Showing papers in "Crop & Pasture Science in 2015"

Break crops and rotations for wheat

Abstract: Wheat crops usually yield more when grown after another species than when grown after wheat. Quantifying the yield increase and explaining the factors that affect the increase will assist farmers to decide on crop sequences. This review quantifies the yield increase, based on >900 comparisons of wheat growing after a break crop with wheat after wheat. The mean increase in wheat yield varied with species of break crop, ranging from 0.5 t ha–1 after oats to 1.2 t ha–1 after grain legumes. Based on overlapping experiments, the observed ranking of break-crop species in terms of mean yield response of the following wheat crop was: oats < canola ≈ mustard ≈ flax < field peas ≈ faba beans ≈ chickpeas ≈ lentils ≈ lupins. The mean additional wheat yield after oats or oilseed break crops was independent of the yield level of the following wheat crop. The wheat yield response to legume break crops was not clearly independent of yield level and was relatively greater at high yields. The yield of wheat after two successive break crops was 0.1–0.3 t ha–1 greater than after a single break crop. The additional yield of a second wheat crop after a single break crop ranged from 20% of the effect on a first wheat crop after canola, to 60% after legumes. The mean yield effect on a third wheat crop was negligible, except in persistently dry conditions. The variability of the break-crop effect on the yield of a second wheat crop was larger than of a first wheat crop, particularly following canola. We discuss the responses in relation to mechanisms by which break crops affect soil and following crops. By quantifying the magnitude and persistence of break-crop effects, we aim to provide a basis for the decision to grow continuous cereal crops, strategic rotations or tactically selected break crops. In many wheat-growing areas, the large potential yield increases due to break crops are not fully exploited. Research into quantifying the net benefits of break crops, determining the situations where the benefits are greatest, and improving the benefits of break crops promises to improve the efficiency of wheat-based cropping systems.

Role of magnesium fertilisers in agriculture: plant–soil continuum

Abstract: In this review, we summarise factors contributing to plant availability of magnesium (Mg) in soils, the role of Mg in plant physiological processes related to yield formation and abiotic stress tolerance, and soil and fertiliser parameters related to Mg leaching in fertilised soils. Mg is a common constituent in many minerals, comprising 2% of Earth’s crust; however, most soil Mg (90–98%) is incorporated in the crystal lattice structure of minerals and thus not directly available for plant uptake. Plants absorb Mg from the soil solution, which is slowly replenished by soil reserves. Duration and intensity of weathering, soil moisture, soil pH, and root–microbial activity in soil are key factors that determine plant-available Mg release from soils. On the other hand, the amount of Mg released from soil minerals is generally small compared with the amounts needed to sustain high crop yield and quality. Thus, in many agro-ecosystems, application of Mg fertilisers is crucial. Magnesium is involved in many physiological and biochemical processes; it is an essential element for plant growth and development and plays a key role in plant defence mechanisms in abiotic stress situations. An early effect of Mg deficiency in plants is the disturbed partitioning of assimilates between roots and shoots because the supply of sink organs with photosynthetic products is impaired, and sugars accumulate in source leaves. Thus, optimal supply of Mg is required to improve crop tolerance to various stresses and to increase yield and quality parameters of harvested products. Unlike other cations, Mg is very mobile in soils because it is less bound to the soil charges. Therefore, Mg losses by leaching might occur in sandy soils with high water conductivity. Leaching of Mg in soils when applied with various water-soluble fertilisers may also vary depending on the fertiliser’s chemical composition, granule size, and effect on soil pH and cation balance, as we discuss in detail.

Optimising grain yield and grazing potential of crops across Australia’s high-rainfall zone: a simulation analysis. 1. Wheat

Abstract: Interest is growing in the potential to expand cropping into Australia’s high-rainfall zone (HRZ). Dual-purpose crops are suited to the longer growing seasons in these environments to provide both early grazing for livestock and later regrow to produce grain. Grain yield and grazing potential of wheats of four different maturity types were simulated over 50 years at 13 locations across Australia’s HRZ, and sowing date, nitrogen (N) availability and crop density effects were explored. Potential grazing days on wheat were obtained by simulating sheep grazing crops to Zadoks growth stage Z30 at 25 dry sheep equivalents (DSE)/ha. Optimal sowing dates for each maturity type at each location were matched to the flowering window during which risk of frost and heat stress was lowest. Overall, we found significant national potential for dual-purpose use of winter wheat cultivars across Australia’s HRZ, with opportunities identified in all regions. Simulated mean wheat yields exceeded 6 t/ha at most locations, with highest mean grain yields (8–10 t/ha) in southern Victoria, and lower yields (5–7 t/ha) in the south-west of Western Australia (WA) and central and northern New South Wales (NSW). Highest grazing days were from winter cultivars sown early (March–mid-April), which could provide 1700–3000 DSE-days/ha of grazing across HRZ locations; this was 2–3 times higher than could be obtained from grazing spring cultivars (200–800 DSE-days/ha). Sowing date was critical to maximise both grazing and grain yield potential from winter cultivars; each 1-week delay in sowing after 8 March reduced grazing by 200–250 DSE-days/ha and grain yield by 0.45 t/ha. However, in Mediterranean climates, a lower frequency of early sowing opportunities before mid-April (<30% of years) is likely to limit the potential to use winter cultivars. Prospects to graze shorter season spring cultivars that fit later sowing windows require further examination in south-west WA, the slopes of NSW and southern Queensland.

Adaptation of wheat, barley, canola, field pea and chickpea to the thermal environments of Australia

Abstract: Warming trends involve two agronomically relevant aspects: a gradual increase in long-term mean temperature with the primary effect of shifting phenological patterns, and an increasing incidence of heat waves. Depending on timing, intensity and duration, heat can reduce crop growth and disrupt reproduction. Agronomic and breeding adaptations to elevated temperature have been listed but there is an overall lack of frameworks for systematic analysis. This paper provides agronomic and physiological background for the quantitative assessment of spatial patterns of the thermal regimes for wheat, barley, canola, field pea and chickpea. First, we revise the notion that Australian agriculture is ‘European’ and ill-adapted to the local environments. By showing that Australian agriculture in the southern and western regions is rather Levantine, we advance a more accurate and relevant framework to the thermal regimes of winter crops. Second, we outline the direct and indirect effects of temperature on crop traits and highlight the limitations of different approaches to investigate crop responses to temperature. This is important to make explicit the assumptions of studies dealing with crop responses to temperature; for example, indirect effects of temperature on crops mediated by effects on weeds, pathogens or herbivores could be important. Third, we compare the cardinal temperatures (including base, optimal, and critical thresholds) of our target crops. Cardinal temperatures respond to both natural and agronomic selection and are relevant for crop adaptation. Fourth, we develop a conceptual framework to assess thermal effects on crop yield and adaptive practices and traits, based on the notions of yield being a primary function of seed number, the species-specific critical window for the determination of seed number, and two complementary perspectives involving the photothermal quotient and crop growth rate in the critical window. The framework accounts for both aspects of warming: non-stressful elevated temperature and heat stress. Testable propositions are advanced that inform future research on crop adaptation to elevated temperature.

Morphological, physiological and yield responses of durum wheat to pre-anthesis water-deficit stress are genotype-dependent

Abstract: Durum wheat production in southern Australia is limited when water deficit occurs immediately before and during anthesis. This study was conducted to determine the effect of genotypic variation on various yield, morphological and physiological responses to pre-anthesis water-deficit stress by evaluating 20 durum wheat (Triticum turgidum L. ssp. durum) genotypes over 2 years of glasshouse experiments. Grain number was the major yield component that affected yield under pre-anthesis water-deficit stress. Genotypes with less yield reduction also had less reduction in chlorophyll content, relative water content and leaf water potential, suggesting that durum genotypes tolerant of water-deficit stress maintain a higher photosynthetic rate and leaf water status. Weak to moderate positive correlations of morphological traits, including plant height and fertile tiller number, with grain number and biomass make the evaluation of high-yielding genotypes in rainfed conditions possible. Morphological traits (such as plant height and tiller number) and physiological traits (such as chlorophyll content, relative water content and leaf water potential) could therefore be considered potential indicators for indirect selection of durum wheat with water-deficit stress tolerance under Mediterranean conditions.

Multiple herbicide-resistant wild radish (Raphanus raphanistrum) populations dominate Western Australian cropping fields

Abstract: Raphanus raphanistrum is a problematic weed, which has become increasingly difficult to control in Australian cropping regions. In 2010, a random survey was conducted across 14 million ha of the Western Australian grain belt to establish the frequency of herbicide resistance in R. raphanistrum and to monitor the change in resistance levels by comparing results with a previous survey in 2003. Screening R. raphanistrum populations with herbicides commonly used to control this weed revealed that most populations (84%) contained individual plants resistant to the acetolactate synthase-inhibiting herbicide chlorsulfuron, whereas 49% of populations also had plants resistant to the imidazolinone herbicides. Resistance to other mode of action herbicides (2,4-D (76%) and diflufenican (49%)) was also common. Glyphosate, atrazine and pyrasulfotole bromoxynil remained effective on most R. raphanistrum populations. These results demonstrate that resistance to some herbicides has increased significantly since 2003 when the values were 54% for chlorsulfuron and 60% for 2,4-D; therefore, a wide range of weed management options that target all phases of the cropping program are needed to sustain these cropping systems in the future.

Magnesium alleviates plant toxicity of aluminium and heavy metals

Abstract: Magnesium (Mg) is an essential nutrient that can alleviate soilborne toxicity of many ions. This review paper critically assesses the literature on interactions and mechanisms influencing Mg alleviation of aluminium (Al) and heavy metal toxicity. Hydrated radii of Mg2+ and Al3+ are similar; therefore, these two ions compete for binding to ion transporters and other important biological molecules. In monocotyledonous species such as rice and wheat, millimolar concentrations of Mg alleviate Al toxicity, mainly by decreasing Al saturation and activity at cell wall and plasma membrane binding sites. In dicotyledonous legume species such as soybean (Glycine max), rice bean (Vigna umbellata) and broad bean (Vicia faba), micromolar concentrations of Mg may enhance biosynthesis of organic ligands and thus underpin alleviation of Al toxicity. Resistance to Al may be enhanced by increased expression of the genes coding for Mg transporters, as well as by upregulation of activity of Mg-transport proteins; intracellular Mg2+ activity may thus be increased under Al stress, which may increase the activity of H+-ATPases. In Vicia faba, Mg-related enhancement in the activity of plasma membrane H+-ATPase under Al stress was found to be due to post-translational modification (increased phosphorylation of the penultimate threonine as well as association with regulatory 14-3-3 proteins), resulting in increased resistance to Al stress. Magnesium can alleviate heavy metal stress by decreasing negative electrical potential and thus metal ion activities at the plasma membrane surface (physico-chemical competition), by enhancing activities of enzymes involved in biosynthesis of organic ligands, and by increasing vacuolar sequestration of heavy metals via increasing H+-pumping activity at the tonoplast. Future work should concentrate on characterising the role of intracellular Mg2+ homeostasis and Mg transporters in alleviating metal stress as well as in transcriptional, translational and post-translational regulation of H+-pumps and enzymes involved in biosynthesis and exudation of organic ligands.

Management strategies for chicory (Cichorium intybus) and plantain (Plantago lanceolata): impact on dry matter yield, nutritive characteristics and plant density

Abstract: Chicory (Cichorium intybus L.) and narrow-leaved plantain (Plantago lanceolata L.) are able to grow a large amount of high-quality summer feed. Limited information is available on the effect of grazing management on plantain, and no comparison been undertaken of modern chicory and plantain cultivars used in dairy production systems. This study determined the effect of defoliation interval (as determined by the extended leaf height, ELH) and residual height on the yield, nutritive characteristics and plant density of chicory and plantain over 18 months. Chicory leaf yield was reduced in swards defoliated at 150 mm ELH compared with those defoliated at 250, 350 or 550 mm (14.3 v. 17.5 t DM ha–1), and chicory stem yield was least in swards defoliated at 150 or 250 mm. Plantain swards defoliated at 350 or 450 mm ELH yielded more leaf than those defoliated at 150 or 250 mm (20.4 v. 16.7 t DM ha–1); however, stem yield also increased with increasing defoliation interval. Over all seasons, as defoliation interval increased, generally, neutral detergent fibre content increased and crude protein, ash and digestibility declined. Residual height had less of an effect on yield and nutritive characteristics than did defoliation interval. To maximise chicory leaf growth while minimising growth of lower quality stem, the optimal ELH over 18 months was 250 mm, or if the chicory was used only as a 9-month ‘summer’ crop, 350 mm. Recommendations for plantain are not as simple because longer defoliation intervals increase both leaf and stem yield and reduce nutritive value. Defoliating plantain swards at 250 mm ELH appeared to provide a balance between yield and nutritive value; however, further work is required to determine the impact of applying these recommendations on a dairy farm system.

Comparative effects of gibberellic acid, kinetin and salicylic acid on emergence, seedling growth and the antioxidant defence system of sweet sorghum (Sorghum bicolor) under salinity and temperature stresses

Abstract: Salinity and high temperature are major abiotic stresses limiting sustainable crop production. Seed priming is a useful tool to enhance seedling growth and the antioxidant defence system of crops under salinity and temperature stress. This experiment was designed to determine the effects of gibberellic acid (GA3, 288.7 µm), kinetin (232.2 µm) and salicylic acid (362 µm) on some morphological and physiological parameters of sweet sorghum (Sorghum bicolor L. Moench) hybrid Yajin 13 under salinity (0, 100 and 200 mm NaCl) and temperature (25°C and 37°C) stress. Salinity and high temperature significantly reduced emergence percentage, shoot and root lengths, number of leaves, shoot fresh and dry weight, and chlorophyll a and b content. The activity of superoxide dismutase (SOD) and malondialdehyde (MDA) content were increased with an increase in both salinity and temperature stress. Hormone treatments positively affected all parameters except root fresh and dry weight, number of leaves, SOD activity and chlorophyll a. Under salinity stress at 200 mm NaCl, treatment with salicylic acid increased emergence percentage, emergence rate, chlorophyll b and protein content by 82.0%, 130%, 7.9% and 1.9%, respectively, relative to the control (no treatment). At 37°C, salicylic acid increased emergence percentage, emergence rate and number of roots by 72.5%, 108.5% and 63.8%, respectively, and decreased MDA content by 17.6% relative to the control. Our study indicated that seed priming with an appropriate concentration of exogenous hormones (salicylic acid, kinetin, GA3) is a useful, easy method for improving germination, seedling growth and the antioxidant defence system of sweet sorghum under conditions of high temperature and salinity.

QTL mapping for plant height and yield components in common wheat under water-limited and full irrigation environments

Abstract: Plant height (PH) and yield components are important traits for yield improvement in wheat breeding. In this study, 207 F2:4 recombinant inbred lines (RILs) derived from the cross Jingdong 8/Aikang 58 were investigated under limited and full irrigation environments at Beijing and Gaoyi, Hebei province, during the 2011–12 and 2012–13 cropping seasons. The RILs were genotyped with 149 polymorphic simple sequence repeat (SSR) markers, and quantitative trait loci (QTLs) for PH and yield components were analysed by inclusive composite interval mapping. All traits in the experiment showed significant genetic variation and interaction with environments. The range of broad-sense heritabilities of PH, 1000-kernel weight (TKW), number of kernels per spike (KNS), number of spikes per m2 (NS), and grain yield (GY) were 0.97–0.97, 0.87–0.89, 0.59–0.61, 0.58–0.68, and 0.23–0.48. The numbers of QTLs detected for PH, TKW, KNS, NS, and GY were 3, 10, 8, 7 and 9, respectively, across all eight environments. PH QTLs on chromosomes 4D and 6A, explaining 61.3–80.2% of the phenotypic variation, were stably expressed in all environments. QPH.caas-4D is assumed to be the Rht-D1b locus, whereas QPH.caas-6A is likely to be a newly discovered gene. The allele from Aikang 58 at QPH.caas-4D reduced PH by 11.5–18.2% and TKW by 2.6–3.8%; however, KNS increased (1.2–3.7%) as did NS (2.8–4.1%). The QPH.caas-6A allele from Aikang 58 reduced PH by 8.0–11.5% and TKW by 6.9–8.5%, whereas KNS increased by 1.2–3.6% and NS by 0.9–4.5%. Genotypes carrying both QPH.caas-4D and QPH.caas-6A alleles from Aikang 58 showed reduced PH by 28.6–30.6%, simultaneously reducing TKW (13.8–15.2%) and increasing KNS (3.4–4.9%) and NS (6.5–10%). QTKW.caas-4B and QTKW.caas-5B.1 were stably detected and significantly associated with either KNS or NS. Major KNS QTLs QKNS.caas-4B and QKNS.caas-5B.1 and the GY QTL QGY.caas-3B.2 were detected only in water-limited environments. The major TKW QTKW.caas-6D had no significant effect on either KNS or NS and it could have potential for improving yield.

Crop sequences in Western Australia: what are they and are they sustainable? Findings of a four-year survey

Abstract: A survey was conducted of commercial broadacre paddocks in the south-west cropping zone of Western Australia from 2010 to 2013. In total, 687 paddock years of data were sampled from 184 paddocks. The land use of each paddock was recorded together with measurements of weed density, the incidence of soilborne pathogen DNA, and soil inorganic nitrogen (nitrate and ammonium). The dynamics of these biophysical variables were related to the crop and pasture sequences employed. Wheat was the most frequent land use (60% of paddock years), followed by canola and pasture (12% each), and lupins and barley (6% each). Four crop species, wheat, canola, barley and lupins, accounted for 84% of land use. By region, wheat, canola, barley and lupin accounted for 90% of land use in the Northern Agricultural Region (NAR), 83% in the Central Agricultural Region (CAR) and 78% in the Southern Agricultural Region (SAR). Conversely, pasture usage in the SAR was 21%, compared with 12% in the CAR and 7% in the NAR. Over the surveyed paddocks, weed density, soilborne pathogens and soil N were maintained at levels suitable for wheat production. The inclusion of land uses other than wheat at the frequency reported maintained the condition of these biophysical variables.

Influence of biochar application on nutritional quality of tomato (Lycopersicon esculentum)

Abstract: The potential of biochar to improve crop productivity has received interest in recent years; however, little is known about the effects of biochar on crop nutritional quality. In this study, effects of three different biochars (wheat straw biochar, poplar biochar and olive residues biochar) were determined on the major fruit-size parameters, physico-chemical and nutritional properties of tomato (Lycopersicon esculentum L.) cv. Rio Grande. Application of biochar alone was sufficient to sustain the fruit growth, but results were affected by feedstock source of biochar. There were no significant differences in size and weight parameters and the sugar content was not significantly modified by biochar amendment. On the other hand, secondary metabolites showed changes relating to biochar type. Total phenol and flavonoid contents, as well as antioxidant activity, were higher in fruits grown in substrate amended with straw biochar and olive residues biochar. Lycopene, β carotene and lutein concentrations from tomato fruits grown on substrates amended with different biochars were significantly lower than from the control. The data require confirmation in field experiments; however, this study offers new knowledge about the biochar effects on horticultural crops.

Responses to phosphorus among wheat genotypes

Abstract: Phosphorus (P) recovery and P-use efficiency (PUE) by wheat are low, and genetic improvement in PUE is a potential means of improving the effectiveness of P in farming systems. We examined variation in response to P in wheat to identify genotypes that showed consistent responsiveness to P fertiliser in the field and which may be the target of future studies, and examined differences in P uptake and partitioning. The response to P was studied among a diverse set of bread wheat germplasm at three sites in South Australia between 2009 and 2012. Up to 53 varieties and breeding lines were grown at two rates of P, 0 kg/ha and 30 kg/ha. Grain yield at 0 kg P/ha and response to P varied independently among genotypes. There were large effects of site and season on the response to P, but some genotypes showed consistently low and others high response to P. Analysis of a subset of lines revealed large responses in vegetative growth to P but the response diminished as crops matured, and variation in early vegetative growth was unrelated to the responses in biomass at maturity or grain yield. Genotypic variation in grain yield was more strongly related to variation in P utilisation efficiency than to variation in P uptake among wheat genotypes, which was associated with differences in P harvest index (PHI). Although breeding has improved yield, there has been no significant genetic gain in total P uptake; rather, improvements in PUE have been associated with an increase in P utilisation efficiency and PHI.

Statistical methods for analysis of multi-harvest data from perennial pasture variety selection trials

Abstract: Variety selection in perennial pasture crops involves identifying best varieties from data collected from multiple harvest times in field trials. For accurate selection, the statistical methods for analysing such data need to account for the spatial and temporal correlation typically present. This paper provides an approach for analysing multi-harvest data from variety selection trials in which there may be a large number of harvest times. Methods are presented for modelling the variety by harvest effects while accounting for the spatial and temporal correlation between observations. These methods provide an improvement in model fit compared to separate analyses for each harvest, and provide insight into variety by harvest interactions. The approach is illustrated using two traits from a lucerne variety selection trial. The proposed method provides variety predictions allowing for the natural sources of variation and correlation in multi-harvest data.

Dual-purpose cropping - capitalising on potential grain crop grazing to enhance mixed-farming profitability

Abstract: Mixed farming enterprises throughout the world balance and integrate crop and livestock enterprises to spread economic risk and capture synergies in terms of forage supply, but in many areas of the world these have become increasingly separated and specialised (Wilkins 2008).

Integrating dual-purpose wheat and canola into high-rainfall livestock systems in south-eastern Australia. 2. Pasture and livestock production

Abstract: In south-eastern Australia, low winter temperatures often reduce pasture growth and thus winter herbage supply relative to livestock requirements. Grazing of vegetative grain crops in winter is one strategy that might overcome this feed gap. In a study with young sheep over two seasons near Canberra, ACT, we compared pasture-only grazing with three separate crop–livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these, for intervals over the period May–August. We measured forage biomass, sheep grazing days (SGD) and liveweight accumulated per ha. Crop-grazing treatments resulted in much more winter forage for grazing sheep (t DM ha–1): in 2010, one crop 2.5–3.0, two crops 3.5 v. pasture only 1; in 2011, one crop 2, two crops 3 v. pasture only 1.4. In the first season, grazing one crop resulted in ~2000 extra SGD ha–1 and the accumulation of more liveweight per ha than in the pasture-only treatment; grazing of two crops resulted in >3500 extra SGD ha–1. Equivalent values in the second, drier season were: one crop, ~1000 extra SGD ha–1; two crops, 2600 extra SGD ha–1. Spelling of pastures during crop grazing led to extra pasture growth, such that in each of the two seasons, 40% of the total benefit in extra SGD per ha came from the extra pasture. The results indicate that, like grazed wheat, grazed canola can provide valuable winter forage, especially when used together with wheat. The data also provide the first quantification of the effect of crop grazing on pasture spelling and subsequent pasture supply, and suggest value in the incorporation of grazing wheat and canola into grazing systems in the high-rainfall zone.

Saline water irrigation of quinoa (Chenopodium quinoa) under Mediterranean conditions

Abstract: Field experiments were set up in order to evaluate the yield response of quinoa (Chenopodium quinoa Willd. cv. Titicaca) to irrigation with saline and fresh water under Mediterranean climate from 2010 to 2012 in Adana, Turkey. Irrigation treatments in 2010 and 2011 comprised full irrigation with fresh water, full irrigation with saline water of different salt concentrations (40, 30, 20, 10 dS m–1), deficit irrigations with fresh water (50%, 75% of full irrigation), partial root-zone drying, and deficit irrigation with saline water of 40 dS m–1 (50%). In 2012, in addition to the full irrigation treatments, two deficit irrigation levels of 67% and 33% of full irrigation with fresh or saline (30, 20, 10 dS m–1) water were considered. The results indicated that grain yields were slightly reduced by irrigation water salinity up to 30 dS m–1 compared with fresh water irrigation. Salinity and drought stress together interfered considerably with crop grain and biomass yields. However, salinity stress alone did not interfere with grain and biomass yield significantly; therefore, quinoa may be defined as a crop tolerant to salinity. Yield parameters such as aboveground biomass, seed yield and harvest index suggested a good adaptation of quinoa cv. Titicaca to Mediterranean environments.

Role of arbuscular mycorrhizal symbiosis in phosphorus-uptake efficiency and aluminium tolerance in barley growing in acid soils

Abstract: Arbuscular mycorrhizal fungi (AMF) play an important role in protecting plant growth against such stresses as phytotoxic aluminium (Al) in soil. To understand some of the AMF interactions that relate to amelioration of Al phytotoxicity and phosphorus (P)-uptake efficiency in barley (Hordeum vulgare L.), this study examined the effect of soil Al levels and mycorrhizal symbiosis on plant response, including root colonisation, AMF propagules and glomalin production. A greenhouse experiment was conducted using two native barley cultivars, Sebastian and Aurora, grown in an acidic soil at two Al-saturation levels (80% Al-sat, unlimed soil; 7% Al-sat, limed soil) with and without AMF propagules. Root dry weight, total and colonised root lengths, and root P and Al contents were determined at 60 and 150 days after sowing. AMF spore density, total hyphal length, glomalin-related soil protein (GRSP) and Al bound to GRSP (Al-GRSP) were analysed at final harvest. AM root colonisation was not inhibited in limed soil, mycorrhizal propagule numbers increased at high Al levels, and Al-GRSP ranged from 5.6% to 8.3% of the total GRSP weight. These values also increased in unlimed soil, particularly those associated with cv. Aurora. Root Al concentration correlated inversely with AMF spores (r = –0.85, P < 0.001) and Al-GRSP (r = –0.72, P < 0.01), but only in plants growing in limed soil. Conversely, the AMF treatments in which Al was present showed a greater relationship between total root length and both root Al (r = –0.72, P < 0.01) and root P (r = 0.66, P < 0.01) concentrations. Sebastian showed a greater response to lime, whereas Aurora responded better to mycorrhizal presence. The relative growth rate of roots, P uptake efficiency and mycorrhizal parameters such as root colonisation, spores, hyphae and GRSP showed Aurora to be more Al-tolerant than Sebastian. In conclusion, the greater rate of increase of AM propagules, GRSP and Al-GRSP associated with cv. Aurora supports the hypothesis that AMF play an important role in the Al-tolerance capacity and P-uptake efficiency of H. vulgare growing in soils with high Al levels.

Biomass, fruit yield, water productivity and quality response of processing tomato to plant density and deficit irrigation under a semi-arid Mediterranean climate

Abstract: A 2-year study was conducted to examine the impact of deficit irrigation on dry biomass, water-use efficiency (WUE), fruit yield and quality in open-field processing tomato at high plant density in a semi-arid environment. Three irrigation treatments (nil; and 100% (full) and 50% (deficit) restoration of crop evapotranspiration (ETc), respectively) and two plant densities (2.5 (P1) and 5.0 (P2) plants m–2) were studied. Dry biomass and fruit yield per plant were lower in P2 than in P1, but at high plant density the crop compensated for biomass and yield decrease at the plant level. Fruit yield in P2 was greater than that in P1, by 36% in 2004 and 33% in 2005. Water limitation improved quality traits compared with full irrigation. Deficit irrigation, especially in P2, enhanced WUE and allowed a water saving of >45% relative to full irrigation, while keeping high levels of fruit quality. The yield response factor, Ky, which correlates relative fruit yield losses to relative ETc reduction, was higher (0.63) than Kss (0.44), which correlates relative total dry biomass losses to relative ETc reduction, revealing a greater crop sensitivity to soil-water deficit in terms of fruit yield than dry biomass. Therefore, Ky may of use in identifying the plant density at which water productivity is maximised or yield losses are minimised.

Break-crop effects on wheat production across soils and seasons in a semi-arid environment.

Abstract: In low-rainfall environments, a high frequency of cereal crops has been favoured for optimising productivity and risk. However, cereals at high intensity often lead to declining water-use efficiency and increasing inputs to cope with emergent nutritional, disease and weed problems. The value of including breaks in the cropping sequence can involve a high level of uncertainty in low-rainfall areas where non-cereal crops are more risky and profitability is largely determined by the subsequent benefit to cereal productivity. In this study, we aimed to improve understanding of the magnitude and primary source of break benefits such as nutrition, water and disease management in a low-rainfall environment where a high level of within-field soil variability can also contribute to uncertainty about the value of breaks. In on-farm field experiments near Karoonda in the South Australian Mallee, breaks were grown in 2009 or 2010 on four distinct soil types across a dune–swale catena. The effect of these breaks on subsequent cereal production was measured for up to 3 years. In addition, the effect of breaks on nutrition and water available, along with disease infection in subsequent cereal crops, was explored and actual yields were compared with nitrogen and water-limited potential yields. Consistent cumulative benefits to subsequent cereal crops of at least 1 t ha–1 after 3 years accrue from breaks grown on the different soil types. The inclusion of breaks had beneficial effects on the cycling and supply of nutrients along with some short-term impacts on infection by Rhizoctonia solani AG8 in subsequent cereals, whereas there were no conclusive effects of breaks on the supply of water to subsequent crops. This study suggests that the inclusion of both legume and brassica breaks is likely to be beneficial to subsequent cereal production where nitrogen is a factor limiting productivity in low-rainfall, semi-arid environments.

Effect of defoliation by grazing or shoot removal on the root growth of field-grown wheat (Triticum aestivum L.)

Abstract: Dual-purpose crops for grazing and grain production can be highly profitable, provided grazing does not cause significant loss of grain yield. In many plants, defoliation causes a transient reduction in the allocation of resources to stem and root growth and remobilisation of soluble resources to re-establish leaf area rapidly. In Australia, the usual autumn and winter period of defoliation for grazed crops, May–July, coincides with a phase of near-linear root depth penetration in ungrazed crops, and the crop recovery period after grazing occurs during stem elongation, when grain number and yield potential are determined. However, few studies have investigated the potential impact of crop defoliation through grazing on root growth of wheat in the field. We investigated the effect of defoliation by grazing or shoot removal on the root growth of wheat crops in four field experiments in south-eastern Australia in which the timing, frequency and intensity of defoliation varied. Despite significant impacts of defoliation on aboveground biomass (50–90% reduction) and grain yield (10–43% reduction) in all experiments, we found little evidence of effects on the rate of root penetration or final rooting depth. A notable exception was observed in one experiment when defoliation commenced very early (four-leaf stage, Zadoks growth stage Z14) in a repeatedly defoliated crop, reducing rooting depth from 1.65 to 1.35 m. The only other measured impact on roots was in an early-sown winter wheat crop grazed by sheep for 3 months (6 June–3 September), in which root length density was reduced by ~50% in surface layers above 1.0 m depth, but there was no impact on maximum root depth or root length density at 1.0–2.0 m depth. Our results suggest that grazing has little impact on the rooting depth of wheat unless it occurs very early and repeatedly, when plants are allocating significant resources to establish the primary roots. However, there may be some reduction in the density of roots in surface layers during recovery after long-term grazing, presumably associated with reduced proliferation of the nodal root system. We conclude that most significant yield penalties due to grazing relate to impacts on the assimilation of aboveground resources, rather than to reduced water or nutrient acquisition by roots.

Potential legume alternatives to fallow and wheat monoculture for Mediterranean environments

Abstract: Growing populations and intensification of land-use in West Asia and North Africa (WANA) are prompting a need for viable alternatives to fallow and cereal mono-cropping systems common in dry areas of this region. The sustainability and economic viability of such rotations can only be assessed accurately by using long-term trials. A two-course rotation experiment was established in 1986 in north-eastern Syria, comparing yields and profitability of wheat (Triticum aestivum L.) when grown after wheat, fallow, a grazed mixture of medic species (Medicago spp.) and common vetch (Vicia sativa L.) cut for hay, over 10 growing seasons. Lentils (Lens culinaris Medik.) were introduced into the experiment in 1990. On average over the course of the experiment, the highest wheat grain yields were obtained following fallow (2.57 t ha–1), the lowest in continuous wheat (1.14 t ha–1), and intermediate following medic and vetch (1.90–2.01 t ha–1). Compared with wheat grown after fallow, wheat grain yields declined following vetch, medic and lentils in only three of the 10 seasons, which were drier than average. Yields of wheat after lentils were generally lower (2.22 t ha–1) than after vetch (mean 2.56 t ha–1) and after medic (2.40 t ha–1). Inclusion of grain legumes in the rotations boosted profits considerably because of their high grain prices and valuable straw. Replacing fallow with vetch for hay production increased the average gross margin by US$126 ha–1 year–1, and growing vetch for hay in rotation with wheat produced greater profit than continuous wheat, by $254 ha–1 year–1. The wheat–vetch-for-grain and wheat–lentil rotations were especially profitable, at least twice as profitable as wheat–fallow and three times continuous wheat. This experiment adds to the growing body of field data in Syria and in Australia showing that forage and grain legumes are excellent alternatives to wheat–fallow rotation and continuous wheat production in areas that experience a Mediterranean-type climate, and help support more efficient and sustainable cropping systems.

Integrating dual-purpose wheat and canola into high-rainfall livestock systems in south-eastern Australia. 3. An extrapolation to whole-farm grazing potential, productivity and profitability

Abstract: Dual-purpose crops can provide valuable winter forage in livestock production systems and increase subsequent pasture availability. Using experimental measurements of sheep grazing on pasture only or dual-purpose crops of wheat, canola, and wheat and canola in combination, and their associated effects on subsequent pasture grazing, we estimated for two different years the whole-farm changes in whole-farm sheep grazing days (SGD), relative farm production and farm economic impact. The increased winter feed supply and higher grazing intensity on dual-purpose crops allowed 2–3 times the area of pasture to be spelled, which together enabled increases in potential year-round pasture stocking rate. Up to 20% of farm area could be allocated to dual-purpose crops while still obtaining the same number of SGD per farm ha with additional grain production (5.0–5.4 t wheat ha–1 and 1.9–3.6 t canola ha–1) adding significantly to farm profitability and production. Allocating 10–20% of the farm to a combination of dual-purpose wheat and canola grazed in sequence could increase whole-farm SGD by 10–15%, increase farm output by >25% and increase estimated farm profit margin by >AU$150 farm ha–1 compared with pasture-only livestock systems. The long crop-grazing period from wheat and canola in combination providing a large pasture-spelling benefit was a key factor enabling these economic and productivity increases. Introducing wheat or canola alone on up to 30% of the farm is likely to reduce SGD per farm ha, but still significantly increase whole-farm productivity (10–20%) and estimated profit margin ($50–100 farm ha–1). Over the two very different experimental growing seasons, the estimated relative changes in whole-farm productivity and estimated profit margin were similar, indicating that these benefits are likely to be consistent over a range of years. Together, these findings suggest that once whole-farm livestock feed-base effects are considered, large economic and productivity benefits can be attributed to dual-purpose crops when integrated into livestock production systems in Australia’s southern high-rainfall zone.

Integrating dual-purpose wheat and canola into high-rainfall livestock systems in south-eastern Australia. 1. Crop forage and grain yield

Abstract: The development of guidelines for successful dual-purpose (graze and grain) use of wheat and canola in Australia’s high-rainfall zones (HRZ) has mostly emerged from separate wheat- and canola-focused research. Less attention has been placed on the benefits of integrating dual-purpose wheat and canola into pasture-based grazing enterprises. We conducted a farming systems experiment during 2010–11 to evaluate the benefits of integrating wheat and canola as dual-purpose crops into a pasture-based grazing system in Australia’s south-eastern tablelands. We compared forage production and grain yield in three separate crop–livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these. Initial growth rates were higher in early-autumn-sown canola than wheat in 2010, but were much lower although similar in both crops in 2011. Significant forage was available from both canola (3.1–3.4 t ha–1) and wheat (2.3–2.4 t ha–1) at the onset of grazing, but winter growth rates of wheat were higher than those of canola, leading to increased sheep grazing days (SGD). In the favourable 2010 season, dual-purpose wheat and canola separately provided 2393 and 2095 SGD ha–1, and yielded 5.0 and 1.9 t ha–1 grain, respectively, with an apparent nitrogen limitation in canola. In the drier season of 2011, grazing was reduced to 1455 and 735 SGD ha–1 in wheat and canola, respectively. Wheat yield was reduced from 5.9 to 5.4 t ha–1 grain by grazing, whereas canola yield was unaffected (3.6 t ha–1). In both years, grazing did not affect harvest index or oil content of canola, but harvest index was higher in grazed wheat crops. The yield of wheat and canola crops grazed in sequence did not differ from yield in treatments where animals grazed only a single crop, but the total overall grazing window when crops were grazed sequentially increased by 1054 and 618 SGD ha–1 in wheat, and by 1352 and 1338 SGD ha–1 in canola in 2010 and 2011, respectively. The major benefits of including crops that can be grazed sequentially were the widening of the grazing window and other operational windows (sowing, harvest), along with the rotational benefits for wheat by including canola in the system. Additional benefits to pastures may include eliminating the need to re-sow, because a more productive pasture composition is maintained under lower grazing pressure while stock are on crops, and reduced weed invasion. The commercial availability of new, herbicide-tolerant winter canola varieties provides significant opportunities to underpin the performance of dual-purpose crop sequences on mixed farms in the high-rainfall zone.

Water use, transpiration efficiency and yield in cowpea (Vigna unguiculata) and peanut (Arachis hypogaea) across water regimes

Abstract: Genotypic variation in crop response to drought depends on agronomic, environmental and genetic factors, and only limited work has compared responses of crop species to water limitation. Twenty genotypes of peanut (Arachis hypogaea L.) and of cowpea (Vigna unguiculata (L.) Walp) were tested in lysimeters under well-watered (WW) and water-stress (WS) conditions during two seasons, a post-rainy season with high evapotranspiration and a rainy season with low evapotranspiration (ET), in order to assess: (i) variability in the agronomic response to stress within and between species across the seasons; (ii) the water requirement of the two crops in each season; and (iii) the stress effect on harvest index (HI), transpiration efficiency (TE), pod yield and haulm yield. Cowpea required less water than peanut during the two seasons, and water use in cowpea varied less across seasons than in peanut. Peanut yield was more sensitive to water stress than cowpea yield, although its water use under WS was higher than in cowpea. Also, under WS conditions, TE, HI and pod yield were more stable across season in cowpea than in peanut. In the post-rainy season, the decrease in pod yield and HI under WS was higher in peanut (95% and 80%, respectively) than in cowpea (70% and 35%). In addition, TE was less affected by WS in cowpea (5%) than in peanut (24%). HI explained a large part of yield variation in both crops, especially under WS. Under WW, water use explained a large portion of the residual yield variations unexplained by HI, although TE also explained a substantial part of the variation in cowpea. Under WS, the main determinant of residual yield variations in both crops was TE. Generally, genetic variation for water use, TE and HI was found in both species across water regimes and seasons. A notable exception was the absence of variation in peanut water use and TE in the rainy season. Our results showed that cowpea, with lower water requirement and efficient water use under a high-ET season, was more resilient to water-limited and high-ET conditions than peanut.

Global magnesium supply in the food chain

Abstract: Magnesium (Mg) is an essential mineral micronutrient in humans. Risks of dietary Mg deficiency are affected by the quantity of Mg ingested and its bioavailability, which is influenced by the consumption of other nutrients and ‘anti-nutrients’. Here, we assess global dietary Mg supplies and risks of dietary deficiency, including the influence of other nutrients. Food supply and food composition data were used to derive the amount of Mg available per capita at national levels. Supplies of Mg were compared with estimated national per capita average requirement ‘cut points’. In 2011, global weighted mean Mg supply was 613 ± 69 mg person–1 day–1 compared with a weighted estimated average requirement for Mg of 173 mg person–1 day–1. This indicates a low risk of dietary Mg deficiency of 0.26% based on supply. This contrasts with published data from national individual-level dietary surveys, which indicate greater Mg deficiency risks. However, individuals in high-income countries are likely to under-report food consumption, which could lead to overestimation of deficiency risks. Furthermore, estimates of deficiency risk based on supply do not account for potential inhibitors of Mg absorption, including calcium, phytic acid and oxalate, and do not consider household food wastage.

Forage and grain yield of diverse canola (Brassica napus) maturity types in the high-rainfall zone of Australia

Abstract: Cropping has recently expanded into arable areas of the high rainfall zone (HRZ) of Australia. We assessed the suitability of canola varieties of winter, winter × spring and spring-maturity at six sites across the south-eastern, northern and western HRZ of Australia for their suitability for dual-purpose production. Experiments measured potential forage production and the effect of defoliation or grazing on grain yield of crops sown from mid-March to mid-May. Overall, these experiments demonstrated the potential for dual-purpose canola across a wide area of the HRZ. In the south-eastern HRZ where winter conditions were sufficient for vernalisation and spring conditions were mild, winter and winter × spring types outperformed spring types as they provided an extended vegetative period for ‘safe’ grazing (prior to stem elongation), producing 3.0–6.8 t dry matter (DM) ha–1 of forage and recovered to produce 2.5–4.9 t ha–1 of grain yield. In the south-eastern region, early-sown winter types produced more forage than other canola types for grazing in late autumn and winter. In one experiment with four sowing times, consecutive delays in sowing of 2 weeks reduced forage available for grazing by 58%, 72% and 95% compared with the earliest sowing time of 10 March (6.1 t DM ha–1). Although spring types in this region provided some potential for grazing, the phenology was unsuitable for early sowing as the rapid onset of flowering reduced the period of safe grazing. Winter types were not suited to the western region, but the winter × spring and spring types produced >1.0 t DM ha–1 of forage and grain yield of 2.3 t ha–1. In the northern region, spring types produced the highest grain yield (>3.0 t ha–1) but suffered significant yield penalties associated with grazing. In other regions there was generally little or no effect of grazing on grain yield when crops were grazed or defoliated before stem elongation. These experimental studies confirm the potential for dual-purpose canola across all regions of the HRZ when suitable maturity types are sown, managed and grazed appropriately.

Evaluation of faba bean breeding lines for spectral indices, yield traits and yield stability under diverse environments

Abstract: Drought is a major limiting factor in faba bean (Vicia faba L.) production in the Mediterranean region, which is known for its irregular water distribution and moderate moisture levels (~500 mm rainfall). In this study, faba bean genotypes were evaluated for spectral indices, yield traits, rhizobium nodulation and yield stability under diverse environments, and their relationships. Eleven faba bean genotypes were evaluated under two water regimes, rainfed and supplemental irrigation (SI), in 2008–09; and under three water regimes (rainfed, 50% and 100% soil water capacity irrigation) for three consecutive growing seasons (2009–10, 2010–11, 2011–12), at Tel Hadya in Syria. They were also evaluated at Terbol in Lebanon for one season (2011–12) in a split-plot experiment with three irrigation treatments and at Kfardan in Lebanon for two seasons, 2008–09 (rainfed) and 2010–11 (rainfed and SI). The genotypes included three cultivars and eight drought-tolerant breeding lines selected at <300 mm annual rainfall. Phenological and morphological traits were recorded, as well as nodule weight per plant, grain yield, biological yield and spectral reflectance indices. Data were statistically analysed for each year. There were significant genotypic differences for seed yield under SI and rainfed conditions in 2008–09, and full irrigation in 2009–10 and 2011–12. Days to flowering and maturity were significantly different among genotypes for rainfed and irrigated conditions. There were significant differences between water regimes and genotypes, but their interactions were not significant. FLIP06-010FB was the highest yielding and most stable among the tested genotypes across different environments. Days to flowering and days to maturity were positively correlated with grain yield. The spectral indices structure-insensitive pigment index and normalised pheophytinisation index were found to correlate positively with grain yield and could therefore be used for selection under drought-prone environments.

Evaluation of the biochemical and physiological activity of the natural compound, 2,4-ditert-butylphenol on weeds

Abstract: 2,4-Di-tert-butylphenol (2,4-DTBP) is a natural compounds present in medicinal plants. It is reported to have herbicidal properties. However, the mechanism of action is unknown for use in weed management. Measurements were made of lipid peroxidation, ion leakage, antioxidant enzymes, chlorophyll content, chlorophyll fluorescence and photosynthesis in the grassy weed Leptochloa chinensis (L.) Nees and the broadleaf weed Hedyotis verticillata (L.) Lam. at 7 and 14 days, respectively, after treatment with 2,4-DTBP. The 2,4-DTBP reduced the shoot fresh weight of L. chinensis and H. verticillata by 50% when applied at concentrations of 50 and 200 µg mL–1, respectively. Treatment with 2,4-DTBP significantly increased levels of malondialdehyde, caused excessive ion leakage and increased activities of antioxidant enzymes such as superoxide dismutase, peroxidase and catalase in leaf and root tissues of the two bioassay species. Most notably, 2,4-DTBP treatment caused great reduction in chlorophyll content, thereby decreasing chlorophyll fluorescence, transpiration and net photosynthetic rate in the leaf tissues. The results suggest that 2,4-DTBP induces oxidative stress through the generation of reactive oxygen species, which cause lipid peroxidation and membrane damage in root tissues and chloroplast in leaf tissues, thus leading to increased levels of antioxidant enzymes.

Discovery and characterisation of novel asexual Epichloë endophytes from perennial ryegrass (Lolium perenne L.)

Abstract: Asexual fungal endophytes of the genus Epichloe form mutually beneficial associations with cool-season pasture grasses such as ryegrasses (Lolium spp.). Alkaloid production by the fungus confers both beneficial (deterrence of invertebrate herbivory) and detrimental (toxicity to mammalian livestock) attributes. A few novel strains with desirable metabolite profiles have been advanced into commercial production by inoculation of perennial ryegrass cultivars. In the present study, an integrated process for discovery of novel endophytes based on exploitation of genotypic information has been designed and implemented. A survey of genetic diversity was performed on a large-scale, customised germplasm collection (containing 244 accessions) in order to identify previously uncharacterised endophyte genotypes. Preliminary qualitative metabolic profiling in the endogenous genetic background permitted elimination of undesirable combinations, and definition of a subset of priority candidates. A novel method was developed for inoculation of endophytes into meristem-culture-derived callus tissue of single genotypes from multiple perennial ryegrass cultivars, in order to allow isogenic comparisons with respect to both host and endophyte genotype. Beneficial toxin profiles were confirmed for associations formed with the grass genotypic panel, and semi-quantitative metabolite analysis provided evidence for genotype-specific effects of both host and genotype on levels of alkaloid production. Vegetative stability was also assessed over both shorter and longer terms. A final set of three prioritised candidates was obtained, two of which (belonging to the known taxa E. festucae var. lolii and LpTG-2) produce the alkaloids ergovaline and peramine. The third candidate endophyte, belonging to a putative novel taxon, solely produces representatives of an additional alkaloid class, the epoxy-janthitrems.