The root system of a grain sorghum crop

Abstract

Measurements were made on the root system of grain sorghum grown on a red earth soil at Katherine, N.T. Samples were taken at floral initiation, mid-elongation, anthesis and maturity. Root length, root mass, and nitrogen and phosphorus concentration were measured throughout the profile to 150 cm depth. Root development reached a maximum of approximately 1000 kg ha −1 by the mid-elongation sampling (44 days after emergence). As root development and above ground development patterns differed, root: total dry matter ratios varied, declining from 0.8 at floral initiation to 0.1–0.2 at maturity. The final root yields of nitrogen (12–22 kg N ha −1) and phosphorus (0.4–0.7 kg P ha −1) are significant proportions of total plant nutrient yield and thus roots should not be neglected in drawing up nutrient balance sheets. It was found that 53–65% of the root mass was in the 0–10 cm layer, 76–79% in the 0–20 cm layer, and 86–87% in the 0–40 cm layer. For root length the corresponding figures were 42, 60–63 and 77–78%. Root dry matter could not be estimated from measurements on above ground parts. Relationships were derived by which total root mass could be estimated from 0–10 cm root mass ( r = 0.938, P < 0.001) or 0–20 cm root mass ( r = 0.990, P < 0.001). Total root length was also a good predictor of total root mass ( r = 0.799, P < 0.001), and 0–10 cm root length proved equally satisfactory ( r = 0.802, P < 0.01). In experiments where root measurements are desirable but not logistically feasible, good estimates may be possible using total root length, or root mass in the surface soil.