Agronomy, Volume 6, Issue 4 (December 2016) – 19 articles

Water use efficiency (WUE) is a trait of prime interest in cases of drought stress because it provides information on biomass production in limited water conditions. In order to get information on WUE and additional water use related traits, i.e., dry weight (DW), fresh weight (FW), total leaf water (LW) and leaf water content (WC), greenhouse pot experiments were conducted on 156 barley genotypes (Hordeum vulgare L.) for control (70% maximal water capacity of soil) and drought stress conditions (20% of the maximal water capacity of soil). Significant correlations between WUE and the other water use related traits (r ≤ 0.65) were determined in juvenile barley, and genotypes suited for improving drought stress tolerance in early developmental stages were identified. Furthermore, based on the significant effects of genotypes and treatments, as well as their interaction, data were used for genome wide association studies (GWAS) resulting in the identification of 14 marker trait associations (MTAs) corresponding to four quantitative trait loci (QTL). For WUE, four MTAs were detected mostly located on barley chromosome 4H. For four MTAs, functional annotations related to the involvement in response to abiotic stress were found. These markers may be of special interest for breeding purposes in cases when they will be validated and also detected in later growth stages. Full article

Efforts to improve water-soluble carbohydrate (WSC) concentrations are common in perennial forage grass breeding. Perennial ryegrass (Lolium perenne) breeding has been very successful in developing new cultivars with high WSC and high agronomic performance. Breeding efforts are ongoing to improve the WSC of other perennial forage grasses, such as orchardgrass (Dactylis glomerata). The United States Department of Agriculture Forage and Range and Deutsche Saatveredelung orchardgrass breeding programs cooperated to characterize the expression and genotype by environment interaction (GEI) of water-soluble carbohydrates in a collection of orchardgrass populations from both breeding programs. Additionally, the effort characterized the relationship between water-soluble carbohydrates and other agronomic and nutritive value traits in these populations. Overall, the Deutsche Saatveredelung populations had higher herbage mass (15%), rust resistance (59%), and later maturity. The Forage and Range Research populations had higher water-soluble carbohydrates (4%), nutritive value, and earlier maturity. However, results were highly dependent on GEI. Differences were very pronounced at the French and German field locations, but less pronounced at the two US locations. Combining the germplasm from the Forage and Range Research and Deutsche Saatveredelung programs may be a way to develop an improved base germplasm source that could then be used separately in the EU and US for water-soluble carbohydrate and other trait improvement. Full article

The importance of haploid and doubled haploid (DH) techniques for basic and applied research, as well as to improve the speed of genetic gain when applied in breeding programs, cannot be overstated. They have become routine tools in several major crop species, such as maize (Zea mays L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.). DH techniques in perennial ryegrass (Lolium perenne L.), an important forage species, have advanced to a sufficiently successful and promising stage to merit an exploration of what their further developments may bring. The exploitation of both in vitro and in vivo haploid and DH methods to (1) purge deleterious alleles from germplasm intended for breeding; (2) develop mapping populations for genetic and genomic studies; (3) simplify haplotype mapping; (4) fix transgenes and mutations for functional gene validation and molecular breeding; and (5) hybrid cultivar development are discussed. Even with the comparatively modest budgets of those active in forage crop improvement, haploid and DH techniques can be developed into powerful tools to achieve the acceleration of the speed of genetic gain needed to meet future agricultural demands. Full article

Many of the major forage species used in agriculture are outcrossing and rely on the exchange of pollen between individuals for reproduction; this includes the major species used for dairy production in grazing systems: perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.). Cultivars of these species have been co-existing since contrasting cultivars were developed using plant breeding, but the consequences and need for strategies to manage co-existence have been made more prominent with the advent of genetic modification. Recent technological developments have seen the experimental evaluation of genetically modified (GM) white clover and perennial ryegrass, although there is no current commercial growing of GM cultivars of these species. Co-existence frameworks already exist for two major cross-pollinated grain crops (canola and maize) in Europe, and for alfalfa (Medicago sativa L.) in the US, so many of the principles that the industry has developed for co-existence in these crops such as detection techniques, segregation, and agronomic management provide lessons and guidelines for outcrossing forage species, that are discussed in this paper. Full article

Most of the Western World banned the cultivation of Cannabis sativa in the early 20th century because biotypes high in ∆⁹-tetrahydrocannabinol (THC, the principal intoxicant cannabinoid) are the source of marijuana. Nevertheless, since 1990, dozens of countries have authorized the licensed growth and processing of “industrial hemp” (cultivars with quite low levels of THC). Canada has concentrated on hemp oilseed production, and very recently, Europe changed its emphasis from fiber to oilseed. The USA, historically a major hemp producer, appears on the verge of reintroducing industrial hemp production. This presentation provides updates on various agricultural, scientific, social, and political considerations that impact the commercial hemp industry in the United States and Canada. The most promising scenario for the hemp industry in North America is a continuing focus on oilseed production, as well as cannabidiol (CBD), the principal non-intoxicant cannabinoid considered by many to have substantial medical potential, and currently in great demand as a pharmaceutical. Future success of the industrial hemp industry in North America is heavily dependent on the breeding of more productive oilseed cultivars, the continued development of consumer goods, reasonable but not overly restrictive regulations, and discouragement of overproduction associated with unrealistic enthusiasm. Changing attitudes have generated an unprecedented demand for the cannabis plant and its products, resulting in urgent needs for new legislative, regulatory, and business frameworks, as well as scientific, technological, and agricultural research. Full article

Use of electromagnetic induction (EMI) sensors along with geospatial modeling provide a better opportunity for understanding spatial distribution of soil properties and crop yields on a landscape level and to map site-specific management zones. The first objective of this research was to evaluate the relationship of crop yields, soil properties and apparent electrical conductivity (ECa) at different topographic positions (shoulder, backslope, and deposition slope). The second objective was to examine whether the correlation of ECa with soil properties and crop yields on a watershed scale can be improved by considering topography in modeling ECa and soil properties compared to a whole field scale with no topographic separation. This study was conducted in two headwater agricultural watersheds in southern Illinois, USA. The experimental design consisted of three basins per watershed and each basin was divided into three topographic positions (shoulder, backslope and deposition) using the Slope Position Classification model in ESRI ArcMap. A combine harvester equipped with a GPS-based recording system was used for yield monitoring and mapping from 2012 to 2015. Soil samples were taken at depths from 0–15 cm and 15–30 cm from 54 locations in the two watersheds in fall 2015 and analyzed for physical and chemical properties. The ECa was measured using EMI device, EM38-MK2, which provides four dipole readings ECa-H-0.5, ECa-H-1, ECa-V-0.5, and ECa-V-1. Soybean and corn yields at depositional position were 38% and 62% lower than the shoulder position in 2014 and 2015, respectively. Soil pH, total carbon (TC), total nitrogen (TN), Mehlich-3 Phosphorus (P), Bray-1 P and ECa at depositional positions were significantly higher compared to shoulder positions. Corn and soybeans yields were weakly to moderately (<±0.75) correlated with ECa. At the deposition position at the 0–15 cm depth ECa-H-0.5 was weakly correlated (r < ±0.50) with soil pH and was moderately correlated (r = ±0.50–±0.75) with organic matter (OM), calcium (Ca) and sulfur (S). Slope variation from 1%–20% at the research site had a strong influence on soil properties at watershed scale. When data from all topographic positions were combined together in all basins spatial interpolation between Mehlich-3 P and ECa-H-0.5 resulted in a larger cross validation RMSE compared to individual shoulder and backslope positions. Results demonstrated that topographic position should be considered while making correlations of ECa with soil properties. Methods of delineating topography positions presented in this paper can easily be replicated on other fields with similar landscape characteristics and EMI sensor based survey techniques can certainly improve and help in making detailed prediction maps of soil properties. Full article

Molecular breeding tools, such as genetic modification, provide forage plant breeders with the opportunity to incorporate high value traits into breeding programs which, in some cases, would not be available using any other methodology. Despite the potential impact of these traits, little work has been published that seeks to optimize the strategies for transgenic breeding or incorporate transgenic breeding with other modern genomics-assisted breeding strategies. As the number of new genomics assisted breeding tools become available it is also likely that multiple tools may be used within the one breeding program. In this paper we propose a strategy for breeding genetically-modified forages using perennial ryegrass as an example and demonstrate how this strategy may be linked with other technologies, such as genomic selection. Whilst the model used is perennial ryegrass the principles outlined are valid for those designing breeding strategies for other outcrossing forage species. Full article

Surface soil sodicity as well as subsoil salinity, acidity, and phytotoxic concentrations of chloride (Cl) are major soil constraints to crop production in many soils of sub-tropical, north-eastern Australia. The identification of genotypes tolerant to these soil constraints may be an option to maintain and improve productivity on these soils. We evaluated performance of 11 barley and 17 wheat genotypes grown on two sites <0.5 km apart. Compared to the non-sodic site, the sodic site had significantly higher Cl concentration (>800 mg·Cl·kg⁻¹) in the subsoil (0.9–1.3 m soil depth) and higher exchangeable sodium percentage (ESP) (>6%) in the surface and subsoil. Barley grain yield and plant available water capacity (PAWC) were reduced between 5%–25% and 40%–66%, respectively, for different genotypes at the sodic site as compared to the non-sodic site. For wheat genotypes, grain yield was between 8% and 33% lower at the sodic site compared to the non-sodic site and PAWC was between 3% and 37% lower. Most barley and wheat genotypes grown at the sodic site showed calcium (Ca) deficiency symptoms on younger leaves. Analysis of the youngest fully mature leaf (YML) confirmed that genotypes grown at the sodic site with Ca concentration < 0.2% exhibited deficiency symptoms. Grain yields of both barley and wheat genotypes grown on the sodic and non-sodic sites increased significantly with increasing Ca and K in YML and decreased significantly with increasing Na and Cl concentrations in YML. Sodium (Na) concentrations in YML of wheat genotypes grown at the sodic site were 10-fold higher than those from the non-sodic site whereas this increase was only two-fold in barley genotypes. In step-wise regression, the PAWC of barley and wheat genotypes grown on sodic and non-sodic sites was the principal determinant of variability of barley and wheat grain yield. Including the Ca concentration in the YML of wheat genotypes and K:Na ratio in the YML of barley genotypes significantly improved the prediction of grain yield in the regression analysis. Barley genotypes, Mackay and Kaputar, were relatively susceptible while Baronesse and Grout were relatively more tolerant to sodicity. Wheat genotypes Gregory and Stampede were generally relatively more susceptible to sodicity, and genotypes Baxter, Hume, and the experimental line HSF1-255 were relatively more tolerant than the former group. Full article

Rice (Oryza sativa L.) is an important staple crop that feeds more than one half of the world’s population and is the model system for monocotyledonous plants. However, rice is very sensitive to salinity and is the most salt sensitive cereal crop with a threshold of 3 dSm⁻¹ for most cultivated varieties. Despite many attempts using different strategies to improve salinity tolerance in rice, the achievements so far are quite modest. This review aims to discuss challenges that hinder the improvement of salinity stress tolerance in rice as well as potential opportunities for enhancing salinity stress tolerance in this important crop. Full article

The yield response of various crops to salinity under field conditions is affected by soil processes and environmental conditions. The composition of dissolved ions depend on soil chemical processes such as cation or anion exchange, oxidation-reduction reactions, ion adsorption, chemical speciation, complex formation, mineral weathering, solubility, and precipitation. The nature of cations and anions determine soil pH, which in turn affects crop growth. While the ionic composition of soil solution determine the osmotic and ion specific effects on crops, the exchangeable ions indirectly affect the crop growth by influencing soil strength, water and air movement, waterlogging, and soil crusting. This review mainly focuses on the soil chemistry processes that frustrate crop salinity tolerance which partly explain the poor results under field conditions of salt tolerant genotypes selected in the laboratory. Full article

The accumulation of biomass and mineral nutrients during the post-anthesis period was investigated in field-grown rice plants cultivated in phosphorus (P)-sufficient vs. P-deficient soil. Phosphorus deficiency reduced biomass accumulation by around 30%, and reduced the accumulation of all nutrients in aboveground plant biomass except sulfur (S) and copper (Cu). Ultimately, grain zinc (Zn), Cu, and calcium (Ca) concentrations were significantly higher in P-deficient plants, while grain magnesium (Mg) concentrations were significantly lower. While P deficiency caused a 40% reduction in the concentration of the anti-nutrient phytate in the grain, this was offset by a 40% reduction in grain starch lysophospholipids, which have positive benefits for human health and grain quality. Full article

Connected multiparental crosses are valuable for detecting quantitative trait loci (QTL) with multiple alleles. The objective of this study was to show that the progeny of a polycross can be considered as connected mutiparental crosses and used for QTL identification. This is particularly relevant in outbreeding species showing strong inbreeding depression and for which synthetic varieties are created. A total of 191 genotypes from a polycross with six parents were phenotyped for plant height (PH) and plant growth rate (PGR) and genotyped with 82 codominant markers. Markers allowed the identification of the male parent for each sibling and so the 191 genotypes were divided into 15 full-sib families. The number of genotypes per full-sib family varied from 2 to 28. A consensus map of 491 cM was built and QTL were detected with MCQTL-software dedicated to QTL detection in connected mapping populations. Two major QTL for PH and PGR in spring were identified on linkage groups 3 and 4. These explained from 12% to 22% of phenotypic variance. The additive effects reached 12.4 mm for PH and 0.11 mm/C°d for PGR. This study shows that the progenies of polycrosses can be used to detect QTL. Full article

Soil humic substances (HS) are known to be beneficial for soils and plants, and most published studies of HS and humates, usually conducted under controlled conditions, show benefits. However, the value of commercial humate application in the field is less certain. This review attempts to answer the question: How effective are commercial humates in the field? Commercial humates, especially K humate, are used widely in agriculture today as “soil conditioners”. A wide range of benefits is claimed, including growth of beneficial soil microbes; deactivation of toxic metals; improvements in soil structure including water retention capacity, enhanced nutrient and micronutrient uptake and photosynthesis; resistance to abiotic stress, including salinity; and increased growth, yield and product quality. Despite this, there is a surprising lack of solid evidence for their on-farm effectiveness and findings are often inconsistent. The industry relies largely on anecdotal case studies to promote humates, which are often applied at unrealistically low levels. It is recommended that products should be well characterised, physically and chemically, and that careful field studies be conducted on foliar humate application and pelletised humates at realistic rates, targeted to the seedling rhizosphere, for a variety of crops in a range of soils, including low C sandy and saline soils. Full article

Italian ryegrass is one of the most important temperate forage grasses on a global basis. Improvement of both dry matter yield and quality of herbage have been major objectives of pasture grass breeding over the last century. F₁ and F₂ progeny sets derived from controlled pair-crosses between selected Italian ryegrass genotypes have been evaluated for yield and nutritive quality under field conditions. Linear regression of the performance of F₁ families under sward conditions on parental genotype means in a spaced plant trial was significant for quality characteristics, but not for herbage yield. This result suggests that phenotypic selection of individual plants from spaced plant nursery is feasible for improvement of nutritive quality traits, but not for yield. The presence of significant heterosis within F₁ populations was demonstrated by reduced herbage production in subsequent F₂ populations (generated by one cycle of full-sib mating), an up to 22.1% total herbage yield in fresh weight, and a 30.5% survival rate at the end of the second reproductive cycle. Potential optimal crosses for exploiting such heterosis are discussed, based on construction and the inter-mating of complementary parental pools, for the implementation of a novel F₁ hybrid production strategy. Full article

Fermentation quality of dwarf napiergrass (Pennisetum purpureum Schumach) was estimated for additives lactic acid bacteria and Acremonium cellulase (LAB + AC), fermented juice of epiphytic lactic acid bacteria (FJLB), and a no-additive control in 2006 via two ensiling methods—round-bale and vinyl-bag methods in 2006—and via two ensiling seasons—summer and autumn of 2013. Fermentation quality of dwarf napiergrass ensiled in the summer season was improved by the input of additives, with the highest quality in LAB + AC, followed by FJLB; the lactic acid content was higher, and the pH and sum of the butyric, caproic, and valeric acid contents were lower, resulting in an increase in the V-score value by each additive. The ensiling method in autumn without additives affected fermentation quality, mainly due to the airtightness, which was higher for round-bale processing than in vinyl bags, even with the satisfactory V-score of 72. Fermentation in round bales without additives had a higher quality in autumn than in summer, possibly due to the higher concentration of mono- and oligo-saccharides. Thus, it was concluded that dwarf napiergrass can be produced to satisfactory-quality silage by adding LAB + AC or FJLB in summer and even in the absence of additives in autumn. Full article

Post-rice irrigated soils offer several potential advantages for the growth of subsequent crops, but Australian producers have often been reluctant to grow grain legumes immediately following a rice crop due to physico-chemical constraints. A field experiment was thus conducted to explore the potential for producing grain legumes following rice in comparison to those following a fallow during 2012 and 2013. Two grain legumes, field pea and faba bean, were sown 5, 7 and 12 weeks after rice harvest in 2013 at Yanco, NSW, and plant growth indicators and grain yield were compared. Early sowing of field pea following rice gave the best outcome, with plants flowering three weeks earlier and yielding 1330 kg·ha⁻¹ more grain than after fallow. In contrast, faba bean yield was 35 kg·ha⁻¹ less after rice than after fallow across the three sowing dates. Higher pea yield was consistent with the early emergence of seedlings, higher light interception and overall greater plant growth following rice. Post-rice crops also had 10-fold less weed infestation than crops in a similarly-established fallow treatment and, thus, required far less weed management. Legume crops sown at the later seeding date had significantly reduced (~50%–60%) yields compared to those of the first two sowings; this is most likely a reflection of reduced temperatures and day lengths experienced during vegetative and reproductive growth phases. Full article

Unique, variable summer climate of the lower Mississippi (MS) Delta region poses a critical challenge to cotton producers in deciding when to plant for optimized production. Traditional 2–4 year agronomic field trials conducted in this area fail to capture the effects of long-term climate variabilities in the location for developing reliable planting windows for producers. Our objective was to integrate a four-year planting-date field experiment conducted at Stoneville, MS during 2005–2008 with long-term climate data in an agricultural system model and develop optimum planting windows for cotton under both irrigated and rainfed conditions. Weather data collected at this location from 1960 to 2015 and the CSM-CROPGRO-Cotton v4.6 model within the Root Zone Water Quality Model (RZWQM2) were used. The cotton model was able to simulate both the variable planting date and variable water regimes reasonably well: relative errors of seed cotton yield, aboveground biomass, and leaf area index (LAI) were 14%, 12%, and 21% under rainfed conditions and 8%, 16%, and 15% under irrigated conditions, respectively. Planting windows under both rainfed and irrigated conditions extended from mid-March to mid-June: windows from mid-March to the last week of May under rainfed conditions, and from the last week of April to the end of May under irrigated conditions were better suited for optimum yield returns. Within these windows, rainfed cotton tends to lose yield from later plantings, but irrigated cotton benefits; however, irrigation requirements increase as the planting windows advance in time. Irrigated cotton produced about 1000 kg·ha⁻¹ seed cotton more than rainfed cotton, with irrigation water requirements averaging 15 cm per season. Under rainfed conditions, there is a 5%, 14%, and 27% chance that the seed cotton production is below 1000, 1500, and 2000 kg·ha⁻¹, respectively. Information developed in this paper can help MS farmers in decision support for cotton planting. Full article

For many decades, it was commonly believed that humic acids were formed in soils by the microbial conversion of plant lignins. However, an experiment to test whether these humic acids were formed prior to plant matter reaching the soil was never reported until the late 1980s (and then only as a side issue), even though humic acids were first isolated and reported in 1786. This was a serious omission, and led to a poor understanding of how the humic acid content of soils could be maintained or increased for optimum fertility. In this study, commercial sugar cane mulch and kelp extracts were extracted with alkali and analyzed for humic acid content. Humic acids in the extracts were positively identified by fluorescence spectrophotometry, and this demonstrated that humic acids are formed in senescent plant and algal matter before they reach the soil, where they are then strongly bound to the soil and are also resistant to microbial metabolism. Humic acids are removed from soils by wind and water erosion, and by water leaching, which means that they must be regularly replenished. This study shows that soils can be replenished or fortified with humic acids simply by recycling plant and algal matter, or by adding outside sources of decomposed plant or algal matter such as composts, mulch, peat, and lignite coals. Full article

Expanding grain sorghum [Sorghum bicolor (L.) Moench] production northward from southeastern Colorado is thought to be limited by shorter growing seasons due to lower temperatures and earlier frost dates. This study used a simulation model for predicting crop phenology (PhenologyMMS) to estimate the probability of reaching physiological maturity before the first fall frost for a variety of agronomic practices in northeastern Colorado. Physiological maturity for seven planting dates (1 May to 12 June), four seedbed moisture conditions affecting seedling emergence (from Optimum to Planted in Dust), and three maturity classes (Early, Medium, and Late) were simulated using historical weather data from nine locations for both irrigated and dryland phenological parameters. The probability of reaching maturity before the first frost was slightly higher under dryland conditions, decreased as latitude, longitude, and elevation increased, planting date was delayed, and for later maturity classes. The results provide producers with estimates of the reliability of growing grain sorghum in northeastern Colorado. Full article