N fixation and N transfer in Maize/Cowpea and Sorghum/Cowpea intercropping systems as determined by ISN isotope dilution technique

Abstract

N fixation and N transfer in maize/cowpea and sorghum/cowpea intercropping systems, as determined by 1SN isotope dilution technique was studied in two field trials conducted at Bata-atha, in the dry zone of Sri Lanka. Two cvs. of cowpea Le; Bombay and MI-35 were used in maize/cowpea intercropping system, with following combinations of treatments; maize/Bombay, maize/MI-35, Bombay (monocrop), MI-35 (monocrop) and maize (monocrop). A similar set of treatments was used in sorghum/cowpea intercropping system also. The l5N atom excess, % Ndffa, total amount of N fixed, N yield and the total dry matter production were estimated. Maize/cowpea intercropping resulted in an increase in total dry matter production and total N yield compared to monocrop treatment. However the %Ndfa and total N fixed showed a decrease compared to monocrop stand. The %Ndfa was 60-65% in monocrop while the same was 45-50% in intercropped treatments.