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Abstract
A pot experiment was carried out in the greenhouse to study the response of plants to P-fertilization, at increasing rate, under increased salinity levels. Barley (Hordum vulgare cv. Giza 123), which is characterized by tolerance to salinity, was used as an indicator plant. Two soils differed mainly in texture were used; the first is a sandy soil from Meet Kenana vallege and the second is a clayey soil from the farm of the Faculty of Agriculture, Moshtohor Qalubiya Governorate. Pots each containing 6 Kg soil were used and twenty barley grains per pot were sown. The N and K fertilizers were added. The recommended dose for N fertilizer 45 mg N/kg. The recommended dose for K fertilizer was 24 mg K/Kg. The design of the experiment was a randomized complete block design, factorial which involved three factors follows:
Factor A : Soil, two soils as mentioned above
Factor B : Salinity, 6 levels of salinity stress as follows:
S0:Tap water (EC of 0.90 dS/m); S1:Sea water diluted by 1 : 10
(sea water : tap water, V/V) ratio (EC of 7.35 dS/m); S2: Sea water diluted by 1 : 5 ratio (EC of 12.8 dS/m); S3: Sea water diluted by 1 : 4 ratio (EC of 14.8 dS/m); S4: Sea water diluted by 1 : 3 ratio (EC of 18.1 dS/m); S5: Sea water diluted by 1 : 2 ratio (EC of 23.5 dS/m).
Factor C : Fertilization, there were 4 treatments as follows:
R0: non-fertilized (R0) no P- added; R1: 7.5 mg P kg-1 soil; R2: 15 mg P kg-1 soil; R3: 30 mg P kg-1 soil
Nutrients were applied in a form of a water solution. P and K were added with the 1st irrigation. N was added in 3 equal splits, with 1st; 2nd, and the 3rd irrigation.
Irrigation was done to about the water holding capacity. Germinated grains were counted for ten days and germination rate and germination percentage were calculated after complete germination. After 18 days of planting, plants were thinned to 10 plants/pot were and continued growth under irrigation till maturity. 200 ml of Hoglands solution per pot was added twice during plant growth. At maturity number of tillers and spikes were counted and plant height was measured, then plants were harvested (after 106 days for sandy soil and 130 days for the clayey one) and separated into grains and straw, oven dried at 70oC for 24 hours and the dry weight of both grains and straw were recorded. Plant samples were ground digested for analysis for contents of N, P, K, Na, Ca and Mg.
The obtained results could be summarized as follows:
Germination :
1- Barley grains, on the average of the two studied soils, respond negatively to P fertilization at germination stage under all of the studied salinity levels stress, where germination rate increased with increasing applied P.
2- With no clear significant effect on germination percentage.
Plant growth
1- Application of P, in general, particularly at increasing rate, under increased salinity levels stress, caused a general increase in plant growth on the average of the two soils particularly in the clay soil than in the sandy one.
2- The increase in plant growth with application of P was reflected on increasing plant yield due to more plant tillering, number of spikes and plant height.
3- Barley plants grown on the sandy soil responded positively to P at the high rate; the increase in salinity levels stress beyond S4 caused a death of plants at the stage of spikes emergence (after 60 days from sowing).
4- Plants responded positively to P at increasing rate;
5- Negative effect of salinity on plant growth and yield was alleviated by applying P.
6- Under salinity levels stress S2 (EC = 12.80 dS m-1). The highest plant growth occarved under R0
7- In the clayey soil, plants responded positively to P-fertilization at increasing rate under all of salinity levels stress and growth decreased with increasing salinity level.
8- Salinity levels stress S2, S3, S4 and S5 the highest response occurred at R2, R3 R1, and R3 of P , respectively.
9- Application of P in the clay soil gave greater growth for barley plants on the sandy one.
Number of tillers and spikes:
1- Application of P, increased the number of tillers especially at the highest rate of application
2- Under conditions of sandy soil, barley plants respond positively, at tillering stage, to the application of P fertilizer under increased salinity level stress up to S4 . The S5 caused plant death.
3- In the clayey soil, increasing the rate of applied P was associated with increased number of tillers.
Barley straw yield.
1- Plants responded positively to P-fertilization.
Effect on grain yield.
1- Application of P increased barley grain yield. Plant growth was enhanced by P through increasing its tolerance to the adverse effect of salinity especially when applied at a low rate.
2- Increasing salinity decreased grain yield.
3- In the sandy soil, application of P increased grain yield and the highest.
4- In the clayey soil, P fertilization increased grain yield. The highest grains yield was obtained under R1 of P fertilization.
5- Increasing salinity level stress was associated with a significant decrease in barley grains yield under all rates of the applied P death to plants occurred under S5 in the sandy soil and no grains were obtained at S2 onwards. With the clay soil no grains were obtained at S5.
Effect on nutrients uptake by barley plants:
Nutrients uptake by barley straw:
1. Nitrogen uptake by barley straw:
1- P rates showed decreases of 3.3, 6.8 and 9.5 % at R1, R2 and R3, respectively. Increasing salinity was associated with a decrease in N-uptake by straw.
2 - Phosphorus uptake by barley straw:
P rates showed an increase of 5.1 % at R1, whereas showed decreases of 12.1 and 17.6 % at R2 and R3, respectively.
3 - Potassium uptake by barley straw:
Increasing salinity decreased K-uptake tended to once.
4 - Sodium uptake in barley straw:
Application of P resulted in a decrease in Na-uptake straw. The decrease was progressive with increasing P of application, salinity decreased Na-uptake decrease occurred under R2 of P. Na-uptake decreased with increasing salinity levels stress.
5 - Calcium uptake in barley straw:
P application slightly increased Ca-uptake then decreased it in the clayey soil. In the sandy soil, increasing P application was associated with a progressive decrease in Ca-uptake. Increasing salinity was associated with decreases in Ca-uptake
6 - Magnesium uptake in barley straw:
1- Mg-uptake in straw took a trend almost similar to that of calcium, under conditions of the sandy soil Mg-uptake increased with increasing P at R2 of phosphorus.
2- Increasing salinity to S1 was associated with an increase in Mg-uptake then decrease occurred.
Nutrients uptake by barley grains:
1. N-uptake in grains:
1- There was a progressive increase in N-uptake with increasing P.
2- Increasing salinity decreased N-uptake by barley grains. And a decrease occurred by increasing salinity S0 to S1, then the decrease was gradual with increasing salinity.
2. P-uptake in grains:
1- There was an increase in P- uptake with increasing P application rate up to R1 then decreased at R2 and slightly increased at R3 in the clayey soil, In the sandy soil P-uptake decreased with increasing P up to R2 then decreased at R3 .
2- Increasing salinity was associated with a decrease.
3. K-uptake in grains:
1- Increases of 1.37, 4.48 % occurred at R1 and R2, respectively and a decrease of 1.30 occurred at R3.
2– The interaction effect caused by P on the negative effect of salinity was manifested by causing a mild decrease due to salinity by applying P to plants.
4. Sodium-uptake in grains:
The main effect of the applied P rate showed decreases of 19.32, 5.60 and 8.49 % at R1, R2, and R3, respectively. Application of P decreased Na- uptake by barley grains.
5. Calcium-uptake in grains:
There were increases of 13.86 and 2.44 %, and a decrease of 15.38 % at R1, R2, and R3, respectively.
6. Magnesium-uptake in grains:
There were decreases of 21.67 and 30.75 % at R1 and R3, respectively; and an increase of 0.30 % at R2 in the clayey soil in particular, whereas, in the sandy soil each increase in P application was accompanied with an associated decrease in Mg uptake.
Conclusion
from the obtained results it could be concluded that P- fertilizer increased the tolerance of barley plants to the hazardous effect of the increased salinity levels stress and the increase being depended upon the applied P rate under the considered salinity level. The response of barley plants to P-fertilization under the increased salinity levels stress was more pronounced in the clayey soil than in the sandy one; this probably may be due to its high buffering capacity compared with that of the sandy soil which would affect the osmosity of the soil solution by decreasing it through the adsorption of ions on the surface of soil colloids and thereby reducing the harmful effect of salinity and sodicity on the growing plants.