The effects of some organic wastes i.e. sewage sludge and town refuse on soil pH. P availability and soil productivity of calcareous soils were investigated. Surface soil samples differing in their contents of CaCO3 collected from three locations beside the Cairo-Alexandria desert road were used for an incubation experiment and a greenhouse trial. In the incubation experiment, the soils were mixed with either of the tested organic wastes at a rate of 2% O.M. Inorganic P was also added as KH2PO4 at a rate of 0, 50, 100 or 200 μ/g in combination with the organic wastes. The treated soil samples were incubated at the field capacity. Sub*samples were taken after 0, 1, 2, 4, 6 and 8 weeks of incubation for determining available P and soil pH. The aforementioned treatments were also tested in a greenhouse experiment where barely plants (Giza 124) were grown on the investigated soils. Plants were harvested after growth period of 60 days. Dry matter yield, P-concentration and P uptake by barely plants were determined.
Due to incubating the calcareous soils with sewage sludge or town refuse, the pH values of the investigated soils were generally decreased. Sewage sludge was more effective in reducing soil pH than the town refuse. Also, the soils content of available P was materially increased. Sewage sludge was more effective in enriching the soils with available P than the town refuse. The effect was partially depended on the type of soil and the incubation period. Fertilizing the soils with either sewage sludge or town refuse increased the dry matter yield as well as P-uptake of barely plants grown thereon. Application of the inorganic P fertilizer together with the organic wastes enlarged the increase in the dry matter yield and P-uptake.
The most interesting result is that, the highest rate in yield increase due to organic manuring, was achieved in soil (3) which could be considered saline-sodic (EC = 8 dSm-1) and SAR = 13) Accordingly, the use of organic wastes as soil manures is recommended, particularly in newly reclaimed calcareous soils, to achieve more than one objective i.e. freeing the environment from wastes and hence minimizing the pollution hazards, reducing the salinity and sodocity effects on soil productivity, modifying the high relatively pH-values in calcareous soils and hence improving the nutrients status, particularly P, and increasing the soil productivity, in general as result such treatment. |
