Seth Laurenson

Chapter Five – The Influence of Wastewater Irrigation on the Transformation and Bioavailability of Heavy Metal(Loid)s in Soil

Abstract With pressure increasing on potable water supplies worldwide, interest in using alternative water supplies including recycled wastewater for irrigation purposes is growing. Wastewater is derived from a number of sources including domestic sewage effluent or municipal wastewater, agricultural (farm effluents) and industrial effluents, and stormwater. Although wastewater irrigation has many positive effects like reliable water supply to farmers, better crop yield, pollution reduction of rivers, and other surface water resources, there are problems associated with it such as health risks to irrigators, build-up of chemical pollutants (e.g., heavy metal(loid)s and pesticides) in soils and contamination of groundwater. Since the environment comprises soil, plants, and soil organisms, wastewater use is directly associated with environmental quality due to its immediate contact with the soil–plant system and consequently can impact on it. For example, the presence of organic matter in wastewater-irrigated sites significantly affects the mobility and bioavailability of heavy metal(loid)s in the soil. Wastewater irrigation can also act as a source of heavy metal(loid) input to soils. In this chapter, first, the various sources of wastewater irrigation and heavy metal(loid) input to soil are identified; second, the effect of wastewater irrigation on soil properties affecting heavy metal(loid) interactions is described; and third and finally, the role of wastewater irrigation on heavy metal(loid) dynamics including adsorption and complexation, redox reactions, transport, and bioavailability is described in relation to strategies designed to mitigate wastewater-induced environmental impacts.

Evaluating the benefits of standing cows off pasture to avoid soil pugging damage in two dairy farming regions of New Zealand

Abstract Many dairy farms in the Manawatu and Southland regions of New Zealand are situated on poorly drained soils that are prone to treading damage – an undesirable occurrence on grazed pastures during the wetter months of the year. Standing cows on a loafing pad (stand-off) during wet conditions can reduce damage, but will incur costs. The objective of this study was to evaluate the trade-offs of grazing duration (from 0 to 10 hours grazing/day for lactating cows) versus pasture damage (wastage), feed and stand-off expenses, and farm operating profit. A simulated farm from each region was used in a farm systems model. This model simulates pasture-cow-management interactions, with site-specific climate data as input for the soil-pasture sub-models. Days to recover previous yield potential for damaged paddocks can vary widely. A sensitivity analysis (40 to 200 days to recover) was conducted to evaluate the effect of this parameter on results. Full protection when there is risk of damage (0 grazing hours/day) appeared to be less profitable compared with some level of grazing, because advantages of reduced damage were outweighed by disadvantages of managing infrequently grazed pastures. The difference in operating profit between full protection and some level of grazing became less as the recovery time increased, but for both regions, grazing durations of 6–8 hours/day when risk of damage is present appeared to be a sensible option irrespective of recovery time.

The Role of Bioretention Systems in the Treatment of Stormwater

Abstract Urbanization leads to water catchments becoming more impervious and channelized. These modifications to the natural landscape result in reduced water infiltration into soils and base flow components that cause a greater volume and rate of surface water runoff. In contrast to conventional stormwater management systems, water-sensitive urban design (WSUD) technologies manage rainfall where it falls, through enhancement of infiltration capacity of impervious areas and rerouting runoff across pervious areas. WSUD aims to better incorporate several urban water sources, including stormwater, into the local hydrological cycle so as to (1) reduce demand on potable water, (2) minimize pollutant loading to surface waters, and (3) restore or maintain predevelopment hydrological processes. Bioretention systems are designed to remove both dissolved pollutants and particulate matter from stormwater runoff and reduce the volume and rate of stormwater discharged. Treatment is achieved via a number of chemical, biological and physical processes including sedimentation, filtration, sorption, reduction, vegetative uptake and microbial biomass assimilation. The efficiency of bioretention systems in the treatment of contaminants in stormwater depends on a number of factors including substrate conditions, type of vegetation, climatic conditions and on the volume and rate of stormwater infiltrated and discharged. This chapter discusses the various processes involved in the treatment of stormwater within bioretention systems; in particular, the fate of nutrients such as nitrogen and phosphorus, and metals, and the soil–plant processes involved in their retention. The factors affecting treatment efficiency are also examined.

Effect of application of dairy manure, effluent and inorganic fertilizer on nitrogen leaching in clayey fluvo-aquic soil: A lysimeter study

Dairy farm manure and effluent are applied to cropland in China to provide a source of plant nutrients, but there are concerns over its effect on nitrogen (N) leaching loss and groundwater quality. To investigate the effects of land application of dairy manure and effluent on potential N leaching loss, two lysimeter trials were set up in clayey fluvo-aquic soil in a winter wheat-summer maize rotation cropping system on the North China Plain. The solid dairy manure trial included control without N fertilization (CK), inorganic N fertilizer (SNPK), and fresh (RAW) and composted (COM) dairy manure. The liquid dairy effluent trial consisted of control without N fertilization (CF), inorganic N fertilizer (ENPK), and fresh (FDE) and stored (SDE) dairy effluent. The N application rate was 225kgNha-1 for inorganic N fertilizer, dairy manure, and effluent treatments in both seasons. Annual N leaching loss (ANLL) was highest in SNPK (53.02 and 16.21kgNha-1 in 2013/2014 and 2014/2015, respectively), which were 1.65- and 2.04-fold that of COM, and 1.59- and 1.26-fold that of RAW. In the effluent trial (2014/2015), ANLL for ENPK and SDE (16.22 and 16.86kgNha-1, respectively) were significantly higher than CF and FDE (6.3 and 13.21kgNha-1, respectively). NO3- contributed the most (34-92%) to total N leaching loss among all treatments, followed by dissolved organic N (14-57%). COM showed the lowest N leaching loss due to a reduction in NO3- loss. Yield-scaled N leaching in COM (0.35kgNMg-1 silage) was significantly (P<0.05) lower than that in the other fertilization treatments. Therefore, the use of composted dairy manure should be increased and that of inorganic fertilizer decreased to reduce N leaching loss while ensuring high crop yield in the North China Plain.

Assessing the production and economic benefits from preventing cows grazing on wet soils in New Zealand.

BACKGROUND Intensive grazing by cattle on wet pasture can have a negative effect on soil physical quality and future pasture production. On a North Otago dairy farm in New Zealand, experimental plots were monitored for four years to assess whether preventing cow grazing of wet pastures during the milking season would improve soil structure and pasture production compared with unrestricted access to pastures. The DairyNZ Whole Farm Model was used to scale up results to a farm system level and ascertain the cost benefit of deferred grazing management. RESULTS Soils under deferred grazing management had significantly higher total porosity, yet no significant improvement in macroporosity (values ranging between 0.112 and 0.146 m(3)  m(-3) ). Annual pasture production did not differ between the control and deferred grazing treatments, averaging 17.0 ± 3.8 and 17.9 ± 4.1 t DM ha(-1) year(-1) respectively (P > 0.05). Furthermore, whole farm modelling indicated that farm operating profit was reduced by NZ

Evaluating the economic and production benefit of removing dairy cows from pastures in response to wet soil conditions

1683 ha(-1) year(-1) (four-year average) under deferred grazing management. CONCLUSION Deferring dairy cow grazing from wet Pallic soils in North Otago was effective in improving soil structure (measured as total soil porosity), yet did not lead to a significant increase in pasture production. Whole farm modelling indicated no economic benefit of removing cows from wet soils during the milking season.

Grazing strategies for reducing contaminant losses to water from forage crop fields grazed by cattle during winter

ABSTRACT This study used the DairyNZ Whole Farm Model to assess the cost–benefit of duration-controlled grazing (DCG) to reduce the time dairy cows spend on pastures with high soil water content. Within the model, grazing duration was reduced from 21 hours down to 17, 13 or 0 hours when soil moisture was above a critical water content. Scenario farms encompassed four climatic regions of New Zealand and two soil types. Regardless of region, soil type or grazing duration, implementation of DCG was not profitable except in one single instance. Furthermore, increased pasture production in response to DCG was minimal due to poor pasture management. Farms located on poorly drained soils experienced more wet days per year, thereby increasing the frequency of standoff pad use and higher operational costs. Results indicate that any financial benefit that was gained from protecting imperfectly drained and poorly drained soils through DCG was diminished by a high capital repayment and operational cost associated with the off-paddock facility.

Identifying critical soil water thresholds to decrease cattle treading damage risk

ABSTRACT A paired catchment study quantified fluxes of Nitrogen (N), Phosphorus (P), sediment and Escherichia coli (E. coli) in flow from fields where cattle were wintered on swede (Brassica napus) and kale (Brassica oleracea) crops. The effectiveness of a strategic grazing approach that protected critical source areas was evaluated to determine if these fluxes could be reduced. Reduced soil infiltration caused by cattle treading was a contributing factor to overland flow events that mostly occurred in the six to eight weeks following crop grazing. Estimated annual fluxes of contaminants in overland flow ranged up to 27, 3.8 and 3740 kg ha−1 for N, P and sediment, respectively, and up to 4.3 × 1010 MPN ha−1 for E. coli. Strategic grazing significantly reduced overland flow volumes compared to standard grazing practice, reducing contaminant fluxes to levels similar to those observed when the catchments were returned to pasture and lightly grazed by sheep.

Assessing the environmental implications of applying dairy cow effluent during winter using low rate and low depth application methods

ABSTRACT To minimise soil compaction, land managers should limit cow grazing periods when soil water content (SWC) is greater than a critical water content (CWC) at which point soils are prone to treading damage. A laboratory-based method, the ‘proctor test’, has been used to identify the CWC in two intact Pallic soils collected from North and South Otago, New Zealand. We have attempted to relate the CWC to a simple field-based metric—the soil plastic limit—which can be measured by farmers as a proxy for CWC. Plastic limit was a suitable proxy for CWC in the North Otago soil only. In the South Otago soil, the CWC occurred at a lower SWC than the plastic limit. Although CWC varied across the two soil types, in both instances, it was reached at an SWC less than field capacity, while this was not always the case for plastic limit.

Economic benefits of mechanical soil aeration to alleviate soil compaction on a dairy farm

ABSTRACT Dairy cow effluent collected over winter from a loose-housed barn was applied to a series of large infield plots (400 m2) using low rate and low depth (LRLD) application methods. Applications were confined to the winter period, at a time when soil moisture content was often at or very near to field capacity and was applied over two seasons. Cows were confined to the housing facility during winter only, and outside of this period they remained on pasture. Losses of nitrogen (N), phosphorus (P) and the faecal indicator bacterium Escherichia coli (E. coli) in surface runoff and subsurface drainage from the LRLD treatment were compared with losses from effluent applications that occurred during spring to autumn, at an application depth not exceeding the soil water deficit, i.e. a standard practice treatment (SP, typically 10–15 mm per application). The annual quantities of nutrients applied by the treatments and the grazing managements imposed were similar. Although winter losses of N were significantly greater for the LRLD treatment (15 vs. 8 kg N ha−1 for the SP treatment), on an annual basis fluxes were similar between treatments (approximately 20 kg N ha−1 year−1). Effluent management had no significant effect on the annual fluxes of P and E. coli although the latter varied considerably. Average contaminant fluxes over a 2-year period indicated that the LRLD management system did not lead to a significantly greater risk to water quality compared with standard practices.