Growth, Nitrogen Uptake, and Partitioning in Nitrogen-Fertilized Nodulating and Nonnodulating Peanut

Peanut (Arachis hypogaea L.) is known to be effective in symbiotic N2 fixation, but N deficiencies may occur during rapid vegetative and/or reproductive growth. The effects of N fertilization on growth, N uptake, and N partitioning in nodulating and nonnodulating peanut genotypes were studied during 1982 in the field and a greenhouse experiment at the University of Florida, Gainesville. Three lines, 'Florunner' (FL), 'Early Bunch' (EB), and a nonnodulating line ('M4-2') were grown in the field on a Lakeland sandy soil (hyperthermic coated Thermic Quartzipsamment) at four N rates (0, 6, 12, and 24 g m~2 N) and in pots in the greenhouse at N rates at a factor of 0.05, 0.50, 0.95, and 1.40 N-strength of Hoagland no. 2 solution, modified to adjust the other nutrients at 0.50 strength. In the field experiment, only the biomass crop growth rate (CGR) and leaf area index (LAI) of all genotypes were significantly increased by N rates. A leaf area index of 3.0 was achieved at 60 days after planting (DAP) when 6 g m~2 N or more was applied on the nodulating genotypes. For the nonnodulating genotype (M4-2), 120 days at 6 g m~2 N or 85 days at 24 g m~2 N were required to achieve LAI of 3.0. The vegetative and reproductive responses of M4-2 to N increments were highly positive and essentially linear. Pod and seed yields of nodulated genotypes in field-grown plants were not significantly influenced by N fertilization. Pod yields were increased in pot-grown plants in the greenhouse, but nodule number and weight were reduced. A genotype X N rates interaction for plant component yield, leaf N concentration, and N content was observed due primarily to the differential response to N between the nodulating and nonodulating lines. Partitioning of photoassimilate to pods was generally reduced by N fertilization, probably due to vegetative growth stimulation. Florunner cultivar biologically fixed more N2 than EB, the amount in FL exceeding the seed requirement (12.2 m 2) if fertilizer N rate was low. These studies suggest that the practice of N fertilization of well-nodulated peanut does not increase pod or seed yield and is economically counter-productive.