Status of Different Forms of Nitrogen in Soils of Navsari District of South Gujarat, India

To study the nitrogen fraction under different cropping and management system, the present investigation was carried out at NAU, Navsari (Gujarat) during year 2022-2023. From each taluka of Navsari district, ten soil samples were collected randomly from 0-15 cm and 15-30 cm depth by using different cropping and management systems by GIS base grid sampling method. Soil samples were subjected to preliminary analysis for pH, EC, SOC and then analysis of different N-fractions was carried out. Nitrogen is one of the main limiting factors of crop productivity and many studies have sought possibilities to reduce the need for N application and extend the period of availability to plants. Organic N forms constitute up to 90% of the total N in the plow layer of mineralsoils and only about 1–4% is mineralized as plant- available N (NH4–N and NO3–N). Plant-available N released from soil organic N (SON) or applied in fertilizer is highly susceptible to loss from the soil– plant system through leaching and denitrification. The overall distribution of avail. N, NO3-N, NH4-N and total N in Navsari district was ranged from 72.80 to 375.20 mg kg-1, 5.60 to 92.40 mg kg-1, 30.80 to 114.80 mg kg-1 and 140.00 to 1036.00 mg kg-1, respectively for surface soils while, 61.60 to 364.00 mg kg-1, 8.40 to 72.80 mg kg-1, 25.20 to 100.80 mg kg-1 and 140.00 to 924.00 mg kg-1 for sub-surface soils, respectively. At surface layer, total N was correlated significantly and positively with SOC, CEC and it was negatively correlated with pH and EC. However, total N showed similar correlation with SOC and EC at sub-surface layer. NH4-N and NO3-N were positively and significantly correlated with each other at the same depth. The result also revealed that the N fractions were significantly decreased with increasing depth of soil. Overall, our findings suggest that vegetation restoration improved the soil N availability.