The effect of four calcium‐based amendments on soil aggregate stability of two sandy topsoils

The structural stability of soil is a physical characteristic that affects soil degradation processes. Calcium‐based amendments, such as calcium carbonate, calcium sulfate, and calcium oxide/hydroxide, have been shown to improve the stability of soil aggregates. This study seeks to determine which calcium‐based soil amendments, and at what concentration, are the most efficient in improving aggregate stability of sandy topsoils derived from granitic and metamorphic parent materials, and to analyze the mechanisms involved. In the pot experiment, soils amended with CaCO₃, CaCl₂, and CaSO₄ did not present significant differences in aggregate stability compared to the control or among each other. In contrast, Ca(OH)₂ soil amendment brought the greatest stability to the soil aggregates. A dose of 1% Ca(OH)₂ significantly increased the stability of soil aggregates. This effect is due to the reaction of Ca(OH)₂ with atmospheric CO₂ which leads to the formation of CaCO₃, a delayed reaction not showed by the other soil amendments tested. Likewise, the greater solubility of Ca(OH)₂ compared to CaCO₃ exerts a greater aggregation effect on soil. Thus, the mechanism of action of Ca(OH)₂ is related to cementation, rather than flocculation. Future studies should be carried out to demonstrate the effectiveness of Ca(OH)₂ under field conditions.     

First indications for the involvement of strigolactones on nodule formation in alfalfa (Medicago sativa)

Strigolactones have recently been suggested to be phytohormones that are present in all plants. Strigolactones are released by roots into the rhizosphere, stimulating the seed germination of parasitic plants such as Striga spp. and Orobanche spp. and play a crucial role in the interaction between plants and symbiotic arbuscular mycorrhizal fungi.By applying different concentrations of the synthetic strigolactone analogue GR24 to alfalfa (Medicago sativa) inoculated with Sinorhizobium meliloti we could show that in alfalfa nodulation is positively affected by the presence of the strigolactone analogue GR24. Moreover, we could show that this increased nodulation cannot be linked with a stimulatory effect of GR24 on the growth or the expression of nod genes of S. meliloti.Putative mechanisms operating in the plant in response to the addition of GR24 and leading to increased nodule formation by rhizobia are discussed.     

Narrow genetic base in forest restoration with holm oak (Quercus ilex L.) in Sicily

In order to empirically assess the effect of actual seed sampling strategy on genetic diversity of holm oak (Quercus ilex) forestations in Sicily, we have analysed the genetic composition of two seedling lots (nursery stock and plantation) and their known natural seed origin stand by means of six nuclear microsatellite loci. Significant reduction in genetic diversity and significant difference in genetic composition of the seedling lots compared to the seed origin stand were detected. The female and the total effective number of parents were quantified by means of maternity assignment of seedlings and temporal changes in allele frequencies. Extremely low effective maternity numbers were estimated (Nf _e ≈ 2–4) and estimates accounting for both seed and pollen donors gave also low values (N _e ≈ 35–50). These values can be explained by an inappropriate forestry seed harvest strategy limited to a small number of spatially close trees.     

Coffee agroecosystem performance under full sun, shade, conventional and organic management regimes in Central America

Changes in coffee economics are leading producers to reduce agrochemical use and increase the use of shade. Research is needed on how to balance the competition from shade trees with the provision of ecological services to the coffee. In 2000, long-term coffee experiments were established in Costa Rica and Nicaragua to compare coffee agroecosystem performance under full sun, legume and non-legume shade types, and intensive and moderate conventional and organic inputs. Coffee yield from intensive organic production was not significantly different from intensive conventional in Nicaragua, but in Costa Rica it was lower during three of the six harvests. Full sun coffee production over 6 years was greater than shaded coffee in Costa Rica (61.8 vs. 44.7 t ha^?1, P = 0.0002). In Nicaragua, full sun coffee production over 5 years (32.1 t ha^?1) was equal to coffee with shade that included Tabebuia rosea (Bertol.) DC., (27?C30 t ha^?1) and both were more productive (P = 0.03) than coffee shaded with Inga laurina (Sw.) Willd. (21.6 t ha^?1). Moderate input organic production was significantly lower than other managements under all shade types, except in the presence of Erythrina poepiggina (Walp.) O.F. Cook. Inga and Erythrina had greater basal area and nutrient recycling from prunings than other shade species. Intensive organic production increased soil pH and P, and had higher K compared to moderate conventional. Although legume shade trees potentially provide ecological services to associated coffee, this depends on management of the competition from those same trees.     

Bi-objective multi-period planning with uncertain weights: a robust optimization approach

Decisions resulting from multi-objective planning models are quite sensitive to objective weights, and the latter are hard to determine accurately. We describe a robust formulation of a bi-objective multi-period planning problem where objective weights are random, independent and uniformly distributed in a predetermined range. We apply this model to a 245,090 ha forest in British Columbia, Canada, where the amount of employment and the proportion of old forest through the planning horizon are the two management objectives. Evaluated under simulated scenarios of weights, robust solutions produce more stable weighted sum of the objectives through the planning periods than traditional deterministic solutions. In other words, no large changes in the weighted sum of the objectives are expected even when the weights change over time. With this approach, we envision that these types of decisions will be better accepted by stakeholders and other social actors involved in the decision-making process.     

Global genotype by environment trends in growth traits for Eucalyptus dunnii

New Forests - Eucalyptus dunnii Maiden (Dunn’s white gum) is a fast-growing tall tree with a restricted natural distribution in south-east Australia and favorable wood properties for pulp...     

Spatial patterns of diversity and genetic erosion of traditional cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz) in the Peruvian Amazon: An evaluation of socio-economic and environmental indicators

This study evaluates quantitatively the suitability of the use of site-specific socio-economic and environmental data as indicators to rapidly assess patterns of diversity and genetic erosion risk in cassava. Socio-economic data as well as farmers’ estimation of genetic erosion were collected in the study area, the Ucayali region of the Peruvian Amazon, through interviews with 285 cassava farmers in 50 communities, while diversity was assessed based on agromorphological characterization of 295 cassava accessions. Using multivariate regression analyses, 50 and 45% of the variation in respectively diversity and genetic erosion estimation could be explained by a selected set of socio-economic and environmental indicators. In both regression models four out of the total of 38 variables proved to contribute significantly (at p < 0.10 level). Additionally, the study revealed that farmers are a good direct source of information on the diversity present at community level, which can contribute to the development of methodologies to assess diversity more rapidly. The results of this study are valuable for the development of models to rapidly assess diversity dynamics in large areas.