Nitrogen Fixation of Legumes and Yield of Wheat under Legumes-wheat Rotation in Pothwar

Legumes build soil fertility and contribute substantial amounts of N for sustainability of cereal based cropping systems. These lacking information for the system as a whole in rainfed pothwar were investigated through field experiments at two different locations i.e. (Research farm of University of Arid Agriculture Rawalpindi, UAAR and farmer’s fields in Chakwal district). Mung bean (Var. NM-92) and mash bean (Var. Mash-3) were rotated with wheat (Var. Wafaq 2001) with the objectives to assess N2-fixation of these legumes and study their residual effects on soil NO3-N and subsequent wheat yield. Sorghum (Var. YSS-98) was also grown as non-legume reference crop. Mash bean not fertilized with P produced 4.27 t ha of dry matter compared with 4.38 t ha when fertilized with P @ 80 kg ha. Similarly, mash bean fertilized with P yielded 4% more grain followed by mung bean and response of P fertilizer was 13%. Legumes N2-fixed ranged from 13-80 and 18-38 kg ha at UAAR and Chakwal site, respectively. The NO3-N contents in the soil under non-legume sorghum were less compared with legumes. Maximum contents of total NO3-N, 58 kg ha in soil profile was observed under mash bean fertilized with P. Additional residual soil NO3-N under legumes relative to adjacent sorghum crop were 22 kg ha at UAAR site, 83 % higher when compared to Chakwal site. Both legumes with and with out P fertilization increased the biomass and grain yield of succeeding wheat with an increase of 18% over non-legume sorghum. Legumescereal sequence improved NO3-N status of soil as well as yield of subsequent wheat.