•Starch-based three hydrogels were prepared by gamma-radiation technique.•The swelling degree of the IPN hydrogels decreases with increased starch content.•The IPN hydrogels were evaluated as soil conditioner in heavy metals and alkaline soil pH > 9. This article highlights the advance of the radiation synthesis of starch-based hydrogel to be used as a soil conditioner. The hydrogels samples have been prepared in weight ratios 1:3, 2:2 and 3:1 (wt:wt) for starch (St), polyvinylpyrrolidone (PVP) and acrylamide (Am), individually. At dose of 30 kGy, the polymerization reaction is occurred to produce IPN hydrogels using gamma irradiation technique. The impact of starch content on the behavior of swelling and water absorption from moisture soil for the (PAAm/PVP), (PAAm/St) and (PVP/St) INP hydrogels was investigated. The chemical composition and morphology of the (PVP/PAAm), (PAAm/St) and (PVP/St) IPN is described using Fourier Transform Infrared Spectroscopy (FTIR) and the Scanning Electron Microscope (SEM). X-ray diffraction (XRD) confirm the effect of starch on the crystanillity of (PAAm/St) and (PVP/St) INP hydrogels. The result indicated that, the degree of swelling of the IPN hydrogels decreases with increased starch content. This is attributing to the existence of intra- and inter-molecular H bonds in the IPN hydrogels are increased with increased starch content as performed by FT-IR. Three soil conditioners of ratio PVP/St, PAAm/St and PVP/PAAm INP hydrogels (3/1) were chosen to determine the effectiveness of heavy metals and alkaline soil pH > 9 for sunflower plating (Helianthusannuus). The treatments were irrigated weekly, the obtained result showed that the effectiveness of soil conditioner is in this order: PVP/PAAm > control > PVP/St > PAAm/St.