Effect of nitrogen fertilizer and compost rates addition at different depths on some soil chemical properties

Two field experiments were conducted on clay loam soil during the two successive seasons, summer season 2017 using maize plants and winter season 2017/2018 using barley plants at El-Gemmeiza Agricultural Research Station, El-Gharbia Governorate to evaluate the direct and residual effects of compost rates mixed with the surface soil layer to 10 cm or added in 30 cm mole depth, arranged in parallel orientation with respect to one another and spaced at 3 m apart besides the nitrogen fertilizer rates on improving some soil chemical properties. Furthermore economical analysis was done by calculating the net income for every treatment to determine the economical treatment.
The rates of compost were 0.0, 2.5, 5.0 and 7.5 Ton fed-1, while the nitrogen rates were 0.0, 50, 75 and 100 % of the recommended dose for every growing crop. The experiments were conducted in a split-split plot in a randomized complete block design (RCBD) with three replicates. Results can be summarized as follows:
1- All treatments slightly decreased the soil reaction (pH) in the two growing seasons.
2- Soil salinity (EC), soluble cations and anions and total soluble salts (TSS) significantly increased by increasing nitrogen or compost rates and significantly decreased by increasing application depth. On the other hand, SAR values were significantly decreased with all treatments.
3- All treatments led to significant increases in Ex. Ca, Mg, K and cation exchange capacity (CEC), whereas Ex. Na and ESP were significantly decreased with all treatments in the two seasons.
4- All treatments clearly enhanced total nutrients (N. P and K) of the investigated soil. Also, Organic carbon (O.C, %) and C/N ratio were significantly increased with all treatments.
5- According to the economical analysis, the application of 5 ton compost fed-1 in 30 cm mole depth with 100 % the recommended dose of nitrogen fertilizer for every crop was the best treatment compared with the other treatments, since it gave the highest net income (16809.80 L.E fed-1).
6- Therefore, it is more useful to use those treatments (compost rates at 30cm mole depth with nitrogen fertilizer) to get a markedly improve in chemical properties which reflect on higher yield.