A grain sorghum (Sorghum vulgare Pers.) variety Martin was grown in high and low nitrogen soil with and without soil and foliar application of nitrogen. Plant samples taken at various stages of growth were utilised for the determination of dry weight, moisture, total nitrogen, protein nitrogen and hydrocyanic acid. Available soil nitrogen was determined at two dates in ease of low nitrogen soil.An analysis is presented of the determination of the ontogenetic changes noted throughout the investigations.Sorghum makes a slow growth in the early stage. Application of sbout 40 pounds nitrogen at planting, both in high and low nitrogen soil, increases the percentage of nitrogen in the plant in the early stage. However, in high nitrogen soil, very little difference in percentage of nitrogen was observed towards maturity although the grain produced was 1.5 times as much. In low nitrogen soil the percentage of nitrogen in the grain was increased from 1.14 to 1.33 and the yield of the grain was nearly doubled. But the divided application of 20 pounds nitrogen at planting and 20 pounds approximately six weeks after, further increased the nitrogen percentage to 1.38 though there was very little difference in the yield of the grain between the two methods of nitrogen application. Recovery of soil applied nitrogen with 40 pounds nitrogen application at planting in low nitrogen soil was 52 per cent, while with divided application it was 70 per cent.Application of 25 pounds of urea in 100 gls. of water per acre at flowering increased the percentage of nitrogen in the grain in low nitrogen by about 7 to 16 per cent of the content without the spray application. The plants most benefitted by the spray were those receiving divided application of nitrogen to the soil. The recovery of foliar applied nitrogen is higher with this treatment, being about 71 per cent. Hydrocyanic acid production capacity of the plant is increased in the early stage, by nitrogen fertiliser, when the protein synthesis is rapid.