The Influence of Available Nitrate Levels on Nitrogen Fixation in Three Cultivars of Cowpea¹

Abstract

Soil N is known to affect N2 fixation in legumes. Increased cowpea yields might be achieved by increasing N assimilation through greater symbiotic fixation, but identification of high‐fixing genotypes requires an effective screening technique. The purpose of this investigation was to determine the optimum level of supplemental N for maximum N2 fixation in cowpeas grown under greenhouse and field conditions, and the relative contributions of the measured variables on nitrogenase activity. Three cowpea cultivars were tested for N2 fixation, N2 (C2H2), under greenhouse conditions with 0, 5, 10, and 20 ppm N applied as Ca(NO3)2, and under field conditions with 0, 11.2, 22.4, and 44.8 kg/ha N applied as Ca(NO3)2. The soil was Vertic Albaqualf, fine, Montmorillonitic thermic. Nitrogenase activity decreased with increasing rates of N. Path analysis indicated that nitrate effects on N2 fixation activity were primarily on nodule mass, with the inhibition of nodule growth rather than nodule initiation. Nodule number was not a reliable predictor of N2 fixation potential of cowpea genotypes and was negatively correlated with nitrogenase activity. The results clearly indicated no advantage of applied nitrate in promoting maximum genotypic differences for N2 fixation.

Effect of low static nitrate concentrations on mineral nitrogen uptake, nodulation, and nitrogen fixation in field pea

“…Our results support the work of Miller et al (23) which indicated that the relative proportion of N that a plant obtains from different sources is dependent on availability. The NO3-assimilation rates (Fig.…”

Contribuição da fixação biológica de nitrogênio, fertilizante nitrogenado e nitrogênio do solo no desenvolvimento de feijão e caupi

“…Com base nesses resultados, confirmam-se as observações de outros estudos de que altas doses de N afetam a fixação em caupi (Miller et al, 1982;Berverly e Jarrel, 1984;Graham e Scott, 1984;Agbenin et al, 1990;Alfaia 1997). Neste contexto, Eaglesham et al (1982) concluíram que embora as taxas de utilização do N-fertilizante pelo caupi tenham sido baixas, de 12% e 28% com a aplicação de 25 e 100 kg ha -1 de N respectivamente, a menor dose promoveu efeito adverso sobre o desenvolvimento dos nódulos e a maior dose de N, proporcionou efeito adverso prolongado na formação e desenvolvimento dos nódulos.…”

Nitrogen transfers from Vicia sativa L. and Trifolium resupinatum L. to the companion grass and the following crop

“…The N-NO 3 -amounts in the soil of the grass/legume swards are only slightly reduced compared to legumes in monoculture when the catch crops are sown late or during the second research year, when growth conditions are sufficient until late autumn. Under conditions that enable growth of grass and legume, the N-NO 3 -uptake of the grass causes a temporary decrease of N-NO 3 -amounts in soil, which causes an increase of N 2 fixation (= g N/ plant) of the legume (Miller et al 1982, Mallarino et al 1990a) because nitrate affects the number and size of nodules and the fixation in active nodules (Giller 2001). This is the reason for estimated high amounts of fixed N 2 even by mixed swards.…”