Relationships between relative seasonal pasture yields (total, spring, or summer/autumn) and soil physical properties were investigated. Dairy farm data were collected from trials over 7 years. There were few significant response relationships between total relative yield and each soil physical property at each soil depth, from 0 to 20 cm. Macroporosity (air-filled porosity; pores >30 μm), percentage of pores >300 μm, and total porosity at both 0–5 and 5–10 cm soil depths all had highly significant positive relationships with spring relative yield, with the best fit being for macroporosity. Summer/autumn relative yield had significant but negative relationships with macroporosity and the percentage of pores >300 μm at both 0–5 and 5–10 cm soil depths, and saturated hydraulic conductivity at 0–5 cm. Summation of yield data into seasonal totals gave more meaningful relationships with macroporosity, compared with summation over several individual yield harvests within a season. Macroporosity at 0–5 and 5–10 cm was the most useful indicator for predicting spring and summer/autumn pasture yields, but none of the physical measurements was a reliable indicator of total yield.

The leaching of nitrogen (N) from agricultural soils is undesirable for environmental and health reasons. We investigated the effects of adding dairy shed effluent (DSE), irrigated on a weekly basis during the milking season, on the amounts and forms of N leached from large undisturbed soil monolith lysimeters of a Gley Soil over a period of 2 years. Drainage was managed using a weir that maintained the water table at 3 depths: 25 (high), 50 (medium), or 75 (low) cm below the soil surface. The low water table treatment represented the usual situation for the soil when drained. If undrained, it would be usual during wet periods in the field for a perched water table to form on the slowly permeable horizon at 75 cm depth. The total amount of N irrigated onto the lysimeters in the first milking season was equivalent to a total of 511 kg N/ha.year, and up to 33.3 kg N/ha.year leached from the soil. The losses from lysimeters receiving effluent were nearly double those from lysimeters receiving an equivalent amount of water only, when the high and medium water tables were imposed. Adding effluent caused only a small increase (7 kg N/ha) in total N leached in the low drainage treatment. In the second milking season, the effluent-N loading was increased to 1518 kg N/ha.year and the pasture was managed to simulate a ‘cut and carry’ land treatment system. Under these conditions, up to 131.4 kg N/ha.year leached from the soil, which was nearly 100 kg N/ha more than lysimeters receiving only water. The total N leaching losses represented a similar proportion of added N (7% and 9%) for years 1 and 2, respectively. Most of the leached N (80—90%) was in organic N form. The managed drainage treatment in which the water table was nearest the soil surface resulted in less N being leached in the nitrate-N (NO 3 -N) form (<2.5 kg N/ha.year) than the other drainage treatments (6—12 kg N/ha.year); however, it did result in the greatest amount of organic and total N leached (33 and 131 kg N/ha for Year 1 and 2, respectively). The smaller amount of NO 3 -N leached from the high water table treatment is attributed to enhanced denitrification, and the greater amount of organic N is attributed to preferential flow. Although NO 3 -N concentrations in leachate generally remained below World Health Organisation (WHO) standards in all treatments, the large amount of N leached in organic form would suggest that inorganic N should not be the only form of N considered when measuring N leaching losses.

Over recent years regulatory authorities in New Zealand have promoted irrigation of dairy farm effluent (DFE) onto the land, to protect surface water quality. The rate at which the resistant organic matter from DFE accumulates in the soil and the effect of any accumulation on other soil organic matter (SOM) related pools, such as microbial biomass, are, however, unknown. This information is necessary to determine the long-term impact and sustainability of land-applied DFE.In this paper we report on changes over 4 years in organic carbon (C-org) and total nitrogen (N-t) from a soil receiving a high application rate of DFE. Soil microbial biomass (C-mic) measurements were also included to test the hypothesis that C-mic or the C-mic/C-org ratio can be used as an early indicator of changes in SOM.The regular irrigation with DFE at the high rates used in this study increased the C-mic, pH, C-org, and N-t of the soil receiving the effluent. The time series of C-mic showed that this measurement is suitable as an early indicator of changes in C-org and N-t, whereas a single determination of the C-mic/C-org ratio was not.The sustainability of DFE application onto land in terms of N leaching can be maintained only when the supply of inorganic N is continually matched by the demand of the pasture. This means that inorganic N fertilisation has to be reduced concurrently with the gradually increasing N mineralisation from the accumulating organic matter.

Abstract 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 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.

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 mum, 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.

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.

Particle density is used to calculate total soil porosity and related measurements such as macroporosity and water storage capacity. Methods for measuring particle density often advise using dry samples. This study measured particle density by displacement of water using both field-moist and oven-dry samples from 4 New Zealand Allophanic Soils. There were significant differences in particle density between the 2 methods. Oven-dry samples under-estimated particle density by up to 0.33 Mg/m(3) and as a result, calculations of porosity were under-estimated by up to 0.05 m(3)/m(3). Under-estimation of porosity can result in incorrect interpretation of a soil's aeration and water holding status. Allophanic Soils are known to undergo irreversible physical changes on drying and it is likely that these changes caused the difference in measurements. Only field-moist samples should be used to determine particle density of Allophanic Soils to ensure accurate calculation of soil porosity.

The distribution of a solution simulating cow urine in soil was measured within 6 hours of deposition, by applying 2 litres of KBr-pyranine dye solution to the soil surface at a rate of 0.2 litres s(-1) followed by excavation and sub-sampling of the area affected by urine in 10-cm depth increments until no further pyranine dye could be detected under UV fluorescence. Preferential flow of simulated cow urine to below 20 cm soil depth occurred in 9 of the 10 soils examined, tip to 68% of applied solution moved below 20 cm, at an average of 17% over all soils examined. Two soils exhibited a high degree of preferential flow and excluding these from the data reduced the average loss to 11%. Although this preferential flow was significant, much of the urine nutrients moving via preferential flow would still be available for uptake by plant roots at depth, and therefore cannot be considered a loss to pasture. The movement of urine to below 20 or 30 cm soil depth was best predicted by saturated hydraulic conductivity calculated as the mean for the 0-30 cm soil layer. Saturated hydraulic conductivity measurements made for any one 5-cm depth increment, particularly the 0-5 cm soil depth, were poor predictors of urine flow to below 20 or 30 cm depth.

The wide application of hydraulic conductivity data depends on linking hydraulic parameters to soil morphology. Conventional morphology has been found to be a poor predictor of hydraulic conductivity. In this study we present new methods of characterising soil morphology to provide key morphological descriptors that can be related to hydraulic conductivity. Relationships were established between morphological properties (macrovoids, ped size, and associated surface features), and in situ consistence (degree of packing) with measured saturated and near-saturated hydraulic conductivity (Ks and K−40). These relationships were applied to estimate Ks and K−40 classes for soil horizons of pedal and apedal soils. In pedal soils, K is estimated from the area of macrovoids and from the proportions of different-sized peds in each horizon, their closeness of fit, and their degree of packing. Low packing and fine peds with rough surfaces is indicative of rapid conductivity, whereas high packing and coarse peds with smooth/shiny ped surfaces is indicative of slow conductivity. In apedal soils, K is estimated from the area of macrovoids and from degree of packing and particle-size class. Low packing with coarse particles indicates rapid conductivity, whereas high packing with fine particles indicates slow conductivity. Field characterisation of soils to determine functional morphology requires: (i) a dye to measure extent and continuity of cracks and macrovoids; (ii) a metal blade (Singleton Blade) and a hand-held penetrometer to measure soil consistence in situ; and (iii) weighing different-sized peds and describing their surface features.

The use of land for the treatment of effluent is increasing within New Zealand. However, shallow groundwater aquifer systems in several parts of the country already have elevated nitrate-N levels due mainly to non-point source contamination. The use of controlled drainage on poorly drained soils provides an opportunity to enhance nitrate removal in treatment systems through increased denitrification rates. A lysimeter study showed that increasing soil water content substantially reduced nitrate leaching. Nevertheless, the bypass flow characteristic exhibited by this soil resulted in substantial amounts of untreated effluent moving past the root zone and into the drainage system.Using bromide as a conservative tracer showed that the application rate and history of effluent application affects the amount of bypass from an effluent irrigation. The breakthrough curves were dominated by the initial bypass flow event and then a slow release from the immobile soil-water zone. Dilution of the applied effluent increased with increasing watertable height but the leachate remained at higher concentrations for a longer time period compared with conventionally drained soil profiles. More of the dissolved fraction of an effluent is recovered earlier from profiles that have higher water tables, as more diffusion from the immobile zone is possible.

Sediment and chemical losses in surface runoff can be significant on land with rolling topography. These effects can be more severe in grazed pasture systems because of animal treading damage to the ground surface. The phenomenon of treading includes soil compaction, pugging, creating tracks and surface cracking. Modelling results presented in the paper provide estimation of changes in water infiltration rate with land of different topography, soil physical condition, season and grazing. These models were derived from field data collected over 3 years and were specified for micro-sites (0.5 m2). The modelling results identified that micro-site infiltration analysis was appropriate to land with complex grazing and topographic conditions. The correlation between the model estimation and field measures was up to 73% (adjusted R2). Keywords: animal treading, infiltration rate, soil compaction, runoff, cellular automata, spatial modelling

Two hydrological models, which used different methods to determine the soil water distribution in a soil profile, were evaluated against 4 years of data from large soil lysimeters. SWIM determines soil water distribution from a finite difference implementation of the Richards' equation. DRAINMOD uses a soil-specific relationship between the air volume in a profile and the watertable height to locate the depth to the saturated zone. An 'equilibrium' relationship between soil water tension and depth is then assumed to distribute the soil water in the unsaturated zone. Predicted values and measured values for drainage and watertable heights were compared for 3 drainage treatments. The drainage in the lysimeters was achieved by installing an outlet tube on the slowly permeable layer at 0.75 m from the soil surface. The conventional drainage treatment allowed gravity drainage to occur directly from this drainage outlet tube. The other 2 drainage treatments employed controlled drainage, where a step (or weir) is installed in the outlet tube. No drainage can occur from the lysimeters until the water table within the lysimeters reaches the step height. Two different step heights provided 2 controlled drainage treatments. Independently determined model parameters were used without additional calibration for the analysis. Both models performed well. DRAINMOD over-predicted the 4-year cumulative drainage for all treatments, with the largest error being 7%. SWIM conversely under-predicted cumulative drainage, with a maximum error of 16%. The standard error of estimation for the watertable height over the full 4-year data period was lower for SWIM., ranging from 0.06 to 0.12 m. DRAINMOD's standard error over the same period for the watertable height ranged from 0.09 to 0.21 m. Generally, error values from this work were smaller than comparable values from other studies. The hydrology of the lysimeters where there was no lateral inflow, surface runoff, or deep seepage losses, coupled to an essentially 1-dimensional flow domain, probably contributed to the lower errors. Furthermore, limitation of the maximum watertable heights by the controlled drainage regime in the lysimeters also reduces the maximum possible magnitude of the standard error term.

The water extraction patterns of grapevines (Vitis vinifera) growing on two Waikato soils of contrasting properties were investigated. One soil, the Horotiu silt loam, consisted of silt loam on gravelly coarse sand. In this soil 50% of the water extraction occurred in the top 40 cm of soil. Extraction was highest in the top 20 cm and gradually reduced down to c. 70 cm depth which corresponded to the change from silt loam to gravelly coarse sand. The measured rate of water extraction by the vine corresponded to the predicted evapotranspiration rate up to 62 mm of extraction. Above 62 mm the measured rate of extraction from the soil fell off rapidly but all the vine's water needs were supplied by deep subsurface roots. The second soil studied, the Te Kauwhata clay loam, consisted of clay on a firm sandy clay pan at 110 cm. Fifty percent of water extraction occurred in the top 80 cm of soil. Water extraction was highest in the top 10 cm and also in the 70-110 cm zone. Water moving downslope above the pan was able to supply water to the plant.

Soils within the Te Kauwhata Irrigation Scheme were sampled to determine the extent of soil acidity and aluminium (A1) and manganese (Mn) toxicity. Most soils belonged to yellow-brown earth or brown granular loam soil groups. Forty-one soil profiles were sampled at 20 cm intervals to 80 cm. Samples were analysed for pH, and A1 and Mn extracted by 1M KC1 and 0.02M CaCl2. Mn was also extracted using 1M NH4OAc, and 0.2% hydroquinone in 1M NH4OAc (easily reducible Mn). The results show that the soils have strongly acid subsoils. Toxic levels of extracted Al were common in most subsoils and some topsoils. The toxic levels of Mn are likely in many topsoils and soil horizons with Mn concretions. Incorporation of lime into the subsoil to increase soil pH and reduce Al toxicity and potential Mn toxicity may be necessary for some crops.