Nitrous oxide (N2O) is a potent greenhouse gas predominantly emitted from grazed pasture through denitrification, driven by soil oxygen (O-2) availability and urine-derived nitrogen (N). Pasture soils are vulnerable to compaction from animal treading, restricting gas diffusion and enhancing N2O emissions. Although subsoiling alleviates compaction, its impact on soil O-2 status and N2O emissions, particularly under high urine N load, remain poorly understood and rarely investigated. This in-situ field study (March-August 2023) evaluated the effect of subsoiling on soil moisture, O-2 content, relative gas diffusivity (D-p/D-o), functional gene abundance, N2O emissions, and pasture production. Treatments included non-subsoiling or subsoiling, each with or without synthetic ruminant urine (713 kg N ha(-1)). Subsoiling improved macroporosity, enhanced O-2 availability, increased D-p/D-o at 5, 10 and 20 cm depth (P < 0.001), and reduced moisture at 10 cm depth (P < 0.001). Subsoiling significantly reduced N2O emissions by 52% and 81% of non-subsoiled plots for non-urine and urine treatments, respectively (P < 0.05). D-p/D-o was strongly correlated with N2O fluxes during the first 15 days following urine application (R-2 = 0.59-0.87), suggesting its utility as a predictive indicator under high substrate availability. Molecular analysis showed reduced nirK gene abundance under subsoiling, with limited response for other denitrification genes. Subsoiling had no significant effect on pasture yield or N uptake. Overall, subsoiling mitigates N2O emissions by improving soil aeration and D-p/D-o while maintaining productivity, offering a promising strategy for sustainable N management in grazed pasture soils.

Pasture soils are major sources of nitrous oxide (N2O), a potent greenhouse gas mainly produced through microbial denitrification. However, interactions between soil aeration status and microbial responses involved in regulating N2O emissions remain poorly understood. We investigated denitrifier gene expression together with N2O and dinitrogen (N2) emissions using repacked cores of three pasture soils with contrasting bulk densities incubated across ten matric potentials (−1 to −10 kPa). Peak N2O fluxes occurred at matric potentials of −1 to −2 kPa and were strongly related to relative gas diffusivity (Dp/Do) and water-filled pore space (WFPS). In contrast, the expression of nirS, norB, and nosZ was more closely associated with matric potential and volumetric water content than with Dp/Do and WFPS. However, denitrifier gene transcription alone did not explain the observed gaseous N emissions, indicating that microbial transcriptional responses and measured N fluxes were decoupled under changing soil aeration conditions. These findings suggest bulk soil aeration indices (e.g. Dp/Do or WFPS) do not fully represent the local conditions regulating microbial response, whereas measured gaseous N emissions are additionally constrained by soil physical processes governing gas transport. Overall, these results highlight the importance of integrating microbial responses with soil physical processes to improve our mechanistic understanding of N2O emissions from grazed pasture soils.

The safe application of farm dairy effluent (FDE) to land has proven to be a challenge for dairy farmers and regulatory authorities throughout New Zealand. Poorly performing FDE systems can have deleterious effects on water quality because contaminants such as phosphorus, nitrogen and faecal microbes enter receiving waters with minimal attenuation by soil. We present a decision framework that supports good management of effluent, particularly during its application to land. The framework considers how FDE management can be tailored to account for soil and landscape features of a location that pose varying levels of contaminant transport risk. High risk soils and landscapes are vulnerable to direct losses via preferential and/or overland flow pathways and include sloping land (e.g. slopes greater than 7 degrees) and soils with mole drainage, coarse structure, poor natural drainage or low surface infiltration rates. Soil types that are well‐drained with fine structure typically exhibit matrix flow characteristics and represent a relatively low risk of direct contaminant loss following FDE application. Our framework provides guidance on FDE application timings, rates and depths to different landform and soil types so that direct losses of contaminants to water are minimal and the opportunity for plant uptake of nutrients is enabled. Some potential limitations for using the framework include the potentially severe effects of animal treading damage during wet conditions that can reduce soil hydrological function and consequently increase the risk of overland flow of applied FDE. The spatial distribution of such treading damage should be considered in the framework’s application. Another limitation is our limited understanding of the effects of soil hydrophobicity on FDE infiltration and application of the framework.

Plant-available water and adequate soil aeration are two fundamental requirements for successful plant growth. These prerequisites have generally been assessed independently in relation to plant growth, with limited focus on their complementary and competing behavior in a soil-water matrix. In this study we introduce a corequisite index adopted from a complex number representation by linking soil-water (the real component) and soil-air (the imaginary component) as the orthogonal counterparts in an Argand diagram. The new corequisite index constitutes a soil-water component defined based on field capacity and permanent wilting point, and a soil-air component defined based on critical soil-gas diffusivity. To calibrate model parameters, the soil-water characteristics were measured in vadose soil profiles (0- to 60-cm depth) from 48 replicate sites. Results revealed that the corequisite index, with its magnitude (0.5-1) and corequisite angle (0-30 degrees) in the given range, provided the best combined soil water and aeration status for the selected soil. The majority of the selected soils were affected by insufficient aeration (gas diffusivity < 0.01) when at field capacity (drained to -10 kPa), requiring the soils to drain further (-50 to -100 kPa) to satisfy the corequisites. The derived soil aeration parameters showed promising relationships with measurable soil physical properties. We further recommend adopting a 15% volumetric soil air content as a general threshold for minimum soil aeration in the absence of measured soil-gas diffusivity data.

Subsoiling is a common practice for improving soil structure and has recently been recognised for its potential to reduce nitrous oxide (N2O) emissions. However, its impact on nitrate (NO3--N) leaching must also be considered if it is to be used as a mitigation strategy. This study investigated N2O emissions, NO3--N leaching and grass yield in an Italian ryegrass pasture soil with a compacted subsoil layer using a lysimeter study. Additionally, a separate field study examined mineral nitrogen (N) concentration and the abundance of nitrifying and denitrifying genes. Both studies have four treatments, with non-subsoiling (NS), subsoiling (SS), non-subsoiling and urine (NSU), subsoiling and urine (SSU), and the urine treatments were applied at a rate of 700 kg N ha(-1). The results showed that 6 months after subsoiling, soil macroporosity in all treatments remained elevated at a depth of 0-20 cm (p < 0.01) compared with all non-subsoiling treatments. This created more aerobic conditions, which suppressed N2O emissions from denitrification by 20.3% (p < 0.05) during 190 days after urine application (NSU vs. SSU). Additionally, subsoiling had no significant effect on NO3--N leaching in the presence of winter-active Italian ryegrass. Molecular analysis of N-cycling microbial communities revealed that subsoiling had no effect on the abundance of amoA gene-carrying microorganisms involved in nitrification but reduced the abundance of nirS denitrifier genes, indicating that subsoiling primarily affected the denitrification process. These findings suggest that subsoiling can effectively reduce N2O emissions without increasing NO3--N leaching when combined with winter-active ryegrass.

Plant-available soil-water and adequate soil aeration within the root zone are essential corequisites for successful plant growth. Characterization of these two requirements for plant growth is generally done by independent measurements of water and air phase properties and functions in soil, with limited emphasis on their combined effect. This study investigated soil-water characteristic (SWC) measurements in vadose soil profiles (up to 117-cm depth) in six pasture soils to examine the combined behavior of soil-water and diffusion-controlled aeration within the root zone. The soil moisture measurements were made over matric potentials ranging from -1 to -1500 kPa using tension table and pressure plate apparatus. The van Genuchten model was used to parameterize the measured SWC curve, while the Millington-Quick model was used to derive soil-gas diffusivity from measured soil physical properties. Based on two simple indices, derived to represent plant-available soil-water and soil aeration status at a given moisture content, we propose an assessment matrix, which illustrates how a soil satisfies the corequisites for successful plant growth, as it drains to different matric potentials upon irrigation. Results show a pronounced effect of soil texture and, to a lesser extent, soil structure on satisfying these corequisites. With the aid of the assessment matrix, we observed that loam, sandy loam textures exhibited a good overall performance, while sand, clay loam, and clay soils struggled to meet these corequisites during drainage. Soil-water characteristic in vadose soil profiles (up to 1.17-m depth) in six pasture soils was investigated. Both soil-water and diffusion-controlled aeration were considered as corequisites. A simple assessment matrix is introduced to assess the status of soil-water and soil-air as the soil drains.

IntroductionThrough the combined use of two nitrification inhibitors, Dicyandiamide (DCD) and chlorate with nitrogen amendment, this study aimed to investigate the contribution of comammox Nitrospira clade B, ammonia oxidizing bacteria (AOB) and archaea (AOA) to nitrification in a high fertility grassland soil, in a 90-day incubation study.MethodsThe soil was treated with nitrogen (N) at three levels: 0 mg-N kg-1 soil, 50 mg-N kg-1 soil, and 700 mg-N kg-1 soil, with or without the two nitrification inhibitors. The abundance of comammox Nitrospira, AOA, AOB, and nitrite oxidising bacteria (NOB) was measured using qPCR. The comammox Nitrospira community structure was assessed using Illumina sequencing.Results and DiscussionThe results showed that the application of chlorate inhibited the oxidation of both NH4+ and NO2- in all three nitrogen treatments. The application of chlorate significantly reduced the abundance of comammox Nitrospira amoA and nxrB genes across the 90-day experimental period. Chlorate also had a significant effect on the beta diversity (Bray-Curtis dissimilarity) of the comammox Nitrospira clade B community. Whilst AOB grew in response to the N substrate additions and were inhibited by both inhibitors, AOA showed litle or no response to either the N substrate or inhibitor treatments. In contrast, comammox Nitrospira clade B were inhibited by the high ammonium concentrations released from the urine substrates. These results demonstrate the differential and niche responses of the three ammonia oxidising communities to N substrate additions and nitrification inhibitor treatments. Further research is needed to investigate the specificity of the two inhibitors on the different ammonia oxidising communities.

Mitigation practices for nitrogen leaching losses from livestock agriculture are needed to protect freshwater quality and increase the efficiency of agricultural production. Within New Zealand, the most common pasture type is a two-species mix of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Ecological theory suggests that increasing species and functional diversity improves ecosystem function, including nitrogen (N) retention. Use of more diverse pasture types, including a mix of pasture grasses, legumes and other forbs, particularly plantain (Plantago lanceolata), with functional traits, including winter activity, deep-rooting, N fixation, and biological inhibition of nitrification in the soil, is a potential mitigation practice that requires further verification with long-term field measurements. Here we utilize a network of large lysimeters to make field-based measurements of N leaching from 5–8 species diverse pasture, including plantain, under a range of soil, climate and management conditions, for comparison with losses from traditional ryegrass-clover pasture. Over 3 years of measurements, leaching from fully established diverse pasture was 2–80 kg N ha−1 y−1. No differences were observed in dry matter production or N leaching of diverse pasture compared to ryegrass-clover lysimeters. Large losses, up to 120 kg N ha−1, were observed during periods when pasture was not fully established, including cultivation and sowing of new pasture, depending on season. Timing of management activities could be optimized to minimize these losses. These data provide critical assessment of diverse pasture as a mitigation approach for reducing N losses. Further work on diverse pastures should include higher diversity mixes as well as consideration of animal mediated effects of diverse pasture diets on N inputs.

The analysis and characterization of soil minerals rely on the availability and capability of experts, therefore greatly influencing the efficiency and accuracy of mineral analysis. Mid-infrared (MIR) spectroscopy offers a low-cost, high-throughput alternative, as it instantly records the spectral signatures of soil minerals through the absorption of infrared radiation. This study investigates the potential of MIR spectroscopy to identify and quantify the most common minerals in the clay (<2 jim) fraction of New Zealand soils. We analysed 3,097 samples and developed partial least squares regression (PLSR) models to quantify the concentration for each of the 11 mineral types in the collated database. In addition, we developed a partial least squares discriminant analysis (PLS-DA) model to identify the dominant mineral of the analysed soil samples. Most models used for quantifying mineral compositions indicate high accuracy. The highest values of R2 (0.81), Lin's concordance correlation coefficient (0.90), RPIQ (4), and the lowest bias (-0.26 %) were obtained for the quantification of mica on the test set. For the identification of the dominant mineral, the overall accuracy was 75 % on the test set. In addition, we could correctly classify 94 % of the samples dominated by mica, 86 % of the samples by volcanic glass/amorphous silica, 82 % of the samples by allophane/imogolite, and 77 % of samples dominated by kaolin-smectite. Thus, MIR spectroscopy offers a valuable solution for mineral quantification and identification, especially in areas where quantified mineral databases are not readily available and human expertise is lacking.

Global food production relying on irrigated agriculture accounts for >70% of the global freshwater withdrawal. A thorough understanding of soil–water characteristics (SWCs) and critical soil–water values in the soil and subsoil is important for effective management of irrigated water. A critical soil–water “window” for plants is generally taken as the plant‐available water window without considering diffusion‐dominated soil aeration as a co‐requisite. This study examined SWC curves in vadose soil profiles (up to 1.5‐m depth) in eight pasture soils. The soil moisture measurements were made over matric potentials ranging from −1 to −1500 kPa using tension table and pressure plate apparatus. The van Genuchten model was used to parameterize the measured SWC curve, while the Millington‐Quirk model was used to derive soil–gas diffusivity from measured soil physical properties. We defined critical soil–water windows considering the threshold values for both plant‐available water and soil–gas diffusivity to ensure water and aeration corequisites for plant growth. The results clearly distinguished depth‐dependent regimes of gravitational, plant‐available, and unavailable water in selected profiles and their responses to soil structural changes across the depth. In some of the observed soil profiles, only 30%–60% of the plant‐available water window was able to be utilized by plants because the remainder existed under soil conditions where soil aeration was inadequate for plant growth, emphasizing the importance of considering both the plant's water and aeration requirements during irrigation scheduling. Further, the infiltration profiles in two selected soils under simulated irrigation highlighted the importance of a priori knowledge of the soil structure in deeper soil layers for scheduling irrigation.

Diffuse reflectance spectroscopy, both in the visible and near-infrared (vis-NIR: 350-2500 nm) and the mid infrared (MIR: 2500-25,000 nm) ranges, has been increasingly employed as an alternative to obtaining a multitude of soil information and data non-destructively, rapidly, and cost-effectively. Soil spectral libraries (SSLs) have been developed across the world to calibrate prediction models for rapid and non-destructive assessment of soils at local, regional, national and global scales. Several continental or national libraries exist, for example, vis-NIR SSL in Europe, Australia, Czech Republic, Denmark, France, China and Brazil, and MIR SSL in the U.S., Switzerland and Brazil. In this study, we document the development of a vis-NIR and MIR SSL of New Zealand based on legacy and modern samples that have been sieved to 2 mm and air-dried, and explore the application of such libraries for predicting a wide range of soil properties, including soil carbon (total carbon or organic carbon), total nitrogen, pH, soil texture (sand, silt and clay), phosphate retention and available water capacity (field capacity and permanent wilting point). The vis-NIR and MIR spectral features were compared between New Zealand Soil Classification (NZSC) soil orders and the performances of both vis-NIR and MIR SSLs were compared with other national SSLs. Results of the study indicate that both vis-NIR and MIR SSL demonstrated reliable modelling performance using the PLSR model. However, MIR outperforms vis-NIR for all soil attributes. Furthermore, the study found that both vis-NIR and MIR have the potential to distinguish different soil orders within the NZSC.

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.

Mole channel drainage is a cost-effective and efficient way to drain slowly permeable agricultural soils. Artificial drainage has the potential to significantly influence catchment hydrology and contaminant source areas, but there is little information available about the extent, connectivity, layout, density or longevity of mole channel networks, which are commonly estimated to deteriorate within 5-20 years. Such information is important for understanding landscape hydrodynamics but, currently, there are no established techniques for calibrating estimates of mole network characteristics at the paddock or larger scale. This study characterised a 30-plus-yearold mole channel network in a small agricultural basin in Southland, New Zealand, and tested the utility of ground-penetrating radar (GPR) for identifying, mapping, and characterising mole channel drainage. A dual frequency GPR antenna (700 and 250 MHz), connected to a high-precision, real-time kinematic global positioning system, was tested and proved effective at locating mole channels and a tile drain with high lateral precision and accuracy. Surveying of six plots demonstrated that the mole network was complex in design and had a high density (1.6 m m(-2)) of interconnected, multidirectional mole channels. Significantly, the mole channels were predominantly in good condition and spatially well connected. Visual observations found no evidence that the blade slot and secondary soil fractures, formed by the mole plough during installation, persisted after 30 years. However, root growth and worm burrowing into the mole channels suggest they are hydraulically connected to the surrounding soil through natural macropores. Our results provide the first attempt at mapping and characterising mature, multi-generational mole channel networks in slowly permeable loess soils. The results have significance for understanding catchment-scale hydrodynamics in mole-drained landscapes, especially considering that the life span of these artificial drainage networks is shown to be considerably longer than previous estimates for loess-derived, silt loam soils.

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.

Efficient simulation of water-flow processes in the vadose zone is crucial to increase agricultural productivity within environmental limits. This requires deriving detailed soil hydraulic parameters of the soil profile that is highly challenging, particularly for heterogeneous soils. We therefore developed an alternative indirect methodology to calibrate the hydraulic parameters from soil water content time series measured at multiple depths by using the new physically based hydrological model HyPix. We propose a novel, efficient, multistep optimization algorithm for layered soils that derives an optimal set of hydraulic parameters for a desired number of soil layers. For each selected soil layer, HyPix derives five physical, bimodal, Kosugi hydraulic parameters that describe the soil water retention and hydraulic conductivity by using a novel algorithm that reduces the degree of sensitivity and freedom of the parameters. The optimization algorithm upscales the soil hydraulic parameters by gradually incorporating the soil heterogeneity. This method overcomes the problems associated with optimization of the hydraulic parameters of each layer individually, which leads to poor results because it does not represent the cohesive soil water dynamics across the unsaturated zone. We tested the method using soil water content measurements at different depths at five heterogeneous experimental sites in New Zealand. We show how the accuracy of the simulated water balance components increases with the number of soil layers. The multistep optimization upscales a detailed, layered profile of soil hydraulic parameters into a model with fewer layers. The methodology developed provides an estimate of the uncertainty of using a reduced number of soil layers. We also show that a pedological description can provide an indication of the minimum soil layers of vertical discretization required to accurately compute the soil water balance components.

Hydrological modeling for landscape and catchment scale applications requires upscaling of soil hydraulic parameters which are generally only available at point scale. We present a case study where hourly root zone soil water content and drainage observations from nine flat, pastoral sites (Waikato and Canterbury regions in New Zealand) were used to develop an upscaling approach to parameterize the soil water balance module of the TopNet catchment model, based on scaling multi-layer soil profile information from the national soil data base, S-map, to the single-layer soil profile used in TopNet. Using a Bayesian calibration approach, the hydraulic behavioral parameters of TopNet's soil water balance module were identified. Of the eleven calibration parameters considered three were found to be insensitive to data (stress point, unsaturated hydraulic conductivity and infiltration rate); three were correlated and could be determined from specific soil water content observations (wilting point, field capacity and drainable water); and five were correlated and could be determined from combined specific soil water content and drainage observations (drainage rate, saturated hydraulic conductivity profile, effective soil depth, soil water holding capacity and wetting front suction). Based on the eight correlated parameters, upscaling functions were then developed to derive suitable model parameters from S-map-hydro for each site. The validity of the upscaling functions was verified at each site. The approach used in this research can be used to parameterize the TopNet model at other similar locations, and also provides a transferable framework to parameterize other catchment-scale hydrology models where point-scale soil hydraulic data available.

This study tested the effect of oat catch crops on mineral nitrogen (N) leaching losses from cool season fodder beet grazing. Undisturbed soil monolith lysimeters were collected from two grassland sites with soils featuring contrasting texture and water holding capacity (WHC) characteristics. After simulated fodder beet grazing in late autumn or winter, synthetic dairy cow urine was applied. Nitrogen leaching losses were measured from lysimeters sown with oats after urine application and compared with those under fallow conditions until spring. Oat dry matter (DM) production and N uptake measurements were obtained. Sowing oats reduced total mineral N leaching losses by up to 59%. Reductions in mineral N leaching were inconsistently affected by soil type but were strongly influenced by urine application timing. Nitrogen uptake by oats (52–143 kg N ha−1) drove reductions in N leaching losses compared with fallow soil. Oats yielded 4–17 t DM ha−1, and both yield and N uptake were strongly affected by urine application timing (winter > autumn) and soil type (high WHC > low WHC). Sowing oats after fodder beet grazing instead of leaving the ground fallow can reduce the environmental impacts of these systems, while simultaneously increasing annual feed supply. Catch crop gains can be maximised by avoiding or delaying autumn grazing of fodder beet, particularly on low WHC soils.

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.

Soil hydraulic properties (SHPs), including available water content and near-saturated hydraulic conductivity (K-ns), affect hydrological and biochemical processes. The SHPs information is crucial to agricultural water management. The objective of this study using paired sites was to investigate the effects of land use on SHPs in two contrasting soil orders. Soil water retention curves and Kns at three soil depths (0-10, 10-20 and 20-30 cm) were measured under two land uses (pasture, consisting of a rye grass [Lolium perenne L.] and white clover [Trifolium repens L.] mix, and maize [Zea mays L.] cropping > 10 years) in Waikato, New Zealand. For each land use, two soil orders with contrasting soil structural vulnerability were selected: less vulnerable Allophanic soil and more vulnerable Gley soil. Compared with pasture, maize cropping reduced macroporosity, readily available water capacity and K-ns of 0-30 cm, and the effect was greater in the deep layer (20-30 cm). This indicated that maize cropping practices result in greater structural degradation to soils compared with pasture, which include the potential for greater subsoil compaction. There was no land use by soil order interaction effect on SHPs, suggesting that the relative SHP degradation under maize cropping compared with pasture grazing was not associated with soil structural vulnerability. Our study emphasised that long-term continuous cropping with maize on the more vulnerable soil (i.e. Gley soil) resulted in the poorest soil physical health.

Intensification of agricultural management practices, including irrigation and addition of nitrogen (N) fertilizers, can lead to enhanced N leaching and loss of soil fertility. In New Zealand, expansion of the dairy industry has rapidly increased irrigated land area, particularly on shallow, stony soils of the Canterbury region that are prone to leaching, leading to degradation of surface- and ground-water quality and losses of soil N and carbon (C). In this study, we measure components of N balance for two adjacent fields of lucerne (Medicago sativa L., alfalfa) harvested for cut-and-carry feed and grazed in situ. One field was non-irrigated and one irrigated with both water and dairy effluent. Inputs from N fixation associated with the legume crop were quantified using a natural abundance isotopic approach. Drainage from the root zone and leaching were measured with 6 large lysimeters in each field. Leaching losses from non-irrigated lucerne were 7-30 kg N ha(-1) y(-1) with the largest losses occurring in a year with primarily grazing management. Losses from irrigated lucerne were 39-102 kg N ha(-1) y(-1) , with the largest losses resulting from summer drainage events exacerbated by irrigation. Fixation of N was the largest input to both systems, contributing 192-257 kg N ha(-1) y(-1) for non-irrigated lucerne. Under irrigation, biomass production increased, but N uptake from effluent and soil stocks contributed to biomass N to a greater extent and fixation was 262-286 kg N ha(-1) y(-1) . Management influenced N balance through inputs from animal excreta and effluent additions and exports through harvest and grazing removals. Management practices which reduce N losses from the soil are needed to minimize environmental impacts and protect soil fertility.