Intensive agriculture can impair river water quality. Soil quality monitoring has been used to measure the effect of land use intensification on water quality at a point and field scales but not at ...the catchment scale. Other farm scale land use pressures, like stocking rate and the value of land, which relate to land use intensity are now publicly available, nationally. We therefore tested whether point scale soil quality measures, together with newly available farm scale land use pressures (land valuation and stocking rate) and existing catchment and climatic characteristics could help predict the behaviour of water quality data across 192 catchments in New Zealand. We used a generalised additive model to make predictions of the change in nitrogen fractions (r2 = 0.65–0.71), phosphorus fractions (r2 = 0.51–0.70), clarity and turbidity (r2 = 0.42–0.46), and E. coli (r2 = 0.35) over 15 years. The state and trend of water quality was strongly related to a refined farm scale land use classification, and to catchment and climatic characteristics (e.g. slope, elevation, and rainfall). Relationships with point scale soil quality measures and the land use pressures were weak. The weak relationship with land use pressures may be caused by using a single snapshot in time (2022), which cannot account for lag times in water quality response but leaves room for additional temporal data to improve predictive power. The weak relationship to soil quality measures was probably caused by limited data points (n = 667 sites) that were unrepresentative of land use, and areas of catchment subject to processes like runoff or leaching. While national soil quality measures might be useful for evaluating environmental risk at the field or farm scale, without a large increase in sampling, they were not relevant at the catchment scale. Additional analyses should be performed to determine how many samples would be needed to detect a change using an environmentally focused soil test that can guide water quality management.
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•Land pressures and soil quality can influence local water quality.•Land use, catchment and climatic factors were strong predictors of 15 years of water quality.•A snapshot of land value and stocking rate poorly predicted catchment water quality.•Too few soil quality samples were available to predict catchment water quality well.•Increasing the temporal frequency of pressures and spatial frequency of soil quality data may improve predictions.
This paper reviews the effects of irrigation on soil physical properties, particularly soil water movement and storage, under predominantly pastoral systems. Few studies address how irrigation ...impacts these in temperate climates, with very few studies under modern spray irrigation and intensive pastoral farming. Irrigation generally means intensive land use will occur. It is difficult to uncouple factors affecting physical conditions such nutrient cycling, land use, stock class, grazing management and animal treading. Irrigation (with associated increased land use intensity) tends to alter soil physical properties, changing them to be like soils formed under higher rainfall particularly in arid and semi-arid climates. Changes in physical properties under irrigation in temperate and sub-humid climates were more variable. Some studies showed increased available water capacity, while others showed no change. Knowledge gaps include effects of irrigation intensification on soil physical properties under modern farm systems to improve process, management, spatial and temporal information.
In Canterbury, New Zealand, there has been a widespread conversion of dryland sheep grazing to more intensive irrigated dairying. We determined the effects of these land uses on soil physical ...properties, and water release characteristics, on adjacent sites: a centre-pivot sprinkler-irrigated dairy farm site, a dryland sheep site, and a non-grazed, non-irrigated control site. Despite the Pallic Soil being well drained, greater soil compaction occurred at the dairy site than at other sites, to at least 30 cm depth. The dairy site typically had significantly lower total porosity and macroporosity, and greater bulk density and volumetric water content, than the other sites. Available water capacity varied but was greater at the dairy site (0–30 cm) than at the sheep site and control site. Further research is required across more farms and soils to confirm these results in other conditions.
Improved process understanding of temporal change in soil hydraulic, water retention, and soil physical properties is required to improve modelling of soil-water dynamics. This study reports on ...temporal trends in soil physical properties for intensive till and no till irrigated wheat, from autumn sowing to summer harvest. There were significant temporal trends for bulk density, readily available water capacity, and unsaturated hydraulic conductivity (at three matric potentials). Using a simple two-parameter exponential model for unsaturated hydraulic conductivity, the model coefficients appeared to increase over the first 10 weeks, followed by a decrease and later increase, but the temporal effect when using this model was not significant given the parameter uncertainty. Daily rainfall, irrigation, and evapotranspiration were evaluated as possible explanatory variables, but these were not generally significant in explaining temporal trends of soil properties. An implication is the need to provide temporal data to parameterise hydrological models for more accurate modelling, including irrigation scheduling.
Soil Olsen phosphorus is used for regional and national environmental reporting, and for farm soil fertility assessment. In New Zealand, the laboratory measurement using sieved and air-dried soil is ...undertaken gravimetrically (by weight), or volumetrically, so can be reported on either basis. Olsen P 'stocks' can also be calculated using field bulk density. These methods have led to inconsistencies in environmental reporting. This study compares and quantifies the relationships between the laboratory-determined gravimetric and volumetric Olsen P for a range of soil orders, by developing a statistical model. Our study showed there is a significant difference in Olsen P determined by volumetric and gravimetric methods, and the relationship varies with soil order. The gravimetric method gave elevated values for all soil orders compared with the volumetric method. Bulk density was generally significantly different from, and greater than, volume weight, for many soil orders. From the statistical modelling, look-up tables are provided for converting from volumetric-to-gravimetric, and gravimetric-to-volumetric, in the absence of volume weight, such as for legacy data. Several recommendations to improve national environmental reporting are provided, including that, if the volumetric method is used, volume weight should be requested from the laboratory to enable consistent conversion for national reporting.
In Canterbury, New Zealand, there has been widespread conversion of dryland sheep grazing to more intensive irrigated dairying. We determined the effects of these land uses on soil carbon on a ...centre-pivot sprinkler-irrigated dairy farm site, a dryland sheep site, and a non-grazed control site. The dairy site had significantly greater carbon density and carbon storage at 10–20 cm and 0–30 cm depths than the sheep farm site. The dairy farm site had significantly greater carbon stock (equivalent soil mass method) than the sheep farm site at 10–20 cm depth. The dairy farm site intensification did not adversely affect soil carbon, including carbon stock by the equivalent soil mass method. The effects of dairy effluent application on soil water repellency and water movement were investigated. The dairy site had significantly greater subcritical repellency index than the sheep site and a dairy effluent site. Further research is required across more farms and soils to confirm these results in these land uses and under other management and climate conditions.
Land fragmentation is a growing issue in New Zealand, however, no consistent or regular national monitoring has been established. A methodology for assessing land fragmentation was applied nationally ...for the first time, revealing that the greatest proportion of fragmentation occurred on land used for diffuse rural residence (>0.40 to ≤2.0 ha) and small parcels (>2.0 to ≤8.0 ha) with a 128% and 73% increase, respectively, between 2002 and 2019. In New Zealand, the most highly productive land (Land Use Capability (LUC) class 1, 2 and 3) is most impacted by continued fragmentation with 38%, 28% and 17% of baseline area, respectively, occupied by medium sized parcels or smaller (≤40.0 ha) with a dwelling in 2019. Impacts were greatest for Auckland with 40%, 44% and 25% of the region's LUC 1, 2 and 3 land, respectively, occupied by small sized parcels or smaller with a dwelling, increasing to 64%, 67% and 47%, respectively, when including parcels ≤ 40.0 ha. Protection of LUC class 1 and 2 land, particularly, requires national attention. This metric provides an opportunity to evaluate land fragmentation and development over time that could serve both the assessment of policy performance and environmental reporting at national and regional levels.
Application of phosphate (P) fertilizers to farmland is projected to be causing worldwide accumulation of fluorine (F) in agricultural soils and associated ecosystems, but wide-scale field data have ...been lacking. We report results of sampling across two large regions of New Zealand involving soils of 298 native and farmed properties. This has enabled the first wide-scale retrospective estimates of anthropogenic F enrichment in pastoral and horticultural soils. Results validate earlier projections: F accumulation in farmed soils has been comparatively rapid (mean increase 2.1 % per year) and widespread. Over 50 years, average total F concentrations in surface soils have doubled from ~220 to 440 mg/kg. Thresholds protective against chronic fluorosis in grazing animals are being substantively passed, indicating that land may be rendered unsuitable for pastoral production in the mid-term future: when sampled 44 % of dairy farm soil samples exceeded 500 mg/kg total F, and 10 % exceeded 650 mg/kg. Potential for F toxicity to plants and wildlife appear to be significant and marginal, respectively, at current soil F concentrations. Relationships between F and other elements suggest P fertilizers are also a source of several elements geochemically linked to F, and that anthropogenic F modifies soil aluminium (Al) chemistry, potentially opening a broad-scale Al exposure pathway to pollinating insects. Findings signal a need for systematic examination of the range of possible affects that may be linked to increasing soil F, which include various types of ecotoxicity, altered Al chemistry, reduced P availability, and potential for increased dietary intakes of F, Al and aluminofluoride (AlF
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A hydrological framework encompassing nitrogen (N), phosphorus (P) and microbial (E. coli) transfer from land to water was developed to provide a consistent and rapid approach for assessing the ...potential impacts of land activity on water quality in New Zealand. A flow partition approach was used to route precipitation via surface and subsurface pathways from land to water. The framework included a typology-based inventory that estimates annual yields of transportable N and P from land, a regional-scale spatial layer that attenuates N in groundwater, and literature-based estimates of E. coli concentrations in surface runoff and artificial drainage. Application of the framework in four catchments highlighted the importance of local catchment knowledge of dominant hydrological processes that was needed to ensure flow partitions derived were a realistic representation of transport processes. While the approach was promising, additional refinements are needed to improve process representation (e.g. effects of groundwater lags) and ensure input data (e.g. soil attributes) have appropriate resolution to describe hydrological pathways. We contend that such a framework would provide a consistent and relatively rapid approach for identifying contaminant transfer pathways from land to water that can inform assessments of the potential consequences of land use change and intensification.
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