DIFFERENCES IN ROOT-SYSTEM MORPHOLOGY AND ROOT RESPIRATION IN RELATION TO NITROGEN UPTAKE AMONG 6 CROP SPECIES

Cereals and legumes that originated from the semi-arid tropics (SAT) a re mainly grown in marginal soils with limited water and nutrient reso urces. Initial root system development is crucial for crop establishme nt in order to acquire these minimal resources. A comparative study of the root system morphology and of some physiological parameters at in itial growth stages was carried out for 3 legumes: pigeonpea, chickpea and groundnut, and 3 cereals: sorghum, pearl millet and maize, the co mponent crops of the semi-arid tropics. Considerable differences were observed for all the root morphological traits among the species. Amon g the legumes, chickpea produced few thick and lengthy laterals, while pigeonpea produced a high frequency of thinner laterals. However grou ndnut had a larger root system than the other 2 legumes. Among the cer eals, maize formed a large root system followed by sorghum with a high frequency of laterals, while millet displayed a smaller root system w ith thin roots. The root respiration rate was significantly correlated with the N uptake activity. The legumes showed a higher efficiency of N uptake in terms of respiratory requirement. The transpiration rate showed a significant correlation with total N concentration in shoot, indicating that transpiration may be partly related to nitrogen flow t o and accumulation in shoot in case of nitrate nitrogen as a sole nitr ogen source. Morphological and physiological characters of the root sy stem using rather simple indices were found to be better criteria for describing functional differences among crop species.