Determination of Total Nitrogen in Soybean Using Nuclear Technique

Abstract

          Chiang Mai 60, SJ 5, and Doi Kham soybean varieties were grown in pots and fertilized with 0, 20, 40 kg N/ha. It was found that these 3 soybean varieties gave higher seed yield with increasing of N fertilizer. The harvested seeds then were analyzed for nitrogen content using nuclear technique (neutron activation) and
standard chemical analysis.

           For neutron activation analysis, seeds were irradiated with fast neutron at the flux of 2.5×10¹¹ n.cm^-2.s^-1 from Thai Research Reactor, TRIGA Mark 3 type, at the Office of Atomic Energy for Peace. The emitted gamma rays of 0.511 MeV from ¹³N of nuclear reaction ¹⁴N(n,2n)¹³N caused by the annihilation of positron disintegrated were measured by the semiconductor detector (HPGe). Ammonium nitrate was used as standard and the interfering activities induced by phosphorus and potassium and from recoil proton were also corrected.

            From qualitative analysis using neutron activation, N, P, K, Mn, Mg, Ar, and Al were found in the soybean seed. The average nitrogen contents in soybean are 7.024% and 6.809% as determined by nuclear technique and by chemical method, respectively. The results from these two methods of analysis were considerably comparable.