Evolution of nitrogen (N), a life-essential volatile element, in highly reduced magmatic systems is key for the origin of N on terrestrial planets formed via accretion of reduced chondritic parent body materials, planetesimals, and embryos, which themselves underwent partial or complete differentiation. To investigate the stability of N-bearing minerals in partially molten silicate-rich systems as well as solubility of nitrogen in silicate melts and silicate minerals, we performed laboratory experiments at pressures (P) of 1.5-3.0 GPa and temperatures (T) of 1300-1600 °C in a graphite capsule with oxygen fugacity conditions ranging from IW – 5.87 to IW – 8.35. All experiments yielded silicate melt + nierite (Si3N4) + Fe-rich alloy melt + N-rich vapor ± sinoite ± cpx. Sinoite was restricted to above 1400-1500 °C, while cpx was restricted to below these temperatures. Solubility of nitrogen and Nitrogen Concentration at Silicon-Nitride Saturation (NCNS) increases with increasing pressure and temperature and ranges between 3.57 and 9.46 wt %. Using high pressure N solubility data from this study and similar solubility data for silicate melts at ambient and low pressures, we derive the following N solubility model N(ppm)=〖P_(N_2)^0.5exp〗⁡(8.12(±1.56)+(1000(-12.23(±2.81)-0.61(±0.29) P_total^0.5 ))/T-1.45(±0.06)(∆IW)) +P_(N_2 )*exp⁡(7.96(±0.48)-18.59(±7.17) X_MgO+2.57(±0.94)(NBO/T)) where T is temperature in K, P_(N_2 ) is partial pressure of N2 in GPa, P_(total ) is the equilibrium pressure in GPa, IW is the log oxygen fugacity relative to the IW (oxygen fugacity imposed by coexistence of Iron, Fe, and iron oxide, wüstite) buffer, XMgO is the mole fraction of MgO in the silicate melt, and NBO/T is total non-bridging oxygen relative to tetrahedral cations (NBO/T = (2 × Total O)/T – 4, where T = Si + Ti + Al + Cr + P (e.g. (Mysen et al., 1982)). Solubility of nitrogen in cpx was measured to between 1.51 and 2.05 wt% and resulted in cpx/silicate melt partition coefficients for nitrogen of ~0.4 to ~0.2. These cpx/silicate melt nitrogen partition coefficients (DNcpx-melt) are much larger than that previously estimated at more oxidizing conditions, suggesting N maybe less incompatible during thermal processing of rocky reservoirs at extremely reducing conditions. Similar to previous studies, N also shows lithophile behavior at extremely reduced, graphite saturated conditions, with partition coefficient of N between Fe-rich alloy melt and silicate melt to be between 0.2 and 0.7 at our experimental conditions. While partition coefficient of N between cpx and Fe-rich alloy melt was found to be between 1.6 and 2.1, but there lacks enough data to determine a dependence with P-T-fO2. The application of our N solubility data and model suggests that mobilization of N from the deeper, partially molten reservoir to shallower reservoirs is possible in reduced planetesimals and internally differentiated meteorite parent bodies. Similarly, enrichment of N in the planetary atmosphere may be a result of gradually more oxidizing accreting materials, which would lead to N being more and more incompatible during internal and external magma ocean processing of rocky bodies.