Effects of nitrogen on growth,and nitrogen and phosphorus uptake in tops and roots of sorghum grown in an Alfisol and a Vertisol

A greenhouse pot experiment was conducted to study the effects of added nitrogen (0, 10, 25, 50 and 100 mg N kg^–1 soil) on dry matter production, and N and P uptake in tops and roots of sorghum (cv CSH6) grown in a Vertisol and an Alfisol for 42 days at field capacity soil moisture content. More dry matter accumulated in the tops and roots of sorghum growing in the Alfisol than in the Vertisol. This resulted in higher N and P uptake. Top dry weight responded to N application up to 50 mg N kg^–1 soil, whereas the root weight increased at N application up to 25 mg N kg^–1. Ratios of root dry weight to total plant dry weight and N uptake in roots/total N uptake were similar in the two soils. Ratio of P uptake in roots to total P uptake was higher in Alfisol than in Vertisol. This result was attributed mainly to higher ratio of P content in roots compared to tops in the Alfisol.Approved for publication as ICRISAT Journal Article No. 709.