Academic literature on the topic 'Medic-cereal'

Soils with toxic levels of boron (B) are widespread in the cereal-livestock zone of southern Australia. The annual pasture legume burr medic (Medicago polymorpha L.) is widely grown in rotation with grain crops in this zone, but current cultivars are susceptible to high levels of B. We tested the boron tolerance of several putative B tolerant burr medic accessions and developed four F2 populations by crossing two tolerant accessions with two susceptible cultivars. We tested a B tolerance SSR marker developed for barrel medic (M. truncatula Gaernt) on tolerant burr medic accessions but found a new marker was required. We identified several B tolerant burr medic accessions. In our four F2 populations tolerance was inherited in a 3:1 (tolerant:susceptible) ratio and we identified a molecular marker that accounts for 0.84 of the variation. The B tolerant accessions, along with the B tolerance marker, will allow for the efficient introgression of B tolerance into widely adapted genetic backgrounds and will allow breeders to efficiently develop cultivar(s) that are tolerant of a widespread subsoil constraint.

AbstractIn an earlier paper, we argued that medic pasture was probably an important component of the ancient farming regime in Libya. The success of modern experiments which have reintroduced medicago pasture was also described.In this paper, the analysis is taken further and the results of different types of crop rotation are compared. The Waite experiment in Australia has shown that the most intensive systems of cereal cultivation are not necessarily the most productive, when soil exhaustion and long term decline in yields are taken into account. In fact, the highest profits and best returns of both cereals and livestock are obtained from low intensity systems.It is possible that increased emphasis on cereal production in the Roman period may have led to a diminuation of the medic pasture, to the exhaustion of the soils and falling yields. By its own initial success, Romano-Libyan agriculture may have contributed to its own decline.

The annual medic Medicago truncatula cv. Paraggio has been widely sown in pastures throughout the Victorian Mallee region; however, its ability to persist in cereal pasture rotations is not known. Seed permeability and production, and plant regeneration of Paraggio, were studied in the field over 4 years, and the changes in its seed reserve were examined under 3 different cereal-pasture rotations. When compared with medic cvv. Parabinga, Harbinger, and Jemalong, Paraggio had up to twice the level of permeable seed over the summer-autumn period in 2 years (7-36% v. 2.5-19%). Paraggio produced 336-928 kg/ha of seed over 3 years, and after seed production was halted, it regenerated at densities of 150-1438 plants/m2 over the next 4 years. These results were generally the same as, or better than, the other cultivars. When seed set occurred in 1 and 2 years in the pasture phase of a 2- and 3-year rotation, respectively, Paraggio seed reserves were maintained at >4000 seeds/m2. This study demonstrated that Paraggio resulted in superior plant densities when grown in a number of typical rotations. It persisted satisfactorily and is expected to improve agricultural productivity in shor-tterm cereal-pasture rotations.

Summary. To produce seed to determine the rates of seed softening of annual medics in the subtropics, 8 lines of barrel medic (Medicago truncatula), 3 lines of burr medic (M. polymorpha), 4 lines of snail medic (M. scutellata), and 1 line of each of button medic (M. orbicularis), strand medic (M. littoralis) and gama medic (M. rugosa) were grown at Warra in southern inland Queensland, in 1993. Seed of a fourth line of burr medic, a naturalised line, was harvested from Hermitage Research Station at that time. Pods were placed on the soil surface and buried at a depth of 7 cm, both in flywire envelopes and as free pods. Residual hard seed numbers were determined each year for 3 years from the envelopes, and seedlings were counted and removed from the free pods after each germination event. Patterns of softening of seeds from the same seed populations were also determined after placing them in a laboratory oven with a diurnal temperature fluctuation of 60/15° C for periods of 16, 40 and 64 weeks followed, after each time period, by 4 diurnal cycles of 35/10°C. More than 90% of the original seeds were hard. Seed softening at the soil surface ranged from 26% after 3 years in button medic to almost complete softening in the gama medic after only 2 years. Burial had little effect on the rate of softening of the button medic but about halved the rate of softening of the other lines. The barrel medics were vulnerable to losses of large numbers of seedlings which softened and germinated in January–February and the snail medics from seedlings emerging in August–December. The proportion of soft seeds recovered as seedlings in the buried compared with the surface pods was higher in the larger-seeded medics, snail and gama, and lower in the other, smaller-seeded medics. Laboratory techniques effectively ranked the medic lines for their rate of seed softening in the field and provided some insight into their seasonal patterns of seed softening. A wide range of seed softening patterns is available for fitting the requirements of various farming systems. The most appropriate pattern of softening will depend on the variability of medic seed production between years and the need for self regeneration of the medic after a cereal crop.

SUMMARYThe Mediterranean region is experiencing unrelenting land-use pressure, largely driven by population growth. Long-term cropping system trials can guide crop and soil management options that are biophysically and economically sustainable. Thus, an extensive cereal-based rotation trial (1983–98) was established in northern Syria, to assess various two-course rotations with durum wheat (Triticum turgidum Desf.). The alternative rotations were: continuous wheat, fallow, chickpea (Cicer arietinum), lentil (Lens culinaris), medic (Medicago spp.), vetch (Vicia sativa) and watermelon (Citrullus vulgaris) as a summer crop. Ancillary treatments were: nitrogen (N) fertilizer application to the cereal phase (0, 30, 60 and 90 kg N/ha) and variable stubble grazing management (zero or stubble retention, moderate and heavy grazing). Both phases of the rotation trial occurred each year. The soil is a fine clay, thermic Calcixerollic Xerochrept. Seasonal rainfall was the dominant factor in influencing overall yields. Rotations significantly influenced yields, being highest for fallow (2·43 t/ha), followed by watermelon (similar to fallow), vetch, lentil, medic and chickpea, and least for continuous wheat (1·08 t/ha). Overall, yields increased consistently with added N, but responses varied with the rotation. The various stubble grazing regimes had little or no effect on either grain or straw yields. While the trial confirmed the value of fallow and the drawbacks of continuous cereal cropping, it also showed that replacing either practice with chickpea or lentil, or vetch for animal feed, was potentially a viable option. Given favourable economics, legume-based rotations for food and forage could contribute to sustainable cropping throughout the Mediterranean region.

Continuous cereal production in the summer-dominant rainfall region of north-eastern Australia has depleted native soil nitrogen fertility to a level where corrective strategies are required to sustain wheat grain yields and high protein levels for domestic and export markets. Annual medic pastures, along with other strategies, were evaluated from 1986 to 1998 on a Vertisol at Warra, southern Queensland, for their benefit to subsequent grain yield and protein content of wheat.Annual medic production and nitrogen yields were closely correlated with the growing season rainfall (March–September). Each 100 mm of growing season rainfall resulted in 1.39 t/ha of dry matter and 40 kg/ha of N yield. There were significant increases in soil mineralisable nitrogen following annual medic leys compared with continuous wheat in most years, but increases in total soil nitrogen were only observed in 1990, 1991 and 1992. However, pre-plant nitrate-nitrogen following an annual medic ley was always higher than that of continuous wheat without nitrogen fertiliser. This resulted in significant increases in wheat yield (6 of 9 seasons) and grain protein (in all seasons) compared with continuous wheat. The overall responses in yield and protein were similar to those of 50� kg/ha of fertiliser nitrogen applied to continuous wheat crops. A nitrogen harvest budget for the annual medic–wheat rotation over 11 years showed that it contributed 131 kg N/ha more than continuous wheat. Thus, using the seasonal conditions experienced from 1987 to 1998 as a reasonable representation of the rainfall range in the region, sustainable productivity can be maintained where annual medics are grown in short rotations with wheat.

Sulfonylurea (SU) herbicides are extensively applied to crops in the cereal-livestock zones of southern Australia. In low rainfall areas with alkaline soils, SU residues can persist over summer and can severely affect sown or regenerating medic pastures. A cohort of early season barrel medics (Medicago truncatula) bred and selected for tolerance to SU herbicide residues were evaluated at multiple field sites over 3 years (year of establishment and subsequent regeneration). Two lines (Z2438 and Z2415) were identified which had dry matter production and seed yield in the establishment year equivalent to their recurrent parent, Caliph, an early maturing, aphid-tolerant, barrel medic cultivar. They also had lower levels of hardseededness than Caliph, enabling them to regenerate in greater numbers in the following year and thus produce more dry matter. The two lines demonstrated good tolerance to simulated SU herbicide residues, producing up to 10 times the dry matter of the SU-intolerant parent Caliph. We anticipate that one or both of the two lines will be commercialised soon, enabling farmers in low rainfall areas with neutral-to-alkaline soils to successfully grow barrel medic pastures in the presence of SU herbicide soil residues resulting from applications to prior crops.

Annual medic pastures are an effective component of ley-farming systems (cereal–legume rotations) in Australian areas with a Mediterranean climate, but they have been unsuccessful in areas near the Mediterranean Sea. In some zones with a Mediterranean climate, like Iran and Syria, root-zone temperature is considered the major growth-limiting factor for annual medic early in the growing season. In order to study the effect of low root-zone temperature (RZT) on growth and development, yield, and yield components of some annual Medicago species, an experiment was conducted in a controlled-environment chamber. In this experiment, 3 species of annual medics, namely Medicago polymorpha, M. radiata, and M. rigidula, thought to be adapted to cold and temperate conditions, were used. Four root-zone temperatures (5, 10, 15, and 20�C) were considered. The experimental layout was a completely randomised block design with 4 replications. There were differences among the annual medics for dry matter and yield components. Two species, M. polymorpha and M. rigidula, had more leaf, stem, and root dry matter, plant height, leaf and stem to root ratio, leaf to stem ratio, and leaf area and yield than M. radiata. Therefore, M. polymorpha and M. rigidula may be better suited for ley-farming systems in cold and temperate zones. The results also showed that the 5�C RZT effectively decreased the yield and yield components of the annual medics. In conclusion, application of ley-farming is not likely to be successful when RZT is below 5�C, especially during vegetative development. Therefore, in the zones where soil temperature is greater than 10�C, annual medics have normal growth and produce average yields. Ley-farming (cereal–legume rotation) could be replaced with fallow–cereal rotation.

Summary. The productivity of an annual medic-based pasture–pasture–wheat rotation in response to chemical grass control and stocking rate treatments was evaluated over 3 years. Fluazifop applied in 1991 reduced the annual grass component during the pasture years (to <2% in 1991 and <5% in 1992) and grass densities in the 1993 wheat phase. This improved winter herbage production in 1992 (>50%) and the 1993 wheat yield (>40%). Glyphosate applied during the winter of 1991 reduced the grass component and the winter and total herbage production in that year, and grass populations in 1992. Glyphosate applied during the spring of 1991 reduced the medic seed yields and the grass and medic densities in 1992. There were no pasture or cereal production benefits measured from the 1991 glyphosate applications. All the above comparisons were made with no herbicide in 1991 followed by glyphosate applied during the winter of 1992, a common district practice. Stocking at twice the district average, over all herbicide treatments, reduced the 1991 winter herbage production but maintained or improved the 1992 winter and total herbage production, compared with the district average stocking rate. The high stocking rate resulted in lower grass densities in the 1993 wheat crop and increased the wheat grain yield by 0.5 t/ha.

Increasing soil organic matter (SOM) is a major factor in overcoming soil degradation. An incubation experiment using 2 soil types (Red Clay and Black Earth) and 2 different rotations, a clover (Trifolium subterraneum)/cereal rotation and a long fallow/cereal rotation, from a long-term crop rotation trial located at Tamworth, NSW, Australia was conducted to investigate the decomposition of 3 different plant materials, medic (Medicago truncatula) (C : N = 13), rice straw (Oryza sativa) (C : N = 25) and flemingia leaf (Flemingia macrophylla) (C : N = 13), labelled with 13C and 15N. A control treatment with no added residue was also included. The impact of the residue decomposition on total organic carbon, labile carbon, total nitrogen, aggregate stability and the formation of large macro-aggregates from smaller macro-aggregates were studied. Total C (CT), stable carbon isotope composition (δ13C), total N (NT), and %15N excess were measured by catalytic combustion and an isotope ratio mass spectrophotometer, while labile C (CL) was determined by oxidation with KMnO4. Aggregate stability [mean weight diameter (MWD)] was determined by immersion wet sieving. Correlations of C fractions with MWD were also investigated. The location of the newly added plant residue materials within soil aggregates was studied using a soil aggregate eroding machine. Loss of C from the added plant residues was highest for the medic and lowest for the flemingia, while the rice straw initially lost C at a slower rate but by 200 days was equal to the medic. The medic treatment was the only residue to lose N by gaseous loss during the experiment and it was all lost during the first 10 days. In both soils, the addition of residues increased CT and CL compared with the control treatment, with flemingia showing the greatest increase. Factors other than their C : N ratio were clearly determining C turnover. Addition of medic residues resulted in a rapid increase in MWD in both soils in the first 10 days compared with that at the commencement of the experiment. However, this was not maintained for the 200 days by which time MWD had decreased, but it was still greater than the starting point. By contrast, the addition of flemingia leaf exhibited a slower but more sustained increase to have the highest MWD at 200 days, equal to that of the medic treatment at 10 days. There was a positive correlation of CL with MWD at 200 days for both soils. Results from the soil aggregate eroding machine showed that a higher percentage of CT was derived from added plant residues in the outer one-third of the soil aggregates than in the inner two-thirds, with the greatest difference being for the flemingia treatment. There was no difference between different residue materials in the amount of CT derived from the added residues in the inner parts of soil aggregates. These results showed that soil macro-aggregates were forming around a central old aggregate by binding of smaller aggregates to it, with products formed as a result of the breakdown of plant residues binding them together. From the results obtained, and those of other researchers, a concept of macro-aggregate formation under different agricultural systems is proposed.

The removal of volunteer annual grasses from annual medic pastures can dramatically improve the following cereal crops by providing important cereal root disease breaks, improved biological nitrogen fixation and reduced grass weed competition in medic-cereal rotations. Early removal of these volunteer grasses has the disadvantage of creating a winter feed shortage due to low medic productivity. A comparison of adding cereal root disease resistant oats to medic based pastures with the effects of either early removal or retention of volunteer grasses was conducted. Adding oats increased total pasture production and improved early dry matter production, so that sheep were introduced 21 days earlier than the grass-free medic pasture and 11 days earlier than the grass+medic pasture type. Final sheep liveweight gain was similar between all pasture types (128g/sheep/day) suggesting compensatory growth in spring was occurring, particularly on the grass-free medic pasture type. Wheat yield and quality were directly related to the previous pasture type, with significant reductions after grass+medic and oat+grass+medic pasture types (average both pasture types 53% less) due to take-all disease, grass weed competition and reduced available N. Improving the low productivity of medic when grown in grass mixtures was the focus of additional experimentation. Establishment in autumn (20/10°C day/night) simulated temperatures compared to winter (15/8°C day/night) improved the productivity and competitevness of medic in both monocultures and mixtures, particularly after defoliation and a period of regrowth (66% increase in medic dry matter in medicl2:2 oats mixture). Total season dry matter production was always greater in medic/oat mixtures than monocultures with sowing ratios that strongly favour increased medic density (> medic 3:1 oat) maximising medic production in mixtures. Delaying defoliation and high medic populations were the most successful management methods to maximise medic production in medic/oat mixtures. Delayed sowing of low density oats into established medic stands reduced seedling competition but provided little gain to early pasture productivity. This relationship did not alter with stocking rate. Appraisal of the Australian Medicago Genetic Resource Centres collection of medics and a limited number of CSIRO plant industries Rhizobium meliloti strains failed to find accession x rhizobium combinations better than the current commercial cultivar Paraggio for medic/oat mixtures. The capacity to improve the competitvness of the medic component in medic/oat mixtures was found to be limited as was the usefulness of this mixture to medic-cereal rotations.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004