Performance of Satellite-Based Evapotranspiration Models in Temperate Pastures of Southern Chile

Farmers in the temperate zone of southern Chile have started to irrigate historically rainfed pastures during recent years to reduce dairy productivity losses against increasingly severe summer droughts. The lack of information on pasture water requirements (i.e., evapotranspiration), however, hampers the implementation of efficient irrigation programs. Here, we use in-situ observations to evaluate the skill of four remote sensing Surface Energy Balance (SEB) models and two satellite-based global evapotranspiration products (PML_V2 and GLEAM) to estimate actual evapotranspiration (ETa) of pastures in southern Chile during 2014–2017. Daily ETa measured at an evaluation site over the period ranges between 1.2 mm and 6.2 mm day−1 during the growing season (October–March), with an annual maximum of about 4.8 mm day−1 in January and a minimum 0.6 mm day−1 in June. Only the Simplified SEB (SEBS) model and its operational variant (SSEBop) and the PML_V2 global evapotranspiration product perform well, capturing 63–79% of the variance of in-situ evapotranspiration with an error between 0.75 mm day−1 and 1.1 mm day−1. The readily available PML_V2 product can be used as a convenient way to determine average water footprint of pastures and the two SEBs models can be implemented to monitor irrigation requirements in near-real time from field to regional scales. These results demonstrated a high potential of satellite observations for monitoring evapotranspiration and quantify the water footprint of pastures in southern Chile for a sustainable irrigation practice.

Population genetics and diversity structure of an invasive earthworm in tropical and temperate pastures from Veracruz, Mexico

Pontoscolex corethrurus (Müller, 1857) is an invasive tropical earthworm, globally distributed. It reproduces through parthenogenesis, which theoretically results in low genetic diversity. The analysis of the population structure of P. corethrurus using molecular markers may significantly contribute to understanding the ecology and reproductive system of this earthworm species. This work assessed the genetic diversity and population structure of P. corethrurus with 34 polymorphic inter simple sequence repeat markers, covering four populations in tropical and temperate pastures from Veracruz State. Nuclear markers distinguished two genetic clusters, probably corresponding to two distinct genetic lineages. The number of clones detected in the AC population was lower than expected for a parthenogenetic species. Also, the apparent lack of differences in population structures related to the geographic region among the populations studied may indicate that human-mediated transference is prevalent in these areas. Still, most individuals apparently belong to lineage A, and only a few individuals seem to belong to the lineage B. Thus, the admixture signatures found among the four populations of P. corethrurus may have facilitated a successful invasion by directly increasing fitness. In summary, addressing the genetic variation of P. corethrurus with ISSR markers was a suitable approach, as it evidenced the genetic diversity and relationships in the populations evaluated.

Forage Legume Establishment under Exposure to Progressive Declines in Aminocyclopyrachlor and Aminopyralid in Temperate Pastures

Legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.) increase forage productivity and quality in northern temperate pastures, but require re-establishment following broadleaf weed control using herbicides. To quantify the residual effects of two herbicides (aminocyclopyrachlor and aminopyralid) on potential legume re-establishment we examined alfalfa and clover recruitment at two field sites over two years. Sites were over-seeded with alfalfa and clover to populate the seed bank, and then sprayed with herbicide, after which seedling densities were monitored in late summer and fall of the current growing season. Defoliation (via mowing) effects were also assessed to evaluate the role of vegetation competition on legume establishment. Herbicides were applied at recommended rates (1.0), and 0.5, 0.25, 0.125, 0.0625, and 0 times recommended field rates, emulating exponential herbicide degradation (one through four half-lives). Alfalfa and white clover seedling densities were negatively impacted by all rates of herbicide, with modestly greater negative impacts from aminopyralid than aminocyclopyrachlor, although responses to herbicides remained site and legume specific. Reductions in alfalfa and clover were particularly evident through the 0.25 (i.e., two half-life) herbicide rate, with reductions in alfalfa ranging from 78% to 95%, and in clover from 73% to 88%. Legume densities at the 0.125 (three half-life) rate were 39%–68% lower than those in nonsprayed control plots. Our results suggest that at least three half-lives of degradation must occur, and likely four or more, before these legumes can re-establish at densities acceptable for pasture production. These findings have implications for producers seeking to promptly re-establish forage legumes within pastures sprayed for broadleaf weed control in northern temperate regions.

Lamb Fattening Under Intensive Pasture-Based Systems: A Review

The benefits of pasture-based systems on the fatty acid composition of sheep meat appear to be achievable despite variability in the quality of the pastures. Lambs fed high levels of temperate pastures have an excess of N-ammonia derived from protein degradation. Furthermore, animal performance is highly variable depending on the quality of the pasture at the time of grazing, and high animal performance in these systems appears to be linked to the use of high-quality pastures with high availability, and is possibly added to by the inclusion of concentrates that allow increasing energy intake and a better use of the N in the pasture. The combination of high-quality pastures and total mixed ration offers a good alternative to the inclusion of concentrates in the diet, improving the use of N, and avoiding acidosis problems. However, information to determine the effect of a number of nutritional strategies on meat quality, and the minimum level of pasture intake necessary to achieve the benefits of pastoral systems is still lacking.

Do calcium and magnesium deficiencies in reproducing ewes contribute to high lamb mortality?

High lamb mortality continues to be a significant economic and welfare problem within the Australian sheep industry, with 20–30% of lambs born in commercial flocks dying mostly within 3 days of birth. Clinical hypocalcaemia and hypomagnesaemia cause ewe mortality, and, subsequently, either fetal or lamb death, but it is not known whether subclinical deficiencies of calcium (Ca) and magnesium (Mg) compromise lamb survival. This review considers the potential mechanisms through which Ca and Mg deficiencies may influence lamb survival, and factors influencing the risk of deficiency. Pastures grazed by lambing ewes may be marginal in calcium (Ca; <4 g/kg DM) and magnesium (Mg; <0.9 g/kg DM) but also have a high dietary cation–anion difference (>12 meq/100 g DM) and high concentrations of potassium (K; >30 g/kg DM) and nitrogen. In young cereal crops, sodium concentrations are also often low (<0.9 g/kg DM). This combination of minerals and other nutrients creates an imbalance in supply and increases susceptibility to acute Ca (hypocalcaemia) and Mg (hypomagnesaemia) deficiency. Calcium is required for smooth muscle function and has a direct role in uterine contraction, so may influence the duration of parturition. Low Ca and Mg intake both influence insulin release and sensitivity, low Mg results in poor glycaemic control and insulin resistance by impairing both insulin secretion and its action on peripheral tissues, also potentially altering the duration of parturition as well as risk of metabolic disease. Magnesium is also a neuroprotectant that slows the neuronal damage during hypoxia and has been linked with thermogenesis in offspring and increased immunoglobulins in colostrum. These functions indicate potential importance in improving the ease of parturition and improved ability of the newborn lamb to thermoregulate and survive after birth. Subclinical Ca and Mg deficiencies commonly occur in 20% of lambing ewes grazing temperate pastures, so further studies are warranted to investigate whether correction of these deficiencies can improve lamb survival.