EFFICIENCY OF LEVELS OF PREPARED SLOW-RELEASE FERTILIZERS (NPK-CHITOSAN), ORGANIC MANURE AND INCUBATION PERIODS ON NITROGEN AVAILABILITY IN TWO DIFFERENT TEXTURE SOILS

The study was conducted at laboratory experiment included a completely randomized design (CRD) to study the efficiency of NPK-Chitosan fertilizers derived from shrimp shells with a ratio of1:1,1:2and 1:3 (NPK-Chitosan) (coating and mixing) at four fertilizers levels (0,500,1000 and 2000 mg kg-1 soil) and two levels of organic fertilizer (0 and 2.5%) Cow waste in terms of nitrogen availability in two types of soil (Silty clay and sandy loam soil comparing with NPK15-15-15 fertilizer (commercial) control treatment and incubated for four periods (7, 14, 28, and 56 days) to evaluate nitrogen availability. The results showed that adding fertilizers and organic fertilizer significantly increased the availability of nitrogen in both soils, NPK-Chitosan fertilizers, with a ratio of 1:3 coating and 1:3 mixing treatments, outperformed control treatment (fertilizer NPK alone) in increasing of available nitrogen. The results also revealed a significant effect of fertilizer levels on increasing of nitrogen concentration in both soils. The concentration increased with higher fertilizer level, (2000 mg kg-1 soil) achieving the highest nitrogen values of both soils, 90.9 and 91.47 mg kg-1 soil, respectively, with a significant difference compared to 500 and 1000 mg kg-1 soil levels. Furthermore, the 1000 mg kg-1 soil level outperformed the NPK fertilizer (control treatment). The results revealed a significant interaction effect between type and level of fertilizer on nitrogen available concentration. The treatment NPK-Chitosan fertilizer with a ratio of 1:3 for coating at level of 2000 mg kg-1 soil outperformed the other treatments, providing the highest nitrogen concentration of 129.00 and 167.40 mg kg-1 soil for both soils, respectively. The availability of the element increased with higher levels of added fertilizers and the addition of organic matter, but decreased with longer incubation periods. Keywords: NPK-Chitosan Fertilizer, available nitrogen, organic manure, calcareous soils.