الفهرس 
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Abstract
Soil characterization in relation to evaluation of fertility status of soils of an area or region is an important aspect in context of sustainable agricultural production. Because of imbalanced and inadequate fertilizer use coupled with low efficiency of agriculture practices reduced the efficiency of chemical fertilizer under intensive agriculture. Productivity of crop can be boosted by judicious use of macro and micro nutrient fertilizers and focus on improving the soil physicochemical nature or soil health. Optimal use of nutrients based on soil analysis can improve crop productivity and minimize wastage of these nutrients thus mitigate hazardous impact on environment leading to bias through optimal production. The information on the availability of macro nutrients status in soil of Assiut Governorate is meager. Therefore this study aimed to assess forms of both potassium and phosphorus in soil and the relationship between both elements and some soil properties. The study area (Assiut Governorate) is located between 26° 50ُ to 27° 37ُ N latitude and 30° 39ُ to 31° 35ُ E longitude, representing 0.15% of the total area of Egypt. The study area was divided into 10 transects, that were taken across the Nile Valley in the east-west direction, with a distance almost about 8.0 km between consecutive transects leaving 12 km north the first one and south the last one. Number of soil profiles were selected in each transect according to the Nile valley width in each transect using the global positioning system (GPS) for localizing each profile. Soil samples were collected in May 2014 from fifty four locations of Assiut Governorate under different cropping pattern. All soil profiles in each transect had known longitudes at one definite latitude. Soil samples from two depths (0- 30 and 30- 60 cm) at every location were collected, air dried, crushed then pass through 2.0 mm sieve to obtain a uniform representative sample then they were analyzed by standard methods. Available and total of both Phosphorus and potassium were measured.
The obtained results could be summarized as follows:-
1. Physical soil properties:
1- The soil samples having sandy loam, loam, clay loam, sand clay loam, loamy sand, clay and silt clay texture represented 43.52, 27.78, 11.11, 8.33, 4.63, 3.70 and 0.93% of the total soil samples, respectively.
2- There is a wide variation in CaCO3 content in soils of Assiut Governorate. It varied from 0.61 to 36.26% with an average value of 5.01%. 75% of soil samples were found non-calcareous (CaCO3 content < 5%) and 19.44% were slightly calcareous (CaCO3 content between 5 to 15%) while the remaining 5.56% were calcareous (CaCO3 content > 15%).
3- There is a wide variation in organic matter content in soils of Assiut Governorate. It varied from 0.23 to 4.09% with an average value of 1.52%.
2. Chemical soil properties:
1- The total soluble salt contents expressed as electrical conductivity (ECe) varied from 0.63 to 7.80 dS/ m with an average value of 1.39 dS/ m at 25°C. The majority of soil samples (96.30 %) were in the normal EC range (< 4 dS/ m) and it decrease with depth.
2- The soils pH varied from 7.22 to 8.92 with an average value of 7.97. Nearly 84.26% of the soil samples had pH 7.22 - 8.2 and the remaining 15.74% had pH higher than 8.2. In most soils profiles, the pH values increased with soil depth.
3- Soluble anions could be arranged in descending order of Cl > SO4 > HCO3 with nil carbonate content.
4- Soluble cations distribution in most soil samples followed the order of Ca > Mg > Na > K if the soil salinity < 5 dS/m. If soil salinity > 5 dS/m this distribution changed to follow the order of Na > Ca > Mg > K.
5- Soluble potassium ranged from 0.04 to 1.19 meq./ L with irregular trend through soil depth.
6- Sodium Adsorption Ratio (SAR) values ranged from 0.46 to 16.50. The high values of SAR were compatible with high soil salinity.
7- Cation exchange capacity (CEC) values ranged from 14.01 to 49.43 meq./ 100 g soil and it increased toward the south direction.
8- Exchangeable sodium percent (ESP) varied from 0.77 to 28.70. All the studied soil profile could be considered non alkaline soils except the profiles No. 1 and 7 in transect No. 6 and 7, respectively which could be considered alkaline soils since the ESP values varied from 10.18 to 28.70.
9- Exchangeable potassium values were in a narrow range, varying between 0.46 to 25.34 meq./ 100 g and it decreased with soil depth.
10- Total potassium values varied between 0.02 and 0.50% and it decreased with soil depth while it increased toward south direction.
11- Available potassium values varied between 38.0 to 710.0 ppm and it decreased with soil depth. Also, available K coincided with total one since it increased toward south direction.
12- Total phosphorus values varied between 0.001 and 0.235% and it decreased with soil depth.
13- Available phosphorus values varied between 2.73 and 110.08 ppm. According to Olsen and Sommers, 59.25 % of Assiut soils are deficient in P and it decreased with soil depth.
3. Correlation matrix of soil properties
1- Available phosphorus (Pa) was insignificant and positively correlated with silt (r= 0.193) and clay (r= 0.045). It was insignificant and negatively correlated with CaCO3 (r= -0.118) and pH (r= -0.049). Pa was significant and positively correlated with EC (0.197*). It was high significant and positively correlated with both OM (r= 0.515**) and CEC (r= 0.258**).
2- Total phosphorus (Pt) was insignificant and positively correlated with silt (r= 0.192), CaCO3 (r= 0.039) and pH (r= 0.166). It was insignificant and negatively correlated with EC (r= -0.007). Pt was high significant and positively correlated with clay (r= 0.395**), OM (r= 0.558**), CEC (r= 0.277**), Pa (r= 0.285**), available potassium (r= 0.336**) and total potassium (r= 0.643**).
3- Positive insignificant correlation of EC was found with available potassium (r = 0.001) while there was negative insignificant correlation with pH (r = - 0.129). Available potassium (Ka) found to be positive and significant correlated with clay content (r = 0.214*). It was positive and highly significant correlation with each of silt, OM, CEC. Ka negatively and highly significant correlated with CaCO3.
4- Total potassium (Kt) positively insignificant correlation with CaCO3 (r= 0.055) and Pa (r= 0.171) while it negatively insignificant correlation with EC (r= -0.02). Kt was positive and highly significant correlated with each of silt, clay, OM, pH, CEC and Ka.
5- CEC was insignificant and negatively correlated with EC (r= -0.050) while it was highly significant and negatively correlated with CaCO3 (r= -0.424**) and pH (r= -0.266**). It was high significant and positively correlated with silt (r= 0.57**), clay (r= 0.45**) and OM (r= 0.556**).
6- EC was insignificant and positively correlated with CaCO3 (r= 0.033), OM (r= 0.122) and pH (r= 0.147). It was insignificant and negatively correlated with silt (r= -0.096) and clay (r= -0.134).
7- pH was insignificant and positively correlated with clay (r= 0.023) while it was insignificant and negatively correlated with OM (r= -0.086). It was highly significant and negatively correlated with silt (r= -0.282**) and it was highly significant and positively correlated with CaCO3 content (r= 0.550**).
8- OM was highly significant and positively correlated with silt (r= 0.427**) and clay (r= 0.296**) while it was significant and negatively correlated with CaCO3 (r= - 0.201*).
9- CaCO3 was highly significant and negatively correlated with silt (r= -0.558**) while it was insignificant and negatively correlated with clay content (r= -0.036).
10- Clay content was significant and positively correlated with silt (r= 0.234*).
D) Nutrients index
1- For judging soil salinity problem, 37.0, 52.8, 7.4 and 2.8 % of the samples were found in category of no deleterious effect on crop, critical for germination, critical for salt sensitive crop and injurious to most crops, respectively. Most of soil samples were found in normal category (EC < 2 dS/m).
2- OM was low (< 0.86%) in 22.2% soil samples and 18.5% soil samples were medium (0.86- 1.29%). The remaining 59.26% soil samples were high (> 1.29%).
3- Soil nutrient index for organic matter content was 2.4 which considered high fertility status.
4- Soils of the studied area were found in category of low fertility status for available phosphorus (2.1).
5- Soils of the studied area were found in category of medium fertility status for available potassium (2.1)
It might be recommended that
1. 59.25 and 16.67 % of the total soil samples of Assiut soils are considered P and K-deficient, respectively. So, these soils have to be fertilized with P and K fertilizers.
2- Build up of organic carbon status by different means is a practicable tool in our hands to minimize deficiency area of these soils with reference to phosphorus.
3- Phosphorus fixation continues to receive much attention, it is more important to know the effect of soil characteristics on phosphorus fixation.
4- The soil properties pH, EC, CaCO3 and OM as the main characteristics playing major role in controlling the availability of macronutrients. These factors could be manipulated in order to combat any present or future deficiencies of macronutrients in these soils.
5- Challenges remain to improve understanding of changes to soil K forms across the spectrum from deficiency to excess and to determine the effect on soil K availability.
6- It is advisable to consider the amount of exchangeable K, non-exchangeable K content and clay mineralogy while recommending the potassium fertilizer in different altitude.
7- Most soils in Assiut contain abundant soil potassium (K) reserves, and it is often assumed that there are no problems with soil K status. Assessment of the ability of soils to release K for plant uptake is important for proper management of K in crop production.
8- The soils require attention regarding nutrient management practices and regular monitoring of soil health for better crop production.
9- On the basis of these results farmers are advised to use integrated nutrient management practice to maintain optimum concentration of all the essential nutrients for plants. Farmers are also advised to add bio-fertilizers.