Two field experiments were carried out during two successive seasons (2004/2005 and 2005) to investigate the effect of some soil amendments on productivity of wheat and soybean and mobility and availability of nitrogen in soil. A split- split plot design with three replicates was used. The main plots were devoted to compost application levels, C(0 and 20 m³/fed). The subplots were allocated to sulphur application levels, S ( 0, 450 and 900kg/fed). The sub-subplots were assigned for mineral fertilizers, NP(50,75 and 100% of the recommended dose). The main results could be summarized as follows:
The 1000 grain weight of wheat, 100 seed weight of soybean and productivity of both crops were influenced significantly by alternative soil amendments treatments. The highest mean values of wheat grain and soybean seed yield were achieved from the interaction between application of 20m³ compost/ fed, 900kg sulphur/ fed, and 100% NP mineral fertilizer of the recommended dose. The application of compost increased the total nitrogen content in soil by 22.5 and 56.96% over the control after the harvesting of wheat and soybean, respectively. Application of sulphur had a positive effect on total nitrogen content in soil. The N content in soil was significantly increased with increasing the rate of sulphur up to 900kg/fed and NP up to100% from the recommended dose.
The most effective interaction effect on increasing the NO-3 concentration in soil after harvesting of wheat was under 20m³compost, 900kg sulphur/ fed and mineral fertilizer at rate of 100% from the recommended dose.While after soybean the best interaction was detected between 20m³ compost, 900kg sulphur/ fed and adding NP mineral fertilizer at rate of 75% from the recommended dose. With regard to the interaction effect of different treatments on NH4+ concentration in soil the data demonstrated that the highest values were resulted from combination between applications of 20 m3 compost, 900 Kg sulphur/fed. and application of mineral fertilizers at rate of 75 % or 100 % from the recommended dose after harvesting of wheat and soybean, respectively.