Conditioning Effect of Composts and Acrylamide Hydrogels on a Sandy Calcareous Soil. II-Physico-bio-chemical Properties of the Soil

A complete randomized field experiment with four replications was conducted at El-Saff (Giza overnorate) Egypt, using drip irrigated tomato (Lycopersicum esculentum, hybrid Wady), as the indicator plant. The treatments were: 1) un-treated sandy calcareous soil. 2 and 3) soil treated with organic compost (OM) at the rates of 1 kg/plant pit (12 tons/fed.) or 2 kg/plant pit (24 tons/fed.). 4 and 5) soil treated with 2 g plant pit (24 Kg/fed. or 4 g/plant pit (48 Kg/fed.) of a mixture of the anionic hydrogel (polyacrylamide K polyacrylate gel 30% anionicity and the cationic hydrogel polyacrylamide allylamine hydrochloride gel 20% cationicity at the ratio of 2:3 (G). 6, 8 and 9) soil treated with mixtures of OM and G at the rates of 1 kgOM + 1 gG, 1 kgOM + 2 gG, 2 kgOM + 1 gG, 2 kgOM + 2 gG/plant pit, respectively. At the end of the growing season i.e. after 150 days from plantation some physical, chemical and biological properties of the soil were determined Obtained results could be summarized as follows: 1. Applied conditioners positively affect hydrophysical properties of the soil. These include, (a) improving soil structure expressed by water stable structure units > 0.25 mm in diameter and structure coefficient, dry stable structural units > 0.84 mm in diameter and wind erosion parameter indicating high resistance of the soil against both wind and water erosion and the destruction of the soil by tillage operations, (b) decreasing soil bulk density as well as macro porosity (drainage pores) on the expense of micro ones. Therefore, water holding pores were increased, (c) increasing retained moisture in the soil at all suctions under study (from 0 - 15 atmo), because the increase in water retained in the soil at field capacity is far beyond that at wilting percentage, available water was highly increased. Decreasing mean diameterof soil pores and turn its water transmitting properties namely, infiltrationrate, hydraulic conductivity and transmissivity for vertical flow of water through soil profile. 2. Soil conditioning positively effect chemical and biological properties of the soil these effects are assembled in the following: (a) slightly decreasing soil pH, (b) increasing both CEC of the soil and its specific surface area indicating an improvement in activating chemical reactions in the soil, (c) increasing OM, organic carbon, total nitrogen % in the soil, Because the increase in total nitrogen is higher than that in organic carbon, narrower C/N ratio of treated soils were obtained indicating the mineralization of organic nitrogen compounds and hence the possibility to save and provide available forms of N to growing plants, (d) increasing N, P and K in treated soil. (c) improvingthe biological activity expressed as total count of bacteria, i.e. Azotobacter sp., PDB, fungi and actinomycetes/g soil and the activity of both dehydrogenase and phosphatase. 3. Mixing both types of soil conditioners together i.e. OM and G was more efficient in improving physico-bio-chemical properties of the soil than applying each of them alone Application rate of mixtures components is considered of the important factors that highly affect soil conditioning.