20 Indian Journal of Agricultural Sciences 90 (7): 1236–40, July 2020/Article https://doi.org/10.56093/ijas.v90i7.105567 Impact of amendments on soil organic nitrogen fractions irrigated with sodic water DEEPIKA RATHI*, DEVRAJ, R S ANTIL and SUNITA SHEORAN CCS Haryana Agricultural University, Hisar, Haryana 125 004, India Received: 08 October 2018; Accepted: 01 October 2019 ABSTRACT Present study was carried out to evaluate the effects of FYM and gypsum on organic nitrogen fractions in soil of long-term field experiment irrigated with sodic water since 1994 at research farm of Department of Vegetable Science, CCS Haryana Agricultural University Hisar, India (2014-2015). Field was irrigated with high RSC (11.5 me/l) sodic water having three levels of gypsum G 0 (control), G 1 (50 % neutralization of RSC), G 2 (100% neutralization of RSC), along with three levels of FYM; F 0 (control), F 1 (10 tonnes/ha), F 2 (20 tonnes/ha). The Results obtained in April 2014 showed that all N fractions (Non hydrolysable-N, NH 3 -N, amino acid-N, amino sugar-N, hydrolysable unknown-N and total hydrolysable-N) were more dynamic in various treatments consisting FYM and gypsum levels. All nitrogen fractions increased with increasing levels of FYM and gypsum. Averages of amino acid nitrogen, amino sugar nitrogen, ammonia nitrogen and hydrolysable unknown nitrogen constituted about 28-30, 9-12, 27-29 and 29- 36% of total hydrolysable nitrogen, respectively. Adverse effect of residual alkalinity of irrigation water was quite prominent on chemical properties (pH, EC, organic carbon) of soil. The pH of soil was found to be very high under F0G0 and decreased with the use of FYM and gypsum as amendments. This result indicates that the combined use of FYM and gypsum improved soil health and maintained the sustainability of the different vegetable cropping system. Key words: Amino acid nitrogen, Amino sugar nitrogen, Ammonia nitrogen, Hydrolysable nitrogen *Corresponding author email: dhangerdeepika@gmail.com Long term and indiscriminate use of sodic water cause accumulation of salt which not only adversely affects the physical and chemical properties due to swelling and dispersion of clay particles in addition to increased pH, EC and exchangeable sodium percentage (ESP) (Minhas et al. 2007), But also modifies the quality of soil organic matter as well as soil organic nitrogen. To offset the harmful sodic water effect, application of gypsum is a common recommendation; organic amendments such as FYM have been used as these can modify Ca from CaCO 3 and other Ca bearing minerals in soils (Chaudhary et al. 2007). Soil organic matter is the key contributors to soil productivity directly through controlling the availability of soil available nitrogen (N) and indirectly through regulating the soil physical, chemical and biological properties. The soil organic nitrogen fractions are widely used as measures for evaluating the soil fertility. Main difference among these fractions is related to degree of decomposition, recalcitrant, and turnover rate. Easily hydrolysable fractions, especially amino acid N, amino sugar N, amine N and hydrolysable NH 4 -N can provide an assessment of soil organic N changes induced by management such as cropping system and inorganic and organic fertilizations (Wander et al. 2007, Kaushik et al. 2018) A better understanding of N transformation processes that occur in key labile organic N fractions is necessary to recognize their role in N cycling and their relative contribution to N mineralization. Understanding the effect of organic amendments on the transformation of organic N into different forms is a prerequisite for managing N inputs in a given soil. So, identifying the fraction of soil organic nitrogen into different pools and quantitatively analyzing these pools are better means of understanding C and N dynamics. The present study was undertaken to quantify changes in soil organic N fractions under continuous application of FYM and gypsum under sodic water irrigation conditions. MATERIALS AND METHODS Site characteristics The present study was conducted using the experiment units (plots) of an ongoing permanent long-term experiment started in 1994 and it is located at Vegetable Research Farm, Department of Vegetable Science, CCS Haryana Agricultural University, Hisar (2014-15) situated at 29°10' North latitude and 75°46' longitude at the mean elevation of 215.2 m. Temperature fluctuated between 1.9°C (January) and 47°C (May) during the year. Normal annual rainfall of