A field experiment (four acres) was conducted on a clay soil at graduated youth fields, El-Zawia region, Al-Hamool District, Kafer El-Shiek governorate to evaluate subsoiling combined with gypsum application for improving hydro-pedological soil properties when a surface drainage system is existed. The subsoiling treatments were 0.8 and 1.6 m spacing at 0.60 m depth and the gypsum application levels were 5.0 and 7.5 ton/fd. Sugar beet crop was grown as an indicator for soil improvement.
Salinity of soil profile was reduced by 35.10 and 12.10 % at 0.8 and 1.6 m subsoiling, respectively with adding 5.0 ton/fd of gypsum. It reduced by 24.39 and 28.88 % with applying 7.5 ton/fd of gypsum due to the corresponding treatments. Despite the gypsum treatments, the average soil salinity was decreased by 29.74 and 20.49 % when the soil was subsoiled at 0.8 and 1.6 m, respectively. In general, the decrease in the ESP values was realized in all soil layers for all treatments and diminished with soil depth giving a good indication of soil improvement. The ESP value was reduced by 41.61 and 33.59 % at 0.8 and 1.6 m subsoiling, respectively with applying 5.0 ton/fd of gypsum. It was reduced by 40.70 and 38.25 % with adding 7.5 ton/fd of gypsum due to the corresponding treatments.
The applied treatments resulted in a remarkable decrease in soil bulk density through the soil profile. The treatments gave a marked positive effect on soil porosity in the topsoil (0-50 cm). Nevertheless, such effect on soil porosity disappeared by increasing the soil depth. An increase in accumulated intake rate at the end of the elapsed time was realized in the treated soil in comparison with the untreated one. Such increase approached 58.19 and 71.77 % when the soil was subsoiled at 0.8 and 1.6 m, respectively with adding 5.0 ton/fd of gypsum. It increased by 63.64 and 61.12 % with adding 7.5 ton/fd of gypsum due to the corresponding treatments. Increasing the gypsum rate increased the accumulated intake rate by 64.98 and 62.38 % at gypsum application levels of 5.0 and 7.5 ton/fd, respectively.
The sugar beet yield increased by 26.86 and 23.27 ton/ fd over the control when the soil was subsoiled at 0.8 and 1.6 m, respectively at a gypsum application level of 5.0 ton / fd. Moreover, it increased by 28.35 and 25.25 ton/ fd at gypsum level of 7.5 ton/fd due to the corresponding treatments.