Nitrogen (N) uptake and utilization efficiency (N(UtE)) of the high-yielding cultivars 'Gemini' of wheat and 'Jaidor' of barley were tested with N rates of 0, 140 and 210 kg ha and 0, 80 and 140 kg ha , respectively. The different grain yield response was linked to their difference in nitrogen. Uptake and utilization efficiency. The highest yield in barley was recorded with 80 kg N ha and in wheat with 210 kg Nha . Nitrogen application affected the accumulation of biomass up to heading in wheat and barley. While N uptake during grain filling did not show any correlation to N applied in barley, it was markedly correlated in wheat. At N and N N applied, barley exhibited a 32 and 8% higher N(UtE) than wheat. N agronomic efficiency; a parameter representing the ability of the plant to increase yield in response to N applied, was similar in barley and wheat (8.7 and 9.2 kg kg of N applied, respectively), suggesting that both species respond equally to nitrogen fertilization. Nevertheless; due to its lower N(UtE), wheat requires high N fertilization to optimize yields; by contrast, in barley the lower N rate needed to achieve highest yields enables this crop to perform better in low-input conditions. As a results, the reduced N requirements for barley highest yield associated with a better R(F) value (apparent N fertilizer recovery of 63% in barley and 49% in wheat at N ) makes barley crop a better choice to reduce ground-water pollution due to nitrate leaching in winter and early spring.
In the present study species which colonize the stem base of winter wheat and cause different types of diseases were analyzed. It was demonstrated that Fusarium avenaceum, F. culmorum, Pseudocereosporella herpotrichoides and Rhizoetonia cerealis were most of ten isolated from the stem base of winter wheat. It was not always possible to determine the pathogen which was responsible for the specific disease symptoms.
Single irrigation, compared to the conventional four or five irrigations, has been practised in northern China on winter wheat on a relatively large scale since 1991. In a field study, irrigation was reduced from normally four times (I , 4 x 75 mm) to one (I , 75 mm at the end of the second internode elongation) in an area with an annual rainfall of about 600 mm. A control without irrigation (I ) was also included. Late sowing and early soil drying at seedling stage resulted in a relatively deep root system. Leaf area index, the size of upper leaves and the length of base internodes were also significantly reduced under I , but kernel number per panicle was not reduced, suggesting that the development of inflorescence was not disrupted. During the active grain-filling stage, it was found that leaf water potential under I was maintained similar to that of I , while daytime stomatal conductance was substantially reduced. Leaf temperature was increased, indicating an inhibited leaf transpiration. Early senescence was induced in I and I crops and resulted in a substantially lower kernel weight. Although the grain yield of I was reduced by about 15% from I , the water-use efficiency (WUE) for total water consumption was increased by 24-30%. Single irrigation can potentially make wheat cropping sustainable in this area in terms of water usage and prevent further depletion of the underground water resource. Explanations for the small or zero reduction in yield are: (1) the encouraging development of a deep root system that enabled the plants to use more water at depth (below 1 m), which is recharged annually by the relatively high summer rainfall. (2) A large portion of root system in the drying soil and its induced shoot physiological changes, that is, reduced leaf expansion and stomatal conductance, which helped the plants to establish a better canopy structure with a much reduced water consumption. (3) An improved harvest index.
Cropping and tillage management can increase atmospheric CO2, N2O, and CH4 concentrations, and contribute to global warming and destruction of the ozone layer. Fluxes of these gases in vented surface chambers, and water filled pore space (WFPS) and temperature of survace soil were measured weekly from a long-term winter wheat (Triticum aestivum L.)-fallow rotation system under chemical (no-tillage) and mechanical tillage (noninversion subtillage at 7 to 10 cm or moldboard plowing to 15 cm) follow management and compared with those from "native" grass sod at Sidney, NE, from March 1993 to July 1995. Cropping, tillage, within-field location, time of year, soil temperature, and WFPS influenced net greenhouse gas fluxes. Mean annual interrow CO2 emissions from wheat-fallow ranged from 6.9 to 20.1 kg C ha(-1) d(-1) and generally increased with intensity and degree of tillage (no-till least and plow greatest). Nitrous oxide flux averaged autumn > winter. Winter periods accounted for 4 to 10% and 3 to 47% of the annual CO2 and N2O flux, respectively, and 12 to 21% of the annual CH4 uptake. Fluxes of CO2 and N2O, and CH4 uptake increased linearly with soil temperature. No-till fallow exhibited the least threat to deterioration of atmospheric or soil quality as reflected by greater CH4 uptake, decreased N2O and CO2 emissions, and less loss of soil organic C than tilled soils. However, potential for increased C sequestration in this wheat-fallow system is limited due to reduced C input from intermittent cropping.
The LT50 values and soluble carbohydrate levels in wheat (Triticum aestivum L.) crowns and leaves were monitored throughout autumn and winter in cultivars varying in freezing tolerance and snow mold resistance during 1993/1994 and 1994/1995 in the field at Sapporo, Japan. During the first stage of hardening, from sowing to mid-November, the pattern of accumulation of mono- and disaccharides was similar for all cultivars. During the second stage of cold hardening, from mid-November to mid-December, the greatest accumulation of mono- and disaccharides, without a corresponding increase in fructan, was observed among the freezing-tolerant cultivars; and levels of simple saccharides rapidly decreased under snow cover. Conversely, levels of mono- and disaccharides in snow mold-resistant cultivars were less than 70% of those in freezing-tolerant cultivars before snow cover and maintained low levels throughout winter, while polysaccharide levels in snow mold-resistant cultivars were about 120% of those in freezing-tolerant cultivars in December. Sugar metabolism during the winter was examined using 18 cultivars in 1994/1995. LT50 values were correlated to the greatest extent with total mono- and disaccharide and fructan content among wheat cultivars excluding snow mold-resistant cultivars in December. Snow mold-resistant cultivars tended to metabolize carbohydrates more slowly until the end of the snow cover period. This result suggested that the enzymatic metabolism of the synthesis of sugars and the conversion of fructan to cryoprotective sugars in response to low temperatures, especially subzero ones, might be different between the two contrasting types in resistance to winter stress.
Wheat models such as CERES-wheat, AFRCWHEAT2 and SIRIUS predict grain yield and have been widely used, in particular to assess possible effects of climate change. Here, observed yields from well-managed and documented UK agricultural experiments were used for a large-scale study of these models' grain yield predictions. None of the models accurately predicted historical grain yields between 1976 and 1993. Substantial disagreement was found between the models' predictions of both yield and yield loss due to water limitation. A regression of observed yields on monthly climatic variables indicated that indirect climatic effects play a considerable role in UK well-managed yields. The study shows that more work is needed before such yield predictions can be used with confidence in decision support or climate change assessment in the UK.
The relationships among winter cover cropping, inoculum potential of vesicular-arbuscular mycorrhizal (VAM) fungi, and the growth and yield of a subsequent maize crop were investigated. In the first experiment, an autumn-sown winter wheat cover crop increased VAM fungal inoculum potential of a field soil as measured by an in situ maize bioassay during the following growing season. Infective extra-radical hyphal densities were significantly increased by cover cropping as interpreted from the effect of soil disturbance on infection of the maize bioassay plants. In a second experiment the following year, the winter wheat cover crop again increased VAM fungal inoculum potential as assessed by an in situ maize bioassay during the following growing season. Moreover, the degree of mycorrhizal infection of maize was correlated with maize growth and yield. This study suggests that the management of mycorrhizal fungi by cover cropping may be a useful practice in sustainable agriculture.
Previous studies on the fate of fertiliser nitrogen applied to winter wheat in temperate climates have shown that nitrogen (N) applied early, at tillering for wheat, was less efficiently taken up than N applied later in the growth cycle. We examined the extent to which the soil microbial N immobilisation varied during the wheat spring growth cycle and how microbial immobilisation and plant uptake competed for nitrogen. We set up a pulse-¹⁵N labelled field experiment in which N was applied at eight development stages from tillering (beginning of March) to anthesis (mid-June). Each application was 50 kg N ha⁻¹ as ¹⁵N labelled urea except for the first application which was 25 kg N ha⁻¹. The distribution of fertiliser ¹⁵N in shoots, roots, mineral and organic soil N was examined by destructive sampling 7 and 14 days after each ¹⁵N pulse. The inorganic ¹⁵N pool was almost depleted by day 14. The N uptake efficiency increased with later applications from 45% at tillering to 65% at flowering. N immobilisation was rather constant at 13-16% of N applied, whatever the date of application. The increase in plant ¹⁵N uptake resulted in an increase in the total ¹⁵N recovery in the plant-soil system (¹⁵N in soil + ¹⁵N in plant), suggesting that gaseous losses were lower at the later application dates.
Immature and mature embryos of 12 common winter wheat (Triticum aestivum) genotypes were cultured in vitro to develop an efficient method of callus formation and plant regeneration from mature embryo culture, and to compare the responses of both embryo cultures. Fifteen days after anthesis, immature embryos were aseptically dissected from seeds and placed with the scutellum upwards on a solid agar medium containing the inorganic components of Murashige and Skoog (MS) and 2 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). Mature embryos were moved slightly in the imbibed seeds. The seeds with moved embryos were placed furrow downwards in dishes containing 8 mg/l 2,4-D for callus induction. The developed calli and regenerated plants were maintained on 2,4-D-free MS medium. Plants regenerated from both embryo cultures were vernalized and grown to maturity in soil. Regenerated plantlets all maintained the hexaploid chromosome number. A strong genotypic effect on the culture responses was found for both explant cultures. Callus induction rate, regeneration capacity of callus and number of plants regenerated were independent of each other. Mature embryos had a high frequency of callus induction and regeneration capacity, and therefore, being available throughout the year, can be used as an effective explant source in wheat tissue culture.
A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production.