Elevated carbon dioxide (e-CO₂) levels from ambient (a-CO₂) enhance plant biomass production and yield. However, this response is highly dependent on the availability and possibly the form of nitrogen (N) supply to plants. This study aimed to investigate changes in C and N metabolism of wheat (Triticum aestivum L.) in response to e-CO₂ and N source. e-CO₂ enhanced net CO₂ assimilation but at highly variable rates depending on the form of N supply. Under e-CO₂, net CO₂ assimilation rate was in the order NO₃^– > NH₄NO₃ > NH₄⁺ > urea. Plants supplied with ammonium and nitrate (i.e. NH₄NO₃) performed better in terms of biomass production and expressed a higher biomass enhancement ratio by e-CO₂ than plants receiving sole applications of NO₃^–, NH₄⁺ or urea. Supply of NH₄NO₃ also resulted in lower intercellular CO₂, higher photoassimilate translocation to roots and lower accumulation of free amino acids than other N forms, indicating a better exploitation of the e-CO₂ environment. Our results conclude that major physiological pathways of photosynthesis and protein and carbohydrate metabolism are differentially influenced by e-CO₂ depending on the source of N supply. A balanced supply of NO₃^– and NH₄⁺ to plant roots is the key to harnessing e-CO₂ while minimising its adverse effects on quality of the produce.

Critical ranges for soil tests are based on results that inevitably involve some broad variance around the fitted relationship. Some of the variation is related to field-based factors affecting crop response to nutrients in the soil and some to the efficiency of the soil-test extractant itself. Most attempts to improve soil tests focus on the extractant, whereas here, we explore the variation that could be accounted for by field-based factors in the soil-test calibration relationship between Colwell phosphorus (P) and wheat yield, using the Australian Better Fertiliser Decisions for Crops database—the biggest dataset available for this relationship. Calibrations developed from this dataset have been criticised, and so we aimed to explore factors accounting for more of the variation in the relationships for the dryland, winter-dominant rainfall region of southern New South Wales.

As reported previously, soil type was shown to influence the critical range and r-value for the Colwell P soil-test calibration for P responses by wheat. We also identified a tendency for dry conditions, at sowing or during the season, to lower relative yields for a given soil-test value, indicating increased reliance on fertiliser P over soil P. A similar trend was evident for later sowing date, again suggesting an increased probability of crop P requirements being met from the fertiliser P. However, additional records need to be generated to establish definitively that early sowing or subsurface P reserves minimise response to fertiliser P. In general, factors that influence crop access to soil P will have an impact on response to fertiliser P.

Although this analysis shows that it is possible to ‘tighten’ the response curve for Colwell P and wheat by restricting the data for a given soil type to ideal management and seasonal conditions, the ‘outliers’ that are excluded frequently reflect an important subset of environmental conditions encountered by wheat crops in dryland agriculture.

The pathogenic fungal species Pyrenophora tritici-repentis (Ptr) and Parastagonospora nodorum (Pan) are common in many wheat-producing parts of the world. These two fungi cause tan spot and septoria nodorum blotch, respectively, frequently co-infecting wheat leaves. Empirical studies of this and other co-infections are rare because of the visual similarity of symptoms and the lack of robust methods for quantifying the abundance of pathogens associated with the co-infection. Here, we use a recently developed molecular method that simultaneously distinguishes and quantifies, in DNA equivalent, the abundance of Ptr and Pan, thereby allowing the prevalence of co-infection to be determined. The study examines the prevalence of co-infection under field conditions, at three widely spaced sites and on three wheat (Triticum aestivum L.) cultivars varying in disease resistance. Co-infection by Ptr and Pan was almost ubiquitous (overall prevalence 94%), and Pan DNA was detected only in association with Ptr. Although Ptr and Pan commonly co-infected, Ptr was more abundant during early and mid-season, at 80% of total fungal abundance when crops were tillering and 67% at booting stage. Pan became as abundant as Ptr when crops reached flowering. Variability in total fungal abundance and disease severity was primarily determined by cultivar; however, Ptr was the more abundant despite differences in cultivar resistance to this pathogen.

The shift in Indian Ocean sea surface temperatures in 1976 led to a change in rainfall for the broad-scale winter annual grain cropping and pasture region in the south-west of Western Australia (the WA wheatbelt). Agriculture in the eastern part the WA wheatbelt was particularly sensitive to the change in rainfall because it is a marginal area for agronomic production, with low rainfall before changes in sea surface temperature. A second shift in sea surface temperature occurred in 2000, but there has been no analysis of the resulting impact on rainfall in the eastern WA wheatbelt. An analysis of rainfall pre- and post-2000 was performed for sites in the eastern WA wheatbelt in three groups: 19 sites in the west, 56 central, and 10 east. The analysis found a decline in growing-season rainfall (i.e. April–October), especially during May–July, post-2000. Rainfall declines of 49.9 mm (west group), 39.1 mm (central group) and 28.0 mm (east group) represented respective losses of 20.1%, 17.4% and 14.2% of growing-season rainfall. Increases in out-of-season rainfall in the respective groups of 31.0, 33.6, and 50.7 mm (57.8%, 60.8% and 87.6%) meant that annual rainfall changes were smaller than growing-season losses. The west and central groups lost 17.5 and 6.16 mm annual rainfall, whereas the east group gained 15.6 mm. Analysis of wheat yield indicated reductions of 13.5% (west) and 9.90% (central) in the eastern WA wheatbelt; the small group of east sites had a potential yield gain of 8.9% arising from the increased out-of-season rainfall. Further, increased out-of-season rainfall will exacerbate weed and disease growth over the summer fallow.

The yield of direct-seeded rice has been shown to decrease after straw amendment. However, the reasons for the yield decrease, and any measures to alleviate it, are currently unknown. We hypothesised that straw return exerts negative effects on soil fertility and on root growth of direct-seeded rice, which subsequently reduces the remobilisation of reserves to grains under continuous flooding (CF); and that alternate wetting and drying (AWD) irrigation can alleviate these negative impacts. Field and greenhouse experiments were conducted to test the hypotheses, by comparing CF and AWD in combination with two wheat-straw treatments (incorporation and mulching). Under CF, wheat-straw incorporation decreased soil available phosphorus by 23–79%, root biomass by 10%, leaf biomass by 13%, and leaf area by 15% compared with the control with no straw incorporation; negative effects on these characteristics were lessened if the straw was mulched. The AWD treatment alleviated the negative effects of straw incorporation compared with CF, and straw mulching with AWD had no negative effects or resulted in positive effects. The results suggest that CF along with straw incorporation limits soil phosphorus availability, root growth and grain yield by affecting photosynthate accumulation and remobilisation. AWD irrigation mitigates these undesirable effects by decreasing soil total reductants, which subsequently increases soil pH and plant-available phosphorus. The proposed AWD treatment could be a promising strategy for the sustainable production of direct-seeded rice.

Faba bean (Vicia faba L.) is a significant rotation crop in northern New South Wales. However, drought limits yield, and the reproductive structures of faba bean are sensitive to high temperatures and frost. Although early sowing can avoid terminal heat and drought stresses, the accumulation of large amounts of vegetative biomass may result in low yield. Experiments were conducted over 2 years at Breeza and Narrabri in north-western New South Wales, Australia, to examine the influence of sowing time on yield, yield components, maturity, pod distribution and biomass production. The second sowing date (early May) produced the highest yield and seed weight at both sites. However, the third sowing date (late May) produced greater yield than the first (mid-April) at Breeza, and this was associated with very high final biomass. At Narrabri, the first and third sowing dates produced similar low yield.

Poorer yield in late-sown materials was likely due to terminal stress, and the impact will be greater in less favourable locations and seasons. The poorer yield of faba bean from the first sowing date was likely driven by excessive biomass accumulation, an effect that would be exacerbated in favourable seasons and locations. The lower seed weight observed at Breeza was possibly a result of greater intra-plant competition. The earliest maturing genotype had the highest yield and seed weight at both sites, indicating the importance of rapid pod growth and senescence in these warm and often water-limited environments. Dry matter production was greater with early sowing, higher moisture and warmer temperatures. In contrast to other studies, a weak relationship between biomass and yield was observed.

Assessment of genetic diversity among chickpea (Cicer arietinum L.) germplasm at the morphological and molecular levels is fundamental for chickpea breeding and conservation of genetic resources. Genetic variability of 46 chickpea genotypes including 42 Algerian genotypes and four control varieties was evaluated by using 15 agro-morphological traits. Eleven molecular markers including nine simple sequence repeats, one sequence characterised amplified region (SCY17) and one gene-specific (CaETR4) were used to characterise the 46 genotypes and eight references varieties added for disease resistance or susceptibility. Genotypes resistant to ascochyta blight were identified by the markers SCY17 and CaETR4 present together. High diversity was observed for all measured morphological traits between genotypes. Yield components, plant height, phenological traits and growth habit were the traits most involved in variation among genotypes and were partitioned into four groups by using principal component analysis. All molecular markers were polymorphic. In total, 91 alleles were obtained ranging from 2 to 21 per locus with average of 8.27 alleles per marker. Polymorphism information content ranged from 0.58 to 0.99 with an average value of 0.87. UPGMA clustering and Bayesian-based model structure analysis grouped genotypes into two clusters, but the distribution of the genotypes by cluster was not the same for the two analyses. According to the presence of markers indicating resistance to ascochyta blight (SCY17 and CaETR4), three resistant genotypes (FLIP 82-C92, ILC 6909, ILC 7241) were selected and should be tested in controlled conditions for confirmation. Considering the narrow diversity of cultivated chickpea, the Algerian genotypes can be considered as interesting for future breeding programs.

Cultivation of buckwheat (Fagopyrum esculentum Moench) under Mediterranean photothermal conditions could affect synthesis of the flavonoid rutin and its partitioning within the plant, thus affecting the nutraceutical value of plant products. We examined rutin concentration and yield in the forage and the grain of common buckwheat grown under Mediterranean field conditions, in response to sowing time, irrigation, growth stage at harvest, and variety. The highest rutin concentration and yield in the forage were obtained with late spring sowing, thanks to greater accumulation of solar radiation and higher efficiency of rutin synthesis per photothermal unit. Water supply promoted a more efficient use of light resources for both biomass accumulation and rutin synthesis. Rainfed conditions reduced biomass accumulation to a greater extent than rutin synthesis. Rutin concentration was highest in leaves, followed by inflorescences, stems and achenes, and in all plant parts it decreased with plant age. In the grain, rutin concentration was highest with late spring sowing, and rutin yield was highest with early spring sowing. Correlation analyses suggest that rutin synthesis proceeds from the leaves to the other plant parts. Our research demonstrates that buckwheat can be cultivated in Mediterranean regions as a source of rutin for medicine and for food and feed supplementation.

Effect of thermo-photoperiod conditions on pre-flowering phasic development, number of unfolded leaves, verticillaster dry weight at flowering (VDW_FL) and grain yield were evaluated for chia (Salvia hispanica L.). The objectives of this study were to: (i) characterise the pre-flowering response of chia to thermo-photoperiod conditions during and pre- and post-inductive subphases; and (ii) determine the relationships between the duration of pre-flowering subphases, the VDW_FL and grain yield. Sowing-date experiments were conducted during three consecutive growing seasons with two chia genotypes under non-stressed conditions. Responses to thermo-photoperiod conditions were characterised by fitting a bi-linear model. All pre-flowering subphases showed a quantitative short-day response with a decrease in sensitivity to photoperiod in the later post-inductive subphase. The duration of the pre-inductive subphase was associated with the number of accumulated unfolded leaves, whereas the durations of the post-inductive subphases were not determined by the number of accumulated unfolded leaves. Higher VDW_FL was achieved when durations of the pre-flowering subphases increased. In addition, increases in the VDW_FL explained most of the variation in grain yield along the thermo-photoperiod conditions. Accordingly, this study suggests that developmental responses of chia and their relationships with VDW_FL and grain yield should be taken into account for grain-yield improvement of this orphan crop.

Grazing, flooding and their combination are major disturbances that could affect plant performance in humid grasslands. We performed two experiments to study the tolerance of the forage grass Paspalum dilatatum Poir. to different submergence depths and defoliation frequencies. First, we addressed whether this species can shift from the escape strategy to ‘quiescence’ when completely submerged for 30 days. Second, we explored to what extent partial or complete submergence produced by defoliation compromises plant regrowth. The results showed that regardless of the depth of water at submergence, P. dilatatum always responded by attempting to expose its leaf area above water, by increasing the tiller angle and/or blade length (i.e. tiller height). Partially submerged plants showed a reduction in starch concentration (89%) but biomass was unaffected, whereas completely submerged plants did not survive. After one defoliation event, 77% of aerial biomass of partially submerged plants was removed and the concentration of carbon reserves (water-soluble carbohydrates and starch) decreased to half that of control plants. A second event of defoliation (20 days later) of plants with few reserves removed 50–52% of shoot biomass and compromised plant survival, with plants dying before the end of the experiment. In conclusion, P. dilatatum does not tolerate prolonged conditions of complete submergence caused by either deep water columns or repeated defoliation.