Debbie L. Sparkes

A calibrated model of wheat lodging compared with field measurements

This paper describes how an existing model of lodging in winter wheat (Triticum aestivum L.) has been further developed to enable it to predict the timing and amount of lodging from inputs about the crop, soil and weather. Improvements include the use of recently specified values for the drag coefficient and damping ratio of wheat shoots, accounting for temporal and spatial non-uniformity of plant characteristics, and using daily rainfall and wind run data. Stem and root lodging are predicted when the base bending moment of the shoot(s) exceed the failure moments of the stem base and anchorage system, respectively. Tests show that the model can predict the timing and quantity of lodging in crops with a wide range of lodging risks. Each area of further development contributed to the improvement of the model. Using accurate values of drag coefficient and damping ratio reduced failure wind speeds by 44% to more realistic values. Accounting for temporal non-uniformity of plants meant that the increase in lodging risk towards harvest was correctly predicted. Accounting for spatial non-uniformity enabled different sized areas of lodging to be predicted.

To what extent can zero tillage lead to a reduction in greenhouse gas emissions from temperate soils

Soil tillage practices have a profound influence on the physical properties of soil and the greenhouse gas (GHG) balance. However there have been very few integrated studies on the emission of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and soil biophysical and chemical characteristics under different soil management systems. We recorded a significantly higher net global warming potential under conventional tillage systems (26–31% higher than zero tillage systems). Crucially the 3-D soil pore network, imaged using X-ray Computed Tomography, modified by tillage played a significant role in the flux of CO2 and CH4. In contrast, N2O flux was determined mainly by microbial biomass carbon and soil moisture content. Our work indicates that zero tillage could play a significant role in minimising emissions of GHGs from soils and contribute to efforts to mitigate against climate change.

Carpel size, grain filling, and morphology determine individual grain weight in wheat

Highlight A high level of QTL coincidences was found for the traits that determine individual grain weight in wheat: carpel size, grain dry matter and water accumulation, and grain morphology.

Food and bioenergy: reviewing the potential of dual‐purpose wheat crops

Within the bioenergy debate, the ‘food vs. fuel’ controversy quickly replaced enthusiasm for biofuels derived from first‐generation feedstocks. Second‐generation biofuels offer an opportunity to produce fuels from dedicated energy crops, waste materials or coproducts such as cereal straw. Wheat represents one of the most widely grown arable crops around the world, with wheat straw, a potential source of biofuel feedstock. Wheat straw currently has limited economic value; hence, wheat cultivars have been bred for increased grain yield; however, with the development of second‐generation biofuel production, utilization of straw biomass provides the potential for ‘food and fuel’. Reviewing the evidence for the development of dual‐purpose wheat cultivars optimized for food grain and straw biomass production, we present a holistic assessment of a potential ideotype for a dual‐purpose cultivar (DPC). An ideal DPC would be characterized by high grain and straw yields, high straw digestibility (i.e. biofuel yield potential) and good lodging resistance. Considerable variation in these traits exists among current wheat cultivars, facilitating the selection of improved individual traits; however, increasing straw yield and digestibility could potentially have negative trade‐off impacts on grain yield and lodging resistance, reducing the feasibility of a single ideotype. Adoption of alternative management practices could potentially increase straw yield and digestibility, albeit these practices are also associated with potential trade‐offs among cultivar traits. Benefits from using DPCs include reduced logistics costs along the biofuel feedstock supply chain, but practical barriers to differential pricing for straw digestibility traits are likely to reduce the financial incentive to farmers for growing higher ‘biofuel‐quality’ straw cultivars. Further research is required to explore the relationships among the ideotype traits to quantify potential DPC benefits; this will help to determine whether stakeholders along the bioenergy feedstock supply chain will invest in the development of DPCs that provide food and fuel potential.

Examining the potential for climate change mitigation from zero tillage

The benefits of reduced and zero-tillage systems have been presented as reducing runoff, enhancing water retention and preventing soil erosion. There is also general agreement that the practice can conserve and enhance soil organic carbon (C) levels to some extent. However, their applicability in mitigating climate change has been debated extensively, especially when the whole profile of C in the soil is considered, along with a reported risk of enhanced nitrous oxide (N2O) emissions. The current paper presents a meta-analysis of existing literature to ascertain the climate change mitigation opportunities offered by minimizing tillage operations. Research suggests zero tillage is effective in sequestering C in both soil surface and sub-soil layers in tropical and temperate conditions. The C sequestration rate in tropical soils can be about five times higher than in temperate soils. In tropical soils, C accumulation is generally correlated with the duration of tillage. Reduced N2O emissions under long-term zero tillage have been reported in the literature but significant variability exists in the N2O flux information. Long-term, location-specific studies are needed urgently to determine the precise role of zero tillage in driving N2O fluxes. Considering the wide variety of crops utilized in zero-tillage studies, for example maize, barley, soybean and winter wheat, only soybean has been reported to show an increase in yield with zero tillage (7·7% over 10 years). In several cases yield reductions have been recorded e.g. c. 1–8% over 10 years under winter wheat and barley, respectively, suggesting zero tillage does not bring appreciable changes in yield but that the difference between the two approaches may be small. A key question that remains to be answered is: are any potential reductions in yield acceptable in the quest to mitigate climate change, given the importance of global food security?

Economic Analysis of Conversion Strategies for Stockless Organic Production

ABSTRACT In response to the Curry Report, the U.K. Governments Organic Action Plan aims to increase the area of organic production. In addition, Common Agricultural Policy (CAP) reform will provide an incentive for farmers to become more market-led and examine alternative production possibilities. However, the two-year conversion period represents a barrier to organic production. In a stockless system the typical conversion strategy is a red clover (Trifolium pratense L.)—ryegrass (Lolium sp. L.) green manure, attracting both Area Aid Payments (AAP) and Organic Farming Scheme (OFS) subsidies. Six alternative strategies to this green manure were tested in a replicated randomized block field experiment. Gross margin analysis of the conversion strategies in the presence and absence of AAP and OFS payments are presented. Sensitivity analysis of crop yields and prices indicates the robustness of the gross margin analysis. Where contracts to supply red clover seed can be obtained, growing clover seed in year 1 of conversion followed by a clover green manure in year 2 provides the highest mean annual gross margin, measured over the two-year conversion period and the first organic wheat (Triticum aestivum L.) crop. In the absence of a clover seed contract the two-year red clover-ryegrass green manure provides the highest mean annual gross margin, and is therefore likely to remain a popular conversion strategy. This holds given the decoupling (absence) of AAPs due the enhanced yield of the first organic wheat crop compared with more exploitative conversion strategies. Other strategies that may be appropriate include oats (Avena sativa L.) followed by beans (Vicia faba L.), however a change in policy on acceptable organic conversion crops would be required to enable this strategy to be considered.

Comparison of cell membrane thermostability and chlorophyll fluorescence parameters for the determination of heat tolerance in ten cabbage lines

Summary Cell membrane thermostability (CMT) and chlorophyll fluorescence (CF) were determined for ten lines of cabbage in order to select heat-tolerant varieties, to provide an improved method to screen for heat tolerance, and to determine whether there is a relationship between CMT and CF. Chlorophyll fluorescence parameters, especially variable fluorescence (Fv) and the ratio between Fv and maximum fluorescence (Fm), were found to be better than CMT for screening cabbage lines for heat tolerance. Fv values and the Fv/Fm ratio of stressed plants corresponded to high heat damage for the varieties ‘HRI 002605’, ‘HRI 003202’, and ‘HRI 007827’; and to low heat damage for the varieties ‘HRI 013011’, ‘HRI 005237’, and ‘HRI 006556’. The latter group may therefore be more tolerant of high temperature stress in the tropics. There were significant relationships (P < 0.05) between relative injury (RI), an index of CMT, and two of the CF parameters [miniumum florescence (Fo) and Fv/Fm] under stress conditions (35° – 40°C). This suggests that parameters measured under stress temperatures are more reliable than those measured under non-stressed conditions when determining heat tolerance.

Mitotic and meiotic behavior of rye chromosomes in wheat - Psathyrostachys huashanica amphiploid x triticale progeny.

The dynamics of rye chromosomes during mitosis and meiosis was analyzed in a subset comprising 33 F3 lines from the cross of wheat, Psathyrostachys huashanica amphiploid (AABBDDNsNs) and hexaploid triticale (AABBRR), as visualized by genomic in situ hybridization. The results indicated that 31 of the total lines contained 4-14 rye chromosomes. Twenty-eight combinations had more rye chromosomes than the F1 hybrids, suggesting the occurrence of spontaneous quantitative increment. No P. huashanica chromosomes were detected in all of the combinations tested. Mitotic analysis showed that rye chromosomes progressed normally with the wheat counterparts without loss. However, abnormal meiosis was found in almost all lines. Similar progression between wheat and rye genomes appeared from interphase to metaphase I. It was at anaphase I that many rye univalents lagged behind those of wheat, followed by equational division. This resulted in the formation of chromosomal segments and micronuclei at telophase I or II. Micronuclei could also be generated from the immobilized univalents in the periphery of cells. Synapsis and translocations between wheat and rye genomes, chromosome bridges, and unreduced gametes were detected. Therefore, it is proposed that rye chromosome elimination may involve chromatid lagging, fragmentation and micronucleation, or the immobilization of certain univalents during meiosis instead of mitosis in the relatively advanced generations. This mechanism, together with spontaneous incremental increase of rye chromosome number, permitted the generation of various germplasms for wheat improvement.

Quantification of seed–soil contact of sugar beet (Beta vulgaris) using X-ray Computed Tomography

BackgroundSeed–soil contact is important to ensure successful germination, however, there is a paucity of reported studies that have quantified the microstructure at and around this critical interface, mainly due to the opacity of soil.ResultsHere we describe a novel methodology to non-destructively calculate the seed–soil contact area using X-ray Computed Tomography. Under controlled conditions, we observed that seed–soil contact was strongly influenced by the size and type of seed, with a seed–soil contact of ca. 15% for naked sugar beet seeds compared to ca. 32% for pelleted and coated seeds. Similar results were obtained for seeds sampled from the field albeit with a higher spatial variability.ConclusionsBy application of this new quantification method it is hoped seed enhancement technologies can be optimised and ultimately seedbed preparation improved to ensure better germination.

TEMPERATURE AND DROUGHT STRESS EFFECTS ON GROWTH AND DEVELOPMENT OF BAMBARA GROUNDNUT ( VIGNA SUBTERRANEA L.)

The effect of drought and temperature on the growth and development of bambara groundnut ( Vigna subterranea (L.) Verdc.) was studied in controlled environment glasshouses in the United Kingdom. There were two landraces, S19-3 (from a hot, dry environment; Namibia) and Uniswa Red (from a cool, wet environment; Swaziland), two temperature regimes (23 °C and 33 °C) and three watering regimes (2006; fully irrigated), 2007 (drought imposed at 77 days after sowing (DAS)) and 2008 (drought imposed at 30 DAS)). Bambara groundnut responded to drought by slowing the rate of leaf area expansion and reducing final canopy size and total dry matter (TDM). Drought also caused significant reductions in pod dry matter, pod numbers and harvest index (HI), leading to a decrease in final yield that was different between landraces. Throughout the three growing seasons, landraces grown at 33 °C produced more TDM than the landraces grown at 23 °C. The two landraces differed in their phenology; S19-3 exhibited a reduced phenology where leaf numbers started to decrease before Uniswa Red at both temperatures, while Uniswa Red maintained the longest life cycle. The lowest pod yield was produced by Uniswa Red in 2008 at 33 °C (maximum of 35.5 gm −2 ), while S19-3 produced a minimum pod yield of 56.6 gm −2 at 33 °C, also in 2008. However, both landraces produced considerably more pod yield at 23 °C throughout the three growing seasons (minimum of 151 gm −2 and 162 gm −2 for Uniswa Red and S19-3, respectively). Under moderate drought, S19-3 at 33 °C gave the highest pod yield (365 gm −2 ) among the treatments throughout the three growing seasons and maintained HI better under drought. Despite being from a hot, dry environment, S19-3 also performed well at low temperature, which indicates the adaptation of S19-3 to low temperature that it also experiences in the country of origin.