The objective of this work was to evaluate the efficiency in NITROGEN( N) uptake and use by soybean and bean crops and by weeds in agricultural areas in Brazil. A 6x4 factorial arrangement was employed on a randomized block design, with 6 plant species soybean (Glycine max), bean (Phaseolus vulgaris), two Euphorbia heterophylla (biotypes susceptible and resistant to ALS - inhibiting herbicides), Bidens pilosa and Desmodium tortuosum; and 4 doses of N (0; 20; 40 and 80 mg dm-3), evaluated under greenhouse conditions. N application was performed by adding 60% of the fertilizer ammonium sulfate (20% of N) in the seeding and the remainder in two applications, 20 and 30 days after planting (DAP). B. pilosa. showed the highest leaf area increase with the addition of increasing N doses; however, soybean showed the highest leaf area in the treatments without N application or with application of the smallest doses of this nutrient. Soybean also accumulated the highest biomass in its root system, decreasing with N addition and B. pilosa and E. heterophylla biotypes increased its biomass with increased N supply. No species showed increased N content in their tissues in response to N fertilization; however, the leguminous plants showed a higher N content than the species of the other families. Total N content in the soybean tissues decreased with the increase of the dose applied while in the weed species, accumulated N content increased with dose increase. The highest efficiency of N uptake by the roots was verified in the bean plants. B. pilosa and E. heterophylla biotypes showed the highest efficiency in N use. Weed species not belonging to the leguminous families took the most advantage from N supplementation. Thus, inadequate N management in these crops may worsen the problem of weed interference.
Glycine max; Phaseolus vulgaris; Desmodium tortuosum; Bidens pilosa; Euphorbia heterophylla
