Effect of permanent bed planting combined with controlled traffic on soil chemical and biochemical properties in irrigated semi-arid Mediterranean conditions

Improving agricultural soil quality in semi-arid regions is necessary for reducing soil erosion and improving water use. Conservation agriculture (CA) can increase soil quality and biodiversity, and reduce operational costs without losing crop productivity both under irrigated or rainfed conditions. However, few studies on soil chemical and biochemical status in irrigated farms under CA in the Mediterranean region are available. Permanent beds with crop residue retention (PB) have been proposed as an alternative to conventionally tilled beds with residue incorporation into the soil (CB). These two soil management systems combined with controlled traffic were compared during two different seasons (2009 and 2010) in a loamy alluvial Typic Xerofluvent soil under a maize (Zea mais L.)–cotton (Gossypium hirsutum L.) crop rotation trial established in 2007 in Southern Spain. Total organic carbon (TOC), water soluble carbon (WSC), Kjeldahl nitrogen (Kjel-N), dehydrogenase (DHA) and β-glucosidase (β-Glu) activities and microbial biomass carbon (MBC) and nitrogen (MBN) were analysed in soil from beds and furrows after crop harvest. Results indicated that Kjel-N, TOC and enzymatic activities were significantly higher in soil from furrows in PB than in CB, but practically no differences were found in soil from the bed zone. Moreover, traffic did not affect chemical and biochemical parameters in spite of its compacting effect. Major differences were found between samplings due to different quantity and nature of the residues (maize vs. cotton). Principal component analysis confirmed that TOC, Kjel-N and β-Glu (and DHA to a less extend) are useful indicators of soil management impact on soil quality in this irrigated Mediterranean conditions; however, this is not the case of WSC, a common indicator in rainfed conditions. Results confirmed that conservation agriculture is the better option to increase soil biological and biochemical quality in irrigated farms under Mediterranean semi-arid conditions.

► Soil properties of permanent and conventional beds were compared in an irrigated farm.
► Traffic and residue amounts were controlled.
► Parameters were widely influenced by tillage and residue nature but not by traffic.
► Effects were more relevant in furrows than in beds.
► Conservation agriculture increased soil C and biochemical quality under irrigation.