Aims <p>Soil nitrogen (N) availability and microbial N utilization are highly sensitive to land use change from paddy fields to upland cultivation. However, the mechanisms driving the responses of microbial N limitation and soil N losses to this conversion in tropical agroecosystems remains uncertain.</p> Methods <p>By collecting soil samples from paddy fields and areca nut plantations of different ages (2, 5, 10, 14, and 17&#xa0;years) in tropical areas, we assessed gross N transformation rates using the ¹⁵N tracing technique and soil nitrous oxide (N₂O) emissions, as well as calculated microbial N limitation through the vector-threshold element model.</p> Results <p>The vector-threshold angle (-1.63) in tropical paddy soils was lower than 0, indicating that microbial growth was predominantly N-limited. This N limitation increased by 101%‒258% following conversion to areca nut plantations and intensified with plantation age. Vector-threshold angles were significantly and positively correlated with gross N mineralization, nitrification, ammonium immobilization, and nitrate immobilization rates, indicating that inhibited soil inorganic N supply and reduced microbial immobilization aggravated microbial N limitation. These responses were primarily attributed to declines in particulate organic carbon, hydrolyzable ammonium N, hydrolyzable unknown N, and microbial biomass induced by land use change. In addition, reduced abundances of ammonia-oxidizing archaea and bacteria, as well as denitrifiers (<i>nirS</i>, <i>nirK</i>, and fungi‒<i>nirK</i>), contributed to a 47.6%‒54.1% reduction in soil N₂O emissions after land use change.</p> Conclusions <p>Conversion of paddy fields to areca nut plantations can aggravate microbial N limitation and reduce N₂O emissions by reducing labile carbon and N fractions, inorganic N supply and retention.</p>