Mediterranean-type Environment Research Articles

Modelling of Indoor Air Quality and Thermal Comfort in Passive Buildings Subjected to External Warm Climate Conditions

Air renewal rate is an important parameter for both indoor air quality and thermal comfort. However, to improve indoor thermal comfort, the air renewal rate to be used, in general, will depend on the outdoor air temperature values. This article presents the modelling of indoor air quality and thermal comfort for occupants of a passive building subject to a climate with warm conditions. The ventilation and shading strategies implemented for the interior spaces are then considered, as well as the use of an underground space for storing cooled air. The indoor air quality is evaluated using the carbon dioxide concentration, and thermal comfort is evaluated using the Predicted Mean Vote index. The geometry of the passive building, with complex topology, is generated using a numerical model. The simulation is performed by Building Thermal Response software, considering the building’s geometry and materials, ventilation, and occupancy, among others. The building studied is a circular auditorium. The auditorium is divided into four semi-circular auditoriums and a central circular space, with vertical glazed windows and horizontal shading devices on its entire outer surface. Typical summer conditions existing in a Mediterranean-type environment were considered. In this work, two cases were simulated: in Case 1, the occupation is verified in the central space and the four semi-circular auditoriums and all spaces are considered as one; in Case 2, the occupation is verified only in each semi-circular auditorium and each one works independently. For both cases, three strategies were applied: A, without shading and geothermal devices; B, with a geothermal device and without a shading device; and C, with both shading and geothermal devices. The airflow rate contributes to improving indoor air quality throughout the day and thermal comfort for occupants, especially in the morning. The geothermal and shading devices improve the thermal comfort level, mainly in the afternoon.

Assessment of the phenotypic diversity and agronomic performance of a Mediterranean lentil collection under rainfed conditions: towards efficient use in breeding programs for adaptation to Mediterranean-type environment

Assessment of the phenotypic diversity and agronomic performance of a Mediterranean lentil collection under rainfed conditions: towards efficient use in breeding programs for adaptation to Mediterranean-type environment

Integrating Thermal Indices and Phenotypic Traits for Assessing Tree Health: A Comprehensive Framework for Conservation and Monitoring of Urban, Agricultural, and Forest Ecosystems

Successful conservation through monitoring of ecosystems and species, which entails the quantification of disturbances at the ecosystem, species, and population levels, presents significant challenges. Given the pivotal role of this information in formulating effective strategies for tree conservation, we establish an integrated methodological framework that characterizes the overall health state of trees in urban, agricultural, and forest ecosystems, at species and individual levels, by connecting various non-invasive techniques and field metrics. To accomplish this, we collected thermal and phenotypic information from 543 trees representing five prevalent tree species, distributed across urban, agricultural, and forest settings, within a typical Mediterranean environment, and we developed trunk thermal indicators to describe species’ responses to various disturbances. We (a) examined thermal pattern variations within and among the tree species, (b) explored the relationships between phenotypic traits and trunk thermal indices, (c) quantified the influence of these indices on leaf area index, and (d) classified trees that exhibit defects and fungal pathogens based on these indices. Results showed clear differentiation of thermal and LAI patterns both among tree species and based on the presence or absence of defects. The trunk thermal indices played a significant role in characterizing tree health and predicting LAI, exhibiting strong relationships with phenotypic traits, thereby demonstrating their potential as universal indicators of tree health. Additionally, the inclusion of cavities and fungal presence in the assessment of tree health provided valuable insights into the impact of structural abnormalities on the overall tree condition. Combining trees’ phenotypic traits, vitality indices, and trunk thermal indices allowed the successful classification of defects, cavities, and fungal infestation in 91.4%, 88%, and 88% of trees, respectively. By considering the inter-relationships among thermal indices and phenotypic traits, we can confidently identify and quantify tree health, contributing to the conservation of tree species in diverse ecosystems.

Field Screening of Lentil (Lens culinaris) for High-Temperature Tolerance

Lentil production in arable, Mediterranean-type climates is limited by acute high temperature (HT) commonly occurring during the reproductive stage. With changing climate and greater weather extremes, there is a need to increase the HT tolerance of lentil to sustain production, and global germplasm provides adaptation opportunities. The current study assessed 81 genotypes for HT tolerance from a range of global climatic zones. Field screening of germplasm was undertaken over two consecutive years (2014 and 2015), in southern Australia, using a late-sowing approach, which included a subset of 22 genotypes that were screened in both years. Partially shaded temperature treatments within a split-plot arrangement were used to generate two different HT profiles. Stress indices, i.e., the yield stability index (YSI), the stress tolerance index (STI), and a third proposed high-temperature tolerance index (HTTI), were applied to rank the HT tolerance of germplasm. In 2014, under field conditions associated with natural temperature ranges that were favorable for screening, the following five landraces with increased temperature tolerance were identified: AGG 73838, AGG 70118, AGG 70951, AGG 70156, and AGG 70549. Among the 10 commercial varieties tested, one variety (i.e., cv. Nipper) was observed to have HT tolerance. For the YSI, which had the greatest amount of consistency in response across the 2 years (11 of the 22 genotypes), there were two genotypes (AGG 71457 and Nipper) which maintained their yield stability. These results demonstrate the opportunity that germplasm provides to improve the adaptation of lentil to HT. Ultimately, the late-sowing approach is one possible methodology to integrate into contemporary breeding programs for improving adaptation of lentil within Mediterranean-type environments.

Rooting depth and water use of summer cover crops in a semi-arid cropping environment

Summer cover crops could add biomass (groundcover), fix nitrogen (legumes) and create biopores in Mediterranean-type cropping systems, but soil water use, especially from the subsoil, may reduce yields of the following winter cash crop. Research on rooting patterns/depth of summer cover crops and consequences for soil moisture storage in Mediterranean-type cropping systems is limited. To assess the rooting patterns and water use of a range of legume (sunn hemp, cowpea, mung bean, lablab), non-legume broadleaf (buckwheat, radish) and cereal (millet) summer cover crops in a Mediterranean-type environment, two field trials (2020 and 2021) and one glasshouse experiment were conducted. Root distribution, rooting depth, root diameter, water use and shoot biomass were evaluated. Millet produced the most biomass of any single species in the field (around 4 t ha-1) and had significantly higher water use efficiency (8.4 g L-1) than all legumes (4–6 g L-1). Millet and buckwheat exhibited dense, shallow root systems that exploited water in the profile surface, while legumes, particularly cowpea, had greater root density in the subsoil, resulting in greater subsoil water use. All legumes had significantly greater average root diameter (0.5–0.7 mm) below 40 cm than millet, buckwheat and radish (0.2–0.4 mm). Dual species mixes with millet or cowpea generally led to increased biomass production and increased rooting and water use in deeper soil layers compared to single species cover crops. The results suggest that millet may be preferable in seasons where the key objective of a summer cover crop is to provide ground cover with minimal water use, whereas in wetter seasons, legumes may be beneficial in drying the subsoil and potentially creating biopores. Ultimately, all cover crops significantly reduced stored soil water compared to a chemical fallow, which will likely affect cash crop yield in many seasons.

Adaptation to climate change through strategic integration of long fallow into cropping system in a dryland Mediterranean-type environment

The crop-growing region of Western Australia characterized by a Mediterranean-type climate is projected to become warmer and drier. Appropriate selection of crop sequences will be of importance to cope with these climatic changes for this largest grain-producing region of Australia. Through linking a widely used crop model (APSIM), 26 General Circulation Models (GCMs) with one Shared Socioeconomic Pathway (SSP585) and economic analysis, we explored how the climate change would affect dryland wheat cropping and whether/how long fallow (the practice of leaving a field out of production for an entire growing season) could be integrated into wheat cropping system in Western Australia. The potential adaptation of long fallow into wheat system was assessed with four fixed rotations (fallow-wheat, fallow-wheat-wheat, fallow-wheat-wheat-wheat, and fallow-wheat-wheat-wheat-wheat) and four flexible sowing rule-based rotations (the land was fallowed if sowing rule was not met), compared with continuous wheat. The simulation results at four representing locations show that climate change would have negative impacts on both yield and economic return of continuous wheat cropping in Western Australia. Wheat after fallow out-yielded and out-profited wheat after wheat under future climate. But integrating fallow into wheat cropping systems with the above fixed rotations would lead to yield and economic loss. By contrast, cropping systems in which fallowing took place when sowing condition could not be met at a certain time would achieve comparable yield and economic return to continuous wheat, with wheat yield being only 5 % less than continuous wheat and the gross margin being $12 ha−1 more than continuous wheat averaged across locations. We highlight strategic integration of long fallow into cropping system in a dryland Mediterranean-type environment would have a great potential to cope with future climate change. These findings can be extended into other Mediterranean-type cropping regions in Australia and beyond.

Maize Yield Response, Root Distribution and Soil Desiccation Crack Features as Affected by Row Spacing.

Plant density is among the most critical factors affecting plant yields and resource use efficiency since it drives the exploitation of the available resources per unit area, root distribution and soil water losses by direct evaporation from the soil. Consequently, in fine-textured soils, it can also affect the formation and development of desiccation cracks. The aim of this study, carried out on a sandy clay loam soil in a typical Mediterranean environment, was to investigate the effects of different row spacings of maize (Zea mais L.) on yield response, root distribution and the main features of desiccation cracks. The field experiment compared bare soil and soil cropped with maize using three plant densities (6, 4 and 3 plants m-2), obtained by keeping the number of plants in a row constant and varying the distance between the rows (0.5-0.75-1.0 m). The highest kernel yield (16.57 Mg ha-1) was obtained with the greatest planting density (6 plants m-2) with a row spacing of 0.5 m; significantly lower yields were recorded with spacings of 0.75 and 1 m, with a decrease of 8.09% and 18.24%, respectively. At the end of the growing season, soil moisture in the bare soil was on average 4% greater in comparison to the cropped soil and was also affected by row spacing, decreasing with the decrease in the inter-row distance. An inverse behaviour was observed between soil moisture and both root density and desiccation crack size. Root density decreased to the increase in soil depth and to the increase in distance from the row. The pluviometric regime occurred during the growing season (total rainfall of 343 mm)-resulted in the formation of cracks of reduced size and with an isotropic behaviour in the bare soil, whereas in the cultivated soil, the cracks were parallel to the maize rows and increased in size with decreasing inter-row distance. The total volume of the soil cracks reached a value of 135.65 m3 ha-1 in the soil cropped with a row distance of 0.5 m, and was about ten times greater in comparison to the bare soil and three times greater in comparison to a row spacing of 1 m. Such a volume would allow a recharge of 14 mm in the case of intense rainy events on soil characterised by low permeability.

Productivity and quality of different tomato cultivars under intercropping system with maize and dry farming conditions in Southern Italy

This research, carried out in a typical Mediterranean environment of Southern Italy, reports some quantitative and qualitative traits of three local tomato cultivars (‘Arsicolo’, ‘Crovarese’, and ‘San Marzano’) plus a commercial one (‘Datterino’) cultivated without irrigation and intercropped with maize. For each cultivar, in addition to the determination of fruit production, tomato paste and “conserva” paste were prepared using a traditional technique of the Tanagro Valley (province of Salerno, Southern Italy). Results highlighted that ‘Arsicolo’ showed the best fruit yield (32.2 metric tons ha-1) and tomato paste production (92.9% paste return by tomato fruits weight) due to its ancient peculiar adaptability to cultivation in dry conditions, while ‘Datterino’, ‘Crovarese’, and ‘San Marzano’ had 19, 16.7, 10.5 tons ha-1 of fruit yield and 85.7, 83.9, 76.2% of tomato paste return, respectively. Conversely, for the qualitative traits, such as total solids, soluble solids, titratable acidity, and ascorbic acid, ‘Crovarese’ showed the best results (9.1%, 6.6 °Brix, 0.93%, and 39.7 mg per 100 g of fresh weight, respectively). The two components extracted by the principal components analysis (PCA) explained 84.9% of the total variance in the morphological, quantitative and qualitative traits and the dendrogram obtained by hierarchical cluster analysis allowed to divide the cultivars into three groups. Our findings highlighted that local tomato cultivars, intercropped with maize, can be cultivated adopting only few sustainable field operations and with no irrigation.

Integrating long fallow into wheat-based cropping systems in Western Australia: Spatial pattern of yield and economic responses

CONTEXTLong fallow, once a common management practice in the low-rainfall of Mediterranean-type environments, may provide growers with an opportunity to switch cropping sequence and reduce the risk of yield and income losses during the recent drought period. However, such benefits are usually not uniform across a spatially variable environment. It is important to identify where long fallow would have a role in increasing crop yield and economic return. OBJECTIVETo examine the spatial pattern of yield and economic performance of integrating long fallow into a wheat cropping system in dryland Mediterranean environments of Western Australia. METHODSThe Agricultural Production Systems Simulator (APSIM) driven by 0.05° gridded climate over the dry period of 1990–2020 was used to simulate five rotations (fallow followed by one, two, three or four wheat crops, respectively) and continuous wheat. With offset simulations, simulated wheat yields, plant available water at sowing after a wheat crop or long fallow and N fertilizer requirement were compared and analysed for fallow-wheat and wheat-wheat. Wheat yields and economic returns were also calculated for each rotation and compared with continuous wheat. RESULTS AND CONCLUSIONSWheat yield and economic responses to long fallow showed clear geographic patterns that increased from the south-west to north-east across the wheatbelt, which could be explained by climate and soil conditions. Yield increase from fallow could be >6%, equivalent to 13% of economic increase, in the areas where growing season rainfall was <230 mm and the difference in plant available soil water at sowing between fallowed and continuously cropped soil was >30 mm. Although fallow resulted in overall reduction in crop production, integrating one fallow into a continuous wheat sequence every three or more years might achieve similar profit to continuous wheat for fields with weeds and diseases challenges in the north-eastern wheatbelt. SIGNIFICANCEThe results of yield and economic performance after fallow in the context of space and crop sequence provide a systematic analysis to map where and how fallow could be adopted into cropping systems.

Potential Nitrogen Contributions by Tropical Legume Summer Cover Crops in Mediterranean-Type Cropping Systems

Legume cover crops in temperate cropping systems can fix substantial amounts of nitrogen (N) and reduce N fertiliser requirements for subsequent crops. However, little is known about potential biological N2 fixation by summer cover crop legumes in the short summer fallow in Mediterranean-type cropping systems. Six legume species (balansa clover, barrel medic, mung bean, sunn hemp, lablab and cowpea) were grown for 8–9 weeks in the field in semi-arid southern Australia during the summer fallow, and in a glasshouse experiment, to estimate N2 fixation using the 15N natural abundance method. Cowpea, sunn hemp and lablab produced 1.2–3.0 t ha−1 biomass in the field while balansa clover and barrel medic produced &lt; 1.0 t ha−1. The percent of N derived from the atmosphere (%Ndfa) in the field ranged from 39% in barrel medic to 73% in sunn hemp, but only 15% (balansa clover) to 33% (sunn hemp) in the glasshouse experiment, likely due to higher soil mineral N availability in the glasshouse study. Biological N2 fixation of cowpea and sunn hemp in the field was 46–55 kg N ha−1, while N2 fixation in lablab and mung bean was lower (around 26 kg N ha−1). The N2 fixation in cowpea and sunn hemp of around 50 kg N ha−1 with supplementary irrigation in the field trial likely represents the upper limit of N contributions in the field in typically hot, dry summer conditions in Mediterranean-type climates. Given that any increase in summer cover crop biomass will have implications for water balances and subsequent cash crop growth, maximising N benefits of legume cover crops will rely on increasing the %Ndfa through improved rhizobium strains or inoculation technologies. This study provides the first known estimates of biological N2 fixation by legume cover crops in the summer fallow period in cropping systems in Mediterranean-type environments, providing a benchmark for further studies.

Shifting the Sowing Date of Winter Wheat as a Strategy for Adaptation to Climate Change in a Mediterranean-Type Environment

Shifting the Sowing Date of Winter Wheat as a Strategy for Adaptation to Climate Change in a Mediterranean-Type Environment

Effects of dryland summer cover crops and a weedy fallow on soil water, disease levels, wheat growth and grain yield in a Mediterranean-type environment

Numerous studies have reported wide-ranging benefits of cultivating cover crops during the typical fallow period in temperate cropping systems. However, data on the impacts of summer cover crops in water-limited, Mediterranean-type climates, is lacking. A 3-year field experiment was conducted near the town of Northam in the wheat-belt of Western Australia to test the hypothesis that inclusion of summer cover crops would increase ground cover, water storage and grain yield in subsequent wheat crops. White French millet ( Panicum miliaceum ) and cowpea ( Vigna unguiculata ) cover crops and a weedy fallow were compared to a typical chemical fallow over the summer period. Autumn groundcover was 10–30% higher when summer weeds were left uncontrolled compared to the chemical fallow treatment. Dry-sown and late established (February) millet failed to increase groundcover, whereas cowpea demonstrated a small increase (~9–10%) in one season, when cowpea biomass approached 1 t ha −1 . Cover crops and weeds growing over summer had no significant effect on total plant available water (0–50 cm depth) prior to sowing wheat in any season. However, there was less readily available soil N in the cover crop (less 10–30 kg N ha −1 ) and weedy fallow (less 50 kg N ha −1 ) treatments prior to the second wheat crop. Despite some significant effects of weedy fallow and cowpeas on Gaeumannomyces graminis var tritici (take-all) and Didymella pinodes (causing black pea spot), disease levels were low and thought to pose little risk to following winter crops. Wheat grain yields were not significantly different between treatments, other than a low yield after cowpeas in 2015 due to a low wheat emergence count. Grain protein and screenings were not generally affected by summer fallow treatment in any year, except for higher screenings after the weedy fallow in one year. Given the limited impacts of cover crops and weeds on soil water and disease, it is possible that summer cover crops may be able to be integrated with cereal winter rotations in Western Australia without yield reductions in wheat crops. In light of current chemical usage, issues around herbicide residues in soil and herbicide-resistant weeds, it would be worthwhile revisiting the need for chemical fallow, particularly in the higher rainfall areas.

Grain size variation in two-rowed malt barley under Mediterranean conditions: Phenotypic plasticity and relevant trade-offs

In Mediterranean type environments large variability in grain plumpness, defined as the proportion of grains retained over a 2.5 mm sieve, is a critical source of uncertainty for brewers and farmers. Understanding the mechanisms that regulate grain size under stressful environments will assist breeders to promote stability and improve grain size. Using an unbiased data set ( n = 171) derived from 21 different environments (Years x Locations) and 29 European malt barley varieties, we aimed to (i) analyze the effect of genotype × environment interaction on plump grains and yield components variation from the viewpoint of phenotypic plasticity and (ii) explore the extent to which grain size associates with grain yield (GY) potential, grain number and grain protein content (GPC). Plump grains (% grains>2.5 mm), was the trait with the highest plasticity in two-rowed barley. A thorough assessment of the relationship between Thousand Kernel Weight (TKW) and the different grain size classes (i.e. > 2.8 mm; 2.5–2.8 mm; > 2.5 mm; 2.2–2.5 mm; < 2.2 mm) revealed that the stability of TKW was preserved by adjusting not only the number of seeds set, but also proportions among the different grain size classes. Our data supported the following hierarchy of plasticities: plump grains > grains/m 2 > GY > spikes/m 2 > TKW > Harvest Index > grains/spike . With decreasing GY there was also an apparent decrease in plump grains production. The number of grains/m 2 had a markedly larger negative effect on plump grains under low-yielding conditions compared to medium and high-yielding conditions. In addition, a high inherent number of grains/spike (> 26) not only had a negative effect on GY, but also undermined grain plumpness. Under the tested G × E interaction, both grain yield and plump grains were positively affected when grain yield formation was mainly based on a greater number of spikes/m 2 with fewer and heavier (≈larger) grains/spike. GPC had a relatively strong negative association with plump grains. However, when the conditions favoured plump grains formation, the risk of recording low GPC was increased. This revealed that under Mediterranean conditions the challenge is not only the high values of GPC, but the low ones as well. • Plump grains was the trait with the highest plasticity in two-rowed barley. • Direct selection for grain size under favorable conditions is questioned. • High potential of grains/spike had a negative effect on both grain yield and size. • Grain size was regulated by grain number and yield conditions. • Grain protein content was negatively associated with grain size.

Performance of fourteen genotypes of durum wheat under Eastern Mediterranean conditions

Durum wheat is used as raw material for many foods. Climate change might be responsible for larger or smaller changes in crop yields. For the combined assessment of climate and crop, growing degree days (GDDs) have a crucial role. Two experimental lines and twelve commercial wheat (Triticum durum) varieties from diverse backgrounds were cultivated to compare their crop properties, yield, and protein content in terms of GDDs. The experiment was established in typical Mediterranean environment, using a randomized complete block design with blocks of varieties and lines for two growing seasons. For all varieties, GDDs to head emergence was affected by factor year, whereas GDDs from head emergence to harvest were influenced by both varieties and year. Protein content (%) was not affected by genotypes. Factor of variety and interaction variety × year had an impact on vitreousness; it was ranged from 79.75 % (‘Makaras’ variety) to 44.00 % (‘Levante’ variety). Yield had no statistically significant difference among varieties/lines. In durum wheat cultivation, up to head emergence, when GDDs increased, yield would be declined in contrast to GDDs from emergence to harvest; with the increasing of GDDs to harvest, yield was climbed. Nowadays, the integrations of and interpretation of GDDs in the evaluation of crop performance seem vital.

Variability of black carbon aerosol concentrations and sources at a Mediterranean coastal region

To investigate the temporal variation of aerosol optical properties and evaluate the main emission sources of black carbon (BC) considering different seasons in a typical Mediterranean coastal environment, a field campaign was conducted during February–July 2019 at the Central Adriatic coastal area. Real-time measurements of aerosol light absorption were continuously obtained using an aethalometer while the Aethalometer model source apportionment data, optimized by using levoglucosan measurements, were evaluated against the modelling results of the LOTOS-EUROS chemical transport model. The measured mean equivalent BC mass concentration of 0.57 ± 0.64 μg m−3 was the lowest observed in the Mediterranean region. BC from fossil fuel (BCff) dominated the area throughout the study period with a maximum in winter and elevated levels by the approaching summer tourist season. Diel variability of BC concentrations from biomass burning (BCbb) was observed during stable winter conditions, with clear morning and evening concentration peaks, consistent with the profile of residential heating by wood burning. Up to 88% of BC concentrations were attributed to European emission sectors, with stationary source combustion, transportation, shipping and agriculture sectors being the most influential contributors. Source apportionment of BC highlighted that, in addition to biomass burning, small combustion fossil fuel sources, including land traffic and shipping, should be more strictly controlled in order to limit BC pollution in Mediterranean coastal areas. This study serves as a basis of comparison for future studies addressing air quality and pollution source apportionment in the Adriatic and/or the Mediterranean coastal regions in efforts of mitigation and adaptation to climate change.

Contribution of Wild Relatives to Durum Wheat (Triticum turgidum subsp. durum) Yield Stability across Contrasted Environments

Durum wheat (Triticum turgidum subsp. durum) is mostly grown in Mediterranean type environments, characterized by unpredictable rainfall amounts and distribution, heat stress, and prevalence of major diseases and pests, all to be exacerbated with climate change. Pre-breeding efforts transgressing adaptive genes from wild relatives need to be strengthened to overcome these abiotic and biotic challenges. In this study, we evaluated the yield stability of 67 lines issued from interspecific crosses of Cham5 and Haurani with Triticum dicoccoides, T. agilopoides, T. urartu, and Aegilops speltoides, grown under 15 contrasting rainfed and irrigated environments in Morocco, and heat-prone conditions in Sudan. Yield stability was assessed using parametric (univariate (e.g., Bi, S2di, Pi etc) and multivariate (ASV, SIPC)) and non-parametric (Si1, Si2, Si3 and Si6) approaches. The combined analysis of variance showed the highly significant effects of genotypes, environments, and genotype-by-environment interaction (GEI). The environments varied in yield (1370–6468 kg/ha), heritability (0.08–0.9), and in their contribution to the GEI. Several lines derived from the four wild parents combined productivity and stability, making them suitable for unpredictable climatic conditions. A significant advantage in yield and stability was observed in Haurani derivatives compared to their recurrent parent. Furthermore, no yield penalty was observed in many of Cham5 derivatives; they had improved yield under unfavorable environments while maintaining the high yield potential from the recurrent parent (e.g., 142,026 and 142,074). It was found that a limited number of backcrosses can produce high yielding/stable germplasm while increasing diversity in a breeding pipeline. Comparing different stability approaches showed that some of them can be used interchangeably; others can be complementary to combine broad adaption with higher yield.

Crop rotation can be used to manipulate residue levels under no-tillage in a rainfed Mediterranean-type environment

Fields with low residue levels (<∼2 t ha−1) are prone to erosion and reduced water conservation in semi-arid environments, and high residue amounts (>∼4 t ha−1) can reduce crop establishment and herbicide efficacy. Furthermore, increasing herbicide resistance in southern Australia has resulted in an increase in non-herbicide control measures like ‘windrow burning’, which reduces residue levels. Therefore, it is important to understand crop residue dynamics in this Mediterranean-type environment and any management factors that can be used to regulate amounts of residue. This paper reports on the residue dynamics in a 12-year experiment (2007–2018) in the Wheatbelt of Western Australia, comparing rotations that included: cereal (cereal/cereal/cereal); diverse (wheat/legume/canola); farmer (wheat/barley/break – legume or fallow); and wheat monoculture. Crop residue was either spread behind the harvester (retain) or windrowed at harvest and burnt before seeding (windrow burn). Residue quantity was measured shortly after harvest (usually in December), prior to seeding (usually April), and around anthesis (September).Crop residue amounts were highest after harvest each year and then declined over the next 12 months, until the next harvest. Residue quantity was greatest following years of high rainfall and good crop growth. Within rotations, residue quantity was highest with retained residue in the cereal rotation and wheat monoculture, averaging 5.0 t ha−1 prior to seeding, which could present management problems at seeding time in some years. Residue amounts were lower in the diverse rotation, and levels declined after wheat (4.5 t ha−1) through to legume and canola residue at 3.8 t ha−1. Lowest residue occurred with windrow burning in the farmer rotation, which included one fallow every three years from 2013, with quantities averaging ∼1 t ha−1. Overall, windrow burning before seeding reduced residue amount by ∼50 % compared with retaining the residue.Retaining all residue in a cereal-dominant rotation produced highest residue quantities in this Mediterranean-type environment, but may lead to problems with crop establishment. Residue quantity was reduced to optimal levels by including legume crops or canola in the rotation, as these residues were more rapidly broken down than cereal residues, whilst maintaining residue retention practices.

The utility of combining optical and thermal images in monitoring agricultural drought in semiarid mediterranean environments

Agricultural drought in a typical semiarid Mediterranean environment is investigated during the growing seasons of 1997 through 2020 using a combination of optical and thermal sensors onboard Landsat satellites. The combination of the Normalized Difference Vegetation Index – Land Surface Temperature (NDVI- LST) space was able to distinguish between drought and non-drought years. A distinct trapezoidal shape was clearly defined during non-drought years, reflecting the strong negative correlation between NDVI and LST. The NDVI-LST space was poorly defined for drought-stricken years with no clear link between the two parameters. The non-universal relationship between LST and NDVI was addressed using the Monin- Obukhov similarity formulation which shows that the widely observed convergence of LST at high NDVI values could be explained by the asymptotic nature of LST against surface roughness length for non-stressed vegetation.The NDVI-LST space was compared with seasonal and annual precipitation and different SPI windows to check the ability of the remote sensing metric to identify drought. A high correlation exists between the NDVI-LST space on the one hand and the 9- month, annual precipitation, the SPI-6, SPI-9 and SPI-12 windows, with correlation coefficients of 0.74, 0.76, 0.76, 0.80, and 0.80, respectively, which are statistically significant.

Using Unmanned Aerial Vehicle and Ground-Based RGB Indices to Assess Agronomic Performance of Wheat Landraces and Cultivars in a Mediterranean-Type Environment

The adaptability and stability of new bread wheat cultivars that can be successfully grown in rainfed conditions are of paramount importance. Plant improvement can be boosted using effective high-throughput phenotyping tools in dry areas of the Mediterranean basin, where drought and heat stress are expected to increase yield instability. Remote sensing has been of growing interest in breeding programs since it is a cost-effective technology useful for assessing the canopy structure as well as the physiological traits of large genotype collections. The purpose of this study was to evaluate the use of a 4-band multispectral camera on-board an unmanned aerial vehicle (UAV) and ground-based RGB imagery to predict agronomic traits as well as quantify the best estimation of leaf area index (LAI) in rainfed conditions. A collection of 365 bread wheat genotypes, including 181 Mediterranean landraces and 184 modern cultivars, was evaluated during two consecutive growing seasons. Several vegetation indices (VI) derived from multispectral UAV and ground-based RGB images were calculated at different image acquisition dates of the crop cycle. The modified triangular vegetation index (MTVI2) proved to have a good accuracy to estimate LAI (R2 = 0.61). Although the stepwise multiple regression analysis showed that grain yield and number of grains per square meter (NGm2) were the agronomic traits most suitable to be predicted, the R2 were low due to field trials were conducted under rainfed conditions. Moreover, the prediction of agronomic traits was slightly better with ground-based RGB VI rather than with UAV multispectral VIs. NDVI and GNDVI, from multispectral images, were present in most of the prediction equations. Repeated measurements confirmed that the ability of VIs to predict yield depends on the range of phenotypic data. The current study highlights the potential use of VI and RGB images as an efficient tool for high-throughput phenotyping under rainfed Mediterranean conditions.

Redefining the link between rainfall and crop establishment in dryland cropping systems

ContextThe seasonal break is a rainfall event that has traditionally initiated sowing and enabled plant establishment in Mediterranean-type environments. Despite its importance to crop production, neither the pattern of the seasonal break, nor the impact of recent autumn rainfall decline in eastern Australia on the pattern has been quantified at a national scale. Adaptive strategies to remove reliance on the seasonal break for crop establishment can include combinations of novel genotypes and innovative crop management. ObjectiveThis paper (i) shows how seasonal changes may be altering the pattern of sowing opportunities across southern Australia, and (ii) evaluates the potential for adaptive management to deal with these changes using a case-study in southern Australia involving early, deep-sown wheat cultivars with long coleoptiles to reduce the dependence on the seasonal break for successful crop establishment. MethodsIn the first part of the study, the timing of the seasonal break across the southern Australian cropping regions was determined using the sum of a 7-day rolling mean rainfall to evaporation ratio > 1 to trigger a sowing opportunity between 1 March and 30 July using long-term (1971–2018) gridded (0.05° × 0.05°) historical climate data. The relationship between early-season climatic conditions and adaptive management options was then evaluated using a growth chamber experiment and a field experiment in a Mediterranean-type environment to evaluate the factors leading to successful establishment of earlier deeply sown wheat cultivars with long coleoptiles. Results and conclusionsThe analysis revealed spatial and seasonal variability with the earliest median seasonal break (27-March) in New South Wales (NSW) and Victoria, and the latest (3-June) in Western Australia (WA). The largest shift in seasonal break was a 17-day advance in the Mallee and Sandplain of WA, and an 11-day delay in Central NSW during the period 1990–2018. Evaluation of the factors controlling establishment of a long coleoptile wheat cultivar suggested that soil temperatures in the early sowing windows were unlikely to reduce coleoptile length, but seeding depth, soil type and water availability will play an important role on emergence. SignificanceIn summary, the shifts in the climatic conditions at the break of the growing season have not been the same across the southern cropping region. Adaptations for this climatic shift such as long-coleoptile, deep-sowing strategies for wheat show significant promise but careful consideration of soil factors is required to ensure success and to improve on-farm decision making regarding its use.