Growth and Nitrogen Fixation in Dhaincha/Sorghum and Dhaincha/Sunflower Intercropping Systems Using ¹⁵Nitrogen and ¹³Carbon Natural Abundance Techniques

Abstract

A field experiment on dhaincha, sunflower, and sorghum plants grown in monocropping and intercropping systems was conducted to evaluate growth and nitrogen (N₂) fixation using ¹³carbon (C) and ¹⁵N natural abundance techniques. Intercropping of sesbania/sorghum showed a greater efficiency than monocropping in producing dry matter during the entire growth period, whereas the efficiency of producing dry matter in the sesbania/sunflower intercropping was similar to that in the monocropping system. Moreover, sorghum plants (C4) were more competitive than sesbania (C3) for soil N uptake, whereas sesbania seemed to be more competitive than its associated sunflower (C3). Nitrogen uptake in the mixed stand of sesbania/sorghum was improved as a result of the increase in soil N uptake by the component sorghum and the greater root nodule activity of component sesbania without affecting the amount of N₂ fixed. The Δ ¹³C in plant materials was affected by plant species and the cropping system.

Keywords:

• ¹³C
• intercropping
• ¹⁵N
• N₂ fixation
• sesbania
• sorghum
• sunflower

ACKNOWLEDGMENTS

I thank Professor I. Othman, general director of Atomic Energy Commission of Syria (AECS), for his support. The technical assistance of the staff at the AECS Department of Agriculture is greatly acknowledged.