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

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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.