Rising demand on food is leading to an increase in irrigation worldwide to improve productivity. Irrigation, for pastoral agriculture (beef, dairy and sheep), is-the largest consumptive use of water in New Zealand. There is a potential risk of leaching of microbial contaminants from faecal matter through the vadose zone into groundwater. Management of irrigation is vital for protection of groundwater from these microbial contaminants and maintain efficient irrigation practices. Our research investigated flood and spray irrigation, two practices common in New Zealand. The aim was to identify the risk of microbial transport and mitigation practices to reduce or eliminate the risk of microbial transport into groundwater. Cowpats were placed on lysimeters over a typical New Zealand soil (Lismore silt loam) and vadose zone and the leachate collected after irrigation events. Samples of both cowpats and leachate were analysed for the microbial indicator Escherichia coil and pathogen Campylobacter species.A key driver to the microbial transport derived from the model applied was the volume of leachate collected: doubling the leachate volume more than doubled the total recovery of E. coli. The persistence of E. coli in the cowpats during the experiment is an important factor as well as the initial environmental conditions, which were more favourable for survival and growth of E. coli during the spray irrigation compared with the flood irrigation. The results also suggest a reservoir of E. coli surviving in the soil. Although the same was potentially true for Campylobacter, little difference in the transport rates between irrigation practices could be seen due to the poor survival of Campylobacter during the experiment. Effective irrigation practices include monitoring the irrigation rates to minimise leachate production, delaying irrigation until 14 days post-cowpat deposition and only irrigating when risk of transport to the groundwater is minimal.Aim: To compare the risk of microbial contamination of groundwater from cowpats using two irrigation practices onto pasture. (C) 2015 Elsevier B.V. All rights reserved.

Understanding nitrogen (N) processes within the vadose zone is important to estimate N losses to groundwater systems. A field trial was undertaken to examine the dynamics of nitrate (NO3) and nitrous oxide (N2O) in an alluvial gravel vadose zone underlain by shallow groundwater. Synthetic urine (980 kg N ha−1) with a bromide (400 kg Br ha−1) tracer was applied to the surface of a 10‐ by 20‐m plot, and changes in subsurface NO3, Br, and N2O concentrations were compared with those from an adjacent plot, with just the Br tracer applied. Soil solution and air were monitored at multiple depths (from 0.2 to 5 m) over an 18‐mo period. Transport of solution was rapid in the gravel material with some Br transported to 3‐m depth immediately after the urine application. N2O was produced within the soil after urine application. NO3 to Br ratios indicated denitrification in the soil above the gravels, but none within the alluvial gravel vadose zone. In the “–urine” plot N2O concentrations increased with depth, with upward fluxes above the water table to the soil, suggesting N2O production near the water table. A different pattern was observed in the “+urine” plot where N2O was produced both at the soil zone above the gravels and near the water table leading to both upward and downward N2O fluxes. Overall N2O fluxes in the soil zone were greater than at the water table.

Understanding the physical and hydraulic properties of the vadose zone is important for modeling land use effects on groundwater quality. This study used a variety of characterization methods to derive conceptual understanding and estimates of hydraulic properties of a coarse alluvial gravel vadose zone in New Zealand. Sandy gravel (SG) material constituted approximately 90% of the vadose zone, with the remainder comprising sand lenses and open‐framework gravels. The gravel content of the SG material was approximately 70% (v/v) (range 68–73%). The water content of the bulk SG material (43 samples) ranged from 3.5 to 13.9%. The average bulk density of the SG material was 2.20 g/cm3 (range 2.00–2.33 g/cm3) giving an average calculated porosity of 17%. The average porosity of the open‐framework gravels was 34% and these gravels were often coated with 2‐ to 3‐mm‐thick deposits of amorphous Fe and Mn oxides. Neutron probe (NP) depth profiles indicated unsteady conditions, with variable water contents with depth and time reflecting the vertical heterogeneity and the variably saturated state of the vadose zone. Time series NP data to 3 m indicated water content in the alluvial gravels responded quickly to soil drainage events, and saturation variability was greater in the sand lenses and the SG material immediately underlying. When compared with derived water retention curves, variability in the water content equated to significant fluctuation in unsaturated hydraulic conductivity (Kunsat). Tension infiltrometer measurements were variable but were within the range of the Kunsat estimates from site‐average particle size distribution data. The gravel‐transformed, texture‐based models used to estimate saturated water content values in this study appeared to underestimate the measured values.

The objectives of the current study included the characterization of the temporal changes in indices of sulphur amino acid metabolism in piglets in response to vitamin B6 deficiency and repletion with graded levels of pyridoxine hydrochloride. In Experiment 1, 12 piglets (average initial weight = 5.3 kg; n = 6 per group) were fed a semi-purified diet containing either 0 (deficiency group) or 3 mg (control group) pyridoxine·HCl/kg diet, using a pair-feeding design, for 6 weeks. Piglets consuming vitamin B6-deficient diets exhibited decreased average daily gains on the 4th week and feed conversion efficiency from the 4th week until the end of the trial (P < 0.05). Plasma pyridoxal-5′-phosphate (PLP), in pigs consuming vitamin B6-deficient diets, was significantly lower than controls throughout the experiment (P < 0.01), reaching a nadir of 14% of the control animals’ value by the end of the trial. Indices of sulphur amino acid metabolism, including activities of hepatic cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CGL) and serine hydroxymethyltransferase, as well as hepatic-free cysteine concentrations were markedly decreased after 6 weeks of B6 deficiency (P < 0.05). Total hepatic mRNA expressions for CBS and CGL were not affected. Concurrently, hepatic-free homocysteine concentrations increased by more than eight-fold (P < 0.01) at the end of the trial. An examination of plasma total homocysteine and cysteine concentrations revealed significant (P < 0.05) differences between treatments, with evidence of an abrupt shift in concentrations at 3 weeks post-initiation of dietary treatments (>25-fold increase in homocysteine; halving of cysteine values). At the end of Experiment 1, vitamin B6 deficiency significantly increased plasma methionine and serine levels, but decreased plasma glycine concentrations (P < 0.05). In Experiment 2, 20 pigs of 14 days old (initial BW = 5.0 kg) were subjected to a 4-week vitamin B6 depletion protocol, based on results obtained in Experiment 1. After the depletion period and assessment of baseline status (four pigs), remaining pigs were allocated to one of four dietary vitamin B6 repletion treatments: 0.75, 1.5, 2.25 and 3 mg/kg diet as pyridoxine·HCl (n = 4 per level) for 14 days. Significant dose-dependent increases in plasma PLP and cysteine, and decreases in homocysteine were observed, and these were sensitive to the duration of repletion. In conclusion, data from the current studies support the use of both plasma PLP and homocysteine as sensitive indices of vitamin B6 status in the pig. Additionally, the observed patterns of responses in vitamin B6-sensitive metabolites are supportive of an inclusion level of 2.25 mg/kg diet, as pyridoxine·HCl, in diets for young pigs.

The degradation, sorption and transport of atrazine, hexazinone and procymidone in saturated coastal sand aquifer media were investigated in batch and column experiments. The pesticides were incubated with sterilised and non-sterilised groundwater or a mixture of groundwater and the aquifer material in the dark at 15 degrees C for 120 days. The estimated half-lives of the pesticides (and their ranges) in the mixture of groundwater and aquifer sand were 36 (31-40), 54 (40-77) and 84 (46-260) days for atrazine, procymidone and hexazinone, respectively. Compared with the relevant results for the groundwater-sand mixture phase, the estimated half-life of pesticides in the groundwater phase alone was shorter for procymidone (21 days) but longer for hexazinone (134 days); atrazine was not degraded in the groundwater phase. Chemical degradation appeared to have played the predominant role in the degradation of hexazinone and procymidone in the aquifer system, while both chemical and biological processes seemed to be important for the degradation of atrazine. Batch isothermal experiments were carried out at pH 4.6-4.7 to obtain sorption coefficients under equilibrium conditions. The isothermal data of the pesticides fitted well with the non-linear Freundlich function with an exponent of sorption coefficient that was greater than one. Contrary to reports in the literature, sorption of atrazine was the greatest, and procymidone was slightly more sorbed than hexazinone. A column experiment was conducted at a typical field-flow velocity of 0.5 m day(-1) over 60 days to study pesticide attenuation and transport in flow dynamic conditions. Retardation factors, R, derived from a two-site sorption/desorption model were 8.22, 1.76 and 1.63 for atrazine, procymidone and hexazinone, respectively. Atrazine displayed the lowest mobility and the mobility of procymidone was only slightly less than that of hexazinone, which is consistent with observations in the batch experiment. A possible explanation for these observations is that ionic atrazine is bound to oppositely charged ionic oxides, and ionic oxides have less effect on the sorption of the non-ionic procymidone. The significant tailing in the pesticide breakthrough curves (BTCs) in comparison with the bromide BTC, together with model-simulated results, suggests that the transport of the pesticides was under chemical non-equilibrium conditions with R values that were less than their equivalent values predicted using the batch equilibrium isothermal data. As a result of non-linear kinetic sorption, retardation factors of the pesticides in groundwater systems would not be constant and will decrease with decreasing pesticide concentrations and increasing flow velocities. Hence, the use of equilibrium isotherm data will probably over-predict the sorption of pesticides in groundwater systems. Rhodamine WT, a commonly used groundwater tracer, was significantly retarded (R = 5.48) and its BTC was much more spread out than the bromide BTC. Therefore, it would not be a good tracer for the indication of groundwater flow velocity and dispersion for the coastal sand aquifer system. In contrast to some aquifer media, the dye tracer was unsuitable as a marker of the appearance of atrazine in a coastal sand aquifer system.