No abstract

Farmer concern that compaction and/or surface roughness caused paired root growth (Voorhees, 1992), and reduced transby winter grazing of corn (Zea mays L.) crop residues may reduce port of oxygen and nutrients (Scholefield et al., 1985). subsequent soybean [Glycine max (L.) Merr.] yield prompted this 3-yr, on-farm study near Atlantic, IA. Two 19-ha fields with Marshall

A study of the physical condition of 3 soils used for intensive dairy farming in the Waikato Region was undertaken. The study was to determine the existing physical condition of the soil, the possible long-term changes from pugging damage, and the most appropriate measurements and depth for monitoring change in soil physical properties under dairying. Four dairy farms were selected on each of 3 soils (an Allophanic Soil and 2 Gley Soils). On each farm, 3 sites that corresponded to never trodden, usual (‘average’ paddock and pasture condition for the farm), and previously pugged (pugged >18 months ago) pasture histories were sampled. Undisturbed soil cores were collected at 50-mm depth increments to 250 mm for determination of bulk density, total porosity, saturated and unsaturated hydraulic conductivity, proportion of pores >30 and 60 µm, and aggregate size class. Results showed pugging was having a long-term effect on soil physical properties of all 3 soils, including the well-drained Allophanic Soil that rarely pugged. All measurements showed a decline in values for soil properties from never trodden to previously pugged. The greatest changes were in hydraulic conductivity, proportion of pores, and aggregate size (>60 and <20 mm). The most appropriate depth increment for measuring differences between treatments was found to be 50–100 mm. A comparison of previously pugged to never trodden at this depth showed that hydraulic conductivity had decreased by 80%, pore size by 46% (except for Allophanic Soil), and the proportion of aggregates >60 mm in diameter had increased at least 4-fold. Farming practices that minimise pugging damage, such as on/off grazing, need to be encouraged. It is possible that such programs may permit the soil to recover to a physical state similar to never trodden sites.

A study of the physical condition of soils under dairying in the Waikato and Northland regions was undertaken to determine the physical condition of the soil, possible changes from pugging damage, and the most appropriate measurements and sampling regimes for monitoring change.Sites were selected on widespread soil types (Allophanic and Gley Soils in the Waikato; Allophanic, Ultic, and Podzol Soils in Northland) and corresponded to never trodden, usual usage or conditions, and previously pugged (>18 months ago) pasture. Soil cores were collected at 50-mm depth increments for determination of bulk density, total porosity, saturated and unsaturated hydraulic conductivity, proportion of pores greater than 30 and 60 µm, and aggregate size class.The 0-100-mm depth was best for showing differences between treading regimes. Within this depth, hydraulic conductivity and aggregate size showed the greatest differences between regimes. All measurements were useful for showing differences in the Waikato data. However, for Northland, bulk density, total porosity, and proportion of pores were not always indicators of change. Approximately 20 cores were needed per regime to show differences. Soil properties on most soil types were still affected 18 months after a pugging event. Measurements selected for showing change varied depending on whether data were for geographic regions, a single region, or a particular soil type.

Shallow mechanical loosening of soil to 22 cm deep (aeration) was investigated as a method for ameliorating soil compaction caused by dairy cattle treading. Soil physical and pasture measurements taken over 46 weeks compared plots grazed under normal grazing practice (non-aerated) with plots under normal grazing practice where soil was mechanically loosened (aerated). Aerated soil initially showed reduced (P < 0.05) penetration resistance, degree of packing, and bulk density, and increased (P < 0.05) hydraulic conductivity, total porosity, macroporosity, and proportion of small aggregates, compared with non-aerated soil. However, after 40 weeks aerated soil showed some reversion back to a non-aerated state, and only the most sensitive measurements (penetration resistance, degree of packing, soil structure, and *Author for correspondence A99038 Received 6 August 1999; accepted 13 April 2000 macroporosity) showed significant (P < 0.05) treatment differences. Pasture herbage yield, botanical composition, and root length were unaffected (P < 0.05) by aeration, but aeration increased (P < 0.05) root dry weight and decreased bare ground. This work suggests that timing of aeration with regard to soil moisture and atmospheric conditions is vital for optimal soil and pasture responses. The need to use methods which sample large volumes of soil and pasture to detect soil physical and pasture changes due to loosening is also stressed.