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Sugarcane

Microbial Biomass Turnover in Indian Subtropical Soils under Different Sugarcane Intercropping Systems

Division of Crop Production, Indian Inst. of Sugarcane Research, Rae-Barely Rd., P.O. Dilkusha, Lucknow-226 002 (UP), India

^* Corresponding author (archsuman{at}yahoo.com)

Received for publication June 9, 2005. Changes in soil organic C (C_org), total N (N_t), available nutrients, soil microbial biomass C (C_mic) and N (N_mic), and mineralizable C and N in the sugarcane (Saccharum officinarum L.) rhizosphere were evaluated under intensive sugarcane cropping systems with intercrops including wheat (Triticum aestivum L.), maize (Zea mays L.), rajmash (Phaseolus vulgaris L.), green gram [Vigna radiata (L.) R. Wilczek var. radiata], cowpea [Vign aunguiculata (L.) Walp.], lentil (Lens culinaris Medik.), mustard (Brassica rapa L.), potato (Solanum tuberosum L.), and sesbania (Sesbania rostrata Bremek. & Oberm.) in subtropical soils of India. Organic C increased significantly when maize (25%), wheat (24%), mustard (19%), potato (17%), and rajmash (13%) were intercropped with sugarcane, while legume intercrops substantially increased N_t and available N. Increase in microbial respiration was greater where maize (42%), wheat (37%), or mustard (31%) were intercropped compared with pulse crops. Soil microbial biomass C accounted for 2.7 to 3.3% of C_org content and N_mic accounted for 2.6 to 3.7% of N_t under different intercropping conditions. A higher CO₂ evolution rate and wider C_mic/N_mic ratios were recorded with cereal and mustard intercrops, whereas higher N mineralization was recorded with pulse intercrops. Results indicate that intercropping with pulse crops and incorporation of their labile C substrate improved N mineralization. The build up of the C pool and C_mic in the case of cereals, mustard, and potato intercropping should promote long-term stability.

Abbreviations: C_mic, soil microbial biomass carbon • C_org, organic carbon • N_mic, soil microbial biomass nitrogen • N_t, total soil nitrogen • qCO₂, metabolic quotient