Symbiotic performance, shoot biomass and water-use efficiency of three groundnut(Arachis hypogaea L.) genotypes in response to phosphorus supply under field conditions in Ethiopia

Phosphorus is a key nutrient element involved in energy transfer for cellular metabolism, respiration and photosynthesis and its supply at low levels can affect legume nodulation, N2 fixation, and C assimilation. A twoyear field study was conducted in Ethiopia in 2012 and2013 to evaluate the effects of P supply on growth,symbiotic N2 nutrition, grain yield and water-use efficiency of three groundnut genotypes. Supplying P to the genotypes significantly increased their shoot biomass,symbiotic performance, grain yield, and C accumulation.There was, however, no effect on shoot δ13C values in either year. Compared to the zero-P control, supplying40 kg$ha–1 P markedly increased shoot biomass by 77%and 66% in 2012 and 2013, respectively. In both years,groundnut grain yields were much higher at 20 and30 kg$ha–1 P. Phosphorus supply markedly reduced shoot δ15N values and increased the %Ndfa and amount of Nfixed, indicating the direct involvement of P in promoting N2 fixation in nodulated groundnut. The three genotypes differed significantly in δ15N, %Ndfa, N-fixed, grain yield,C concentration, and δ13C. The phosphorus ? genotype interaction was also significant for shoot DM, N content,N-fixed and soil N uptake.