Summary Differences in Nz-fixation by Phaseolus vulgaris bean cultivars were successfully evaluated in the field using ~ SN isotope dilution technique with a non-fixing test crop of a different species (wheat). The Phaseolus cultivars could have been similarly ranked for N2-fixation capacity from either seed yield or total nitrogen yield, but the isotope method provided a direct measure of N 2-fixation and made it possible to estimate the proportion of fixed to total nitrogen in the crop and in plant parts.Amounts of nitrogen fixed varied between 24.59 kg N/ha for the 60-day cultivar Goiano precoce to 64.91 kg N/ha for the 90-day cultivar Carioca. The per cent of plant nitrogen due to fixation was 57-68% for the 90-day cultivars and 37% for Goiano precoce (60-day cultivar).Fertilizer utilization was 17-30% of a 20kgN/ha fertilizer application. 100 kg N/ha fertilizer application decreased N2-fixation without suppressing it totally.Differences in yield between the highest yielding (Carioca) and the lowest (Moruna) 90-day cultivars were also due apparently to varietal differences in efficiency of conversion of nitrogen to economic matter i.e. seed, as well as to differences in capacity of genotypes for Nz-fixation.

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An examination of the effects of adding phosphorus to the soil on nodulation and P utilization in Phaseolus vulgaris L. showed a positive response in plant weight to increasing rates of phosphorus ( 32 P) when water tension was low in the pots.The efficiency of the utilization of fertilizer-P was directly influenced by the water content of the soil, showing increasing P accumulation after flowering.A highly positive interaction between P addition, water content and nodulation was observed. Nodules were shown to have a high P requirement, with phosphorus ( 32 P) contributing to an increase in the number and size of nodules.

Soil water content affected the nodulation and N 2 fixation of Phaseolus vulgaris by Rhizobium phaseoli and the utilization of mineral N by plants. Plants grown in wet soil produced twice as much as those grown on dry soils. Nodule weight and activity were five to ten times greater than those from dry soils. At 45 days, N additions inhibited nodulation, but this effect was partially diminished in wet soils.The maximum N utilization from fertilizer to produce dry matter did not correspond to maximum N utilization by pods.

Um experimento foi montado em casa de vegetação para testar os efeitos do fósforo (150 ppm), adubação básica (150 ppm P2O5,50 ppm K2O e micronutrientes) e calagem (1 ton CaC0(3)/ha) na nodulação natural do feijoeiro (cultivar Carioca) em 4 diferentes solos: Mediterrâneo, Podzolizado e dois outros de Terra Roxa Estruturada. O peso dos nódulos aumentou em dois solos (Mediterrâneo e Podzolizado), devido à adição de fósforo e em Terra Roxa Estruturada devido ao fósforo mais calagem. A adubação completa (PK + micronutrientes) foi a que proporcionou maior desenvolvimento das plantas, mesmo em ausência de calagem, indicando efeito de micronutrientes e potássio nos solos estudados. No entanto, nos solos de Terra Roxa, a adição de fósforo foi suficiente para o aumento do peso da parte aérea e teor de N total das plantas. O N total aumentou em plantas que receberam adubação completa. A adição de fósforo contribuiu para uma melhor nodulação natural (peso e numero de nódulos).