Root nitrogen transformation and mineral composition in selected forage legumes

Abstract

SummaryA study was conducted at Debre Zeit, Ethiopia to examine the differences in mineral composition, root N contents and their rates of transformation in the soil of different species of four genera of forage legumes,Trifolium steudneri(ILCA D/Z),Trifolium steudneri(Shola),Vicia dasycarpa(ILCA 6795),Vicia benghalensis, Lablab purpureuscv. Rongai,Lablab purpureuscv. Highworth,Medicago scutellatacv. Snail andMedicago truncatulacv. Barrel.M. truncatulacv. Barrel had higher N and P values thanM. scutellatain both roots and tops. Root N contents of the legumes ranged from 2·43% forViciato 0·87% forLablab. These differences were also reflected in the rates of organic root N transformation in soil as determined in laboratory incubation studies.The P concentration in the tops of the legumes ranged from 0·32% inViciato 0·14% inMedicagospp. The observed P concentration in theMedicagospecies suggests a low internal P requirement. Potassium concentrations in theTrifoliumspecies were much higher than the average for all legumes.The results suggest that theViciaspecies used in this study could contribute a considerable amount of N to subsequent crops even when the tops are not returned to the soil. Also, theMedicagospecies are more likely to thrive better under low soil P conditions than the other legumes.