Crescimento, fotossintese e eficiencia do uso de nitrogenio em milho, feijao e mandioca submetidos a dois niveis de N no solo

Growth and N uptake in pot-grown maize, beans, and cassava were evaluated under 2 levels of soil N at CIAT-Palmira (Colombia). The lower amount of the element reduced its uptake by the 3 species, resulting in lower tissue concn., especially in the leaves. Under low N, DM accumulation was also reduced 5 wk. after planting for maize and beans, and 7 wk. after planting for cassava. Higher amounts of N in the soil increased leaf expansion and photosynthesis (Pn) in maize and beans 3 and 4 wk. after planting, resp., and in cassava after 7 wk. Cassava plants tended to increase N-use efficiency, slightly but nonsignificantly, under low N. Maize used N more efficiently; however, the existence of a real difference between crops cannot be affirmed due to the reduced soil N concn. (AS)