Soil acidity, or more specifically aluminium (Al) toxicity, is a major soil limitation to growing wheat (Triticum aestivum L.) in the south of Western Australia (SWA). Application of calcium carbonate (lime) is used to correct Al toxicity by increasing soil pH and decreasing soluble soil Al³⁺. Soil testing using a 0.01 m calcium chloride (CaCl₂) solution can measure both soil pH (pH_CaCl2) and soil Al (Al_CaCl2) for recommending rates of lime application. This study aimed to determine which combination of soil pH_CaCl2 or soil Al_CaCl2 and sampling depth best explains the wheat grain-yield increase (response) when lime is applied. A database of 31 historical lime experiments was compiled with wheat as the indicator crop. Wheat response to lime application was presented as relative yield percentage (grain yield for the no-lime treatment divided by the highest grain yield achieved for lime treatments × 100). Soil sampling depths were 0–10, 10–20 and 20–30 cm and various combinations of these depths. For evidence that lime application had altered soil pH_CaCl2, we selected the change in the lowest pH_CaCl2 value of the three soil layers to a depth of 30 cm as a result of the highest lime application (ΔpH_min). When ΔpH_min <0.3, the lack of grain-yield response to lime suggested that insufficient lime had leached into the 10–30 cm soil layer to remove the soil Al limitation for these observations. Also, under high fallow-season rainfall (228 and 320 mm) and low growing-season rainfall (GSR) (<140 mm), relative yield was lower for the measured level of soil Al_CaCl2 than in the other observations. Hence, after excluding observations with ΔpH_min <0.3 or GSR <140 mm (n = 19), soil Al_CaCl2 provided a better definition of the relationship between soil test and wheat response (r² range 0.48–0.74) than did soil pH_CaCl2 (highest r² 0.38). The critical value (defined at relative yield = 90%) ranged from 2.5 mg Al kg^–1 (for soil Al calculated according to root distribution by depth within the 0–30 cm layer) to 4.5 mg Al kg^–1 (calculated from the highest Al_CaCl2 value from the three soil layers to 30 cm depth). We conclude that 0.01 m CaCl₂ extractable Al in the 0–30 cm layer will give the more accurate definition of the relationship between soil test and wheat response in SWA.

Cytoplasmic male sterile (CMS) lines are important tools for hybrid production but they cannot produce viable pollen. Breeding new CMS lines and studying their sterility mechanism in wheat (Triticum aestivum L.) greatly facilitates the process of hybrid wheat breeding. We conducted transcriptome sequencing for a recently identified Mu-CMS line with Aegilops uniaristata Vis. cytoplasm, named U706A, and its isonuclear maintainer line (706B) at the binucleate stage, which was a critical period when abortion occurred. We found that most of the genes involved in phosphatidylinositol metabolism and pectin degradation were downregulated, as well as genes encoding the MYB21 and MYC2 transcription factors, in U706A compared with 706B. In addition, pectin contents indicated that the production of pectin has been enhanced from the binucleate stage to the trinucleate stage, owing to the downregulation of pectin-degradation-related genes in U706A at the binucleate stage, which confirmed the reliability of the sequencing results. We also discovered that the accumulation period of pectin content in U706A is abnormal compared with 706B, which may be an important reason for abortion. Some differentially expressed genes that might be related to the sterile phenotype were verified by quantitative RT-PCR. Therefore, we suggest that the downregulation of these genes possibly leads to the anther not to crack; the tapetum and microspore membrane system is less metabolised, and the abnormal pectin accumulation results in microspore nutrient deficiencies and abnormal development. These findings provide novel insights into the mechanism responsible for pollen abortion in CMS, which may facilitate hybrid wheat breeding.

An on-farm field-experiment was carried out in north-eastern Victoria in 2011 and 2012 to compare the agronomic effectiveness of surface and subsoil manuring on a Chromosol soil with a compacted clay subsoil. Surface manuring involved the surface application of 20 t poultry litter ha^–1, whereas subsoil manuring involved deep-banding of the same quantity of litter in 30–40-cm-deep rip-lines, spaced 80 cm apart. Treatments were applied at the start of the first cropping season. The objective of the study was to determine whether surface manuring might produce the large yield responses reported for subsoil manuring. Both manuring treatments increased yields of wheat (Triticum aestivum L.) by >2.3 t ha^–1 compared with the unamended control in 2011, when spring rainfall was close to the average. However, only subsoil manuring increased wheat yields in 2012, producing an extra 4.7 t ha^–1 above the control, in a year with a very dry spring. This yield response suggests that subsoil manuring would be more effective than surface manuring in the second year after treatment in years with a dry finish.

This study aimed to support field pea (Pisum sativum L.) breeding strategies for organic systems of southern European environments, by assessing the size of genotype × environment interaction (GEI) due to spatial and temporal factors across climatically contrasting regions and identifying plant characters associated with genotype adaptive responses. Twelve recent varieties were evaluated for grain yield and other traits in six organically managed environments (three sites × two cropping years) of northern, central and southern Italy. GEI for grain yield was large, with the variety × site × year interaction greatly exceeding the variety × site interaction. This finding, and the similar magnitude of the mean genetic correlations for variety yields across pairs of sites (r_g = 0.56) and pairs of years (r_g = 0.51), indicated the difficulty of exploiting variety × site interaction effects by breeding for specific climatic regions. Pattern analysis highlighted the large inconsistency across years for GEI pattern of the sites from central and southern Italy. GEI also complicated the targeting of varieties, owing to inconsistent top-performing material across years according to additive main effects and multiplicative interaction (AMMI)-modelled yields. Higher genotype mean yield was strictly associated (P < 0.01) with lower weed proportion (hence, greater competitiveness against weeds: r = –0.96), taller plants (r = 0.89) and larger seeds (r = 0.78), with looser associations with lower susceptibility to lodging and ascochyta blight. These traits, which also contributed to preferential adaptation to the moisture-favourable environments of northern Italy, could be selected in breeding widely adapted varieties.

Soybean (Glycine max. (L.) Merr.) is a symbiotic nitrogen-fixing crop. In order to increase grain yield, it is important to know how soybean plants respond to nitrogen topdressing for the improvement of nitrogen utilisation. We used two soybean cultivars with different grain yield potentials and applied 13 nitrogen topdressing treatments to determine optimal topdressing time and nitrogen metabolism. Nitrogen treatments included a base fertiliser and single topdressings at different times, in 10-day intervals from 10 to 120 days after emergence (DAE). Among the nitrogen treatments, the optimal times for topdressing were at 40 DAE or 90 DAE to increase grain yield, and both soybean cultivars also had higher nitrate reductase (NR) and glutamine synthetase (GS) activities with topdressing at these times. Higher expression of the NR2 gene was associated with upregulated NR activity in leaves of both cultivars at the early-mature stage. With topdressing at 90 DAE, higher GS1 expression and GS activity were found in the leaves of the higher yielding cultivar at the full-seed stage and the early-mature stage. With topdressing at 90 DAE, the higher yielding cultivar had a higher nitrate metabolism capacity at the late reproductive stages than the lower (common) yielding cultivar.

Low availability of phosphorus (P) is a major constraint to production of cotton (Gossypium hirsutum L.). The extent to which genotypic variation in root traits exists or contributes to P-acquisition efficiency (PAE) in cotton is unknown. To assess genetic variation in PAE, the biomass and P-acquisition characteristics of 32 cotton genotypes were evaluated in a hydroponic experiment. Significant genotypic variation in biomass and P content was detected among the cotton genotypes in two seasons. We then conducted a 2-year pot experiment to compare P-efficiency traits between three P-efficient and two P-inefficient genotypes under P-deficient and P-sufficient conditions (0 and 75 mg P₂O₅ kg^–1 soil, respectively). We detected significant differences in biomass accumulation and allocation, P accumulation and allocation, root traits and PAE among the five cotton genotypes under P-sufficient and P-deficient conditions. Compared with P-inefficient genotypes, P-efficient genotypes had longer surface fine roots, and greater total root surface area, total root length, surface root length, and P concentration (partitioning index) in bolls. Root morphology, especially surface fine root length and middle root length, played an important role in P uptake under P-deficient conditions.

We studied the relative efficacy of different forms of foliar iron (Fe) fertilisation on leaf re-greening in Fe-deficient, purple-fleshed sweet potato (Ipomoea batatas (L.) Lam.) varieties xuzi8 and xuzi6. Activities of ferric chelate reductase (FCR) and concentrations of Fe were measured in the leaves and roots at intervals over 5 days to quantify recovery from leaf chlorosis. Freshly expanded and chlorotic leaves were immersed in one of three different fertiliser compounds containing 9 mm Fe: FeSO₄, Fe₂(SO₄)₃, Fe(III)-EDTA. An Fe-sufficient treatment and an Fe-deficient control were included. The experiment had a completely randomised block design with five replications per treatment and was conducted in a sunlit glasshouse. For variety xuzi8, leaf FCR activity in the Fe₂(SO₄)₃ treatment was highest at 1 h after application, and higher than all other treatments, whereas FeSO₄ and Fe(III)-EDTA treatments showed their highest FCR at day 5 after application, both significantly higher than the Fe₂(SO₄)₃ and control treatments. Furthermore, leaf Fe concentration reached a maximum in the FeSO₄ treatment at day 1, and in the Fe₂(SO₄)₃ treatment at day 3. By contrast, root Fe concentration was relatively constant and lower in the foliar Fe treatments than the Fe-sufficient and -deficient treatments. For variety xuzi6, leaf SPAD was higher with the Fe₂(SO₄)₃ than the FeSO₄ treatment at day 5 after application. In general, FCR activity and Fe concentrations in roots and leaves of xuzi6 were higher than those of xuzi8. Variations in leaf Fe concentrations were similar for both the FeSO₄ and Fe₂(SO₄)₃ treatments of the two varieties. Maximum leaf Fe levels in xuzi6 were ∼4-fold those in xuzi8. The results of the study suggest that foliar-applied Fe₂(SO₄)₃ was the most effective compound at correcting Fe-deficiency symptoms. The higher leaf and root FCR activity and Fe concentration in xuzi6 might explain its higher tolerance to Fe deficiency and better re-greening than xuzi8.

Echinochloa colona L. (Link) (awnless barnyard grass) is one of the top three most problematic weeds of summer crops in Australia. This weed has evolved resistance to glyphosate. A study was conducted to evaluate the effect of environmental factors on the germination and seedling emergence of a glyphosate-resistant (GR) and a glyphosate-susceptible (GS) biotype of E. colona. The two biotypes had similar germination and emergence responses to light and temperature conditions, water stress, solution pH, sorghum residue cover and seed burial depth. Light stimulated germination more than dark conditions, and seeds germinated at a wide range of alternating day/night temperatures, from 20°C/10°C to 35°C/25°C, whereas no seeds germinated at 15°C/5°C. These results suggest that E. colona can emerge in spring, summer and autumn in Queensland. The sodium chloride concentration required to inhibit 50% germination was greater for the GR biotype (209 mm) than the GS biotype (174 mm). Seed germination was not affected by pH in the range 4–10. Water stress reduced germination by 50% at an osmotic potential of –0.44 MPa. In a shade-house study, retention of sorghum residue cover on the soil surface reduced the seedling emergence of E. colona. Emergence was 70% in the absence of crop residue, whereas a residue amount of 8 t ha^–1 reduced emergence to 47%. Emergence was greatest for seeds placed on the soil surface and declined linearly with increasing burial depth; no seedlings emerged from 8 cm depth. The GR biotype had higher germination than the GS biotype under high sodium chloride concentrations; therefore, this biotype may be highly competitive with crops under highly saline conditions. Because germination was high on the soil surface and was stimulated by light, this weed will remain problematic under no-till farming systems in Australia.

The effect of nitrogen (N) application on seed yields and yield components in Leymus chinensis (Trin.) Tzvel., a perennial rhizomatous grass, was measured in a field experiment with two saline-sodic soils at Da’an Sodic Land Experiment Station during 2010–11. Two grassland field sites were classified as moderately saline–sodic (MSSL) and severely saline–sodic (SSSL). Application rates of N at each site were 0, 30, 60, 90, 120, 150, 180 and 210 kg ha^–1. Application of N significantly improved seed yield mainly through increased spike number (R² = 0.96, P ≤ 0.001). Compared with nil N, seed yield increased 7.4–10.9 times with N application of 150 kg ha^–1 at MSSL, and 5.3–7.5 times with N application of 120 kg ha^–1 at SSSL. However, absolute increases at SSSL were relatively small. Some significant differences (P ≤ 0.01) in seed yield occurred between 2010 and 2011 with different N application rates in the same soil, and between MSSL and SSSL in the same year. Increasing N application rate significantly decreased N physiological efficiency (NPE) but increased N apparent-recovery fraction (NRF) and N partial-factor productivity (NPP) at both sites. Seed yield and NPP indicated that the optimal N application rates to increase yield were 150 kg ha^–1 at MSSL and 120 kg ha^–1 at SSSL. High soil pH was the major factor adversely impacting seed yield, and pH and soil salinity were major factors negative affecting NPE, NRF and NPP as well as decreasing the positive effect of N application. Nitrogen application is a practical and effective method to increase seed yield of L. chinensis in saline-sodic grasslands of Northeast China, particularly when soil pH and salinity are not limiting.

Adoption of silvopasture is increasing, but proper design and management of pasture–tree associations is required to sustain pasture productivity. Our objective was to compare agronomic and physiological characteristics of Brachiaria brizantha (Hochst. Ex A.Rich.) Stapf. (palisade grass) cv. Marandu growing in monoculture, or in silvopasture with Eucalyptus urograndis, in the Brazilian Amazon biome. Trees were planted in triple rows (intra-row spacing 3 m, inter-row spacing 3.5 m), referred to as a grove, with three groves per 2-ha silvopasture experimental unit. Space between groves was 30 m, and tree density was 270 ha^–1. From October 2015 to September 2016, all experimental units were stocked continuously with cattle by using a variable stocking rate to maintain a Marandu canopy height of 30 cm. In the silvopasture, sampling occurred at 4, 7.5 and 15 m into the non-treed area from the outer tree row in a grove. Photosynthetically active radiation (PAR) reaching the Marandu canopy averaged 21% less for silvopasture than for grass monoculture; however, forage accumulation was not different between systems, nor were Marandu stomatal conductance, water-use efficiency (WUE), transpiration rate, transpiration ratio and leaf temperature. In silvopasture, PAR and forage accumulation were 33% and 29% less, respectively, at the 4-m distance than the 15-m distance from the edge row of trees, associated with lower transpiration rate and transpiration rate and greater WUE. We conclude that Marandu palisade grass can tolerate PAR reduction in silvopasture up to ∼20% without reduction in forage accumulation, supporting its potential use in agroforestry systems for cattle production in the Brazilian Amazon Biome.