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A transfer function (TF) was developed to assist with the estimation of nitrogen (N) leaching from urine-affected areas in grazed pastures. The proposed TF uses a simple function to describe the likely breakthrough curve for urine-N deposited in different months and in various climates and soils in New Zealand. The TF was designed to be integrated into the OVERSEER® Nutrient budgets model to increase the sensitivity of N leaching to the month of urine deposition, but could also be used in any other model that estimates the water balance and plant N uptake on a monthly basis. The inputs required for the TF are typically readily accessible (e.g. soil texture data) and thus do not add any significant complications when added to OVERSEER. The TF retains OVERSEER as the arbitrator of the main items of N-balance in the farm system, but adds functionality by giving a better temporal discrimination of leaching from the farm system. The procedure for parameterising the TF from a comprehensive set of APSIM (Agricultural Production Systems Simulator) simulations is described. Validation of the leaching estimated by the TF was achieved through a combination of testing against an independent set of APSIM simulations and testing against experimental data. The testing of the TF showed very promising performance. The TF explained 75% of the variability of N leaching simulated by an independent APSIM dataset and agreed well with the experimental data. Additional keywords: APSIM, grazing system, nitrogen leaching, nutrient budget, pastoral farm, urine deposition., Introduction Urine deposited by grazing animals is the major cause of nitrogen (N) leaching from pastoral systems (Ryden et al. 1984; Haynes and Williams 1993; Pakrou and Dillon 2000). The [...]

We have examined the influence of the ionic composition of the soil solution on the movement of sulfate and calcium in 2 New Zealand soils with differing allophane content. For this study, we have carried out a series of miscible displacement experiments using repacked and intact soil columns, in which sulfate was applied in the presence of either calcium or potassium as the accompanying cation. Our results showed that sulfate leaching was significantly retarded in the soil with higher allophane content when applied with calcium. On the other hand, no effects were observed for all studied soils when potassium was used as the accompanying cation. In addition, in soils with high allophane content, calcium also had its retention increased when sulfate was present. The increase in sulfate adsorption was accompanied by corresponding increase in calcium adsorption. These findings evidenced the presence of co-adsorption, or ion-pair adsorption (IPA), in allophane-containing soils. The extent of this adsorption is dependent on the soil pH, the accompanying cation, and the allophane content of the soil. Additional keywords: breakthrough curve, calcium, ion-pair adsorption, miscible-displacement experiment, potassium., Introduction Sulfur deficiencies in soils have been increasingly reported in many countries worldwide including New Zealand (Nguyen and Goh 1994; Schnug et al. 1995; Scherer 2001; Edmeades et al. 2005), [...]

Abstract We report the results from a field experiment in which we examined the spatial and temporal patterns of water uptake by a mature apple tree (Malus domestica Borkh., 'Splendour') [...]

In Part I, we proposed a model for EDTA-facilitated transport of copper, and we tested the robustness of this scheme by reference to experiments with various initial and boundary conditions on a repacked soil. Now we examine a quite different repacked soil, and consider intact cores of the same soil as in Part I. Continuous leaching of an intact core of a contaminated orchard soil of volcanic origin under unsaturated conditions with excess 0.01 M EDTA (510 mm) reduced the copper concentration from 240 down to 80 µg/g in the top 25 mm. When a 480 µmol pulse of 0.001 M EDTA was applied to similar intact cores, 126 µmol of copper came out with immediate leaching, but only 18% of that was leached out from a core that was left for 1 month before leaching. The month's delay caused an increase in the amount of iron leached from 116 to 286 µmol. An experiment in which daily pulses CuEDT[A.sup.2-] were applied to a non-contaminated soil for 3 months indicated that these changes were due to CuEDT[A.sup.2-] slowly changing to Fe(III)EDT[A.sup.-], with the re-adsorption of the [Cu.sup.2+] released. Application of our model from Part I indicated that different rate constants are required for the chemical reactions for different soils, and also for the same volcanic soil when the pH is lower. But by changing just the dispersivity from 3 mm to 23 mm, the model with the same chemical parameters was able to simulate both the repacked columns and the intact core experiments using the volcanic soil. Additional keywords: iron, convection--dispersion equation, heavy metals, repacked soil, intact soil., Introduction In Thayalakumaran et al. (2003), which we will subsequently refer to as Part I, we described the transport, under near-saturated conditions, of copper in repacked columns of a contaminated [...]

The EDTA-enhanced remediation of copper contaminated sandy-loam soil of volcanic origin was investigated. The soil, from an orchard, was contaminated with about 250 mg/kg of copper due to the extensive use of copper sprays. Copper-contaminated soil was packed into 100-mm-long columns, and solutions of [Na.sub.2][H.sub.2]EDTA with Ca[Cl.sub.2], raised to a pH of 6.2, were applied at a flow rate of 24 mm/h. Application of an excess of 0.01 M EDTA leached about half the acid-extractable copper from the soil; most of it coming out in the first 3 liquid-filled pore volumes (PV). Also a 0.5 PV pulse of 0.001 M EDTA was applied to similar soil columns and then either leached immediately with 0.005 M Ca[Cl.sub.2], or left for periods of up to I month before leaching. With immediate leaching, 70% of the EDTA applied was complexed with copper in the leachate, but after a month's delay only 24% was complexed with copper in the leachate, the rest being complexed with iron. There was no evidence of EDTA retardation or adsorption. The experimental results were simulated using the convection--dispersion equation, incorporating a source/sink term. This described the competing time-dependent reactions of copper and iron with EDTA, and the reversion of CuEDT[A.sup.2-] to adsorbed [Cu.sup.2+] and Fe(III)EDT[A.sup.-] in solution. Reasonable simulations were achieved, mostly within errors of observation. Additional keywords: iron, convection-dispersion equation, heavy metals., Introduction There are a number of reasons why the interactions between copper and EDTA in soil are of interest. Copper compounds and EDTA are widely used and are persistent chemicals [...]

When time domain reflectometry (TDR) is used to measure soil water content ([theta]) and salinity, the probes can be installed either horizontally or vertically. We tested the common convention that [theta] values averaged from horizontal probes will be equal to a vertical direct measurement. In a laboratory experiment, a sandy loam soil, packed uniformly (0.02-m layers to 0.18-m depth) into a box, was gradually wetted to saturation by Ca[Cl.sub.2] solutions of 0, 0.5, 1.1, 2.1, 3.1, 4.5, 5.9, and 8.4 dS [m.sup.-1]. Horizontal and vertical TDR probes for measuring [theta] and electrical conductivity of the bulk soil ([[sigma].sub.a]) were installed during soil packing. A comparison between [theta] values averaged from three horizontal probes and from two vertical ones showed deviations of 0.02 (L [L.sup.-1]). A simple water redistribution model was used to attribute this deviation to the process of averaging the horizontal results. The best practical attainable reproducibility, under our experimental conditions, were close to the theoretical limit 0.005 (L [L.sup.-1]) but the average experimental reproducibility of [theta] was 0.01 to 0.02 (L [L.sup.-1]). Width of the soil layer affecting the moisture measurement was reconfirmed to be close to 30 mm. The resistors-in-series model was found to be a good approximation to describe the soil profile [[sigma].sub.a] from separately measured horizontal [[sigma].sub.a]. Final values of the electrical conductivity of the soil solution ([[sigma].sub.w]) after sufficient leaching were in good agreement with [[sigma].sub.w] values calculated by an empirical protocol that uses [[sigma].sub.a], [theta], and a soil texture property.

Time domain reflectometry (TDR) was used to monitor the transport of conservative tracers in the field under transient water flow in a controlled experiment under a kiwifruit vine. A mixed pulse of chloride and bromide was applied to the soil surface of a 16 [m.sup.2] plot that had been isolated from the surrounding orchard soil. The movement of this solute pulse was monitored by TDR. A total of 63 TDR probes were installed into the plot for daily measurements of both the volumetric water content (θ) and the bulk soil electrical conductivity ([σ.sub.a]). These TDR-measured [σ.sub.a] were converted into pore water electrical conductivities ([σ.sub.w]) and solute concentrations using various θ--[σ.sub.a]-[σ.sub.w] relationships that were established in the laboratory on repacked soil. The depth-wise field TDR measurements were compared with destructive measurement of the solute concentrations at the end of the experiment. These results were also compared with predictions using a deterministic model of water and solute transport based on Richards' equation, and the convection--dispersion equation. TDR was found to give a good indication of the shape of the solute profile with depth, but the concentration of solute was under- or over-estimated by up to 50%, depending on the θ-[σ.sub.a]-[σ.sub.w] relationships used. Thus TDR can be used to monitor in situ transport of contaminants. However, only rough estimates of the electrical conductivity of the soil solution can so far be obtained by TDR. Additional keywords: soil water, electrical conductivity, solute transport, modelling., Introduction The dynamics of solute transport in the unsaturated soil affect several aspects of soil management, such as fertiliser applications, wastewater disposal, as well as remediation and soil decontamination. A [...]

To measure soil water content (theta) by time domain reflectometry (TDR), one must know the relationship between the soil's dielectric constant (K(sub a)) and theta, Our objective was to determine K(sub a)-theta calibrations for sandy volcanic soils on the North Island of New Zealand. We collected samples from 24 horizons and 6 soil profiles. The soils were sandy loam and loamy sand textured, with bulk densities between 0.55 and 1.34 Mg m(super -3). Samples were air-dried and packed to their field bulk density in plastic boxes. Time domain reflectometry probes (100 mm long) were inserted, and TDR waveforms were recorded and analyzed. Water contents were increased in approximate steps of 0.05 m(super 3) m(super -3) volume to the liquid limit, which varied between 0.33 and 0.57 m(super 3) m(super -3). Samples were then submerged to obtain water contents as great as 0.646 m(super 3) m(super -3). Measured water contents were greater than those predicted by the Topp equation, but the differences varied according to soil texture. Pooled data from 17 of the samples provided a third-order polynomial calibration with an R(super 2) of 0.977 and root mean square error (RMSE) of 0.026 m(super 3) m(super -3). A third-order mixing model and a linear K(sub a)-theta expression gave greater mean errors. Although the calibration applied to a range of sandy volcanic soils, there were also two small groups of samples that showed distinct calibrations. These were coarser tephras, with at least 75% of particles >0.125 mm diam. By mass, and with bulk densities >l.0 Mg m(super -3).

Productive pasture systems require a regular supply of mineral nitrogen (N) to replace the N removed through the export of animal products and other loss pathways such as leaching and emissions. High spatial and temporal variability of both N supply by the soil and demand by the plant means that synchronizing these is challenging, and early indicators are lacking. Optimum fertilization rates for an irrigated ryegrass pasture in Canterbury, New Zealand, were determined in a simulation study with twenty fertilization rates using the Agricultural Production Systems Simulator with a refined version of APSIM's pasture module (AgPasture). Improvements in AgPasture included ideal N concentrations for tissues of different ages (growing, mature, senescent and dead) and allowing N remobilization to occur from all tissue stages. The critical N concentration curve (the minimum N concentration required to achieve maximum aerial biomass) was tested as an early indicator for guiding N fertilization, which maximizes plant growth while avoiding unnecessary environmental impacts. Highest pasture yields were achieved with application rates of 20, 30, 140 and 160 kg N ha−1 for winter, autumn, summer and spring. These rates also minimized simulated N losses. Pasture N contents corresponding to the standing dry matter of the pastures were similar to the critical N curve in summer and spring, but lower critical N concentrations were obtained for autumn and winter. Before the critical N reference curve can be used to guide fertilization for pastures, further experimental studies, model testing and parameterization are required. It is also possible that season-specific critical N curves need to be established for pastures. [ABSTRACT FROM AUTHOR]

Dairy farms are under pressure to increase productivity while reducing environmental impacts. Effective fertilizer management practices are critical to achieve this. In the present study the effect of timing and rate of nitrogen (N) fertilizer application on pasture production and N losses, either via direct leaching of fertilizer N or indirectly through consumption of N in pasture and subsequent excretion via dairy cow grazing, was modelled. The Agricultural Production Systems Simulator (APSIM) was first tested with experimental data from N fertilizer response experiments conducted on a well-drained soil in the Waikato region of New Zealand. The model was then used in a 20-year simulation to investigate the effect of fertilizer management on the impacts on potential N leaching losses. Year-to-year variability was assessed by incorporating 20 years of climate data into the model. Modelling indicated that N fertilization at rates of 140 and 220 kg N/ha/year, applied in four split applications and avoiding application in winter months, could increase pasture yield on average by 2·2–3·0 t dry matter (DM)/ha (25–38%). There were some significant amounts of direct leaching in some years, related to environmental conditions. The maximum loss was as high as 61 kg N/ha at an N application rate of 220 kg N/ha/year, in a year with low pasture production and high rainfall following fertilizer application. In general, however, the risk of direct N leaching from applied fertilizer was low. It seems the main effect of N fertilization is to increase the risk of indirect N leaching, due to increased N intake and excretion. The modelling indicated that the major contribution to increased indirect N leaching risk was from the extra DM grown (more urine deposited per ha). Increased N concentration in the pasture due to fertilization and the resultant extra partitioning of excretal N to urine had only a minor effect on indirect leaching losses. The exception was N fertilizer applied in late winter/early spring (July), where fertilizer N (55 kg/ha) increased pasture N concentration by c. 25%, suggesting that the N concentration in urine patch areas could increase from c. 550 to 840 kg N/ha. Further measurements are required to test the hypothesis developed from the modelling that the main effect of N fertilizer on urinary N leaching is by increasing DM production rather than increasing pasture N concentration. [ABSTRACT FROM PUBLISHER]