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Two field experiments were conducted for two years with the aim of studying the effects of deep tillage and straw returning on soil microorganism and enzyme activity in clay and loam soil. Three treatments, (1) conventional tillage (CT), shallow tillage and straw returning; (2) deep tillage (DT), deep tillage and straw returning; and (3) deep tillage with no straw returning (DNT), were carried out in clay and loam soil. The results showed that deep tillage and straw returning increased the abundance of soil microorganism and most enzyme activities. Deep tillage was more effective for increasing enzyme activities in clay, while straw returning was more effective in loam. Soil microorganism abundance and most enzyme activities decreased with the increase of soil depth. Deep tillage mainly affected soil enzyme activities in loam at the soil depth of 20–30 cm and in clay at the depth of 0–40 cm. Straw returning mainly affected soil microorganism and enzyme activities at the depths of 0–30 cm and 0–40 cm, respectively.

Subsoil compaction can result in unfavourable soil physical conditions and hinder the root growth of maize. The effects of deep tillage and conventional tillage on soil physical properties and root growth of maize were studied during 2010-2011 at two sites (loam at Hebi and clay at Luohe) in central China. The results showed that soil penetration resistance, bulk density, water content and root length density were significantly affected by tillage, soil depth and year. Deep tillage had lower penetration resistance and lower soil bulk density, but higher soil water content than conventional tillage across years and depths. Averaged over the whole soil profile, deep tillage not only significantly decreased penetration resistance and soil bulk density, but significantly increased soil water content and root length density on loam, while deep tillage only significantly increased the root length density on clay. We conclude that deep tillage on the loam is more suitable for the root growth of summer maize.Keywords: soil compaction; penetration resistance; deep tillage; conventional tillage; root length density B. Ji and Y. Zhao contributed equally to this work. Environ. Vol. 59, 2013, No. 7: 295-302 296 ers to solve the soil compaction by deep tillage. However, there is little information about the effects of deep moldboard tillage on soil properties and root growth in different soil types. Therefore, a two-site study was conducted at two typical and representational soil types in central China. The objectives of this study were to investigate the effects of tillage depth on soil physical properties and root length density of summer maize at two soil types in central China. Plant Soil MATERIAL AND METHODSStudy sites and soil properties. Two field experiments were conducted during 2010-2011 at Hebi (35°67'N, 114°98'E) and Luohe (33°57'N, 113°98'E) in the central China. Both sites have a continental monsoon type climate. The data on solar radiation and temperature during the study period were collected from an adjacent weather station and are presented in Figure 1. There are winter wheat-summer maize rotation at Hebi and Luohe. For several decades, soil tillage is conducted after the harvest of maize and before the winter wheat sowing. Soil tillage is always conventional shallow tillage (20 cm depth) with moldboard plough, followed by a disk harrow for seedbed preparation. Summer maize is sowed under notillage condition. The two year experiments were conducted on the same site with the same plots. Soil basal samples were collected at the beginning of experiment. The main physical and chemical properties of soils in the two study sites are presented in Table 1.Experiment design and crop cultivation. The experiment was designed as a complete randomization with three replications. Soil tillage was conducted before the winter wheat sowing. Conventional tillage (CT) was moldboard plowed to a depth of 20 cm, deep tillage (DT) was moldboard plowed to a depth of 30 cm, followed by a disk harrow for seedbed preparat...