الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 113 |  |  |
| | | from | 113 | | |
Abstract
The present investigation aimed at studying the effect of cultivation periods on the properties of some newly reclaimed desert soils. Two different soils were selected to represent the sandy and calcareous soils located at El- Bustan region, El-Bohira Governorate and El-Nubariya region, respectively. In each region, four profiles were selected to represent different cultivation periods i.e., zero (virgin soil), 10, 20 and 30 years of soil cultivation. Soil profiles were dug and soil samples were taken from 0 — 15, 15 — 60 and 60 - 90 cm depth. All soil samples were subjected to physical and chemical analysis. Also, their contents of available N, P, K, Fe, Mn, Zn and Cu were determined. It is evident that increasing cultivation period from zero to 30 years of cultivation plays an important role for improving the different soil properties, these beneficial effects are represented by:
1.Reduction in soil bulk of both the studied sandy and calcareous soils in all studied profile layers, and the decreases were more pronounced in the surface layers than in the deeper ones. On the other hand, the values of the total porosity exhibited increments, since there is an adverse relationship between soil bulk density and total porosity.
2.The hydraulic conductivity was tended to decrease in the Sandy soil, may be due to the long-term accumulation of clay
and organic matter on the surface layer of soil, where it was 33.72 cm/h in the virgin soil and decreased to 21.92 cm/h in the soils cultivated for 30 years. Within the soil profile, the hydraulic conductivity values were tended to increase with depth in both the virgin and cultivated soils, may be due to the underlain soil are characterized by light texture. As for the calcareous soil, the hydraulic conductivity increased from 14.20 cm/h in the virgin to 18.35 cm/h after 30 years of cultivation. Within the soil profile, there was no distinct pattern for the hydraulic conductivity values with depth.
3.Soil structure factors of both the sandy and calcareous soils in all were tended to increase in profile layers may be due to the pronounced accumulation of fine fraction during soil management practices and flooding with the Nile water, which attained a pronounced content of the suspended
matter.
4.Soil moisture constants showed an increase for each of field capacity, wilting point and available water range in both the sandy and calcareous soils in all profile layers. These increases were more pronounced in the surface layers than in the deeper ones.
5.Soil clay content exhibited an increase after 30 years of cultivation; this feature was confirmed by changing soil texture from sand to sandy loam, and from sandy loam to sandy clay
r-
loam for the sandy and calcareous soils, respectively. The increase may be due to the pronounced addition of fine particles during soil management practices and flooding with
the Nile water.
6.Soil salinity (ECe) of both the sandy and calcareous soils was tended to decrease, where it reached a minimum value after 30 years of soil cultivation. This is true for both surface and
subsurface layers.
7.Soluble cations (CC, Mg++, Na+ and K+) were tended to decrease, where the virgin soils (sandy and calcareous) had the higher values, but the 30 years cultivated soils had the lowest values in both soils. Soluble calcium was the dominant cation in both soils. Soluble anions showed also pronounced decreases. Soluble sulfates was the dominant anions in all layers of calcareous soil, whereas, no specific pattern for anions distribution in sandy soils.
5. Cation exchange capacity values were increased in both the
sandy and calcareous soils; these increases were more pronounced in the surface layers rather than the deepest ones. The increases in the CEC values of both soils are a direct outcome of the increase in the colloidal particles in the soil
including clay and organic colloids. The distribution pattern of individual exchangeable cation in the sandy soil was arranged in the descending order of: Ca> Na> Mg> K.
Whereas, in calcareous soil was found in the descending order of: Ca> Mg> Na> K
6.Organic matter contents in both the sandy and calcareous soils were increased, where it reached the highest value after 30 years. This increase was mainly due to the accumulation of organic plant residues as well as the added organic manure during the soil management practices.
7.Calcium carbonate content was decreased in both the sandy and the calcareous soils. i.e., from 6.43 to 5.61 % in sandy soil and from 42.60 to 32.00 % in calcareous one after 30 years of cultivation. The decrease in soil calcium carbonate content after 30 years of cultivation may be attributed to the invigoration of biological activities, which produces acidic substances which decrease CaCO3 as shown in the following:
CaCO3 + CO2 + H2O - - - - - - - Ca (HCO3)2
Solid Soluble
8.The available N, P and K contents in both the sandy and calcareous soils were increased, especially in the surface layers than in the deeper ones. Also, gradually increases in available Fe, Mn, Zn and Cu contents were occurred in both the sandy and calcareous soils. The increase in available micronutrients was relatively higher in calcareous, except Fe as compared to sandy one.