Sensitivity of Soil P Availability Tests to Ca-P in Oxisols

We assessed the sensitivity of mixed exchange resin (MER) and Mehlich-3 (M3) to calcium-bound phosphate (Ca-P) in Oxisols. These methods were compared with Mehlich-1 (M1) and anion exchange resin (AER), which have high and low sensitivity, respectively, to this soil P form. We used maize (Zea mays L.) as a test plant. Three samples from two Oxisols were treated with five ratios of Triple Superphosphate—TS and Bayóvar Phosphate Rock—BPR (0 + 100; 25 + 75, 50 + 50, 75 + 25 and 100 + 0% TS + BPR). The MER extracted more P than AER and M3 at the highest BPR:TS ratios (high Ca-P) and similar quantities at the higher TS:BPR ratios (low Ca-P) for two soil samples. Unlike M1-extracted P, M3-P, AER-P, and MER-P positively correlated with maize dry matter production and P uptake. Mehlich-3 and MER were suitable to assess P availability in high Ca-P Oxisols.     

Predatory beetles in cacao agroforestry systems in Brazilian Atlantic forest: a test of the natural enemy hypothesis

The natural enemy hypothesis predicts a positive correlation between plant species diversity and natural enemy control. This study aimed to evaluate the role of traditional cacao agroforests, known as “cabrucas,” on the conservation of the predatory beetle community compared to that of monodominant rubber agroforests. Predatory beetles were sampled in three habitats in Southeastern Bahia, Brazil: cabrucas and rubber agroforests and native Atlantic forests. In each habitat, 18 10 m² plots were established, in which canopy cover was measured and beetles were sampled with a modified Malaise/window trap. Land use intensification did not affect the composition of predatory beetles, with the presence of widely distributed species that are also capable of colonizing simpler environments such as the rubber agroforest. Canopy cover had a positive effect on generalist predator diversity and we observed a reduction in the abundance and species richness of generalist predators with increasing habitat homogenization. Despite the simplified structure of the habitat, the remaining tree diversity and canopy cover in cabrucas supported a community of generalist predators similar to the one found in the native forest. Species diversity of bark beetle predators was higher in cabrucas, which may be due to the high diversity of bark beetles and the favorable abiotic conditions, whereas the low abundance of prey in the native forest and severe abiotic conditions in the rubber agroforest probably determined the lower diversity of generalist predators in these habitats. Cabrucas play an important role in the conservation, supporting a community of predatory beetles more similar to the one found in native forest and that is more effective at controlling populations of herbivores than in homogeneous rubber agroforests.     

Constructed wetlands for the treatment of organic pollutants

Background  Constructed wetlands (wetland treatment systems) are wetlands designed to improve water quality. They use the same processes that occur in natural wetlands but have the flexibility of being constructed. As in natural wetlands vegetation, soil and hydrology are the major components. Different soil types and plant species are used in constructed wetlands. Regarding hydrology surface flow and subsurface flow constructed wetlands are the main types. Subsurface flow constructed wetlands are further subdivided into horizontal or vertical flow. Many constructed wetlands deal with domestic wastewater where BOD and COD (Biochemical and Chemical Oxygen Demand respectively) are used as a sum parameter for organic matter. However, also special organic compounds can be removed. Objective  The objectives are to summarise the state-of-the-art on constructed wetlands for treatment of specific organic compounds, to the present the lack of knowledge, and to derive future research needs. Methods  Case studies in combination with a literature review are used to summarise the available knowledge on removal processes for specific organic compounds. Results and Discussion  Case studies are presented for the treatment of wastewaters contaminated with aromatic organic compounds, and sulphonated anthraquinones, olive mill wastewater, landfill leachate, and groundwater contaminated with hydrocarbons, cyanides, chlorinated volatile organics, and explosives. In general the removal efficiency for organic contaminants is high in all presented studies. Conclusion  Constructed wetlands are an effective and low cost way to treat water polluted with organic compounds. There is a lack of knowledge on the detailed removal pathways for most of the contaminants. Removal rates as well as optimal plant species are substance-specific, and also typically not available. If a constructed wetland provides different environmental conditions and uses different plant species the treatment efficiency can be improved. Recommendations and Outlook  There is a great need to lighten the black box ‘constructed wetland’ to obtain performance data for both microbial activity and the contribution of the plants to the overall removal process. Also genetic modified plants should be considered to enhance the treatment performance of constructed wetlands for specific compounds.     

Mesquite pod meal as an additive increases milk total solids,lactose, fat and protein content in dairy cows

The objective was to evaluate the intake, digestibility, milk yield and composition of cows fed mesquite pod meal (MPM). Five crossbred dairy cows, with an average body weight of 450?±?5 kg and producing 10?±?1 kg of milk/day were distributed in a 5?×?5 Latin square arrangement with five periods of 20 days each, comprised of 15 days for adaptation to the experimental diets (T1?=?0%, T2?=?1.5%, T3?=?3.0%, T4?=?4.5% and T5?=?6.0% MPM) and 5 days for data collection. Variables were assessed by analysis of variance and regression at P?<?0.01 and P?<?0.05 of significance, using the Student’s test. Animals were kept on pastures and the concentrates were provided at 6 kg/animal divided in two meals per day. The inclusion of 3.0% mesquite pod meal did not affect the intake, digestibility of nutrients and milk yield, but it changed milk composition. The dietary inclusion of 3.0% mesquite pod meal as a palatability enhancer increases the percentage of milk solids, lactose, fat and protein. Therefore, mesquite pod meal can be included in diets for dairy cows to improve the nutritive value of milk.

     

Nitrate uptake by corn under increasing periods of phosphorus starvation

Single cross seedlings of the male progenitor of the double cross hybrid, BR 201, were grown for seven days in a complete nutrient solution prior to evaluating the kinetics of nitrate uptake under varying periods of phosphorus deficiency. Nitrate uptake decreased 60% after a short period of phosphorus starvation (2 days) and ceased when phosphorus was withheld longer than six days. Nitrate uptake resumed after phosphorus (P) was re‐supplied, but the time required and extent of recovery depended on the length of phosphorus starvation.     

Forest owners and fuels management coordination. When neighbours’ actions matter

Forest owners’ coordination for wildfires prevention is still a largely unexplored area of research, and an important social issue in contexts in which there is an increase in the frequency, extent, and severity of wildfires, such as Portugal. Our approach innovates by introducing a social interaction between plot-neighbourhood owners to the analysis of attitudes and behaviours toward fuels management coordination. As a case study, we focus on a parish in the Northwest of Portugal, and using data from a forest owners’ survey, we compare the owner’s willingness-to-coordinate and his/her current fuels treatments implicit-coordination with his neighbouring property owners. Our findings show that indeed neighbours’ actions count, that is, they are interdependent with the owner’s current management practices and owner-neighbours behaviour interaction is relevant to his/her willingness-to-reduce fuels load. Local social capital favours similarity of behaviour toward bush-clearing by plot-neighbours. The owners’ willingness-to-coordinate, conversely, is not influenced by the plot-neighbours’ actions or by the local social capital, and is instead strongly correlated with the owner’ sociodemographic profile. We conclude for the need to look for context-dependent constraints of the owners’ fuels reduction and coordination practices.     

Eucalyptus urophylla root growth, stem sprouting and nutrient supply from the roots and soil

Lack of information concerning root growth of trees limits our knowledge of plant development and fertilizer response. The objective of this work was to study root growth dynamics of an E. urophylla forest after harvesting and the supply of nutrients from the roots and the soil to the new sprouts originating from the stumps. About 7-year-old eucalypt trees were felled and the sprouts and roots were sampled at 0, 60, 120, 180, 240, 330 days after harvesting. The roots were separated into fine roots (<1 mm), medium roots (1–3 mm), coarse roots (>3 mm), and taproot. Nutrient supply to sprouts from the old roots and the soil was calculated based on the change in nutrient content of the roots with time and accumulation of nutrients in the sprouts. Fine, medium and coarse root biomass increased with time after harvesting. However, the increase was more pronounced with fine roots. Between harvesting and day 60 of the new growth, all nutrients allocated to the sprouts, excluding potassium, were supplied by the soil. K was the nutrient most dependent on root reserves for the initial growth of sprouts. The contribution of the old roots to N, P, Ca, and Mg accumulation in the sprouts increased between day 60 and 120. At 330 days after harvesting, about 9.2, 23.9, and 12.6% of the N, K, and Mg, respectively, that had accumulated in the sprouts were supplied by the roots, while all P and Ca were supplied by the soil.     

Responses of eucalypt species to aluminum: the possible involvement of low molecular weight organic acids in the Al tolerance mechanism

Aluminum (Al) tolerance mechanisms in crop plants have been extensively researched, but our understanding of the physiological mechanisms underlying Al tolerance in trees is still limited. To investigate Al tolerance in eucalypts, seedlings of six species (Eucalyptus globulus Labill., Eucalyptus urophylla S.T. Blake, Eucalyptus dunnii Maiden, Eucalyptus saligna Sm., Eucalyptus cloeziana F. J. Muell. and Eucalyptus grandis w. Hill ex Maiden) and seedlings of six clones of Eucalyptus species were grown for 10 days in nutrient solutions containing Al concentrations varying from 0 to 2.5 microM (0 to 648 microM Al3+ activities). Root elongation of most species was inhibited only by high Al3+ activities. Low to intermediate Al3+ activities were beneficial to root elongation of all species and clones. Among the species tested, E. globulus and E. urophylla were more tolerant to Al toxicity, whereas E. grandis and E. cloeziana were more susceptible to Al-induced damage. Although E. globulus seedlings were tolerant to Al toxicity, they were highly sensitive to lanthanum (La), indicating that the tolerance mechanism is specific for Al. Fine roots accumulated more Al and their elongation was inhibited more than that of thick roots. In E. globulus, accumulation of Al in root tips increased linearly with increasing Al concentration in the nutrient solution. The majority of Al taken up was retained in the root system, and the small amounts of Al translocated to the shoot system were found mainly in older leaves. No more than 60% of the Al in the thick root tip was in an exchangeable form in the apoplast that could be removed by sequential citrate rinses. Gas chromatography/mass spectrometry and ion chromatography analyses indicated that root exposure to Al led to a greater than 200% increase in malic acid concentration in the root tips of all eucalypt species. The increase in malate concentration in response to Al treatment correlated with the degree of Al tolerance of the species. A small increase in citric acid concentration was also observed in all species, but there were no consistent changes in the concentrations of other organic acids in response to Al treatment. In all eucalypt species, Al treatment induced the secretion of citric and malic acid in root exudates, but no trend with respect to Al tolerance was observed. Thus, although malate and citrate exudation by roots may partially account for the overall high Al tolerance of these eucalypt species, it appears that tolerance is mainly derived from the internal detoxification of Al by complexation with malic acid.     

Influence of phosphorus stress on ammonium uptake by maize

The effect of phosphorus (P) starvation on ammonium (NH₄) uptake was evaluated by growing single‐cross seedlings of the male progenitor of the maize double‐cross hybrid BR 201 in nutrient solution. The kinetics of NH₄ uptake were measured after P starvation and non‐starvation periods of 2, 4, 6, 8, and 10 days. The effect of P addition during the study period (resupply) was also tested. Ammonium uptake decreased 45.7% after two days of P stress compared to the fully P‐sufficient control. Ammonium uptake decreased 83.0% when P was withheld for 10 days. The decline in NH₄ uptake was partially reversed when P was resupplied during the early periods of P deficiency, but this effect diminished as the P stress increased. These results suggest that maize plants are physiologically dependent on NH₄ rather than nitrate (NO₃) when under P stress.     

Diffusive flux of cationic micronutrients in two Oxisols as affected by low‐molecular‐weight organic acids and cover‐crop residue

Low‐molecular‐weight organic acids with one or more carboxylic groups are ubiquitous. In soils, they can originate from leaching of plants, litter decomposition, plant‐roots exudation, and microbial activity. Their presence in the soil may favor the formation of soluble organo‐metallic complexes that improve the transport of Zn, Cu, Fe, and Mn to plant‐root surfaces via diffusion. The current study sought to determine if some of the organic acids (OA) in soils and a cover‐crop residue influence the diffusive flux (DF) of Zn, Cu, Mn, and Fe. Two OA were added to two Oxisols (Typic Haplustox): a clayey Dark Red Latosol (DRL) and a sandy‐loam Red Yellow Latosol (RYL). Acetic and citric acid were added to achieve concentrations of 0, 250, 500, 1000, and 2000 mmol (m³ soil)^–1. The effect of adding plant material (pearl millet) on the soil DF of the cationic micronutrients was also determined. Soil diffusive flux was evaluated by incubating positively charged and negatively charged exchange‐resin membranes with the soil in PVC diffusion chambers for 15 d. Desorption of Zn, Cu, Fe, Mn, and OA from the resins was performed with 0.5 mol l^–1 HCl. The results demonstrated that the DF of the cationic micronutrients increased with the addition of organic acid. The DF of Zn and Mn occurred mostly towards the cationic resin, whereas the diffusive flux of Cu and Fe occurred mostly towards the anionic resin. Apparently, the dissolution of oxides and/or complexation of micronutrients adsorbed to the solid phase or in the soil solution contributed to the obtained results. Citric acid was more efficient than acetic acid in maintaining a larger DF value for Zn, Cu, and Fe. The addition of millet plant material to the soil increased the DF in the following order: Mn > Cu > Fe > Zn; Mn moved towards the cationic resin, and the other micronutrients moved towards the anionic resin. These findings suggest that organic compounds play an important role in the short‐distance transport of cationic micronutrients in highly weathered soils.