Mobilization of phosphorus contributes to positive rotational effects of leguminous cover crops on maize grown on soils from northern Nigeria

Previous research has demonstrated a positive rotational effect of tropical leguminous cover crops on maize growth on a luvisol from Nigeria. This effect could not be explained by a better N supply. The objective of the present work was to further clarify whether improved P nutrition has been a contributing factor. Nine cover crops and maize were studied in nutrient solution‐culture with 1 and 20 μM P and with NO₃‐N as N source for root physiological parameters that may affect P mobilization. Zea mays, Lablab purpureus, and Centrosema pubescens responded to P deficiency by higher rates of proton excretion. Clitoria ternatea excreted OH^— with only small differences due to P nutrition. At low P supply, Chamaecrista rotundifolia, Clitoria, and Centrosema had the highest exudation rates of organic acid anions, especially citrate and malate. A major difference between plant species was found in root‐surface acid phosphatase activity. Cajanus cajan expressed the highest phosphatase activity. V_max of P uptake increased markedly under P deficiency, particularly for maize. Compared to the other plant species Cajanus, Chamaecrista, and Clitoria were characterized by a greater capability to absorb P at low external P concentrations. The nine cover crops and maize were also grown in pot experiments using two soils from northern Nigeria low in available P. The ultisol from Jos had a high P fixation capacity and was more acidic than the alfisol from Zaria. All plant species were precultured in the first season at 100 (Zaria) and 250 (Jos) mg P per pot. In the subsequent season, maize was uniformly seeded into all pots containing the remaining roots and the incorporated shoot dry mass (according to 15 mg P per pot) of the pre‐crop. No P and 250 (Zaria) or 500 (Jos) mg P per pot were freshly applied. Maize growth and P uptake were enhanced after legumes in Zaria soil. Cajanus showed the highest residual effect, and also Clitoria, Chamaecrista, and Lablab showed effects superior to the mean. In Jos soil, Clitoria, Cajanus, and Lablab enhanced maize growth above average. Also, a highly significant positive correlation between P uptake and biomass production was obtained. These results indicate that enhancement of maize growth after leguminous cover crops, at the low P supply of the soil used, mainly depends on P mobilization capacity of the cover crop.     

Evaluating water stress in irrigated olives: correlation of soil water status,tree water status,and thermal imagery

Irrigation of olive orchards is challenged to optimize both yields and oil quality. Best management practices for olive irrigation will likely depend on the ability to maintain mild to moderate levels of water stress during at least some parts of the growing season. We examined a number of soil, plant and remote sensing parameters for evaluating water stress in bearing olive (var. Barnea) trees in Israel. The trees were irrigated with five water application treatments (30, 50, 75, 100 and 125% of potential evapotranspiration) and the measurements of soil water content and potential, mid-day stem water potential, and stomatal resistance were taken. Remote thermal images of individual trees were used to alternatively measure average canopy temperature and to calculate the tree’s crop water stress index (CWSI), testing empirical and analytical approaches. A strong non-linear response showing similar trends and behavior was evident in soil and plant water status measurements as well as in the CWSI, with decreasing rates of change at the higher irrigation application levels. No statistically significant difference was found between the analytical and the empirical CWSI, suggesting that the relative simplicity of the analytical method would make it preferable in practical applications.     

Ethylene influences development and flowering of Ptilotus spp. in vitro and ex vitro

The genus Ptilotus has immense potential for ornamental horticulture but its commercial development has been hindered by propagation limitations. Poor seed quality and germination are reported. Cutting propagation is limited by cutting supply as the juvenile phase of Ptilotus is short. Micropropagation has been used in an attempt to overcome these difficulties but explants become floral in vitro and this causes plantlets to elongate. Ethephon has been used to control flowering of stock plants of many ornamental species. This study investigated the effect of ethephon applied to young (3-week-old, deflasked from tissue culture) and mature (1-year-old) Ptilotus plants in a greenhouse. A system of applying gaseous ethylene at 0, 100, 200 and 300 mg l⁻¹ to the headspace of in vitro plantlets in glass jars was developed and the response of in vitro plantlets to ethylene studied. One-year-old Ptilotus plants were treated with 500 mg l⁻¹ ethephon 2 days before pruning or 1 or 2 weeks after pruning. Ethephon application 2 days before pruning decreased the number of inflorescences and increased the number of shoots (compared to the control) but was phytotoxic. Ethephon applications of 150 or 300 mg l⁻¹ applied weekly or fortnightly to 3-week-old plants deflasked from tissue culture reduced plant height and number of inflorescences and at low concentrations increased the number of new shoots. A fortnightly application at 150 mg l⁻¹ is recommended. Previous reports on the effects of ethylene on inflorescence production on plantlets in vitro are limited. Our study showed that exposure of in vitro plantlets of P. nobilis to ethylene gas at 100 mg l⁻¹ for 1 h significantly increased the number of shoots and plant height but this did not occur for plantlets of P. spicatus. Plantlets of P. spicatus exposed to transient ethylene at 200 and 300 mg l⁻¹ showed significantly greater rooting (52.4%) than the control (13.6%).     

Effect of Microparticulate Diets on Growth and Survival of Spotted Sand Bass Larvae, Paralabrax maculatofasciatus, at Two Early Weaning Times

Early weaning in spotted sand bass larvae, Paralabrax maculatofasciatus, was evaluated, testing a combination of two weaning times, 17 and 22 d after hatching (d.a.h.), and three different microparticulate diets. Protein in diets was mainly from sardine meal and from 15% squid meal, beef blood meal, or fish protein hydrolysate. Anatomical (standard length), histological (gut development), and biochemical (highly unsaturated fatty acids) parameters were measured in larvae, as well as survival and resistance to a stress test measured 40 d.a.h. For larvae weaned at 17 d.a.h., the best growth and survival were obtained with diets containing fish protein hydrolysates; for larvae weaned at 22 d.a.h., best results were obtained with squid meal and fish protein hydrolysate. Growth and survival were significantly lower when using beef blood meal in both weaning treatments. The best relative and total survival were for larvae weaned at 22 d.a.h. After the resistance test, 100% survival occurred in larvae fed on any microparticulate diet and either weaning treatment. No significant differences in arachidonic acid, eicosapentaenoic acid, or docosahexaenoic acid concentrations in fish fed on any diet occurred. Results suggest that weaning at 22 d.a.h. with diets containing fish protein hydrolysate or squid meal is preferred by this species.     

Fabrication of amphiphobic softwood and hardwood by treatment with non-fluorinated chemicals

Amphiphobic wood has successfully been fabricated using a combination of O₂ plasma surface activation and coating of pre-hydrolyzed methyltrimethoxysilane (MTMS). The effect of O₂ plasma activation on surface chemistry and surface roughness was investigated using X-ray photoelectron spectroscopy and laser scanning confocal microscope profilometry, respectively. Pre-hydrolyzed MTMS was used to impart oleophobicity to both softwood and hardwood samples with tunable hydrophilicity by adjusting the sonication time during pre-hydrolysis. Depending on hydrolysis time, the coated wood samples display wetting behavior ranging from superhydrophilic/oleophobic (immediate water absorption; motor oil contact angles 63.5° for hardwood and 62.4° for softwood) to amphiphobic (water contact angles 104.3° for hardwood and 91.1° for softwood; motor oil contact angles 68.7° for hardwood and 63.9° for softwood), without affecting visual appearance of the wood. For all plasma-activated MTMS-coated wood samples, no absorption of motor oil is observed for several months, indicating stable oil resistance. The intrinsic porosity of wood is also partially retained after coating.     

Nutritional response of Zea mays L. seedlings to “on plant demand” fertilizer: A vector analysis approach

Glass matrix based fertilizers (GMF) are new mineral fertilizers, able to release nutrients on the basis of plant demand: they are soluble only in metal complexing solutions, such as those exuded by plant roots. Moreover, nutrient release could be increased by mixing the glass-matrix fertilizer to different organic biomasses, such as leather meal, digested vine vinasse, etc. A greenhouse pot experiment was conducted for assessing the effect of an organo-mineral fertilizer, obtained by mixing GMF with increasing percentages of digested vine vinasse [DVV, at 5% (GMF95), 20% (GMF80) and 50% (GMF50) w/w], on the root and shoot biomass and nutritional status of Zea mays L. seedlings. Among tested fertilizers, the formulations GMF80 and GMF50 gave the best results as shoot/root ratio. The treatments with GMF, GMF95 and GMF80 gave rise to a significant increase of both shoot and root biomass and a tendency to increase the macro and micronutrients availability.     

Interrelationship of phytoalexin production and disease resistance in selected peanut genotypes

In peanuts, a mechanism of resistance to fungal infection is reportedly due to the synthesis of stilbene phytoalexins, which are antibiotic, low molecular weight metabolites. The phytoalexin-associated response of different peanut genotypes to exogenous invasion in the field has not been investigated and may be useful for breeding resistant peanut cultivars. Five peanut genotypes, Georgia Green, Tifton 8, C-99R, GK-7 High Oleic, and MARC I, which differ in resistance to major peanut diseases, were investigated for their ability to produce phytoalexins under field conditions in South Georgia in 2001 and 2002. Five known peanut phytoalexins, trans-resveratrol, trans-arachidin-1, trans-arachidin-2, trans-arachidin-3, and trans-3'-isopentadienyl-3,5,4'-trihydroxystilbene, were quantitated. The phytoalexins were measured in peanuts of different pod maturity (yellow, orange, brown, and black) with or without insect pod damage (externally scarified or penetrated). Kernels from insect-damaged pods of C-99R and Tifton 8 genotypes had significantly higher concentrations of phytoalexins than other genotypes. The same genotypes were the most resistant to tomato spotted wilt virus and late leaf spot, while MARC I, which is highly susceptible to these diseases, produced very low concentrations of phytoalexins. However, there was no significant difference in phytoalexin production by undamaged peanut pods of all tested genotypes. trans-Arachidin-3 and trans-resveratrol were the major phytoalexins produced by insect-damaged peanuts. In damaged seeds, the concentrations of trans-3'-isopentadienyl-3,5,4'-trihydroxystilbene were significantly higher in Tifton 8 as compared to other genotypes. There was an association between total phytoalexin production and published genotype resistance to major peanut diseases. Stilbene phytoalexins may be considered potential chemical markers in breeding programs for disease-resistant peanuts.     

Southeast Asia's transboundary haze pollution: Unravelling the inconvenient truth

This paper examines the political intricacies inherent in the management of Southeast Asia's transboundary haze pollution. It argues for a scalar perspective in understanding the complexities of the haze problem. The so‐called ‘inconvenient truth’ is unravelled by teasing out some issues in the national and regional political ecologies, and the challenges of synchronising co‐operation at the national, regional and global scales. Discussion shows that the ‘environment’ takes on different meanings at each scale, and both Indonesia and the Association of Southeast Asian Nations (ASEAN) need to recognise this in order to engage more effectively with the transboundary environmental issue. Specifically, inadequate management of forest resources in Indonesia, ASEAN's principle of ‘non‐interference’ and a lack of a holistic ecosystem perspective are amongst some of the interconnected issues addressed. The paper calls for a greater awareness of structural weaknesses in the management of forest resources and a change in ASEAN's environmental paradigm to a more holistic ecosystem perspective that prioritises not just environmental and human health, but also a healthy and sustainable ecosystem.