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• Assesses adaptation to climate change in agricultural region. • Participatory approach used to co-create regional adaptation pathway. • Adaptations sequenced over time, focusing on incremental changes in near-term. • Highlights long-term strategies towards transformation as impacts accelerate. • Provides the basis for regional adaptation planning and further application. Climate change presents significant risks and opportunities for agriculture. Agricultural producers are likely to be adversely affected by changes in higher mean temperatures, more frequent extreme climatic events, and an increase in inter-annual weather variability, with implications for established management practices. While probabilities of future change in key climatic variables become more refined, significant uncertainties remain, complicating efforts at adaptation action on the ground. Adaptation pathways planning allows stakeholders to consider a range of possible futures, identify and evaluate adaptation options, and sequence them over time. The aim is to have a robust plan that is flexible enough to deliver desired outcomes regardless of how the future unfolds. We developed and applied a pathways approach to support regional adaptation planning in Hawke's Bay, New Zealand, a premier food- and wine-producing region, where changing land use, competition for freshwater, and climate change, are presenting challenges to agricultural producers and rural communities. Working with a range of stakeholders from local government, community and the region's diverse agricultural sectors, comparative case study analysis in two catchments is used to identify values relating to productive landscapes, likely impacts of climate change and potential adaptation options at the local level. Actions for key areas of decision making were evaluated and sequenced over time, providing the basis for a regional adaptation pathway. The results highlight the complex interaction between climatic and non-climatic drivers of change at the local and regional scale, and the need to closely consider trade-offs and synergies in any adaptations. With adaptation rapidly emerging as a priority for policy-making and practice, the results can help inform and empower stakeholders to implement actions towards climate adapted futures, and demonstrate the utility of pathways approaches for local- and regional planning. [ABSTRACT FROM AUTHOR]

The assessment of water uptake in agricultural systems commonly relies on the use of process-based biophysical models. To accurately represent crop-soil relationships, these models require local calibration which is often limited by the availability of site-specific data. This is the case for the water extraction coefficient ( kl ) in perennial forage cropping systems. The kl is critical to control water uptake by roots influencing soil moisture dynamics at different soil depths. This crop-soil parameter is particularly challenging to assess in species that establish deep root systems during long periods of regrowth, such as perennial forages. Using three years of detailed field data, we test a method to estimate kl for two perennial crops of broad socio-economic significance (lucerne and perennial ryegrass). The method is based on three physically meaningful parameters: Root Front Velocity (RFV, mm/day), surface kl ( kl 0 ,/day) and the rate of kl decay with soil depth ( λ kl , dimensionless). Our analysis showed that soil volumetric water content dynamics was most sensitive to kl 0 values. A model fitting procedure showed that the highest accuracy of soil volumetric water content ( θ ) simulations was obtained with RFV of 10 mm/day and a kl 0 of 0.11/day for both forages. In contrast, λ kl estimates differed among species, being higher for shallow fibrous ryegrass roots than for the deep lucerne taproots. The analysis also highlighted that multiple parameter set combinations were found to give simulations of acceptable accuracy. The proposed method can be used as a first approximation to parameterise kl when local calibration data is unavailable. However, even for the fitted parameter sets, the accuracy of θ estimates was low at soil depths where there was a substantial transition of soil texture. These insights highlight important aspects to be considered in future development and parameterisation of water uptake models for perennial forages. [ABSTRACT FROM AUTHOR]

The environmental and economic sustainability of future cropping systems depends on adaptation to climate change. Adaptation studies commonly rely on agricultural systems models to integrate multiple components of production systems such as crops, weather, soil and farmers' management decisions. Previous adaptation studies have mostly focused on isolated monocultures. However, in many agricultural regions worldwide, multi-crop rotations better represent local production systems. It is unclear how adaptation interventions influence crops grown in sequences. We develop a catchment-scale assessment to investigate the effects of tactical adaptations (choice of genotype and sowing date) on yield and underlying crop-soil factors of rotations. Based on locally surveyed data, a silage-maize followed by catch-crop-wheat rotation was simulated with the APSIM model for the RCP 8.5 emission scenario, two time periods (1985–2004 and 2080–2100) and six climate models across the Kaituna catchment in New Zealand. Results showed that direction and magnitude of climate change impacts, and the response to adaptation, varied spatially and were affected by rotation carryover effects due to agronomical (e.g. timing of sowing and harvesting) and soil (e.g. residual nitrogen, N) aspects. For example, by adapting maize to early-sowing dates under a warmer climate, there was an advance in catch crop establishment which enhanced residual soil N uptake. This dynamics, however, differed with local environment and choice of short- or long-cycle maize genotypes. Adaptation was insufficient to neutralize rotation yield losses in lowlands but consistently enhanced yield gains in highlands, where other constraints limited arable cropping. The positive responses to adaptation were mainly due to increases in solar radiation interception across the entire growth season. These results provide deeper insights on the dynamics of climate change impacts for crop rotation systems. Such knowledge can be used to develop improved regional impact assessments for situations where multi-crop rotations better represent predominant agricultural systems. [ABSTRACT FROM AUTHOR]

Early-vigour is a plant trait phenotypically characterised by a rapid expansion of leaf area in early stages of crop growth, before canopy closure. Although early-vigour is already used as a selection criteria in breeding programmes for grain cereals, its genetic variability and potential benefits for oat cover crops is unknown. In this study, we screened 231 oat lines from a commercial forage breeding programme using high-throughput field phenotyping to quantify canopy development rates through aerial photographs. Results showed a wide genetic variability for early-vigour in oats, with canopy cover differences of up to ∼20% during the approximate 30 days period from emergence to full canopy cover. Two oat genotypes with contrasting canopy cover development rates (opposite quartile ranges of the population) were subsequently selected for a detailed investigation of underlying mechanisms explaining early-vigour during two field trials. For these genotypes, the size of individual leaves was found to be the main factor driving differences, with 50% larger leaf area before the sixth leaf from the base of the main tiller in the high early-vigour genotype. A process-based biophysical model (APSIM-NextGen oats) was then parameterised to quantify variability on potential early-vigour benefits across four representative agricultural target environments. This was done by simulating the two selected oat genotypes across 30-years of historical weather data from each of the four distinct climatic zones, considering two contrasting soil types and three possible cover crop sowing dates. Results showed early-vigour to provide overall positive ecosystems services with pooled medians of 7–18% increase in above ground biomass and 5–13% increase in nitrogen uptake which caused a consequent 4–9% reduction in nitrogen leaching losses depending on the location/soil/management combination. Such decline in relative plant-trait effects across different components of the production system (above-ground biomass, above-ground N and N leaching reduction) was also accompanied by increasing variability in responses, with pooled coefficients of variation around 31%, 69% and 80% respectively. Similarly, our results also highlight the relative dilution of trait effects across scales. For instance, a 50–70% difference in basal leaf size at the plant-organ scale caused a 6–10% potential reduction of N leaching at the agricultural system scale. These results highlight the importance of multi-metric evaluations of spatial and temporal variability in trait effects to better inform breeding and selection programmes. Finally, our practical implementation of previously conceptualised methods illustrates the increased depth of understanding about plant-trait benefits when combining interdisciplinary approaches such as high throughput phenotyping, classic crop physiology field experimentation and biophysical modelling. The principles of this approach can be extended to assess the relative value of other traits across different species, managements and environments. • There was phenotypic variability for early-vigour across 231 cover crop oat genotypes. • Early-vigour was mainly explained by a 50–70% larger size of the initial seven leaves. • Long-term simulations showed that biomass and N uptake increased with early-vigour. • This also reduced N leaching but at a smaller magnitude and with greater variability. • Such analysis framework can assess alternative traits in other crops and environments. [ABSTRACT FROM AUTHOR]

The effectiveness of growing winter cover crops to mitigate nitrogen (N) leaching can be widely variable, even within a single climatic zone. We sought to investigate key drivers of this variability for the Canterbury Plains of New Zealand. First, through an analysis of local field experiments, we quantified the local variability in the effectiveness of cover crops to reduce N leaching. We then calibrated and applied a biophysical model to isolate the impact of potential drivers of this variability. Crop management (cover crop sowing date), soil water holding capacity (WHC) and inter-annual weather variability (30 years of historical climate) were selected as main factors to be investigated. The analysis of local literature showed that, compared to fallow treatments, winter cover crops reduced N leaching by an average (±95% CI) of 17 ± 8.2 kg N ha −1 . This represented a median N leaching reduction of ∼50% with a wide interquartile range (6–75%). The modelling study showed that the delay in sowing dates consistently reduced the average effectiveness of cover crops, from >80% for March- to <25% for June-sown crops. For any “sowing date by soil WHC” scenario, there was also a large year to year variability. This was caused by the stochastic effect of inter-annual weather variability on the dynamics of crop N demand and soil N supply. For the conditions assumed in the modelling study, a sensitivity analysis of simulated results showed that sowing dates were the main contributor to total variability in the effectiveness of cover crops, followed by weather, factor interactions and soil WHC. These results suggest the need for caution when interpreting data from individual field trials due to the impact of inter-annual variability and interactions among multiple drivers on cover crop effectiveness. In addition, our analysis highlights the value of complementary methodologies, such as biophysical modelling, for extending the inference space of individual field studies. [ABSTRACT FROM AUTHOR]

Most climate impact assessments for food production simulate single crops with re-initialised soil conditions. However, crop rotations with multiple crops are used in many agricultural regions worldwide. This case-study compares methods to aggregate outputs from simulations of multi-crop systems for climate impact assessments. The APSIM model was used to simulate four crops as monocultures (re-initialised or continuous) or as (single or multiple) instances of continuous rotations. We considered two contrasting climates and two soil types, with four production intensification scenarios (high/low water and nitrogen input). Results suggest that differences among the methods depend on the impact variable of interest and the degree of intensification. Detailed simulations (i.e. multiple runs of continuous rotations) were especially valuable for soil-related variables and limiting growth conditions. These results can indicate sources of uncertainty for large scale impact and adaptation assessments where simplifications of crop rotations are often necessary. [ABSTRACT FROM AUTHOR]

The impact of limited water and nitrogen (N) supply on maize productivity and on the utilisation efficiency of key production resources (radiation, water and N) was quantified in two field experiments during consecutive seasons in Canterbury, New Zealand. In experiment 1 crops were subjected to five N treatment rates (0–400 kg N/ha) and, in experiment 2, to three N (0 to 250 kg/ha N) and two water regimes (dryland and fully irrigated) using a rain-shelter structure. Limited N and water reduced yield and affected resource-use efficiencies. Total biomass ranged from 8 Mg DM/ha for dryland nil N crops to up to 28 Mg DM/ha for fully irrigated and N fertilised crops. Radiation use efficiency declined with N and water limitation from a maximum of 1.4 g DM/MJ to 0.6 g DM/MJ. Transpiration water use efficiency was higher in water stressed crops than irrigated crops (50–70 kg DM/ha/mm) and increased linearly with N fertilizer rates in proportion to the increase in radiation use efficiency. The crop conductance decreased from 0.19 mm/MJ in irrigated crops to 0.07 mm/MJ in dryland crops with negligible response to N fertilizer rates. Nitrogen use efficiency declined with N input rates from 100 to 150 kg DM/kg N, being inversely related to the efficiency of both water and radiation use. Dryland crops recovered 25% less N from applied fertilizer than irrigated crops. These results highlight that benchmarks of resource efficiency need to consider the level of intensification of the production system and illustrate trade-offs between yield targets and the efficiency of water and N use, that depend on the scale of analysis. To establish a balance between economic returns and environmental impacts, these trade-offs need to be managed depending on the relative values assigned to the use-efficiency of each input resource in relation to crop productivity. [ABSTRACT FROM AUTHOR]

Abstract: This study compared physiological responses of fully irrigated seedling and regrowth lucerne crops (Medicago sativa L.) grown under similar environmental field conditions. Measurements occurred for 2–4 years after sowing on 24 October, 15 November, 05 December and 27 December 2000 at Lincoln, Canterbury, New Zealand. Irrespective of the date of sowing, on average lucerne accumulated less shoot dry matter (DM) in the seedling year (11±0.44tha−1) than during the regrowth year (18±0.76tha−1). Slower shoot-growth rates in seedlings were explained by less intercepted light and reduced efficiency in conversion of light to biomass. Specifically, seedlings had a longer phyllochron (47±2.3°Cd leaf−1) and slower leaf area expansion rate (0.009m2 m−2 °Cd−1) than regrowth crops (35±1.8°Cd leaf−1 and 0.016m −2 m −2 °Cd, respectively). There were no differences in canopy architecture with a common extinction coefficient of 0.93. The radiation use efficiency (RUE) for shoot production (RUEshoot) was 1.2±0.16g DM MJ−1 of intercepted photosynthetically active radiation (PARi) in seedlings and 1.9±0.24g DM MJ−1 PARi in regrowth crops. Reproductive development was slower in seedling than regrowth crops due to an apparent juvenile period ranging from 240 to 530°Cd in seedlings. For both seedling and regrowth phases, the thermal time accumulation to reach 50% buds visible (Tt0-bv) and 50% open flowers (Tt0-fl) increased as photoperiod shortened in autumn. The minimum Tt0-bv, or the thermal-time duration of the basic vegetative period (TtBVP), was estimated at 270±48°Cd at photoperiods >14h for regrowth crops. The theoretical threshold below which reproductive development is projected to cease, or the base photoperiod (Ppbase), was estimated at a common 6.9h for seedling and regrowth crops. The transition from buds visible to open flowers (Ttbv-fl) was mainly controlled by air temperature and ranged from 161°Cd for seedlings to 274°Cd for regrowth crops. These results can be used as guidelines to develop differential management strategies for seedling and regrowth crops and improve the parameterization of lucerne simulation models. [Copyright &y& Elsevier]

Abstract: Surface ozone (O3) is a potent phytotoxic air pollutant that reduces the productivity of agricultural crops. Growing use of fossil fuel and climate change are increasing O3 concentrations to levels that threaten food supply. Historically, farmers have successfully adapted agricultural practices to cope with changing environments. However, high O3 concentrations are a new threat to food production and possibilities for adaptation are not well understood. We simulate the impact of ozone damage on four key crops (wheat, maize, rice and soybean) on a global scale and assess the effectiveness of adaptation of agricultural practices to minimize ozone damage. As O3 concentrations have a strong seasonal and regional pattern, the adaptation options assessed refer to shifting crop calendars through changing sowing dates, applying irrigation and using crop varieties with different growth cycles. Results show that China, India and the United States are currently by far the most affected countries, bearing more than half of all global losses and threatened areas. Irrigation largely affects ozone exposure but local impacts depend on the seasonality of emissions and climate. Shifting crop calendars can reduce regional O3 damage for specific crop-location combinations (e.g. up to 25% for rain-fed soybean in India) but has little implication at the global level. Considering the limited benefits of adaptation, mitigation of O3 precursors remains the main option to secure regional and global food production. [Copyright &y& Elsevier]

Abstract: Radiation use efficiency (RUE), and subsequent partitioning between shoots and roots were investigated for ‘Grasslands Kaituna’ lucerne crops grown in the cool temperate climate of Canterbury, New Zealand. Crops were grazed by sheep every 28 or 42 day and yielded 12 and 23tDM/hayear, respectively. The RUE for above ground shoots (RUEshoot) was 1.7–2.0gDM/MJ of intercepted photosynthetically active radiation (PARi) in spring but decreased systematically to ≤1.0gDM/MJ PARi in autumn. The RUE for total biomass (RUEtotal) ranged from 1.3 to 3.1gDM/MJ PARi in response to air temperature and defoliation treatment. The lowest RUEtotal in mid-summer for the treatment defoliated every 28 days was related to a 20% decline in the leaf photosynthetic capacity measured at 1000μmolphotons/m2 s (Pn1000) and at saturating light (P max). In turn, the reduction in Pn1000 was related to differences in specific leaf nitrogen (SLN), through changes in specific leaf weight (SLW) rather than the leaf N concentration of 4–6% DM. The fractional partitioning of DM to roots (p root) increased from near zero in winter/early-spring to >0.45 in autumn, which explained the observed seasonality of RUEshoot. For the treatment defoliated each 42 days, p root increased linearly from ∼0.05 to >0.45 as Pp increased from 10.5 to 16.5h. In decreasing photoperiods p root averaged 0.45. Agronomic treatments that result in suboptimal N reserves post-grazing can be expected to produce conservative canopy characteristics but reduced photosynthetic capacity of the first five main stem leaves. Beyond this development stage, canopy expansion may be reduced with more conservative leaf N. [Copyright &y& Elsevier]

Abstract: The frequency of defoliation is the major management tool that modulates shoot yield and the accumulation of C and N root reserves in lucerne crops. A fully irrigated, 2-year-old lucerne (Medicago sativa L.) crop was grown at Lincoln University (43°38′S and 172°28′E) and subjected to four defoliation treatments. These involved the combination of two grazing frequencies (28 or 42 days) applied before and/or after mid-summer. Annual shoot dry matter (DM) yield ranged from 12 to 23t/ha. These differences were largely explained by the amount of intercepted photosynthetically active radiation (PARi) using a conservative conversion efficiency of 1.6gDM/MJPARi. Part of the reduced PARi in the frequently defoliated treatments was caused by the shorter regrowth period that impeded crop canopy closure to the critical leaf area index (LAIcrit) of 3.6. Canopy architecture was unaffected by treatments and a single extinction coefficient for diffuse PARi (k d) of 0.81 was found for ‘Grasslands Kaituna’ lucerne. The pool of endogenous nitrogen (N) in taproots was reduced by frequent defoliations. This explained differences in leaf area expansion rate (LAER), which decreased from 0.016m2/(m2 °Cday) at 60kgN/ha to 0.011m2/(m2 °Cday) at 20kgN/ha. The pool of soluble sugars was also positively associated with LAER but the concentrations of carbohydrates and N reserves and the pool of taproot starch were poorly related to LAER. The slower LAER in the frequently defoliated treatments was mostly caused by the smaller area of primary and axillary leaves, particularly above the 6th node position on the main-stem. Developmental processes were less affected by defoliation frequency. For example, the phyllochron was similar in all treatments at 34°Cday (base temperature of 5°C) per primary leaf during spring/summer but increased in autumn and ranged between 44 and 60°Cday. Branching and senescence started after the appearance of the 4th main-stem node, and both were unaffected by defoliation frequency. These results suggest that the expansion of individual leaves, both primary and axillary, was the most plastic component of canopy formation, particularly after the appearance of the 6th primary leaf. Future mechanistic modelling of lucerne crops may incorporate the management or environmental responses of LAER that control PARi and impact on shoot DM yields. [Copyright &y& Elsevier]

Abstract: The productive life of lucerne (Medicago sativa L.) stands depends on the rate of mortality of individual plants. However, self-thinning of plant populations may be compensated for by increases in other yield components, namely shoots/plant and individual shoot mass. Frequent defoliation reduces lucerne yield but it is unclear whether this is caused by an acceleration of plant mortality or changes in these other yield components. To investigate this, crops with contrasting shoot yields were created using constant 28 or 42-day regrowth cycles applied to a ‘Kaituna’ lucerne crop in Canterbury, New Zealand during the 2002/2003 and 2003/2004 growth seasons. Two further treatments switched from 28 to 42 or 42 to 28 days grazing frequency in mid-summer (4th February) of each year. The annual yield of shoot dry matter (DM) ranged from 12 to 23t/ha for the treatments defoliated consistently each 28 or 42 days, respectively. Plant population was unaffected by treatments and declined exponentially from ∼130plants/m2 in June 2002 to 60plants/m2 in September 2004. The dynamics of plant and shoot population were associated with the light environment at the base of the canopy. The slope of the size/density compensation (SDC) of plants was −1.67 for the treatment defoliated each 42 days, near the expected self-thinning slope of −1.5 for stands at constant leaf area index (LAI). Self-thinning of shoots resumed after each defoliation when the LAI reached 2.1 and the transmission of photosynthetically active radiation (PARt) was ∼0.20. At this point the proportion of aerial DM in the tallest (dominant) shoots increased non-linearly from ∼30 to >80%, due to the mortality of intermediary and suppressed shoots. The average maximum shoot population in each rotation was ∼780shoots/m2 and unaffected by the decline in plant population due to a compensatory increase from ∼6 to 13shoots/plant as the stand thinned. A lower asymptote of 43plants/m2 was estimated as the minimum plant population at which yield component compensation would maintain the productive potential of these ‘Kaituna’ stands. Differences in shoot yield were explained (R 2 =0.97) by changes in the individual shoot mass (ISM) that were consistently lowered by frequent defoliation treatments. Frequent defoliations reduced crop productivity by limiting the assimilation of biomass into each individual shoot with negligible impact on shoot appearance rate, the number of shoots per plant at an LAI of 2.1 or the rate of plant population decay. Inter-specific competition for light was proposed as the main factor controlling self-thinning of plants and shoots regardless of their individual C:N status. [Copyright &y& Elsevier]

Abstract: Lucerne crops exhibit a seasonal cycle of accumulation and depletion of C and N reserves in perennial organs (crown and taproot). The level of perennial reserves influences shoot growth rate, mainly after defoliation and during early-spring regrowth. The frequency and time of defoliation (grazing or cutting) also influences yield and stand persistence but the impact on the seasonality of perennial reserves is unknown. Patterns of accumulation and depletion of reserves in lucerne crops were examined during two growth seasons in Canterbury, New Zealand. To create contrasting levels of reserves, four defoliation regimes were imposed through a combination of a long (L, 42 days) or a short (S, 28 days) grazing cycle, applied at two times of the growth season (before and/or after mid-summer). Crops grazed consistently every 42 days (LL treatment) yielded 23t/ha/year of shoot dry matter (DM). Those on a year round 28-day regrowth cycle (SS treatment) produced only 50–60% of this. Crown plus taproot DM cycled from ∼3.0 to 5.5t/ha for the LL and from 2.2 to 3.5t/ha for SS treatment. The concentrations of starch in taproots ranged from ∼4 to 30% DM and differed seasonally but were consistently reduced by frequent defoliations. Nitrogen reserves accumulated in autumn to ∼1.8% DM and were depleted in spring to 1.2% DM in the LL and 1.0% in the SS treatment. The levels of soluble sugars declined abruptly from 9 to 4% DM in frequently defoliated crops but recovered to seasonal levels similar to the LL treatment. In the 2003/04 season, the mid-season switch in defoliation frequency from a short to a long regrowth duration (SL treatment) restored C and N in taproots to levels 25–50% greater than the SS treatment. The amount of nitrogen in taproots during winter was the strongest predictor (R 2 =0.76) of spring shoot growth rates. The seasonal patterns of change in crown plus taproot DM and the concentrations of C and N in taproots occurred regardless of defoliation regime. This indicates that environmental signals imposed a strong control over the DM partitioning to lucerne roots. [Copyright &y& Elsevier]

• For lucerne – yield and quality are independent of genotypes and fall dormancy. • Yield and quality can be predicted by allometric relationships between dry matter yield or plant height. • These relationships allow optimal defoliation management regimes and parameters for crop simulation models of lucerne. This study determined how fall dormancy rating (FD2, FD5 or FD10) of lucerne genotypes affected crop yield and quality. One field experiment was measured for three growing seasons as a seedling crop and then three defoliation frequency regimes (DF) of 28 (DF28), 42 (DF42) or 84 (DF84) days were imposed (October 2014 to April 2017). Annual shoot dry matter (DM) yields ranged from 5.2 t DM/ha in DF28 crops to 17.5 t DM/ha in DF84 crops. Higher shoot DM was associated with greater shoot elongation which was modified by photoperiod (Pp). In an increasing Pp environment, the rate of DM accumulation in shoots was ∼ 91 kg/ha for each 1.0 cm increase in shoot height. In a decreasing Pp environment, the rate of DM accumulation in shoots was constant at ∼50 kg/ha/cm. In the DF84 crops, shoot yield declined due to leaf senescence by ∼31 kg/ha/cm when lucerne was ≥65 cm height. The leaf stem ratio (LSR) declined by 0.56 for each 1.0 cm increase in plant height. The crude protein (CP) and metabolisable energy (ME) accumulation in whole shoots or in leaf, soft stem and hard stem followed an allometric relationship. As DM increased, CP and ME increased in a similar pattern for all treatments. Thus the relationship between the yield and quality of lucerne was independent of genotype and phenological stage and was explained allometrically by the leaf and stem ratio, associated with changes in plant height, as affected by photoperiod. These results suggest universal defoliation management strategies can be developed based on ontogeny and independently of genotype, growth stage and growing conditions. [ABSTRACT FROM AUTHOR]

Modelling lucerne growth requires response functions that represent seasonal partitioning of biomass into above-ground and below-ground organs. An additional challenge is to parameterize perennial organ responses across contrasting fall dormancy (FD) genotypes. Current models use empirical approaches to simulate biomass accumulation and partitioning. This research integrated knowledge of lucerne biomass accumulation and partitioning into the Agricultural Production Systems sIMulator (APSIM) next generation (APSIM NextGen) model framework. Biomass supply was calculated from light interception and total radiation use efficiency (RUE total), and then allocated based on the relative demand of each organ. Leaf biomass demand was parameterized as a function of specific leaf area (SLA). Stem biomass demand was parameterized as a positive power function of shoot biomass. Root biomass (taproots and crowns) showed a strong seasonal pattern. The observed decrease of root biomass in periods of an increasing photoperiod (mid-winter to mid-summer) was assumed as remobilization to shoots and carbon loss from maintenance respiration. Periods of decreasing photoperiod showed increased biomass of root caused by greater carbon partitioning to this organ. To capture this, a model optimization approach was used to fit required parameters. Fitted parameters included a remobilization coefficient (percentage of storage biomass per day) of 0.01common to all FD cultivars tested (FD5, FD2 and FD10). The regrowth coefficient (remobilization duration) remained constant at 0.01 post-defoliation until 250 °Cd for FD5, 200 °Cd for FD2 and 300 °Cd FD 10, and then declined to 0 after another 50 °Cd. The model was parameterized to have maximal root demand in a decreasing photoperiod to capture carbon partitioning. The model had good prediction of shoot biomass (NSE=0.70) and fair prediction (NSE=0.60) of root biomass for 42 day defoliation treatments. It was less accurate for predictions of shoot biomass under a frequent (28 day) defoliation regime. This highlights the importance to include the response to limitations caused by depleted root N reserves in future model versions. The APSIM NextGen lucerne model provided a mechanistic framework to model perennial organ biomass dynamics with structural and storage components, root maintenance respiration, remobilization in spring, partitioning in autumn and the regrowth effect. This framework accounted for differences in fall dormancy of genotypes and provided a methodology that can be integrated into models of other perennial crops. • APSIM next generation lucerne model was developed to simulate biomass dynamics. • Root biomass decreased in spring and increased in autumn. • A mechanistic approach was used to capture shoot and root biomass seasonal pattern. [ABSTRACT FROM AUTHOR]

Lucerne (Medicago sativa L.) canopy expansion, as quantified by leaf area index (LAI), is the crop process that determines the amount of intercepted total radiation during each regrowth cycle. A challenge is to capture seasonal changes of canopy expansion rate in response to the environment. This research integrates parameters and functions of lucerne canopy expansion into the Agricultural Production Systems sIMulator (APSIM) next generation (APSIM NextGen) model (LeafArea module) to simulate canopy expansion and light interception. Over 20 years of detailed field experimental datasets, with multiple treatments, from Lincoln University were used for model development. Functions derived from a fall dormancy (FD) 5 rated genotype were grown under an industry standard defoliation treatment to parametrize the model. These functions were tested further using genotypes with an FD2 or FD10 rating under longer and shorter defoliation regimes, all under irrigated conditions. The APSIM NextGen lucerne model predicted the LAI expansion pattern in each growth cycle as a double sigmoid curve requiring functions that define the lag phase, basal bud initiation, the linear leaf area expansion rate (LAER; m2 m-2 °Cd), and canopy senescence which represents the loss of LAI over time. LAI was well predicted for experiments under the standard (42-day) and long (84 day) defoliation treatments for FD5, with Nash-Sutcliffe efficiency (NSE) of 0.61 and 0.55. However, the derived parameters and functions overestimated LAI under an extreme short defoliation treatment (28-day), NSE values ranged from 0.38 to 0.78. LAER was lower for the short-defoliation intervals (28-day), probably due to a depletion of carbon and nitrogen reverses in perennial organs. For FD2 and FD10, different LAER functions were generated from field observed data and used to improve simulation agreement. There was fair agreement for the 84-day treatment (NSE of 0.32) and the 42-day treatment (NSE of 0.38), but poor agreement for the 28-day treatment for FD10 (NSE = −0.88). The estimated extinction coefficient (k) was the same for seedling and regrowth crops, and consistent across defoliation treatments and FD classes. With the LeafArea module and k value, the APSIM NextGen lucerne model can now estimate daily LAI and intercepted radiation. Future model development includes validating the LeafArea module in different environments. However, a more mechanistic model approach is required to link canopy expansion to carbon and nitrogen reserves in lucerne plants that experience intense defoliation. • We developed a LeafArea module in the APSIM NextGen lucerne model. • Lag, linear and declining phase functions were used to model leaf area index. • Leaf area index was accurately predicted for longer defoliation intervals. • Genotypes with three fall dormancy ratings had different leaf area expansion rates. [ABSTRACT FROM AUTHOR]

Abstract: This research quantifies the influence of seasonal variations in solar radiation, temperature and biomass partitioning on lucerne production in a temperate climate. Above ground biomass (shoot) production of fully irrigated ‘Kaituna’ lucerne was measured in the field over 5 years and 33 regrowth cycles in Canterbury, New Zealand. Shoot production increased linearly (R 2 of 0.93±0.07) with intercepted total radiation within each regrowth cycle but radiation use efficiency (RUEshoot, in g DM/MJ total radiation) ranged from 0.29 to 1.09gDM/MJ. Covariate analysis showed season and temperature both influenced RUEshoot with temperature adjusted decreasing from 1.01gDM/MJ in September to 0.77gDM/MJ between October and February, decreasing again to 0.47gDM/MJ in March and April before increasing back to 0.99gDM/MJ in May. A second fully irrigated experiment with lucerne plants grown in plastic columns under near field conditions investigated the seasonality of biomass partitioning between shoots and perennial biomass (roots and crowns). The proportion of total biomass partitioned to shoots (P shoot) was 0.90 in September, ∼0.67 from October to February but only 0.35 in March and could be related to photoperiod. These P shoot values were closely correlated with showing seasonal changes in RUEshoot were partly caused by changes in biomass partitioning. Field data for RUEshoot were divided by P shoot to estimate the RUE for total biomass production (RUEtotal). The RUEtotal increased linearly from 0.60 to 1.60gDM/MJ as mean air temperatures increased from 6 to 18°C. These results quantified the effects of solar radiation and mean temperature on total lucerne biomass production and its seasonal partitioning between shoots and perennial biomass. The influence of regrowth duration on this partitioning was also investigated. [Copyright &y& Elsevier]

Abstract: Irrigated crops of ‘Grasslands Kaituna’ lucerne were grown for 5 years in a temperate climate at Lincoln University, Canterbury, New Zealand (43°38′S, 172°28′E). From these the response of the components of leaf area index (LAI) to environmental factors was determined. A broken stick temperature threshold with a base temperature (T b) of 1°C at air temperatures (T a) <15°C and a T b =5°C for T a ≥15 was required to accumulate thermal time (Tt). Using this, the appearance of nodes on the main-stem (phyllochron) was constant in Tt within a re-growth cycle (30–42 days). The phyllochron was 37±7°Cd but declined from 60 to 37°Cd as photoperiod decreased from 15.7 to 11.4h. Branching began at the appearance of the fifth main-stem node with 2.5 secondary nodes produced per main-stem node in spring re-growth cycles but only 1.7 produced in summer. Leaf senescence increased from 0.3 to 1.08 leaves per main-stem node after the appearance of the ninth node. Spring re-growth cycles had a mean individual leaf area of 170mm2 compared with 400mm2 for summer re-growth cycles. These results demonstrate systematic variation in LAI components and suggest they need to be considered separately in response to environmental factors to provide a quantitative framework for crop simulation analyses of lucerne canopy development. [Copyright &y& Elsevier]

• Lucerne phenological development was not affected by defoliation regime or fall dormancy. • Stem elongation rate was reduced by frequent defoliation. • Phyllochron and heightchron were longer after crops reached bud visible stage. • The APSIM NextGen lucerne model accurately simulates development stages and node appearance. Prediction of lucerne phenological and morphological development is important for optimising the defoliation schedule and time of other management events. A challenge for any lucerne phenology module is to capture the seasonality of development processes in response to environment, management and genotype. To date, lucerne phenological modules have not been evaluated under different defoliation regimes or with genotypes of different fall dormancy (FD) classes. This research integrated data of lucerne phenological development into the Agricultural Production Systems sIMulator (APSIM) next generation (APSIM NextGen) model framework to develop and verify a phenology module. Relationships derived from the FD5 genotype, grown under a 42 day (LL) defoliation treatment were used for model development. These were further tested for two genotypes with contrasting FD (FD2 and FD10) under frequent (28 day: S) or long (84 day: H) defoliation regimes, all under irrigated conditions. Development was parameterized based on thermal time targets to reach specific phenological stages and modified by photoperiod responses. Development stage and node appearance were shown to be independent of defoliation treatment and FD class. Simulation results showed good agreement for prediction of development stages (NSE of 0.77 for days to buds visible and 0.67 for days to flowering stage) and number of main stem nodes (NSE values were ranged from 0.53 to 0.84). However, both defoliation management treatment and FD classes affected stem height. For FD5, there was good agreement for the 84 day treatment (NSE of 0.83) and the 42 day treatment (NSE of 0.66), but it was poor for the 28 day treatment (NSE of -0.08). This was probably due to reduced stem extension rates, limited by low C and N reserves in perennial organs under the frequent (28 day) defoliation regime. For FD2 and FD10, two separate sets of parameters were used to improve model prediction of height to account for their contrasting seasonal C partitioning patterns. These results show that the APSIM NextGen lucerne phenology module was able to simulate crops grown under unconstrained growing conditions. However, the reason for under estimation of stem height for the 28 day treatment needs further investigation. [ABSTRACT FROM AUTHOR]

Worldwide supply of water and nitrogen (N) are critical to crop yield with multiple interactions that need to be untangled. We used an allometric framework to quantify the dynamic relationships between crop growth, transpiration and N uptake in maize (Zea mays L.) and sorghum (Sorghum bicolor L.) using published data from experiments in France, New Zealand and United States. Our analysis highlighted a two-fold effect of drought on crop growth: a direct effect whereby crop growth is reduced proportionally to the reduction in transpiration, and an indirect effect mediated by a drought-induced crop N deficit, quantified as N nutrition index (NNI), the ratio between actual and critical plant N concentration (the minimum plant N concentration for achieving maximum crop mass). Under drought, sorghum maintained NNI and transpiration efficiency (biomass per unit of transpiration) whereas both NNI and transpiration efficiency declined in drought-stressed maize in comparison to well-watered crops. Nitrogen uptake per unit of transpiration (N/T) is a valuable trait for analyzing the combined effect of water and N deficit on water use efficiency (biomass per unit of evapotranspiration). However, both N/T and crop N concentration decline allometrically with biomass, hence comparisons of genotypes, environments and management practices would be biased unless they are scaled by crop biomass. [ABSTRACT FROM AUTHOR]

In up-scaling studies, model input data aggregation is a common method to cope with deficient data availability and limit the computational effort. We analyzed model errors due to soil data aggregation for modeled SOC trends. For a region in North West Germany, gridded soil data of spatial resolutions between 1 km and 100 km has been derived by majority selection. This data was used to simulate changes in SOC for a period of 30 years by 7 biogeochemical models. Soil data aggregation strongly affected modeled SOC trends. Prediction errors of simulated SOC changes decreased with increasing spatial resolution of model output. Output data aggregation only marginally reduced differences of model outputs between models indicating that errors caused by deficient model structure are likely to persist even if requirements on the spatial resolution of model outputs are low. [ABSTRACT FROM AUTHOR]

We compared the precision of simple random sampling (SimRS) and seven types of stratified random sampling (StrRS) schemes in estimating regional mean of water-limited yields for two crops (winter wheat and silage maize) that were simulated by fourteen crop models. We found that the precision gains of StrRS varied considerably across stratification methods and crop models. Precision gains for compact geographical stratification were positive, stable and consistent across crop models. Stratification with soil water holding capacity had very high precision gains for twelve models, but resulted in negative gains for two models. Increasing the sample size monotonously decreased the sampling errors for all the sampling schemes. We conclude that compact geographical stratification can modestly but consistently improve the precision in estimating regional mean yields. Using the most influential environmental variable for stratification can notably improve the sampling precision, especially when the sensitivity behavior of a crop model is known. [ABSTRACT FROM AUTHOR]

The pattern of perennial dry matter (DM) was manipulated over two seasons to determine if the establishment of lucerne ( Medicago sativa L.) is regulated by the demand for assimilate by perennial organs, (taproot plus crown) or crop ontogeny. Crops of ‘Stamina 5’ lucerne were established from spring to late summer at two sites which differed by 230 mm to 2.3 m soil depth in plant available water content (PAWC) at Lincoln University, New Zealand. The establishment phase was characterised from sowing until crops reached a maximum accumulation of perennial biomass of ∼5 t DM ha −1 . Demand for biomass offered insight into the variability in fractional partitioning of DM to the perennial organs ( P root ) during establishment. This showed that P root was 0.48 until a perennial biomass of 2.9 ± 0.28 t DM ha −1 . Lucerne continued to partition DM to the perennial organs until a maximum biomass of ∼5 t DM ha −1 , but at a decreasing rate shown by a linear decline in P root in response to increasing perennial biomass . This meant P root was independent of crop ontogeny, but most likely still under the control of environmental influences, and the establishment phase extended into the second season for crops which had not attained a perennial biomass >3 t DM ha −1 . These crops continued to prioritise the allocation of DM to the perennial organs which explained the 20–25% decrease in shoot yield in the second season when sowing was delayed. This study quantified the establishment phase of lucerne to perennial biomass demand as independent of crop ontogeny. It showed establishment was regulated by biomass demand of these perennial organs. The spring sown crops on the High PAWC soils completed this phase at the earliest in 4 months. In contrast, autumn sown crops on the Low PAWC soils took nearly 9 months to complete this phase. These results indicate different management strategies may be required to establish lucerne rather than solely using first flowering as a sign that the establishment phase is complete. Results can be incorporated into the current partitioning framework to improve the simulation modelling of lucerne. [ABSTRACT FROM AUTHOR]

The Plant Modelling Framework (PMF) is a software framework for creating models that represent the plant components of farm system models in the agricultural production system simulator (APSIM). It is the next step in the evolution of generic crop templates for APSIM, building on software and science lessons from past versions and capitalising on new software approaches. The PMF contains a top-level Plant class that provides an interface with the APSIM model environment and controls the other classes in the plant model. Other classes include mid-level Organ, Phenology, Structure and Arbitrator classes that represent specific elements or processes of the crop and sub-classes that the mid-level classes use to represent repeated data structures. It also contains low-level Function classes which represent generic mathematical, logical, procedural or reference code and provide values to the processes carried out by mid-level classes. A plant configuration file specifies which mid-level and Function classes are to be included and how they are to be arranged and parameterised to represent a particular crop model. The PMF has an integrated design environment to allow plant models to be created visually. The aims of the PMF are to maximise code reuse and allow flexibility in the structure of models. Four examples are included to demonstrate the flexibility of application of the PMF; 1. Slurp, a simple model of the water use of a static crop, 2. Oat, an annual grain crop model with detailed growth, development and resource use processes, 3. Lucerne, perennial forage model with detailed growth, development and resource use processes, 4. Wheat, another detailed annual crop model constructed using an alternative set of organ and process classes. These examples show the PMF can be used to develop models of different complexities and allows flexibility in the approach for implementing crop physiology concepts into model set up. [ABSTRACT FROM AUTHOR]