Growth and distribution of maize roots under nitrogen fertilization in plinthite soil

To improve efficiency of soil N and water use in the savanna, maize (Zea ma ys L.) cultivars with improved root systems are required. Two rainfed field experiments were conducted in Samaru, Nigeria in the 1993 and 1994 growing seasons with five maize cultivars under various rates of nitrogen fertiliz er. The capacity of maize for rapid early root growth and to later develop a deep, dense root system was assessed. In addition, the effect of N fertil ization on root growth of maize was studied in 1994. The widely cultivated cultivar TZB-SR had a poor root system in the surface soil layer and was mo re susceptible to early-season drought, as indicated by low plant vigor and aboveground dry matter yield during that time. It had a lower grain yield and a relatively small harvest index, but ranked among the highest in total aboveground dry matter production compared to other cultivars. The size of root system alone did not always relate well with grain yield among cultiv ars. Partitioning of dry matter within the plant was important in determini ng differences in grain yield and N stress tolerance between cultivars. A s emiprolific cultivar (SPL) had high seedling vigour and a dense root system in the surface soil layer that conferred a greater tolerance to early-seas on drought stress and improved uptake of the early-season N flush, as indic ated by a greater dry matter yield at 35 days after sowing (DAS). It also h ad a fine, deep, dense root system at flowering that could have improved wa ter- and N-use efficiency in the subsoil (> 45 cm), thereby avoiding midsea son drought stress in 1994. SPL had a large harvest index and the greatest yield among cultivars in 1994. Averaged across cultivars, greater root grow th and distribution was observed at a moderate N rate of 0.56 g plant(-1) t han at zero-N or high N (2.26 g plant(-1)). Differences in root morphology could be valuable as selection criteria for N-efficient and drought-toleran t maize. (C) 1999 Elsevier Science B.V. All rights reserved.