Luxury uptake of magnesium by peas,Pisum sativum

Increasing the magnesium (Mg) concentration of vegetables (biofortification) will often require ‘luxury’ uptake where the whole‐plant concentration of Mg (c_p) is greater than required for maximum yield. Our aim was to quantify some of the physiological factors influencing luxury uptake of Mg to aid subsequent development of agronomic techniques for biofortification. Peas, Pisum sativum, were used as a test species. A sand culture experiment related vegetative growth and c_p for plants grown with a range of Mg and potassium (K) supply rates. We developed a model of Mg uptake including feedback control exerted by c_p. The model was parameterised with results from a solution culture experiment and then used to explore ways to increase luxury uptake of Mg. Feedback control of Mg uptake by c_p was weak. Biomass did not increase if the Mg concentration exceeded 0.11% in the whole plant or 0.13% in the shoots. Values obtained in the field are often larger than this. Our results indicate that luxury uptake of Mg by peas is readily achieved, provided that there is ample supply of Mg²⁺ to the root surfaces. In field soils though, transport of Mg²⁺ to the roots may limit uptake and cation exchange processes restrict the ability of Mg fertilisers to substantially increase Mg uptake. Increasing root growth will usually increase Mg uptake, but c_p may not rise if biomass is also increased.     

Denitrification and N2O emissions from a UK pasture soil following the early spring application of cattle slurry and mineral fertiliser

Total denitrification and nitrous oxide (N₂O) losses were measured from three contrasting dairy management systems representing good commercial practice (system 1), production maintained but with reduced N losses (system 2); and nitrate leaching less than 50 mg L^-1 but with reduced production (system 3). Measurements were made following mineral fertiliser application and from two plot experiments where four treatments were applied: control, NH₄NO₃ at 60 kg N ha^-1, cattle slurry applied to the surface (equivalent to 45 kg N ha^-1), and cattle slurry injected. Despite low soil temperatures (<6 °C) and low rainfall (<3 mm), total denitrification and N₂O losses peaked at 56 and 16 g N ha^-1 d^-1, respectively. Total denitrification losses decreased: system 1 system 2 > system 3, whereas N₂O losses decreased: system 2 > system 3 > system 1. Total denitrification losses tended to decrease with decreasing fertiliser application rate, whereas fertiliser application rate was not the sole determinant of the N₂O loss. The system 3 field was injected with cattle slurry for 2 yr, system 2 received some slurry by injection and system 1 received slurry to the surface. Thus, the amount, timing and method of previous cattle slurry application was important in determining the loss following subsequent fertiliser application. For the plot experiments, total denitrification and N₂O losses decreased in the order: slurry injected > mineral fertiliser > slurry applied to the surface > control for 5 days following application. However, 16 and 19 days after application, N₂O losses above the control were measured from plots that had received cattle slurry. It was inferred that the application of cattle slurry to the pasture soil stimulated greater N₂O production and increased losses over a longer time period compared with mineral fertiliser additions.     

Growth of potato cultivars in response to application of phosphate fertiliser

Three experiments examined the response of potato cultivars from different maturity groups to fertiliser phosphorus application under conditions of relatively low residual soil P. Initial expansion of the leaf canopy was much more rapid following P application and maximum cover was attained sooner. In the absence of applied P, maximum ground cover was reduced substantially in early-maturing cultivars but not in maincrop cultivars. At early harvests, all cultivars showed very large growth responses to P application, but cv. Rocket grown from well-sprouted seed showed a significantly larger response than cv. Desiree. In the absence of applied P, ground cover was in some cases higher at later growth stages allowing a substantial degree of growth compensation so that final harvests showed only small effects of P application on dry matter yields. At final harvests, no significant interactions between cultivar and phosphorus fertiliser level were found for either dry matter production or P uptake despite some apparent effects. Phosphorus application increased dry matter production through increased interception of solar radiation with no effect on efficiency of utilisation.     

A decision tree approach to modelling nitrogen fertiliser use efficiency in New Zealand pastures

Quantifying nitrogen (N) fertiliser use efficiency (NFUE) in pastoral systems has important implications for fertiliser management from both economic and environmental points of view. The potential of a decision tree approach for modelling NFUE in New Zealand pastures was investigated. The decision tree model suggested that the time of applying N fertiliser was the most important factor influencing NFUE, with August or September (early spring in New Zealand) being the best time of application. The interaction of rainfall and temperature, rainfall, phosphorus (P) fertiliser history, soil Olsen P and slope were other important factors influencing NFUE. The model was validated for 11 of the 16 trials tested with a predictive accuracy of 69%. The mechanisms by which these factors influenced NFUE and the uncertainty associated with the model prediction were discussed. It was concluded that this type of modelling approach can be used to predict NFUE and thereby to assist decisions on when and where to apply N fertiliser in pastures for increasing productivity while reducing the environmental impact.     

Plant-growth-promoting traits and antifungal potential of the Bacillus amyloliquefaciens YL-25

Biological control of plant soil-borne diseases has been shown as an attractive and an environment friendly alternative to chemical fungicides. Different microbial strains have been reported effective in controlling plant pathogens. Among those, Bacillus strains have their own importance. Bacillus amyloliquefaciens strain YL-25, isolated from the rhizosphere of healthy banana plant, was evaluated as bio-organic fertiliser (BIO) for its ability to promote plant growth and suppress Fusarium wilt of banana in pot experiment. The results showed that the application of the BIO containing strain YL-25 significantly promoted the growth of banana plants and decreased the incidence of Fusarium wilt compared to the organic fertiliser and chemical fertiliser (CF). In order to explore the beneficial mechanisms of strain YL-25, experiments were conducted in vitro. The phytohormones including indole-3-acetic acid and gibberellin A3 and stable antifungal compounds three homologous of iturin A were identified in the culture broth of strain YL-25. The strain YL-25 also showed the ability to degrade extracellular phytate in plate experiment. Owing to its innate multiple functional traits and biocontrol activity, the strain YL-25 may be used as plant-growth-promoting rhizobacterium and biocontrol agent against Fusarium wilt of banana.     

Long-term Effects of Pre-harvest Burning and Nitrogen and Vinasse Applications on Yield of Sugar Cane and Soil Carbon and Nitrogen Stocks on a Plantation in Pernambuco, N.E. Brazil

Since the 1970s the area under sugarcane in Brazil has increased from 2 million to over 5 million ha (M ha), and it is expected to pass the 7 M ha mark in 2007. More than half of the cane is harvested to produce bioethanol as a fuel for light vehicles. The distilleries produce approximately 13 L of distillery waste (vinasse) for each litre of ethanol produced. In the 1980s there was considerable concern over the long-term effects of the disposal of this material (containing about 1% carbon and high in K) on cane yields if it was applied to the field. At the same time there was a growing movement to abandon the practice of pre-harvest burning and some research was showing that some Brazilian varieties of sugar cane were able to obtain significant contributions of N from plant-associated biological nitrogen fixation (BNF). For these reasons an experiment was installed on a cane plantation in the state of Pernambuco, NE Brazil to investigate the long-term effects of vinasse and N fertiliser additions and the practice of pre-harvest burning on crop and sugar yield, soil fertility parameters, N balance and soil C stocks. The results showed that over a 16-year period, trash conservation (abandonment of burning) increased cane yields by 25% from a mean of 46 to 58 Mg ha⁻¹. Vinasse applications (80 m³ ha⁻¹ crop⁻¹) increased mean cane and sugar yield by 12 to 13% and the application of 80 kg N ha⁻¹ as urea increased cane yields by 9%, but total sugar yield by less than 6% (from 7.0 to 7.4 Mg ha⁻¹ crop⁻¹). The total N balance for the soil/plant system when only the surface 20 cm of the soil was considered was positive in plots where no N fertiliser was added. However, the data indicated that during the 16 years of the study considerable quantities of soil organic matter were accumulated below 20 cm depth such that the N balance considering the soil to 60 cm depth was strongly positive, except where N fertiliser was added. The data indicated that there were considerable BNF inputs to the system, which was consistent with its low response to N fertiliser and low N fertiliser-use-efficiency. There were no significant effects of vinasse or urea addition, or trash conservation on soil C stocks, although the higher yields proportioned by trash conservation had potentially significant benefits for increased mitigation of CO₂ emissions where the main use of the cane was for bioethanol production.     

Eutrophication in Australian Rivers, Reservoirs and Estuaries – A Southern Hemisphere Perspective on the Science and its Implications

Australian science has made rapid advances in the last decade in understanding eutrophication processes in inland waters and estuaries. The freshwater research on which these advances are based was triggered by well-publicised blooms of cyanobacteria during the 1980s and early 1990s, particularly a 1000 km long bloom on the Darling River. In estuaries the study which greatly enhanced our understanding but simultaneously served to stimulate further research into estuarine eutrophication, the Port Phillip Bay Study, was initially designed to address perceived problems of toxicants in the Bay but provided profound insights into drivers for, and ecosystem responses to, eutrophication. Subsequent estuarine research has largely been stimulated by management questions arising from Australia’s increasing coastal development for residential purposes. The research has shown that some of the beliefs extant at the time of the blooms were incorrect. For example, it is now clear that stratification and light penetration, not nutrient availability, are the triggers for blooms in the impounded rivers of southeastern Australia, although nutrient exhaustion limits the biomass of blooms. Again, nitrogen seems to play as important a role as phosphorus does in controlling the biomass of these freshwater blooms. The research has also shown that aspects of eutrophication, such as nutrient transport, are dominated by different processes in different parts of Australia. Many of the biophysical processes involved in eutrophication have now been quantified sufficiently for models to be developed of such processes as sediment-nutrient release, stratification, turbidity and algal growth in both freshwater and estuarine systems. In some cases the models are reliable enough for the knowledge gained in particular waterbodies to be applied elsewhere. Thus, there is now a firm scientific foundation for managers to rely upon when managing algal blooms. Whilst these findings have already been presented to managers and communities throughout Australia, there is still a considerable way to go before they are absorbed into their modus operandi.     

Nitrogen fertiliser affects the functional response and prey consumption of Harmonia axyridis (Coleoptera: Coccinellidae) feeding on cereal aphids

Predator–prey interactions are influenced by nitrogen availability. Wheat (Triticum aestivum cv. Solstice) plants were provided with four levels of nitrogen and examined the responses of coccinellid predator, Harmonia axyridis to cereal aphids, Rhopalosiphum padi and Sitobion avenae. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. In no‐choice feeding trials, H. axyridis consumed more aphids on low fertilised plants, suggesting a compensatory consumption to overcome reduced biomass (lower aphid size). Total biomass devoured by H. axyridis on all nitrogen fertiliser treatments was not statistically different. Logistic regression analysis of the proportion of prey consumed demonstrated that all developmental stages (larval and adult) of H. axyridis exhibited the type II functional response on all nitrogen fertiliser treatments. The rate of successful search (a′) of third and fourth instars and adults were the same across all fertiliser treatments suggesting that nitrogen fertilisation did not affect a′. Maximum handling time for the first instars of H. axyridis on R. padi (3.81 h^?1) and S. avenae (4.59 h^?1) was on the highest nitrogen treatment while minimum handling time was for the adults of H. axyridis on R. padi (0.20 h^?1) and S. avenae (0.20 h^?1) on the lowest nitrogen treatment. Handling time varied at varying fertiliser treatments within all instars and affected the predator's efficiency. The functional response curve, rate of successful search and handling time provide the information needed to understand the predator–prey interaction between H. axyridis and these cereals aphids. This could lead to the development of a better strategy for the biological control of R. padi and S. avenae at any particular level of nitrogen fertiliser regime in the field crops.     

Distribution and regulation of urea in lakes of central North America

1. Urea accounts for ～50% of global nitrogen (N)‐based fertiliser; however, little is known of the factors regulating its distribution and abundance in freshwaters. Improved understanding of urea biogeochemistry is essential because its use as fertiliser is expected to double by 2050 and because pollution with urea can promote outbreaks of toxic cyanobacteria in phosphorus (P)‐rich lakes in regions with intensive agricultural or urban development. 2. Biweekly measurements of urea concentration and diverse limnological variables (water chemistry, hydrology, algae, zooplankton) were taken during two summers (2008, 2009) in a chain of seven productive lakes within a 52 000‐km² catchment in central Canada to quantify environmental and anthropogenic correlates of temporal and spatial patterns of urea occurrence. 3. Mean (±SD) urea concentrations varied between 29 ± 14 and 132 ± 65 μg N L^?1, generally increased from headwater to downstream sites and represented 10–50% of bioavailable N (as sum of , and urea). Principal components analysis demonstrated that urea concentrations were elevated in agriculturally impacted lakes with abundant dissolved organic and inorganic nutrients (N, P, C) and low O₂ concentrations, but were not correlated consistently with plankton abundance or community composition. Urea concentrations were more than twofold greater in lakes receiving N from cities than in agriculturally affected basins, despite low summer concentrations of urea in tertiary‐treated urban effluent (c. 50% of lake values). Multiple regression models evaluated using Akaike Information Criterion showed that mean water‐column O₂ concentration was the single best predictor of in situ urea concentrations (r² = 0.91, P = 0.002), but that urea concentrations were also correlated significantly with changes in longitudinal position and Secchi depth and with concentrations of , non‐urea dissolved organic N (DON) and dissolved inorganic carbon. 4. Additional seasonal surveys of up to 69 closed‐basin lakes within a 100 000‐km² region during 2004 and 2008 revealed that urea was abundant in 100% of measured sites and exhibited concentrations (81 ± 48 μg N L^?1) similar to those observed in lakes with surface drainage (58 ± 38 μg N L^?1). Further, non‐urea DON accounted for 50–99% of the total dissolved N pool in both open‐ and closed‐basin lakes. 5. When combined with an extensive literature review and previous mass‐budget analyses of the study lakes, these findings allowed the development of a first‐generation model of the mechanisms regulating urea content of P‐rich lakes of central North America. In this model, water‐column concentrations of urea are predicted to be regulated mainly by algal decomposition in anoxic environments (sediments, hypolimnion), followed by redistribution into surface waters. Consequently, anthropogenic activities can increase the urea content of lakes by stimulating primary production, sedimentation and deepwater anoxia and by increasing influx of undegraded urea from agricultural and urban sources.