Completely randomized drip irrigated field experiments, with three replications for each
treatment, were conducted at El-Saff-Giza Governorate, Egypt to evaluate the beneficial effects of
applying the rice straw (RS)-based hydrogels as soil conditioners for sandy calcareous soil. In this
respect three successive growing seasons (summer season 2010 using tomatoes vs. custle rock, winter
season 2010–2011 using wheat vs. Seds 1 intercropped with onion vs. Giza 20, and summer season
2011 using caw pea vs. Bafb as indicator crops) were carried out. Two rice straw-based hydrogels
(with two rates; 2 and 4 g kg1 soil) were examined. After the third growing season some biochemical
properties of the soil were determined.
The results obtained show that, application of the investigated hydrogels positively affects biochemical
properties of the soil. These effects are assembled in the following: (a) slightly decreasing
soil pH, (b) increasing cation exchange capacity (CEC) of the soil indicating improvement in activating
chemical reactions in the soil, (c) increasing organic matter (OM), organic carbon, total
nitrogen percent in the soil. Because the increase in organic nitrogen surpassed that in organic carbon,
a narrower CN ratio of treated soils was obtained. This indicated the mineralization of nitrogen
compounds and hence the possibility to save and provide available forms of N to growing
plants, (d) increasing available N, P and K in treated soil, and (e) improving biological activity
of the soil expressed as total count of bacteria and counts of Azotobacter sp., phosphate dissolving