Abstract

                                Long term manurial field experiments were conducted with thirteen treatments replicated thrice comprising of full and 50 % recommended dose of N as inorganic and organic source as individual and in combination with and without P (half and full dose) as inorganic in a randomized block design using sorghum (Sorghum bicolor L. Moench) + cowpea (Vigna unguiculata) intercropping system rotated with a cotton (Gossypium hirsutum) + blackgram (Vigna mungo) intercropping system in a semi-arid Vertisol during 1995 to 2008 to evaluate N use efficiency of nutrient management techniques. Generally, the crops were sown in the month of October-November and harvested in the month of January-February during the Rabi season in all the years. Improved crop varieties alone will not be sufficient to increase production unless adopting the suitable agronomic and efficient nutrient management practices. Nitrogen ranks first among the applied inputs to maximize output in agriculture. Nitrogen use efficiency can be described as the output of economic produce by any crop per unit of nitrogen applied under specific set of soil and climatic conditions. In general, the sorghum + cowpea intercropping system was more efficient in utilizing the applied N than the cotton+blackgram intercropping system under long term manurial experiment in dryland vertisols. The average partial factor productivity was 65.93 and 22.63 kg grain kg (N)-1 in sorghum+cowpea and cotton+blackgram intercropping system respectively. The more partial factor productivity in sorghum+cowpea inter-croppings system was due to variation in N uptake between the intercropping systems. The agronomic efficiency was maximum under the incorporation of N in equal combination of organic and inorganic (25.70 and 7.11 kg grain kg (N)-1) in both sorghum+cowpea and cotton+blackgram intercropping systems followed by the application of N as organic. The more physiological efficiency indicated the conversion of absorbed N into economic product more efficiently under the conjuctive use of N as both organic and inorganic in sorghum+cowpea and by the application of organic alone under the cotton+blackgram intercropping system. The higher recovery efficiency under conjunctive use of organic and inorganic in both intercropping system was due to the less leaching loss of N and higher uptake of N. The net negative nitrogen balance registered in the millet intercropping system was due to the poor utilization of nitrogen absorbed by the sorghum+cowpea intercropping system as evidenced from the registered higher mean agronomic efficiency.

Key words : Nitrogen, N use efficiency, Nitrogen balance, Intercropping system, Vertisols, Drylands