Escalating demands for food and green energy have renewed interest in the dual-purpose use of maize (Zea mays L.) for a biofuel and high-energy forage crop. Recently, maize hybrids with high stalk-sugar (sugarcorn) have been developed. It is important to determine how agronomic practices, for example altering plant population density (PPD), affect stalk-sugar yields of these newly developed hybrids and to advance knowledge required for producing sugarcorn as a dual-purpose bioenergy–high energy silage crop in short-season regions unable to grow sugarcane. A field experiment was conducted for 3 years to assess the effect of PPD on stalk-sugar accumulation, dry matter production, silage and sucrose yields of sugarcorn compared with two commercial silage hybrids. Targeted PPD ranged from 75 000 to 150 000 plants ha^–1 in increments of 25 000 plants ha^–1. We found that increasing PPD from 75 000 to 125 000 plants ha^–1 increased stalk sugar concentrations by up to 25% in some of the sugarcorn hybrids, with minimum change in the conventional check hybrids. The sugarcorn hybrid CO348 × C103 had the highest stalk sugar concentration (128 g kg^–1) and sucrose yield of up to 3.8 Mg ha^–1 at the targeted PPD of 125 000 (or actual 118 000 ± 7000) plants ha^–1. By contrast, the check silage hybrids produced at most 2.0 Mg ha^–1 of sucrose yield with much lower stalk sugar concentrations (53–65 g kg^–1). Sugarcorn hybrids had generally lower grain yield with greater plant barrenness (the failure of a plant to produce a normal ear) and severer head smut infestation than the conventional silage hybrids. Our results suggest that as a silage crop, the current recommended PPD of 75 000–85 000 plants ha^–1 for commercial silage maize production in the region is likely suitable for sugarcorn, and a higher PPD is required if sugarcorn hybrids are designated as a biofuel crop or for dual-purpose use.

Several new and existing short-term forage legumes could be used to provide nitrogen (N) inputs for grain crops in subtropical farming systems. The fixed-N inputs from summer-growing forage legumes lablab (Lablab purpureus), burgundy bean (Macroptilium bracteatum) and lucerne (Medicago sativa) and winter-growing legume species snail medic (Medicago scutellata), sulla (Hedysarum coronarium) and purple vetch (Vicia benghalensis) were compared over several growing seasons at four locations in southern Queensland, Australia. Available soil mineral N and grain yield of a following cereal crop were compared among summer-growing legumes and forage sorghum (Sorghum spp. hybrid) and among winter-growing legumes and forage oats (Avena sativa). In the first year at all sites, legumes utilised the high initial soil mineral N, with <30% of the legume N estimated to have been derived from atmospheric N₂ (%Ndfa) and legume-fixed N <30 kg/ha. In subsequent years, once soil mineral N had been depleted, %Ndfa increased to 50–70% in the summer-growing legumes and to 60–80% in winter-growing legumes. However, because forage shoot N was removed, rarely did fixed N provide a positive N balance. Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons. Prior to sowing cereal grain crops, soil nitrate was 30–50 kg/ha higher after summer legumes than after forage sorghum. At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean. Of the winter-growing legumes, sulla had the highest total N₂ fixation (up to 150 kg N/ha.year) and inputs of fixed N (up to 75 kg N/ha), and resulted in the highest concentrations of soil N (80–100 kg N/ha more than oats) before sowing of the following crop. Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops.

New forage legume options, lablab, burgundy bean and sulla, showed potential to increase N supply in crop rotations in subtropical farming systems, contributing significant fixed N (75–150 kg/ha) and increasing available soil N for subsequent crops compared to non-legume forage crops. However, high soil mineral N (>50 kg N/ha) greatly reduced N₂ fixation by forage legumes, and significant N₂ fixation only occurred once legume shoot N uptake exceeded soil mineral N at the start of the growing season. Further work is required to explore the impact of different management strategies, such as livestock grazing rather than harvesting for hay, on the long-term implications for nutrient supply for subsequent crops.

Sulfonylurea herbicides have attracted renewed interest as an alternative for weed management and control of weed resistance in soybean production. In this proteomic study, we compared changes in the protein profiles in 10-day-old seedlings from a simple roll-paper germination method treated with 0.1 µm metsulfuron methyl (MSM), a compound from the sulfonylurea family. Seeds from susceptible or tolerant soybeans, four lines each, were treated with 0, 0.01, 0.1, 1 or 10 µm MSM and the number of normal seeds germinating was counted after 10 days. MSM at ≥0.1 µm significantly reduced normal germination in the sulfonylurea-susceptible group. Comparative proteomic analysis of the proteins extracted from the germinations treated with 0 or 0.1 µm MSM revealed a much greater number of proteins affected in the sulfonylurea-susceptible genotype than the tolerant type. From a total 227 protein spots with significant differential (>2-fold) accumulation, 142 unique proteins were identified. Functional analysis revealed that about one-third of these proteins were associated with metabolism, followed by energy (24.3%), defence–stress response (22.9%), and protein synthesis and storage (16.7%). Sulfonylurea herbicides, specifically MSM, greatly affected these metabolic pathways in the susceptible genotype through changed accumulation of many enzymes and proteins.

Subterranean clover (Trifolium subterraneum L.) is an important pasture legume in many regions of Australia, and elsewhere. A survey was undertaken in 2014 to define the levels of soilborne disease and associated pathogens in annual subterranean clover pastures across southern Australia. Most of the 202 samples processed had very severe levels of taproot rot disease (disease index 60–80%) and extremely severe lateral root rot disease (disease index 80–100%). A complex of soilborne root pathogens including Aphanomyces trifolii, Phytophthora clandestina, and one or more of Pythium, Rhizoctonia and Fusarium spp. was found responsible for severe pre- and post-emergence damping-off and root disease. This is the first study to highlight the high incidence of A. trifolii across southern Australian pastures and the first to highlight the existence of natural synergistic associations in the field between Rhizoctonia and Pythium spp., Pythium and Fusarium spp., Pythium spp. and A. trifolii, and P. clandestina and A. trifolii. Nodulation was generally poor, mainly only in the 20–40% nodulation index range. There was no relationship between rainfall zone and tap or lateral root disease level, with root disease equally severe in lower (330 mm) and higher (1000 mm) rainfall zones. This dispels the previous belief that severe root disease in subterranean clover is an issue only in higher rainfall zones. Although overall the relationship between tap and lateral root disease was relatively weak, these two root-disease components were strongly positively expressed within each pathogen’s presence grouping, providing explanation for variability in this relationship across different field situations where soilborne root disease is a major problem. Most producers underestimated the levels and effect of root disease in their pastures. This study established that tap and lateral root diseases are widespread and severe, having devastating impact on the feed gap during autumn–early winter across southern Australia. Severe root disease was independent of the highly variable complex of soilborne pathogens associated with diseased roots, geographic location and rainfall zone. It is evident that soilborne root diseases are the primary factor responsible for widespread decline in subterranean clover productivity of pastures across southern Australia. Implications for disease management and options for extension are discussed.

Digitaria insularis (sourgrass) is a weed problem emerging in importance in agricultural fields from the north of Argentina and has recently been reported as resistant to glyphosate. Understanding the germination of local biotypes of D. insularis could help to reduce invasion and improve the long-term management strategies for this weed. The objective of this work was to study the effect of environmental factors on germination of D. insularis seeds from two different populations of Argentina. Three experiments were performed in germination chambers by using recently dispersed seeds. Seeds with or without pre-chilling treatments had 95% germination, suggesting the absence of dormancy in freshly harvested seed. Germination at constant temperature of 25°C was ∼55% lower than germination at fluctuating temperature of 20°−35°C. At constant 25°C, germination was higher for seeds from Santiago del Estero than seeds from Córdoba, and as the number of hydration–dehydration cycles increased. Germination was reduced with exposure to far-red light for 1 h. Any crop management decision that reduces soil thermal fluctuations and/or far-red : red ratio (such as stubble or cover crops) could reduce seedling field emergence for this species.

The objective of this study was to compare the dynamics of neutral detergent fibre (NDF), and the 24-h in-vitro digestibility of NDF (NDFD) and dry matter (DMD) in leaf blades of two tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) cultivars of different leaf softness: a soft- and a tough-leaved cultivar. The experiment was conducted during the summer regrowth of three replicated, dense mini-swards per cultivar arranged in a completely randomised design, all grown under non-limiting water, nitrogen and phosphorus. Cultivars were harvested eight times over 14 weeks to measure morphogenetic traits and nutritive value in six predefined leaf-age categories (from growing to complete senescence). The leaf lifespan and leaf length of the first three successive leaves were measured on 30 marked tillers throughout the experiment. Following analysis of variance, linear regression models were fitted to describe variations of NDF, NDFD and DMD with increasing leaf age and leaf length. Similar leaf NDF contents were found for the two cultivars, which remained stable throughout the leaf lifespan and increased markedly during leaf senescence. Leaf NDFD and leaf DMD both declined with increasing leaf age and length for the two cultivars. However, owing to shorter leaf lifespan of the soft-leaved cultivar, this decline in leaf NDFD and leaf DMD was faster for the soft- than for the tough-leaved cultivar. These results suggest that the soft-leaved cultivar will require more frequent defoliations than the tough-leafed cultivar to prevent decreases in nutritive value.

Signal grass (Brachiaria decumbens cv. Basilisk, syn. Urochloa decumbens Stapf R.D. Webster) has been widely grown in the Brazilian tropics over the last 40 years, but management recommendations have been largely empirical and not based on canopy targets. This study was designed to characterise and explain the impact of canopy-based grazing strategies on herbage accumulation, plant-part composition, and nutritive value of signal grass. Treatments were factorial combinations of two stubble heights, 5 cm (SH5) and 10 cm (SH10), and two grazing frequencies, grazing initiated when 95% (LI95) and 100% (LI100) of incoming light was intercepted by the canopy. Rest periods were imposed during summer and autumn of both experimental years. Leaf blade accumulation was greater for LI100 than LI95 (9.5 v. 8.8 t/ha) associated with increased stem accumulation (4.6 v. 3.5 t/ha for LI100 v. LI95). The SH10 pastures produced more stem than SH5 pastures (4.4 v. 3.6 t/ha), with no difference in leaf blade accumulation. In general, SH10 pastures had more residual leaf blade mass post-graze, whereas SH5 pastures combined with higher grazing frequency (SH5-LI95) became more prostrate over time, increasing leaf blade proportion in post-graze forage. Over time, stubble height had more influence than grazing frequency on leaf blade proportion at pre-graze, and SH5 pastures had leafier canopies than SH10 pastures. Digestibility was less under LI100, especially when associated with SH5 stubble (SH5-LI100), regardless of season of the year. To provide optimal leaf blade yield and overall forage digestibility, particularly during warm, rainy seasons, defoliation of signal grass should include pre-graze height varying from 18 to 30 cm (95–100% of light interception) and mean stubble height close to 10 cm.

Several models exist to predict lucerne (Medicago sativa L.) dry matter production; however, most do not adequately represent the ecophysiology of the species to predict daily growth rates across the range of environments in which it is grown. Since it was developed in the late 1990s, the GRAZPLAN pasture growth model has not been updated to reflect modern genotypes and has not been widely validated across the range of climates and farming systems in which lucerne is grown in modern times. Therefore, the capacity of GRAZPLAN to predict lucerne growth and development was assessed. This was done by re-estimating values for some key parameters based on information in the scientific literature. The improved GRAZPLAN model was also assessed for its capacity to reflect differences in the growth and physiology of lucerne genotypes with different winter activity. Modifications were made to GRAZPLAN to improve its capacity to reflect changes in phenology due to environmental triggers such as short photoperiods, declining low temperatures, defoliation and water stress. Changes were also made to the parameter governing the effect of vapour pressure on the biomass-transpiration ratio and therefore biomass accumulation. Other developments included the representation of root development and partitioning of canopy structure, notably the ratio leaf : stem dry matter. Data from replicated field experiments across Australia were identified for model validation. These data were broadly representative of the range of climate zones, soil types and farming systems in which lucerne is used for livestock grazing. Validation of predicted lucerne growth rates was comprehensive owing to plentiful data. Across a range of climate zones, soils and farming systems, there was an overall improvement in the capacity to simulate pasture dry matter production, with a reduction in the mean prediction error of 0.33 and the root-mean-square deviation of 9.6 kg/ha.day. Validation of other parts of the model was restricted because information relating to plant roots, soil water, plant morphology and phenology was limited. This study has highlighted the predictive power, versatility and robust nature of GRAZPLAN to predict the growth, development and nutritive value of perennial species such as lucerne.

Genetic resources of halophytic grass species are vital factors to be explored for improvement in pasture and rangeland productivity and to elucidate mechanisms of salinity tolerance. The objective of the present study was to understand the adaptive strategies of Bromus danthoniae to a hyper-saline environment by using 80 genotypes originated from saline and non-saline areas in West Iran. Salinity treatments of 0 and 350 mm NaCl were applied for 4 weeks, and plant growth, leaf water status, ionic status, oxidative stress and salt-excretion responses were evaluated. Analysis of variance showed significant genotypic (G) variation for all traits as well as significant salinity stress (S) and G × S effects for most of the traits. Dry matter was positively correlated with K /Na (r = 0.69) and Ca² /Na (r = 0.66) ratios, and negatively correlated with Na concentration (r = –0.72). In addition, a coincidence of low concentrations of Na in the leaf tissues and the excretion of salt crystals on the sheath leaves and leaf blades was observed in the hyper-salinity tolerant genotypes. These observations open up new avenues for elucidating potential strategies and pathways used by halophytic grasses to avert the excess Na in their plant tissues.