Influence of tillage systems and wheat stubble levels on the physical, chemical and biological properties of soil

In order to study the effects of tillage systems and wheat residue levels on soil physical, chemical and biological characteristics a randomized complete block design arranged in split block with three replications was set in research farm of Ferdowsi University of Mashhad in 2013-2014 growing season. Four different tillage systems (disk, mouldboard plough disk, sweep plough disk and chisel plough disk) as vertical factor were employed in combination with five different crop residue applications (0, 25, 50, 75 and 100 percent wheat residue) as horizontal factor. Due to soil sampling in April (2013), November (2013) and June (2014), data were analysed as split block in time. According to the results, the lowest total nitrogen (0.094%), available phosphorus (12.50 mg/kg) and organic carbon (0.52%) were observed when mouldboard plough was applied, while the highest values were obtained using chisel plough followed by disk. Irrespective of sampling time, total nitrogen, available phosphorus and potassium as well as organic carbon significantly increased with increasing wheat residue application. Furthermore, crop residue application caused significant reduction in soil pH (up to 0.45 unit) and improved microbial biomass and activity (by 20.6%).