Unexpected increases in soil carbon eventually fell in low rainfall farming systems.

Understanding the drivers of soil organic carbon (SOC) change over time and confidence to predict changes in SOC are essential to the development and long-term viability of SOC trading schemes. This study investigated temporal changes in total SOC, total nitrogen (N), and carbon (C) fractions (particulate organic carbon - POC, resistant organic carbon - ROC and humus organic carbon - HOC) over a 16-year period for four contrasting farming systems in a low rainfall environment (424 mm) at Condobolin, Australia. The farming systems were 1) conventional tillage mixed farming (CT); 2) reduced tillage mixed farming (RT); 3) continuous cropping (CC); and 4) perennial pasture (PP). The SOC dynamics were also modelled using APSIM C and N modules, to determine the accuracy of this model. Results are presented in the context of land managers participating in Australian climate change mitigation schemes. There was an increase in SOC for all farming systems over the first 12 years (total organic C, TOC% at 0-10 cm increased from 1.33% to 1.77%), which was predominately in the POC% fraction (POC% at 0-10 cm increased from 0.14% to 0.5%). Between 2012 and 2015, there was a decrease in SOC back to starting levels (TOC = 1.22% POC = 0.12% at 0-10 cm) in all systems. The PP system had higher TOC%, POC% and HOC% levels on average and higher SOC stocks to 30 cm depth at the final measurement in 2015 (PP = 30.43 t C ha-1; cropping systems = 23.71 t C ha-1), compared to the other farming systems. There was a decrease in TN% over time in all farming systems except PP. The average C:N increased from 14.1 in 1999 to 19.7 in 2012, after which time the SOC levels decreased and C:N dropped back to 15.8. The temporal change in SOC was not able to be represented by the AusFarm model. There are three important conclusions for policy development: 1) monitoring temporal changes in SOC over 12 years did not indicate long-term sequestration, required to assure "permanence" in SOC trading (i.e. 25-100 years) due to the susceptibility of POC to degradation; 2) without monitoring SOC in reference land uses (e.g. CT cropping system as a control in this experiment) it is not possible to determine the net carbon sequestration, and therefore the true climate change mitigation value; and 3) modelling SOC using AusFarm/APSIM, does not fully represent the temporal dynamics of SOC in this low rainfall environment.

Effects of winter and spring housing on growth performance and blood metabolites of Pengbo semi-wool sheep in Tibet.

Objective: Sixty Pengbo semi-wool sheep ewes (approximately 1.5-years-old; 31.33 ± 0.43 kg) were randomly assigned to two groups, either G (grazing) or D (dry lot feeding), to examine the effects of traditional daily grazing and dry lot feeding on performance and blood metabolites during the cold season in Tibetan Plateau. Methods: The ewes in the G group were grazed continuously each day and housed in one shed each evening, while the ewes in the D group were housed in another shed all day. All animals were fed 400 g/day of commercial concentrate, and grass hay was available freely throughout the experimental period. Results: Compared with the G group, the ewes in the D group had higher (p < 0.05) live weight and weight gain. The D group ewes had greater (p < 0.05) numbers of white blood cells and platelets, while they had lower (p < 0.05) platelet-large cell ratios, cholesterol, high-density lipoprotein cholesterol and glutathione peroxidase, as compared with the G group ewes. Additionally, three serum metabolites, abscisic acid, xanthoxin and 3,4-dihydroxy-5-polypren, were upregulated (p < 0.05) in the D group in comparison with the G group. Conclusion: In conclusion, a dry lot feeding regime during the winter and spring period will increase the productivity of sheep and improve blood physiological and biochemical profiles.

Reduced grazing pressure delivers production and environmental benefits for the typical steppe of north China.

Degradation by overgrazing is common in many areas of the world and optimising grassland functions depends upon finding suitable grazing tactics. This four-year study on the northern China steppe investigated combinations of rest, moderate or heavy grazing pressure early in the summer growing season, then moderate or heavy grazing in the mid and late season. Results showed that moderate grazing pressure (~550 sheep equivalent (SE) grazing days ha(-1) year(-1)) gave the optimal balance between maintaining a productive and diverse grassland, a profitable livestock system, and greenhouse gas mitigation. Further analyses identified that more conservative stocking (~400 SE grazing days ha(-1) year(-1)) maintained a desirable Leymus chinensis composition and achieved a higher live weight gain of sheep. Early summer rest best maintained a desirable grassland composition, but had few other benefits and reduced incomes. These findings demonstrate that reducing grazing pressure to half the current district stocking rates can deliver improved ecosystem services (lower greenhouse gases and improved grassland composition) while sustaining herder incomes.

Improved grazing management may increase soil carbon sequestration in temperate steppe.

Different grazing strategies impact grassland plant production and may also regulate the soil carbon formation. For a site in semiarid temperate steppe, we studied the effect of combinations of rest, high and moderate grazing pressure over three stages of the growing season, on the process involved in soil carbon sequestration. Results show that constant moderate grazing (MMM) exhibited the highest root production and turnover accumulating the most soil carbon. While deferred grazing (RHM and RMH) sequestered less soil carbon compared to MMM, they showed higher standing root mass, maintained a more desirable pasture composition, and had better ability to retain soil N. Constant high grazing pressure (HHH) caused diminished above- and belowground plant production, more soil N losses and an unfavorable microbial environment and had reduced carbon input. Reducing grazing pressure in the last grazing stage (HHM) still had a negative impact on soil carbon. Regression analyses show that adjusting stocking rate to ~5SE/ha with ~40% vegetation utilization rate can get the most carbon accrual. Overall, the soil carbon sequestration in the temperate grassland is affected by the grazing regime that is applied, and grazing can be altered to improve soil carbon sequestration in the temperate steppe.

Competition for nitrogen between Australian native grasses and the introduced weed Nassella trichotoma.

BACKGROUND: and Aims Nassella trichotoma is an unpalatable perennial grass weed that invades disturbed native grasslands in temperate regions of south-eastern Australia. This experiment investigated whether elevated N levels, often associated with disturbance, increases the competitiveness of N. trichotoma relative to C3 and C4 native Australian grasses. METHODS: A pot experiment investigated competitive interactions between four native grasses, two C3 species (Microlaena stipoides and Austrodanthonia racemosa) and two C4 species (Themeda australis and Bothriochloa macra), and N. trichotoma at three different N levels (equivalent to 0, 60 and 120 kg ha-1) and three competing densities (zero, one and eight neighbouring plants), using an additive design. KEY RESULTS: All native grasses were competitive with N. trichotoma at low N levels, but only M. stipoides was competitive at high N. High densities of native grasses (8:1) had a major competitive effect on N. trichotoma at all N levels. The competitive ranking of native grasses, across all N levels, on N. trichotoma was: M. stipoides>A. racemosa>B. macra>T. australis. The C3 species were generally more competitive than the C4 species and C4 grasses were not inherently more productive at low N levels, in contrast to the results of other studies. CONCLUSION: To resist invasion from N. trichotoma, these native grasses need to be maintained at a high density and/or biomass. The results do not support the theory that species such as N. trichotoma, with high tissues density, are always less competitive than those of low tissue density; in this case competitiveness depended on N levels. The ability of N. trichotoma to accumulate biomass at a higher rate than these native grasses, helps to explain why it is a major weed in disturbed Australian native grasslands.