Val Snow

• PhD
• Agro-ecosystem modeller at AgResearch - Lincoln Research Centre

CONTEXT Over the last 26 years, researchers globally have successfully applied the soil nitrogen (N) model in the Agricultural Production Systems sIMulator (APSIM) to simulate N cycling and its effects on crop production across a range of agricultural systems and environments. As the modelling community further expands its focus to include environm...

Simple models can help reduce nitrogen (N) loss from land and protect water quality. However, the complexity of primary production systems may impair the accuracy of simple models. A tool was developed that assessed the risk of N loss as the product of N source inputs and relative transport by leaching and runoff. A dynamic process‐based model was...

A response to "An examination of the ability of plantain (Plantago lanceolata L.) to mitigate nitrogen leaching from pasture systems" https://doi. We believe some aspects of the recent article by Eady et al. (2024) recently published in the New Zealand (NZ) Journal of Agricultural Research requires comment to address several flaws and omissions in...

The full article is available free at https://doi.org/10.1016/j.mex.2024.102814 Risk index tools have the potential to assist farmers in making strategic decisions regarding their farm design to manage losses of nutrients. Such tools require a vulnerability framework, and these are often based on scores or rankings. These frameworks struggle to ta...

The determination of optimum nitrogen (N) fertilisation rates, which maximise yields and minimise N losses, remains problematic due to unknown upcoming crop requirements and near-future supply by the soil. Remote sensing can be used for determining the crop N status and to assess the spatial variability within a field or between fields. This can be...

Multi-year datasets from field experiments and simulations at five agricultural sites in the Northern Hemisphere were developed for three cropland sites in Ottawa (Canada), Grignon (France) and Delhi (India) and two grassland sites at Laqueuille 23 (France) and Easter Bush (UK). The cropland sites have rotations with wheat, triticale, maize, rapese...

Multi-model ensembles are becoming increasingly used for estimation of agricultural carbon-nitrogen fluxes, productivity and sustainability. There is mounting evidence that with some site-specific observations available for model calibration (with vegetation data as a minimum requirement), median outputs assimilated from biogeochemical models (mult...

There is a growing realisation that the complexity of model ensemble studies depends not only on the models used, but also on the experience and approach used by modellers to calibrate and validate results, which remain a source of uncertainty. Here, we applied a multi-criteria decision-making method to investigate the rationale applied by modeller...

This editorial observes 200 volumes of Agricultural Systems. Volume 1, dated January 1976, began with an article by the inaugural editor, C.R.W. Spedding (1976), that laid the foundations for this journal. We echo that first editorial with this contribution to begin Volume 201 and review some aspects of the history of the journal. To celebrate thos...

CONTEXT In May 2020, approximately four months into the COVID-19 pandemic, the journal's editorial team realized there was an opportunity to collect information from a diverse range of agricultural systems on how the pandemic was playing out and affecting the functioning of agricultural systems worldwide. OBJECTIVE The objective of the special iss...

Issues of scale pervade every aspect of socio-environmental systems (SES) modeling. They can stem from the context of both the modeling process, and the purpose of the integrated model. A webinar hosted by the National Socio-Environmental Synthesis Center (SESYNC), The Integrated Assessment Society (TIAS) and the journal Socio-Environmental Systems...

Agroecosystem models have become an important tool for impact assessment studies, and their results are often used for management and policy decisions. Soil information is a key input for these models, yet site-specific soil property data are often not available, and soil databases are increasingly being used to provide input parameters. For New Ze...

Soil surface depressions affect overland flow generation and related hydrological processes. Overland flow connectivity (C) of a field increases as more water ponds in and flows through local depressions, leading to flow across field boundaries. Quantifying the development of C during an irrigation or rainfall event is key to predicting the initiat...

In the environmental sciences, there are ongoing efforts to combine multiple models to assist the analysis of complex systems. Combining process-based models, which have encoded domain knowledge, with machine learning models, which can flexibly adapt to input data, can improve modeling capabilities. However, both types of models have input data lim...

Soil processes have a major impact on agroecosystems, controlling water and nutrient cycling, regulating plant growth and losses to the wider environment. Process-based agroecosystem simulation models generally encompass detailed descriptions of the soil, including a wide number of parameters that can be daunting to users with a limited soil scienc...

Acknowledgement that Indigenous Knowledge cannot be assimilated and readily generalised within reductionist scientific paradigms is emerging. The reluctance of Indigenous Peoples to adopt reductionist science-based interpretations is justified. Science that stops at the point where reality is universal excludes consideration of how outcomes are und...

In this work we compare the performance of a location-specific and a location-agnostic machine learning metamodel for crop nitrogen response rate prediction. We conduct a case study for grass-only pasture in several locations in New Zealand. We generate a large dataset of APSIM simulation outputs and train machine learning models based on that data...

On rough agricultural soils, initiation of overland flow is primarily related to the gradual filling of small depressions. As the volume of water ponding in local depressions increases, the connectivity of those depressions increases, and that connectivity permits flow across the field boundaries. Previous studies have aimed at predicting overland...

Climate change will have dire consequences and collaborative efforts are required to quickly develop and assess mitigation solutions. Agriculture is the primary source of the powerful greenhouse gas (GHG) nitrous oxide (N2O) and an important source of GHG emissions. Due to sampling limitations, N2O measurements have traditionally been sparse; appro...

A potential strategy for mitigating nitrous oxide (N2O) emissions from permanent grasslands is the partial substitution of fertilizer nitrogen (Nfert) with symbiotically fixed nitrogen (Nsymb) from legumes. The input of Nsymb reduces the energy costs of producing fertilizer and provides a supply of nitrogen (N) for plants that is more synchronous t...

Irrigation is a useful crop enhancement procedure up to the point where free surface water appears. However, overirrigation can lead to an accumulation of free water on the soil surface, which in turn results in overland flow and a high risk of contaminant loss. The current work addresses the problem of measuring free water on the surface of agricu...

Context Since COVID-19 (SARS-CoV-2) was first identified in the human population, it has had immediate and significant effects on peoples' health and the worldwide economy. In the absence of a vaccine, control of the virus involved limiting its spread through restrictions in the movement of people, goods and services. This has led to unprecedented...

In this synthesis, we assess present research and anticipate future development needs in modeling water quality in watersheds. We first discuss areas of potential improvement in the representation of freshwater systems pertaining to water quality, including representation of environmental interfaces, in-stream water quality and process interactions...

Soil surface roughness controls how water ponds on and flows over soil surfaces. It is a crucial parameter for erosion and runoff studies. Surface roughness has traditionally been measured using manual techniques that are simple but laborious. Newer technologies have been proposed that are less laborious but require expensive equipment and consider...

Global food production is under pressure to produce more from limited resources, with further expectations to reduce waste and pollution and improve social outcomes. Circular economy principles aim to design out waste and pollution, minimise the use of non-renewable external inputs and increase the lifespan of products and materials. Waste sources...

Measurements of nitrous oxide (N2O) emissions from agriculture are essential for understanding the complex soil–crop–climate processes, but there are practical and economic limits to the spatial and temporal extent over which measurements can be made. Therefore, N2O models have an important role to play. As models are comparatively cheap to run, th...

Irrigation is a useful crop enhancement procedure up to the point where free surface water appears. Thereafter, water can begin to flow into waterways, leaching nutrients and giving rise to environmental damage, as well as being a waste of a precious resource. The current work addresses the problem of measuring free water on the surface of agricult...

Over the past year and a half there have been substantial changes to the leadership of Agricultural Systems, both in the Editorial Team and in the Editorial Advisory Board. We have also introduced two new article types.

Croplands and grasslands are agricultural systems that contribute to land–atmosphere exchanges of carbon (C). We evaluated and compared gross primary production (GPP), ecosystem respiration (RECO), net ecosystem exchange (NEE=RECO-GPP) of CO2, and two derived outputs - C use efficiency (CUE=-NEE/GPP) and C emission intensity (IntC= -NEE/Offtake [gr...

Chicory has been promoted as an alternative forage crop for livestock farming. It can produce large biomass yields and is highly palatable to animals. However, managing forage chicory in pastoral farms can be challenging because of its growth pattern and low persistence. There is thus a need for modelling tools that can help to understand and manag...

Agricultural activities can lead to either losses or gains of soil organic carbon (SOC) in croplands and grasslands. Increasing SOC stocks improves soil fertility and is seen as a short- to mid-term solution to mitigate greenhouse gas (GHG) emissions. Emerging ecological and societal challenges (climate change, food security, ecosystem sustainabili...

Process‐based models are useful for assessing the impact of changing management practices and climate on yields and greenhouse gas (GHG) emissions from agricultural systems such as grasslands. They can be used to construct national GHG inventories using a Tier 3 approach. However, accurate simulations of nitrous oxide (N2O) fluxes remain challengin...

Irrigation of crops and grazed pastures can lead to harmful losses of nutrients via overland flow across the edge of the field. While good irrigation design can assist with avoiding overland flow, soil surface conditions can change rapidly and lead to surface flow even under well-designed irrigation systems. Therefore, real-time methods to detect e...

Decision making in farming operations and the environmental regulation of agricultural systems are increasingly dependent on information derived from data-rich, digital sources. Environmental simulation models can help to interpret the growing amount of data and to manage the complex uncertainties that accompany decision making in these contexts. W...

Irrigation is key to maximising productivity and profitability of dryland pasture systems but over-irrigation can lead to an accumulation of surface water, which in turn results in overland flow and a high risk of contaminant loss. Irrigation-induced overland flow can arise either when the irrigation intensity is higher than soil infiltrability or...

Nitrogen (N) leaching losses from grazed pasture systems pose a risk to the environment with mitigation strategies urgently required to achieve regulatory limits. There has been increased interest in alternative forages to manipulate excretion of urinary-N of livestock. This review summarises research on key forage attributes which affect the patte...

The paper addresses the problem of measuring free water on the surface of agricultural soils by an accurate real-time acoustic method. The generation of free water is the result of a fine balance between the irrigation rate and the rate at which the soil can transport water away from the surface and is the primary cause of inefficient and environme...

Grasslands comprised of grass-legume mixtures could become a substitute for nitrogen fertiliser through biological nitrogen fixation (BNF) which in turn can reduce nitrous oxide emissions directly from soils without negative impacts on productivity. Models can test how legumes can be used to meet environmental and production goals, but many models...

The effectiveness of Integrated Water Resource Management (IWRM) modeling hinges on the quality of practices employed through the process, starting from early problem definition all the way through to using the model in a way that serves its intended purpose. The adoption and implementation of effective modeling practices need to be guided by a pra...

Replacing fertiliser nitrogen with biologically fixed nitrogen (BFN) through legumes has been suggested as a strategy for nitrous oxide (N2O) mitigation from intensively managed grasslands. While current literature provides evidence for an N2O emission reduction effect due to reduced fertiliser input, little is known about the effect of increased l...

Simulation models quantify the impacts on carbon (C) and nitrogen (N) cycling in grassland systems caused by changes in management practices. To support agricultural policies, it is however important to contrast the responses of alternative models, which can differ greatly in their treatment of key processes and in their response to management. We...

From 1990, the Agricultural Production Systems sIMulator (APSIM) has grown from a field-focused farming systems framework used by a small number of people, into a large collection of models used by thousands of modellers internationally. The software grew to consist of several hundred thousand lines of code in multiple programming languages. This h...

Replacing fertilizer nitrogen with biological nitrogen fixation (BNF) through legumes has been suggested as a strategy for nitrous oxide (N2O) mitigation from intensively managed grasslands. While current literature provides evidence for an N2O emission reduction effect due to reduced fertilizer input, little is known about the effect of increased...

Nitrate leaching from urine deposited by grazing animals is a critical constraint for sustainable dairy farming in New Zealand. While considerable progress has been made to understand the fate of nitrogen (N) under urine patches, little consideration has been given to the spread of urinary N beyond the wetted area. In this study, we modelled the la...

Simulation models are extensively used to predict agricultural productivity and greenhouse gas (GHG) emissions. However, the uncertainties of (reduced) model ensemble simulations have not been assessed systematically for variables affecting food security and climate change mitigation, within multispecies agricultural contexts. We report an internat...

Abstract Crops and livestock play a synergistic role in global food production and farmer livelihoods. Increasingly, however, crops and livestock are produced in isolation, particularly in farms operating at the commercial scale. It has been suggested that re-integrating crop and livestock systems at the field and farm level could help reduce the p...

Despite the importance of soil physical properties on loss pathways from high nitrogen (N) inputs quantitative information on the effect of soil heterogeneity on the fate of N is lacking. To quantify how changes in the physical description of soil layers, used as model inputs, affect various outputs of the biophysical APSIM model regarding the fate...

Soil organic carbon (SOC) is an important and manageable property of soils that impacts on multiple ecosystem services through its effect on soil processes such as nitrogen (N) cycling and soil physical properties. There is considerable interest in increasing SOC concentration in agro-ecosystems worldwide. In some agro-ecosystems, increased SOC has...

We sought to extend the spatial scale of soil-plant models by including, rather than ignoring, heterogeneity using the deposition of urine patches as an example. Our “pseudo-patches” approach preserves the most important biophysical effects but is computationally-tractable within a multi-paddock simulation. It explicitly preserves the soil carbon a...

C and N models Intercomparison – benchmark and ensemble model estimates for grassland production - Volume 7 Issue 3 - R. Sándor, F. Ehrhardt, B. Basso, G. Bellocchi, A. Bhatia, L. Brilli, M. De Antoni Migliorati, J. Doltra, C. Dorich, L. Doro, N. Fitton, S. J. Giacomini, P. Grace, B. Grant, M. T. Harrison, S. Jones, M. U. F. Kirschbaum, K. Klumpp,...

Uncertainties in the response of crop and grassland models to management and environmental drivers can be attributed to differences in the structure of different models. This has created an urgent need for international benchmarking of models, where uncertainties are estimated by running several models that simulate the same physical and management...

http://www.massey.ac.nz/~flrc/workshops/16/Manuscripts/Paper_Barringer_2016.pdf

Intensification of pastoral dairy systems often means more nitrogen (N) leaching. A number of mitigation strategies have been proposed to reduce or reverse this trend. The main strategies focus on reducing the urinary N load onto pastures or reducing the rate of nitrification once the urine has been deposited. Restricted grazing is an example of th...

Developing agreed definition of agricultural good management practice and estimating the nitrogen and phosphorus losses from a range of farms/soils/climates operating at good management practice

The grassland biome covers about one-quarter of the earth’s land area and contributes to the livelihoods of ca. 800 million people. Increased aridity and persistent droughts are projected in the twenty-first century for most of Africa, southern Europe and the Middle East, most of the Americas, Australia and South East Asia. A number of these region...

The development of climate mitigation services partly depends on our ability to simulate, with confidence, agricultural production and greenhouse gas (GHG) emissions so as to understand the effectiveness of the mitigation approach on both gas emissions and food production. The Soil C‐N Group of the Global Research Alliance (GRA) on GHG has initiate...

The development of climate adaptation services requires an improved accuracy in model projections for climate change impacts on pastures. Moreover, changes in grassland management need to be tested in terms of their adaptation and mitigation potential. Within AgMIP (Agricultural Model Intercomparison and Improvement Project), based on the C3MP prot...

The Matrix of Good Management (MGM) project is a collaborative initiative between Environment Canterbury, three Crown Research Institutes (CRIs; AgResearch, Plant & Food Research and Landcare Research), six primary sector organisations (DairyNZ, Beef + Lamb New Zealand, Deer Industry New Zealand (DINZ), NZPork, Horticulture NZ and the Foundation fo...

This project aimed to quantify the additional nitrogen (N) lost by leaching when fertiliser N was applied on top of a urine patch. A lysimeter study previously suggested an additive effect of fertiliser and urine on N leaching at the urine patch scale at high rates of N fertiliser. Here, we report the use of a process-based model (APSIM) to extend...

We trace the evolution of the representation of management in cropping and grazing systems models, from fixed annual schedules of identical actions in single paddocks toward flexible scripts of rules. Attempts to define higher-level organizing concepts in management policies, and to analyse them to identify optimal plans, have focussed on questions...

The intensification of livestock production has highlighted the importance of balancing production and the environmental impact in grazing systems. With the advent of more distributed computing power we have seen more complex models being developed, capable of simulating most aspects of a livestock production system. Where the modelling objective i...

Recent freshwater policy initiatives in New Zealand have highlighted the need for integrated and interoperable freshwater models and data sources. In response, we evaluated a range of software frameworks for interoperable freshwater modelling. A workshop on user needs identified a spectrum of framework users, ranging from 'indirect users' such as p...

Across New Zealand, regional authorities are taking steps to maintain or improve the quality of freshwater. Although regional differences exist in the approaches being taken, the need to define agricultural good management practices (GMP) and understand the impacts of GMP on freshwater quality is a recurring theme. However, there are no commonly ag...

Ecological studies often suggest that natural grasslands with high species diversity will grow more biomass and leach less nitrogen (N). If this diversity effect also applies to fertilised and irrigated pastures with controlled removal of herbage, it might be exploited to design pastures that can assist the dairy industry to maintain production whi...

A significant challenge for the pastoral farming systems is to maintain or increase production while reducing leaching of nitrogen, and for pastoral systems, this means reducing leaching from urine patches. Here we explore the potential impact of four ryegrass characteristics to increase pasture production and reduce leaching from ryegrass–white cl...

Modelling water and solute transport through soil requires the characterisation of the soil hydraulic functions; however, determining these functions based on measurements is time-consuming and costly. Pedotransfer functions (PTFs), which make use of easily measurable soil properties to predict the hydraulic functions, have been proposed as an alte...

Urine depositions have been shown to be the main source of N leaching from grazing systems and thus it is important to consider them in simulation models. The inclusion of urine patches considerably increases the complexity of the model and this can be further aggravated if the overlaps of urine patches are also considered. Overlapping urine patche...

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...

As pressure on water resources increases, pasture species that express traits for improved water-use efficiency (WUE) while maintaining desirable agronomic and production characteristics are needed. The objective of this study was to use a biophysical modelling analysis to test the sensitivity of key pasture plant functional traits on WUE. Biomass...

The pasture growth module AgPasture was integrated into the APSIM (Agricultural Production System Simulator) simulation model, allowing pasture-based systems to be modelled in combination with other land uses at farm scale or within land use change studies. The model's predictions of pasture growth were evaluated against 32 pasture growth datasets...

This book contains 28 chapters with emphasis on the interactive nature of the relationships between the soil, plant, animal and environmental components of grassland systems, both natural and managed. It analyses the present knowledge and the future trends of research for combining the classical view of grasslands, as a resource for secure feeding...

Agricultural systems with grazing animals are increasingly under scrutiny for their contribution to quality degradation of waterways and water bodies. Soil type, climate, animal type and nitrogen (N) fertilisation are contributors to the variation in N that is leached through the soil profile into ground and surface water. It is difficult to explor...

Urine depositions by grazing animals induce high concentration of ammonium (NH(4)(+)) in soils. The adsorption of NH(4)(+) in the soil plays an important role in the fate of the urine deposited N. However, adsorption isotherms for a wide range of soils are not readily available. Pedotransfer functions (PTFs) that relate easily measurable and widely...