DEPTH DISTRIBUTION OF SOIL ORGANIC CARBON FRACTIONS IN RELATION TO TILLAGE AND CROPPING SEQUENCES IN SOME DRY LANDS OF PUNJAB, PAKISTAN

Depth distribution of soil organic carbon (SOC) fractions depends on the efficiency of agro-technical managements. Information on depth distribution of SOC fractions mostly confined to the plow layer and scant in dry lands of Punjab, Pakistan. Therefore, a field experiment was laid out with moldboard plow (MP) (control), tine cultivator (TC), and minimum tillage (MT) as main plots, and cropping sequences fallow wheat (Triticum aestivum L.), (FW, control), mungbean (Vigna radiata L.) wheat (MW), sorghum (Sorghum bicolor L.) wheat (SW), green manure wheat (GW), and mungbean-chickpea (MC) (Cicer arietinum L.) as sub-plots. Treatment effects were assessed for microbial biomass carbon (MBC), potentially mineralizeable carbon (PMC), particulate organic carbon (POC), dissolved organic carbon (DOC), HCl insoluble carbon (HIC), and stratification ratio (SR) in Rawal series: Udic Haplustalf. Alfisols. The MBC concentration was the highest in MT system, at 15 to 30-cm depth under MW and PMC concentration was highest under SW with MT at 45-60 cm. MP had higher POC in FW sequence. The highest DOC was at 0 to 15-cm depth under MC with TC and stock of HIC was more under TC with FW sequence. The highest SR of PMC was under MT with FW at 0-15: 15-30 and POC was under TC and MP with FW at depths of 0-15: 45-60 cm. The highest SR for DOC was under MP with GW at 0-15: 45-60 cm and HCl insoluble C was under MT with SW at 0-15: 45-60. In broad-spectrum, labile organic fractions revealed differential sensitivity, and POC stocks are also a sensitive indicator to detect the short-management effects. Copyright (C) 2015 John Wiley & Sons, Ltd.