Super-optimal fertilization affects root growth and soil microbial abundance and biomassduring wheat growth

摘要

A field experiment was conducted during 2010-2011 and 2011-2012 to investigate the effect of recommended 100% nitrogen, phosphorus and potassium (NPK) to super-optimal doses (200% NPK) of mineral fertilizers on root growth pattern, microbial biomass and counts, organic carbon and mineral nitrogen at various phenological stages of wheat growth. Super-optimal level of fertilizers (200% NPK) increased the root length density by 71.8% as compared to recommended dose of fertilizers in the surface layer (0-15 cm). There was positive effect of fertilizer addition on soil ammonium-N and nitrate-N contents. Excessive mineral fertilizer did not affect the soil organic carbon (SOC), but SOC was found to be higher at anthesis stage (16.67% and 12.32% higher over maturity and Crown Root Initiation (CRI) stage, respectively). Microbial biomass carbon (MBC) was found to be higher (252.06 |ig g-1 dry soil) at anthesis stage of wheat growth, which declined to 213.28 |ig g-1 dry soil at maturity. Super-optimal application of fertilizers led to significant increase in microbial biomass nitrogen (MBN) at anthesis (+17.7%) and maturity stage (+15.55%) over the 100% recommended dose of fertilizer. Data on microbial count (bacteria, fungi and actinomycetes) revealed a significant decrease in treatments receiving 175% NPK (-64.90% for bacteria, -38.78% for fungi and -16.41% for actinomycetes) as compared to 100% NPK.