الفهرس 
INTRODUCTION
Soil Potassium Content and FormsOnly 14 pages are availabe for public view
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Abstract
Mineral and organic amendments are applied to the newly reclaimed soils in Egypt, especially sandy and calcareous sandy soils. These soils are very poor in organic matter and nutrients that are necessary for plants. So, the addition of organic amendments to these soils does not only improve the physical and chemical properties, but also applying these organic materials has a positive impact on the forms of potassium, especially in calcareous sandy soils.
This study aims to evaluate the application effects of a mineral fertilizer (K2SO4) and certain organic amendments (filter mud cake, sheep manure and poultry manure) on the Q/I relation of soil K and its parameters as well as forms of potassium of clay and calcareous sandy soils. The effects of these amendments on some chemical properties of these soils and K uptake by some crops are also examined.
Two soil samples of clay and calcareous sandy soils were collected from the soil surface (0-20 cm). The clay soil sample represented the cultivated soils that are located in the Faculty of Agriculture, Al Azhar University, Assiut, while, the calcareous sandy soil sample represented the uncultivated ones of Wadi El- Assiuti, Assiut.
This study was carried out in one greenhouse experiment over two growth seasons as follows:
The first growth season (Sorghum plants)
The experiment was conducted in plastic pots where 5 kg of each studied soil sample were used in each pot. Each organic amendment was added as amount equivalent to potassium (K) at levels 0, 25, 50 100 kg K/fed, before 30 days of sorghum sowing and mixed with the soil, except potassium sulfate levels that were was added as a solution. All treatments were in three replications. Soil samples were taken from all pots before cultivation. The plants in all pots were harvested after 60 days of sowing, and dried at 70 OC for 72 hours. Soil samples were also taken from all pots after sorghum harvest.
The second growth season (wheat plants)
After sorghum harvest, wheat seeds were sown in the soil in each pot to study the residual effects of these mineral and organic amendments on the same parameters that were studied in the first season. The plants in all pots were also harvested after 60 days of sowing, and dried at 70 OC for 72 hours. Soil samples were also taken from all treatments after wheat harvest.
The results could be summarized as follow:
1. Chemical Properties of the Studied Soils
Changes in some soil chemical properties of the studied soils occurred depending upon the organic amendment type, its level of application and the soil type as well as the growth period.
1.1 Electrical conductivity (EC)
The EC of studied soils significantly increased with the addition of the investigated mineral fertilizer and organic amendments. Moreover, it increased with increasing the added level of each organic amendment. The highest EC value was recorded for sheep manure at a level of 100 kg K/fed which it increased from 0.86 to 1.24 dS/m for the clay soil before cultivation, and from 0.90 to 1.32 dS/m after the second season. For the calcareous sandy soil it increased from 1.03 to 1.40 dS/m before cultivation, and from 1.09 to 1.54 dS/m after the second season with applying sheep manure at a level of 100 kg K/fed.
Both sheep manure and poultry manure had a similar effect on the EC of both soils and their increase trend. They resulted in higher EC values in both soils than potassium sulfate and filter mud cake treatments.
1.2 Soil pH
The soil pH decreased with adding all organic amendments and K2SO4. The lowest reductions in the soil pH were recorded with applying sheep manure while the highest ones were observed with adding potassium sulfate in both studied soils. So, the investigated mineral and organic amendments, in most cases, could be ranked according to the reduction in the pH in both studied soils in order of potassium sulfate > filter mud cake> poultry manure > sheep manure.
1.3 Organic matter (OM) content
The application of all investigated organic amendments increased the organic matter content of both studied soils compared to the control treatment. The highest increases OM content were recorded for the soils treated with poultry manure. On the other hand, the lowest increases in the OM content were with applying potassium sulfate. The OM content in these treated soils increased according to the organic amendments type in the order of poultry manure < sheep manure < filter mud cake.
2. Soil Potassium Forms
The addition of mineral fertilizer and organic amendments caused increases in most soil K forms of both studied soils. These increases depended upon the type and the level of the organic amendment, the soil type and the growth season.
2.1 Soluble K
The soluble K of both studied soils increased with adding the organic amendments and K2SO4. The highest increases in soluble K were recorded before cultivation for both studied soils while, lowest ones after the second growth season.
The application of K2SO4, filter mud cake, sheep manure, poultry manure at the level of 100 kg K/fed, caused increases in the soluble K of the clay soil from 64.56 mg/kg to 104.50, 95.10, 134.22, 116.14 mg/kg, respectively, before cultivation, and from 46.94 mg/kg to 67.75, 77.69, 108.82 and 91.76 mg/kg, respectively, after the second season. In the calcareous sandy soil, the soluble K increased from 51.63 mg/kg to 91.44, 80.23, 110.12, 101.67 mg/kg before cultivation, and from 45.07 mg/kg to 63.55, 53.51, 80.97 and 65.20 mg/kg after wheat harvest with applying K2SO4, filter mud cake, sheep manure, poultry manure, respectively, at the level of 100 kg K/fed. According to these increases, the investigated amendments could be ranked in the order of sheep manure > poultry manure > K2SO4 > filter mud cake.
2.2 Exchangeable K
The exchangeable K of each soil increased with adding each mineral or organic amendment and with increasing its level. The highest values of the exchangeable K were found with applying sheep manure in both studied soils, while the lowest ones were with adding K2SO4 and filter mud cake. The effect of these organic amendments on increasing the exchangeable K of the studied soils has the order of sheep manure > poultry manure > filter mud filters ≈ K2SO4.
The exchangeable K of the K2SO4, filter mud cake, sheep manure and poultry manure treated clay soil at the level of 100 kg K/fed, increased from 127.12 mg/kg to 166.67, 173.21, 209.77, 196.09 mg/kg, respectively, before cultivation, and from 80.02 mg/kg to 135.48, 123.07, 172.20 and 171.28 mg/kg, respectively, wheat harvest. In the calcareous sandy soil, the exchangeable K increased from 32.34 mg/kg to 53.93, 52.10, 77.71, 63.72 mg/kg, respectively, before cultivation, and from 32.94 mg/kg to 63.94, 60.62, 80.37 and 70.79 mg/kg after the second season, as result of applying K2SO4, filter mud cake, sheep manure and poultry manure, respectively, at the level of 100 kg K/fed.
2.3 Non-exchangeable K
The addition of mineral fertilizer and organic amendments caused increases in the non-exchangeable K of both studied soils. The level of this form, increased with increasing the addition level before cultivation, and then, it decreased after the sorghum and wheat harvest.
The application of K2SO4, filter mud cake, sheep manure, poultry manure at the level of 100 kg K/fed, increased the non-exchangeable K of the clay soil from 502.01 mg/kg to 594.68, 649.06, 946.11 and 886.25 mg/kg, respectively, before cultivation and from 511.51 mg/ kg to 634.09, 692.06, 951.77 and 871.14 mg/kg, respectively, after wheat harvest. The respective increases of non-exchangeable K in the calcareous sandy were from 352.34 mg/kg to 518.82, 472.77, 545.71 and 505.01 mg/kg, before cultivation and from 266.94 mg/kg to 386.46, 421.08, 507.98, 460.53 mg/kg after wheat harvest. Generally, the investigated organic amendments could be ranked according to non-exchangeable-K increases in the order of sheep manure > poultry manure > K2SO4 > filter mud cake.
2.4 Residual K
Generally, levels of residual K in both studied soils decreased with applying the investigated organic amendments, and with increasing the applied level of each organic amendment. The highest values of the residual K were recorded before cultivation while, the lowest ones were after the first and second growth periods in both soils.
Sheep manure caused the highest reduction in the residual K, while, potassium sulfate showed the lowest reduction in this K form before cultivation and after the first and second growth periods in both studied soils. The organic amendments could be ranked in most cases, as sheep manure > poultry manure > filter mud cake > K2SO4 in reducing the residual K in both studied soils.
The addition of potassium sulfate, filter mud cake, sheep manure and poultry manure at the level of 100 kg K/fed to the clay soil resulted in decreases in the residual K from 1449.42 mg/kg to 1376.98, 1326.66, 954.13, 1045.62 mg/kg, respectively, before cultivation and from 1363.87 mg/kg to 1289.95, 12.93.92, 925.12, 1009.45 mg/kg, respectively, after wheat harvest. However, applying these respective K2SO4 and organic amendments at the level of 100 mg/fed to the calcareous sandy soil caused reductions in the residual K form 1156.11mg/kg to 1028.16, 1087.96, 961.60 and 1024.12 mg/kg before cultivation, and from 1061.59 mg/kg to 958.42, 934.30, 933.36 and 928.29mg/kg after wheat harvest.
3. Q /I Parameters of Potassium
3.1 Equilibrium activity ratio of potassium (ARk0)
Applying mineral fertilization and organic amendments caused increases in ARok in both soils under study compared to the control treatment. In addition, the ARok values increased with increasing the applied level of these amendments and mineral fertilizer to both studied soils. The soils treated with the organic amendments, especially sheep and poultry manure showed higher increases in the ARok than the other amended ones.
Additions of potassium sulfate, filter mud cake, sheep manure and poultry manure at the level of 100 kg K/fed to the clay soil increased the ARok values from 0.0079 (mol/l)0.5 to 0.0102, 0.0096, 0.0120 and 0.0117 (mol/l)0.5, respectively, before cultivation and from 0.0100 (mol/l)0.5 to 0.0124, 0.0122, 0.0146 and 0.0139 (mol/ l)0.5, respectively, after the second growth season. For the calcareous sandy soil, the ARok increases induced by applying 100 kg K/fed of potassium sulfate, filter mud cake, sheep manure and poultry manure were from 0.0111 (mol/l) 0.5 to 0.0137, 0.0137, 0.0171and 0.0161 (mol/l)0.5, respectively, before cultivation and from 0.0116 (mol/l)0.5 to 0.0139, 0.0132, 0.0154 and 0.0145 (mol/l)0.5, respectively, after sorghum wheat harvest.
3.2 Labile Potassium (-ΔKo)
The amount of the labile K (-ΔK0) of each organic amendment treated soils increased with increasing the added level, especially before cultivation, and then, it decreased after the two growth periods. The highest increases of labile K were recorded in the sheep manure amended soils followed by poultry manure amended ones and then both filter mud cake amended and K2SO4 treated ones. The addition of potassium sulfate, filter mud cake, sheep manure and poultry manure to the clay soil at the level of 100 kg K/fed increased the labile K from 1.01 cmol/kg to 1.45, 1.42, 1.62 and 1.67 cmol/kg respectively, before cultivation and from 1.14 cmol/kg to 1.54, 1.59, 1.69 and 1.61 cmol/kg, respectively, after wheat harvest. The ΔK0 of the calcareous sandy soil induced applied a highest level (100 kg K/fed.) increased from 1.30 cmol/kg to 1.59, 1.59, 1.98 and 1.86 cmol/kg before cultivation and from 1.25 cmol/kg to 1.47, 1.42, 1.38 and 1.43 cmol/kg, after wheat harvest with applying 100 kg K/fed of potassium sulfate, filter mud cake, sheep manure and poultry manure, respectively. The investigated organic materials could be ranked, in increasing the labile K as sheep manure > poultry manure > filter mud cake > K2SO4.
3.3 Potential buffering capacity of potassium (PBCk)
The potential buffering capacity of K (PBCK) tended to increase with applying K2SO4 and the organic amendments and with increasing their levels to the clay soil, but it decreased in the calcareous sandy soil compared to the control treatments. The highest values of PBCk were recorded with adding filter mud cake, while the lowest ones were observed with applying the sheep manure to both studied soils.
The addition of potassium sulfate, filter mud cake, sheep manure and poultry manure to the clay soil at the level of 100 kg K/fed increased the PBCk from 126.8 [cmol kg-1/(mol l-1)0.5] to 141.8, 148.3, 134.5 and 142.7 [cmol kg-1/(mol l-1)0.5], respectively, before cultivation and from 113.6 [cmol kg-1/(mol l-1)0.5] to 124.3, 130.3, 115.5 and 115.7 [cmol kg-1/(mol l-1)0.5], respectively, after the second growth season. However, the PBCk values of calcareous sandy soil treated with 100 kg K/fed of K2SO4, filter mud cake, sheep manure and poultry manure decreased from 117.0 [cmol kg-1/(mol l-1)0.5] to 115.8, 116.2, 115.3 and 115.8 [cmol kg-1/(mol l-1)0.5], respectively, before cultivation and from 108.0 [cmol kg-1/(mol l-1)0.5] to 105.9, 107.8, 89.73 and 98.64 [cmol kg-1/(mol l-1)0.5], repectively, after the second growth season. The investigated organic materials could be ranked in increasing or decreasing the PBCk as filter mud cake > K2SO4 > poultry manure > sheep manure.
Soluble, exchangeable and non-exchangaeble K forms were significantly, positively correlated to ARoK and -∆K0, while the PBCk was negatively correlated to these K forms of both soils. On the other hand, the residual form was negatively correlated to ARoK, -∆K0 and PBCK of the clay and calcareous sandy soils before cultivation and all grown season.
4. Dry Matter Yield and K Uptake by Sorghum and Wheat Plants
4.1 Dry matter of the plant
The organic amendments added to both studied soils significantly increased the dry matter yield of sorghum and wheat plants compared to the control. The increase in the dry matter yield varied according to the organic amendment type and the soil type used. Sheep manure treated clay and calcareous sandy soils produced the highest dry matter yield followed by poultry manure treated and then, filter mud cake treated ones.
4.2 Potassium Concentration and Uptake
The concentration and the uptake of k by sorghum and wheat plants significantly increased with applying the investigated organic amendments to both soils. The investigated mineral and organic amendments could be ranked in their effects on K concentration and uptake increases in both soils as sheep manure > poultry manure > filter mud cake > K2SO4.
The clay soil showed highest increases in K concentrations from 0.25 to 0.87% and from 0.22 to 0.83% in sorghum and wheat plants, respectively, with applying 100 kg K/fed of sheep manure. The respective K concentration increases in sorghum and wheat plants, grown in the sheep manure treated calcareous sandy soil at the level of 100 kg K/fed were from 0.23 to 0.79% and from 0.19 to 0.64%.
Applying sheep manure at the level of 100 kg K/fed to the clay soil showed increases in the K uptake from 3.21 to 29.06 mg/pot by sorghum plants and from 2.45 to 22.63 mg/pot by wheat plants. However, the highest increases K uptake from the calcareous sandy soil treated with 100 kg K/fed of sheep manure were from 1.38 to 11.99 mg/pot by sorghum plants, and from 0.82 to 8.71mg/pot by wheat plants.
Generally, ARK0 and -∆K0 had significant, positive correlations with both potassium concentration and uptake by sorghum and wheat plants grown in both clay and calcareous sandy soils. On the other hand, the PBCk was negatively correlated to the concentration and uptake of K by these plants in both the clay and calcareous sandy soils.
CONCLUSIONS
The application of the investigated organic amendments improved the soil chemical properties of the studied soils, especially the calcareous sandy one. Levels of all K forms except the residual one, of both studied soils increased with applying all investigated organic amendments compared to those of the control. These organic amendments played an important role in the redistribution of K among its various soil forms. Sheep manure showed the highest levels of K forms (soluble, exchangeable and non-exchangeable) in both studied soils before cultivation. However, the levels of these forms decreased after the first and second seasons. The investigated organic and mineral amendments could be ranked according to their positive effects on K forms as sheep manure > poultry manure > potassium sulfate > filter mud cake.
ARok and –ΔKo of the studied soils increased with increasing the applied level of the investigated organic and mineral amendments. Calcareous sandy and clay soils treated with sheep manure resulted in highest values of both ARok and –Δko. The investigated organic amendments could be ranked as sheep manure > poultry manure > filter mud cake > potassium sulfate according to their positive effects on ARko and –Δko in both studied soils. The clay soil treated with organic and mineral amendments had higher PBCk values than the treated calcareous sandy one. Filter mud cake showed highest levels of PBCk in both treated soils. The investigated amendments could be ranked according to their magnitude effect on PBCk in both soils as filter mud cake > potassium sulfate > poultry manure > sheep manure.
Finally, it is recommended to apply organic amendments to the soils, especially the calcareous sandy ones, to improve their physical and chemical properties, the status and forms of the available K and Q/I parameters of K as well as to decrease levels of calcium carbonate in these soils.