Effect of grazing intensity and dung on herbage and soil nutrients

Dung deposited by grazing animals is a key driver affecting sward structure and nutrient cycling in pastures. We tested herbage and soil properties in three types of tall sward-height patches (> 10 cm): (i) patches with dung under intensive grazing; (ii) patches with dung under extensive grazing; and (iii) patches with no dung under extensive grazing. These patches were compared with grazed swards under intensive and extensive grazing. Analyses indicated no significant effect of different types of patches on plant available nutrients. Herbage nutrient concentrations from the different types of patches differed significantly. The highest concentrations of nitrogen (30.65 g/kg), phosphorus (4.51 g/kg) and potassium (22.06 g/kg) in the herbage dry matter were in the tall patches with dung presence under intensive grazing regime because of nutrients from dung utilized for sward regrowth. Regardless of dung presence, similar herbage nutrient concentrations were revealed in non-grazed tall sward-height patches in extensive grazing regime. The presence of dung did not have any effect on the plant available nutrients in any type of patches, therefore we suppose that non-utilized nutrients were probably leached, volatilised or transformed into unavailable forms and thus soil nutrient enrichment was low.

Microsite effects on abundance of sown species on uncultivable slopes

Hill country has a vast array of microsites that may influence the success and uniformity of establishment of oversown pasture species and their persistence. In spring 2014, studies were conducted at Woodville (southern Hawke's Bay; summer-wet) and Cheviot (North Canterbury; summer-dry) to determine the effect of gentle (14-21o) and steep (32-40o) slopes on the presence and contribution to sward dry matter (DM) of oversown species in rotationally grazed swards aged 30 or 36 months. Gentle slopes had greater soil water content (29 versus 25%) and Olsen P (34 versus 26 μg/ ml) than nearby steep slopes. Perennial ryegrass (94 versus 80%) and phalaris (6 versus 2%) were present in a greater proportion of plots on gentle than on steep slopes, respectively, whereas subterranean clover had a greater presence on steep than on gentle slopes (6 versus 1%). Perennial ryegrass comprised a higher percentage of DM in swards on gentle than on steep slopes (27 versus 11%). The percentage of DM contributed by other individual species did not differ significantly between slope classes. The persistence of most sown species was unaffected by slope; microsite variation was not a major influence on species persistence. Keywords: hill country, microsites, pasture species, plant-microsite matches

Virus diseases of annual pasture legumes: incidences, losses, epidemiology, and management

This paper reviews current knowledge concerning the occurrence, losses caused, epidemiology, and management of virus diseases of annual pasture legumes. The viruses commonly present are spread by contact, or aphid vectors either non-persistently or persistently. Whether they are seed-borne and their means of transmission are critical factors determining their incidences within pastures in climatic zones with dry summers or substantial summer rainfall. Large-scale national or state surveys of subterranean clover pastures revealed that some viruses reach high infection incidences. Contamination with seed-borne viruses was widespread in plots belonging to annual pasture legume improvement programs and seed stocks of subterranean clover, annual medics, and alternative annual pasture legumes, and in commercial annual medic seed stocks. Yield loss studies with grazed swards were completed for three common viruses: two in subterranean clover and one in annual medics. These studies demonstrated considerable virus-induced losses in herbage and seed yields, and established that virus infection causes deteriorated pastures with high weed contents even when foliar symptoms are mild. Comprehensive integrated disease management tactics involving phytosanitary, cultural, chemical, or host resistance measures were devised for these three viruses in infected pastures, and for seed-borne viruses in annual pasture legume improvement programs. Several other viruses are potentially important, but, with these, quantification of losses caused in grazed swards is lacking and information on incidences in pastures is currently insufficient. Critical research and development gaps that need addressing are identified.

Persistence, productivity, nutrient composition, and aphid tolerance of Cullen spp.

The persistence, productivity, and nutrient content of accessions of Cullen australasicum, C. cinereum, C. tenax, and C. parvum were compared with lucerne (Medicago sativa) in grazed swards for 3 years on an acid soil in southern New South Wales. All Cullen spp. established satisfactorily from seed sown into a cultivated seed bed, but C. australasicum accessions were more persistent than C. cinereum, C. parvum, and C. tenax, which declined to a frequency of <5% by the start of the fourth year under rotational grazing. Cullen australasicum was the most productive of the 4 Cullen spp. with herbage yields similar to the lucerne cv. Sceptre. Leaves and stems of the Cullen spp. had significantly lower S, K, B, and Na contents than lucerne. The herbage P content of all Cullen spp., except C. tenax, was lower than in lucerne. Calcium and Mn levels were higher in C. australasicum than in all other species. Sheep often avoided grazing all Cullen spp. when other herbage was available, suggesting that these species had lower palatability. The dry matter digestibility (DMD) of lucerne herbage (76%) in September was higher than in C. australasicum (74.3%), C. cinereum (71.3%), and C. tenax (69.7%) (P < 0.001). The metabolisable energy content of the herbage of C. australasicum was similar to lucerne (10.7–10.9 MJ/kg DM) but was lower in C. cinereum and C. tenax (9.9–10.3 MJ/kg DM). The crude protein content of the 4 Cullen spp. was similar (21.4–22.3%) but significantly lower than for lucerne (33.6%). Glasshouse studies found C. australasicum, C. cinereum, C. pallidum, C. parvum, and C. tenax to be moderately to highly susceptible to bluegreen aphids (BGA) (Acyrthosiphon kondoi Shinji), but one C. australasicum accession was highly tolerant, suggesting that aphid susceptibility can be overcome by selection. All 5 Cullen species proved highly resistant to spotted alfalfa aphids (Therioaphis trifolii Monell). Cullen australasicum was found to be susceptible to Alfalfa mosaic virus, which resulted in stunting of growth of some plants in the field experiment. Of the 4 Cullen spp. examined in the field experiment, C. australasicum demonstrated the most potential as a forage plant for low-rainfall regions with superior persistence and productivity under grazing and the highest resistance to BGA.

The potential of seed-shedding and seedling development to contribute to the persistence of white clover (Trifolium repens) in grazed swards in Uruguay

The present study was conducted to investigate whether white clover (Trifolium repens L.) in grazed swards in Uruguay can produce and shed sufficient seed, and whether sufficient seedlings can develop and survive, to make an important contribution to the long-term persistence of the species. Five sites, on which survival of white clover had been better than is usual in Uruguay, were studied in 1995–97. The sites had been sown with white clover 11–15 years previously and were managed mainly by cattle grazing. The number of white clover inflorescences/m2 was at least 18 at nearly half the counts in the study and the number of viable seeds in the top 5 cm of soil was at least 1500 at half the counts. The results for both the above variables suggest that all five sites had a supply of seed greater than a commercial seed rate at some times of the year. However, the number of seedlings/m2 was >100, a possible target in these conditions, at only one fifth of the counts, and the proportion of seedlings that survived from one recording date to the next (a period of 4–5 weeks) varied from >0·7 to zero. It seems, therefore, that, in these conditions, the failure of seeds to convert to established plants is likely to be a greater constraint than the production and shedding of seeds. There was considerable variability with time, and between and within sites at each stage of the reproductive cycle. On one site, competition from Bermudagrass (Cynodon dactylon) greatly reduced the number of white clover seedlings/m2. Overall, the results suggest that white clover in grazed swards in Uruguay can produce and shed sufficient seed, and that sufficient seedlings can develop and survive, to make a significant contribution to the long-term persistence of the species. However, each year there is a risk of seedlings being killed in dry, hot weather.