Root Development and Distribution in Relation to Soil Physical Conditions on Four Different Native Grassland Sites Fertilized With Nitrogen at Three Different Rates

Root production was slightly increased by nitrogen fertilization on four range sites. A major portion of the total root material was found in the upper 15.2-cm layer of the soil profiles on the Vebar, Rhoades, and Manning sites. A greater proportion of the root material was located at deeper depths in the Havre profile. Significant root increases were observed on the Vebar at the 37-kg nitrogen treatment, mainly at the 0- to 30.5-cm depth and on the Havre site at the 0- to 15.2-cm depth with 75 and 113 kg nitrogen per hectare. Significant increases were observed at the 0- to 15.2-cm and 30.5- to 45.7-cm depths only at the 75- and 113-kg nitrogen treatments on the Rhoades site. Statistically significant differences were observed between control plots and the 113-kg nitrogen treatment at the 15.2- to 30.5-cm depths on the Manning site. Bulk density decreased with increasing rates of nitrogen fertilizer on the Vebar and Manning sites.