Developing a post‐season tissue test for rice nitrogen management

Abstract

Abstract No post‐season analysis method currently exists for rice (Oryza sativa L.) to determine whether N was managed properly during the growing season. Our primary research objective was to determine whether post‐season, rice stem N concentrations can be used to predict if sufficient or excessive N was available. Aboveground biomass samples were taken from N response trials at harvest. Stalks were separated into 5‐cm segments starting at the soil surface and extending upward to 45 cm. One‐half of the samples had all of the leaf material (leaves and leaf sheaths) removed, whereas the other half remained intact. All samples were analyzed for N concentration in the form of amino acids (AA‐N), ammonium (NH4+–N), and nitrate (NO3––N). Samples analyzed with leaf material were found to be statistically different from samples analyzed without leaf material for all three forms of N (P < .0001). Due to significant variability in response, AA‐N and NH4+–N were discovered to be incompatible for a post‐season tissue test in rice. However, NO3––N concentrations showed strong consistency in response to N fertilization rates. Upon further analysis, NO3––N concentrations in the lower portion of the rice stem were found to be more responsive to excessive N fertilization than the upper sections of the rice stem (P < .0001). These results suggest that rice stalks sampled from the lower portion of the plant near maturity and analyzed for NO3––N could be used to predict over‐fertilization and should be investigated further.