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If the production of forage for dairy cattle is to become less reliant on synthetic nitrogen (N) fertilizers, there is need to better understand and account for the N contributed by on‐farm and imported organic amendments. A 254‐day aerobic soil incubation study (typical length of a growing season in many temperate dairying regions) quantified the inorganic (mineral) N supply from a commercial compost and dried bovine dung (i.e., on‐farm effluent solids). Amendments were incubated in soils with contrasting synthetic N fertilization histories (i.e., 70–100 vs. 350–400 kg N/ha per year) to evaluate if higher synthetic N fertilization histories would reduce the lag time that often exists between organic amendment application and significant release of inorganic N for plant uptake. This proposition was based on previous research, which showed greater soil inorganic N availability accelerating organic amendment decomposition. Our experiment did find that the release of inorganic N from evaluated organic amendments was greater in soils with higher synthetic N fertilization histories, but that this effect was not apparent until after the first 6‐months of this 9‐month experiment. Despite this finding, soils with contrasting synthetic N fertilization histories were not found to differ in their initial inorganic N content, nor microbial activity or other physiochemical properties known to affect N mineralization. Our study highlighted the long‐term vision needed when transitioning from synthetic N fertilizers to organic amendments, with most of the N present in the compost and dried dung remaining unavailable for forage production (i.e., remained bound in organic carbon‐based molecules). [ABSTRACT FROM AUTHOR]

Growth of alfalfa (Medicago sativa L.) following the correction of water deficits will depend, in part, on the amount of plant constituents available to support regrowth and the availability of crown buds for the development of new shoots. To investigate if water deficit affected the accumulation of taproot constituents and crown bud development of alfalfa, two alfalfa cultivars were exposed to increasing levels of water deficit (100, 75, 50 25 and 0% of the replacement water requirement) during a regrowth period. Shoot growth was reduced in proportion to the level of water deficit. Taproot starch concentrations decreased while taproot soluble sugar increased in plants exposed to a water deficit. Thirty-five d after initiation of treatments, taproot protein and amino acid concentrations were similar in all treatments that received water. Water deficit increased the relative concentration of low and middle molecular weight taproot vegetative storage proteins (VSP) and water deficits reduced the number and mass of green crown buds. Both cultivars had a similar response to water deficit for all taproot constituents and crown bud development. Further studies are required to determine the influence of increasing VSP abundance and decreasing numbers of crown buds on plant recovery following the removal of a water deficit. doi: 10.2135/cropsci2009.03.0140

Growth of alfalfa (Medicago sativa L.) following the correction of a water deficit will depend in part on the characteristics of the canopy grown during the water deficit. The current study was undertaken to determine the extent to which canopy structure and photosynthetic capacity are affected in alfalfa plants regrowing following defoliation while exposed to a water deficit. The effects of five levels of water application (100, 75, 50, 25, and 0% of the replacement water requirement) during the regrowth of two alfalfa cultivars with contrasting levels of fall dormancy was investigated in a controlled environment. Mass per shoot and shoots per plant were both significantly (P < 0.05) reduced by water applications 75% or less of the replacement water requirement. Dry matter accumulation was reduced in proportion to the level of the water deficit the plants were exposed to. The rate of C[O.sub.2]assimilation and maximum efficiency of photosystem II were unaffected (P > 0.05) by water deficits except for the unwatered plants on which leaf senescence occurred. The only inhibition in the plants' capacity for photosynthesis from a water deficit was reduced leaf area. Shoot density and reduced overall canopy photosynthesis were the only canopy characteristics that were altered by water deficit in a way that could continue to inhibit plant growth following the correction of the water deficit.

Changed spatial configurations at sowing have been investigated as a strategy to minimize interspecific competition and improve the establishment and persistence of multi-species plantings in pastures, but the impact of this practice on the soil microbiome has received almost no previous research attention. Differences in populations of bacteria and fungi in the surface 10 cm of soil in the third year following pasture establishment were quantified using quantitative polymerase chain reaction and terminal restriction fragment length polymorphism methods. Populations were compared on, and between, drill rows sown to either the perennial grass phalaris (Phalaris aquatica L.), perennial legume lucerne (alfalfa; Medicago sativa L.) or the annual legume subterranean clover (Trifolium subterraneum L.). Results showed that soil microbial abundance and diversity were related to plant distribution across the field at the time of sampling and to soil chemical parameters including total carbon (C), mineral nitrogen (N), pH, and available phosphorus (P), potassium (K) and sulfur (S). Despite the 27-month lag since sowing, pasture species remained concentrated around the original drill row with very little colonization of the inter-row area. The abundance and diversity of bacterial and fungal populations were consistently greater under drill rows associated with higher total C concentrations in the surface soil compared with the inter-row areas. Our results showed that the pH and available nutrients were similar between the subterranean clover drill row and the inter-row, suggesting that soil microbial populations were not impacted directly by these soil fertility parameters, but rather were related to the presence or absence of plants. The abundance of bacteria and fungi were numerically lower under phalaris rows compared to rows sown to legumes. The richness and diversity of fungal populations were lowest between rows where lucerne was planted. Possible explanations for this observation include a lower C:N ratio of lucerne roots and/or a lack of fibrous roots at the soil surface compared to the other species, illustrating the influence of contrasting plant types on the soil microflora community. This study highlights the enduring legacy of the drill row on the spatial distribution of plants well into the pasture phase of a cropping rotation and discusses the opportunity to enhance the microbiome of cropping soils on a large scale during the pasture phase by increasing plant distribution across the landscape. [ABSTRACT FROM AUTHOR]

In many south-eastern Australian dairying regions, supraoptimal ambient temperatures (Ta > 30°C) often challenge the perennial ryegrass (Lolium perenne L.)-dominated feed-base during the summer months. A glasshouse experiment was undertaken to identify alternative summer-active temperate (C3) perennial forages more tolerant of supraoptimal temperature stress (day/night Ta of 38/25°C) than perennial ryegrass. Supraoptimal temperature stress was mposed both with and without irrigation. Chicory (Cichorium intybus L.) was the only species to survive 18 days of combined supraoptimal temperature stress and non-irrigation. Lucerne (Medicago sativa L.), plantain (Plantago lanceolata L.), and tall fescue (Festuca arundinacea Schreb.) survived 12 days of this treatment. Twelve days of exposure to these conditions caused death of perennial ryegrass, prairie grass (Bromus catharticus Vahl.), cocksfoot (Dactylis glomerata L.), birdsfoot trefoil (Lotus corniculatus L.), and red clover (Trifolium pratense L.). Irrigation (daily to through drainage) mitigated detrimental effects of imposed supraoptimal temperature stress on the growth and survival of all species. Chicory and to a lesser extent lucerne, plantain, and tall fescue may have a role to play in south-eastern Australian dairying regions, where supraoptimal temperature stress is a frequent and ongoing issue. [ABSTRACT FROM AUTHOR]

Growth of alfalfa (Medicago sativa L.) following the correction of water deficits will depend, in part, on the amount of plant constituents available to support regrowth and the availability of crown buds for the development of new shoots. To investigate if water deficit affected the accumulation of taproot constituents and crown bud development of alfalfa, two alfalfa cultivars were exposed to increasing levels of water deficit (100, 75, 50 25 and 0% of the replacement water requirement) during a regrowth period. Shoot growth was reduced in proportion to the level of water deficit. Taproot starch concentrations decreased while taproot soluble sugar increased in plants exposed to a water deficit. Thirty-five d after initiation of treatments, taproot protein and amino acid concentrations were similar in all treatments that received water. Water deficit increased the relative concentration of low and middle molecular weight taproot vegetative storage proteins (VSP) and water deficits reduced the number and mass of green crown buds. Both cultivars had a similar response to water deficit for all taproot constituents and crown bud development. Further studies are required to determine the influence of increasing VSP abundance and decreasing numbers of crown buds on plant recovery following the removal of a water deficit. [ABSTRACT FROM AUTHOR]