained results can be summarized as follow:
The highest value of chemically available P (15.8 mg.kg-1) was found for 0% CaCO3 at first week, and the lowest value (3.05 mg.kg-1) was found for 18% CaCO3 treatment at fourth week. Analysis of variance and the Duncan’s multiple range test revealed that both of CaC03 and incubation time decreased significantly the NaHCO3ـ extractable P. Such decrease recorded 33.8% and 73.2% due to 6% and 18% CaCO3 treatments, respectively comparing the control one (zero CaCO3).
The main effect of pH, incubation time and the interaction between them were affected significantly the P availability in general. Data showed that in general, the increase of pH from 7 to 7.8 and 8.6 treatments reduced the extracted phosphorus from 14.6 to 9.63 and 7.11 mg.kg-1, respectively. Also the main effect of time showed that phosphorus availability decreased significantly from 12.3, 11.5, 9.35 to 8.62 mg.kg-1 after first week, second week, third week, and fourth week of sand incubation time, respectively.
The application of H.A as 1% and 2% to the incubated sand increased the available P by 28.2% and 38.5% compared with the treatment without H.A, respectively.
As found from the main effect of incubation time the available phosphorus increased by 5.9%, 8.7 and 11.6 for the second, third and fourth week compared with the first week of incubation, respectively. Mostly, the interaction between H.A treatments and the incubation time showed that the available phosphorus increased significantly with increasing of H.A and incubation time. The increase of available phosphorus went hand by hand with increasing both of H.A application to soil and incubation time.
The results of main effects of bentonite and time of incubation show that the available phosphorus decrease significantly with increasing rate of the added bentonite as well as incubation time. Such decrease recorded 20.8% and 56.8% due to 20% and 40% bentonite application, respectively, comparing the nontreated sand. Increasing incubatin time also decreased the available P by about 12.6%, 22.4%, 28.7% and 39.2% after one, two, three and four weeks, respectively. The interaction between bentonite application and the incubation time demonstrate the same trend. Generally, the highest available phosphorus was 15.8 mg.kg-1 for 0% bentonite at first week and the lowest one was 4.78 for 40% bentonite at fourth week of incubation.
Split medium technique experiment.
In this experiment broad bean plant (Vicia faba var. balady) was used as a test plant. Seeds were first germinated between filter papers. After one week, five seedlings were transferred to each of the upper neubauer pots to which 400 g of acid washed sand as pure media were placed.
The seedlings were irrigated with various composition of a nutrient solution (Elgala and Amberger,1988) as follow:
Nutrient solution without P.
Complete nutrient solution with P (NO3- : NH4+ is 1:4)
Solution B with N in the NH4+ form
Solution B with N in the NO3- form.
The pH of the nutrient solution was adjusted to 5.5. The experiment was conducted in green house, After 15 days from seedling, each pot was placed over another one and the solution in the lower pot was contain CaCl2 solution 0.5 × 10-4 M of pH 6.85. The roots penetrated the agar layer and the root system grew normally in the lower pots.
The changes in the pH of the lower solution was recorded, also the root exudate was collected in 500 ml of CaCl2 solution 0.5 × 10-4 M of pH 6.85. After one-week from placing the lower pot containing the CaCl2 solution, the following treatments were applied on the control without P (–P) growing plants:
Nutrient solution without P (Control – P)
Nutrient solution (Control) (NO3- ; NH4+ is 1:4)
3. Nutrient solution whereas N form was NH4+ (Hoagland (N=NH4+))
Nutrient solution whereas N form was NO3- (Hoagland (N=NO3- ))
Nutrient solution without P (-P) + 1 g rock phosphate (P=R.P)
Nutrient solution -P + 1 g super phosphate (P=S.P)
Treatment No 5+ 1 g CaCO3 (P=R.P+CaCO3)
Treatment No 5+ 1 g bentonite (P = R.P + bentonite)
Treatment No 5+ 1 g humic acid (H.A) (P=R.P + H.A)
Treatment No 5+ 1 g bentonite + 1 g H.A (P=R.P + bentonite + H.A)
Treatment No 6 +1 g CaCO3 (P=S.P + CaCO3)
Treatment No 6 +1 g bentonite (P=S.P + bentonite)
Treatment No 6 +1 g H.A (P=S.P + H.A)
Treatment No 6 +1 g bentonite + 1 g H.A (P=S.P + bentonite + H.A)
After one week from applying the treatments, plants were harvested and separated to shoots and roots, and dry weights were recorded then kept for P analyses. The pH of solution in the lower pots of the treatments was measured and then analyzed for soluble P.
The obtained results can be summarized as follow:
The fourth highest significant concentrations of soluble P were given from the humic acid (H.A) treatments. Whereas (S.P + bentonite + H.A) treatment comes first, followed by (R.P+ bentonite + H.A) , ( S.P + H.A) and (R.P + H.A) treatments. The values of soluble phosphorus in growth media were 24.4, 19.5, 13.4 and 11.3 mg.l-1 for the above mentioned treatments, respectively.
The second group of treatments were (S.P), (S.P + bentonite), (R.P), (R.P + bentonite), (S.P + CaCO3) and (R.P + CaCO3) treatments. These treatments had 4.3, 4.0, 2.9, 2.1, 2.0 and 1.37 mg.l-1 soluble phosphorus, respectively.
The lowest significant soluble P values were found in the treatments of (control without P, control, hogland (NH4+) and hogland (NO3-), respectively); the soluble P concentration of these treatments were rare; not increased than 0.001 mg.l-1.
The roots dry weight for all treatments ranged between 0.54 and 0.26 g/pot and for shoots ranged between 0.88 and 0.55 g/pot. The little values and the tight of range of the dry weights of roots and shoots indicated that the growing period of plants was too short and for that there were not clear trend for treatments, and the results of soluble P in different treatments were not matched with the values of dry weights of roots and shoots. The highest concentration of P in roots and shoots was found with the treatments containing humic acid.
The concentrations of P in roots and shoots of bean plant received (S.P + bentonite + H.A, R.P + bentonite + H.A, S.P + H.A and R.P + H.A) treatments were 1.83, 1.17, 1.14 and 1.0% for roots and 2.07, 2.03, 1.72 and 1.25% for shoots, respectively.
The second group of treatments that could supply the plants needs of P, where the concentration of P in roots and shoots was in the normal range. These treatments were (S.P + bentonite), (hogland (N=NH4+)), (SP + CaCo3), (control), (S.P) and (hogland with nitrate (N=NO3- )) treatments for roots. While treatments (S.P + bentonite), (S.P + CaCO3), (hogland with nitrate (N=NO3-)), (S.P), (R.P), (control) and (hogland (N=NH4+) for shoots.
The lowest concentration of P in roots and shoots was found for (R.P+CaCO3) treatment, rather than (control without P) and (R.P + bentonite) treatments for roots and shoots of bean plants. This could be due to these treatments were without P or had a rock phosphate treatment that contain a sparingly soluble P form or a treatment with CaCO3 that precipitate soluble P from growth media.
Pots experiment
This experiment was carried out under greenhouse conditions using Phaseolus (Phaseolus vulgaris - var. Giza 3 (Common Bean)) to study the effect of the different treatments on the availability of P and plant growth in calcareous and noncalcareous soils. The treatments of this experiment depended on the results of the previous experiments.
The soil investigated samples were air dried, crushed and finely ground, then sieved through 2 mm sieve and used for the experiment.
Treatments were applied to the tested soils as follows:
Super phosphate (0.166 g/kg soil (wich equivalent 32 kg P2O5/feddan)) (control) (S.P)
Rock Phosphate (0.330 g/kg soil (wich equivalent 32 kg P2O5/feddan)) (R.P)
Humic acids 1% w.w (H.A)
Treatment No (2) + humic acids 1% (R.P+H.A)
Treatment No (1) + humic acids 1% (S.P+H.A)
Half treatment No (1) + as half No (2) (1/2 R.P + 1/2 S.P)
After planting; moisture content was brought to 70% of water field capacity and fertilized with N and K as recommended by ministry of agriculture. In this experiment, phaseolus plants were planted at May 2018.
Plant samples were taken at vegetable growth stage after 40 days from planting, soil samples were taken from rhizosphere zone and nonrhizosphere zone. The collected soil samples were subjected to P fractionation and pH determination.
After harvest, the plant samples were separated to shoot and root and analyzed for P content.
Soil samples were taken from each pot after 40 days at the end of the experiment to determine pH and phosphorus forms in soil.
The obtained results can be summarized as follow:
The arrangement of the above treatments were different for dry plant roots, whereas their arrangement was as follows: (R.P + H.A) > H.A > S.P > (½ S.P + ½ R.P) > R.P. Root dry weight for such treatments ranged between 1.63 and 1.43 g plant-1.
The comparison between dry weight of shoot and root of grown on the two cultivated soils showed that in general, the dry weights of shoot and root of phaseolus plants grown on noncalcareous sandy soil were higher than those grown on the calcareous one. The negative effect of lime (CaCO3) on plant growth is well known as it turn phosphate as well as some other nutrients less available for the growing plant.
The dry weight of plant shoot for rock phosphate treatment was reduced by 38.1% compared with control (S.P treatment) in calcareous sandy soil, while the dry weight of shoot for this treatment increased by 4.3% compared with S.P treatment in noncalcareous sandy soil.
The concentrations of P in shoot and root of phaseolus plants showed that the highest values of P concentraion in shoot and root were found for (S.P+H.A) treatment in both soils recording values of 1.45% and 1.52% for noncalcareous sandy soil and 1.51% and 1.35% for the calcareous sandy soil, respectively. Effects of other treatments were significantly greater than (S.P) treatment (control) except (R.P) treatment for shoot and root of phaseolus plant grown in noncalcareous sandy and calcareous sandy soils. These increases were 13.4%, 7.1% and 5.5% for shoot in noncalcareous sandy soil with (H.A), (R.P + H.A) and (½ S.P + ½ R.p) treatments, respectively. For calcareous sandy soil the increases were 3.6%, 2.4% and 1.3% with (H.A), (R.P+ H.A) and (½ S.P + ½ R.P) treatments, respectively in shoot.
R.P treatment had the lowest concentration of P in shoot and root of phaseolus plant grown in both soils. The reduction of P concentration in shoot was 2.2% for plant grown in noncalcareous sandy soil and 1.7% for those grown in calcareous soil compared with control (S.P treatment).
Values of total uptake of P, reflects such nutrient concentration more than plant dry weight. Plant uptake of P had the same trend of P concentration in plant for all treatments in noncalcareous sandy and calcareous sandy soils.
At rhizosphere zone pH of soil recorded the lowest values for all treatments applied to the two studied soils. The lowest values of soil pH were 5.41 and 6.24 for (S.P + H.A) treatment in noncalcareous sandy and calcareous sandy soil, respectively. Soil pH values for other treatments of the noncalcareous sandy soil were 7.42, 7.43, 7.09, 6.44 and 5.72 for (R.P), (R.P + H.A), (1/2 S.P + 1/2 R.P), humic acid and super phosphate treatments, respectively at rhizosphere zone. While soil pH values were 8.43, 7.49, 7.45, 7.32 and 6.54 for rock phosphate, (1/2 S.P + 1/2 R.P), (S.P), (R.P + H.A) and humic acid treatments, respectively at rhizosphere zone of the calcareous sandy soil, respectively.
Generally, the results of soil pH showed that pH of calcareous sandy soil increased compared with those of noncalcareous sandy one. Also pH of soil increased with the increasing of the distance from plant root for all treatments as well as for the two soils. Such results indicated the role of CaCO3 and the substances of root exudates in effecting solubility and availability of phosphorus in soils.
The different treatments affected significantly the distribution of P in the various fractions in non-calcareous sandy soils. The distribution of P among the different chemical pools showed that the Ca-P and EXE fractions of the element is the prevalent forms in the cultivated or un-cultivated non-calcareous soil treated with different applications.
For calcareous soil, the highest significant values were SOLU-P and EXE-P for S.P treatment in rhizosphere zone and this represented 13.5% and 22.7% of total P in such treatment. In non-rhizosphere zone the highest SOLU-P value was 16.0% for H.A treatment, and for EXE-P was 25.3% for (S.P + H.A) treatment. While in the non-cultivated soil the highest significant values of SOLU-P and EXE-P were found for (S.P + H.A) and H.A treatments, respectively and equal 16.1% and 23.6% of total P content, respectively.
The highest significant Ca-P and OXD-P fractions were found for S.P treatments for all plant root distances, as well as for non-calcareous soil. The highest significant ORG-P were 24.8% and 26.2% for (S.P + H.A) treatment in rhizosphere and non-rhizosphere zone respectively, while the highest significant ORG-P fraction in non-cultivated calcareous soil was found for H.A treatment and equal 24.4%. On the other hand, the lowest P fractions in general were found for R.P treatment in all plant root distances. This result was found also in non-calcareous soil, it may be due to the lowest total-P content for this treatment.
The distribution of P among the different fractions showed that the Ca-P and OXD forms of the studied element is the dominant in the cultivated or non-cultivated calcareous soil received the different treatments.
Generally, P fractions in rhizosphere zone were > non-rhizosphere zone > non-cultivated soil, and this could be due to plant deplation of P from non-calcareous and calcareous soils. It could be concluded that the applied treatments to the studied soils altered phosphorus concentration in such soil fractions. The highest P values were found in the fractions of soils treated with S.P+ H.A 1%.
Finally, it could be noticed that P have a complicated chemistry in soils, particularly calcareous ones. The relative influence of different soil components on P availability in calcareous soils as well as non-calcarous ones is contradictory. CaCO3, has a series of fixation reactions occur that gradually decrease P solubility and eventually availability to plants. Addition of organic matter (used as H.A) showed significant positive effect, while CaCO3 and / or high pH showed significant negative effects when applied in combinations with P fertilizers to sandy soils. However, bentonite addition resulted slight effect.