High Nutrient Demand Research Articles

Optimizing simulated fertilizer additions using a genetic algorithm with a nutrient uptake model

Intensive management of pine plantations in the southeastern coastal plain typically involves weed and pest control, and the addition of fertilizer to meet the high nutrient demand of rapidly growing pines. In this study we coupled a mechanistic nutrient uptake model (SSAND, soil supply and nutrient demand) with a genetic algorithm (GA) in order to estimate the minimum addition of phosphorus necessary to meet the initial four-year demand. Optimal P additions were estimated using two pine root length density inputs scenarios, a mycorrhizal scenario, and a grass competition scenario. The low root length scenario required 32.5–35.0 kg P ha −1 (depending on the fitness criteria) to best match the four-year loblolly pine P demand. With higher root length density, only 14.5 kg P ha −1 was required to meet demand. Adding a large fungal length density of mycorrhizae changed the simulated P uptake kinetics so that two separate fertilization amendments were optimal, although the total P added was similar to the higher root scenario. GA fitness functions were adjusted to eliminate SSAND uptake underestimates smaller than loblolly P demand, at the cost of an additional 9 kg ha −1 (higher root scenario) or 1–2 kg ha −1 (mycorrhizal scenario). Optimal GA estimates for P addition with grass competition were 1.5–3 kg ha −1 higher, with a sharp fitness peak associated with decline of grass in the first growing season.

Seasonal fluctuations in nutrients and carbohydrates in pecan leaves and stems

SummaryAn integrated study of changes in carbohydrates and nutrients in pecan was conducted and related to developmental changes during a growing season. Perennial woody plants exhibit marked seasonal changes in nutrient content, carbohydrate metabolism, and organ development. Information on nutrient changes may provide insight into seasonal demands and requirements and be useful in developing fertilisation regimes for this crop. Leaf and stem tissues collected at full bloom, leaf maturation, full cotyledon expansion, fruit maturation, and leaf abscission were analysed for starch, specific soluble sugars, and 11 other macro- and micro- nutrients. During leaf expansion, foliar levels of fructose and glucose declined from 12 mg g–1 DW to 5 mg g–1 DW and from 7 mg g–1 DW to 3 mg g–1 DW, respectively. After fruit maturation, stems exhibited an increase in sucrose, from 15 mg g–1 DW to 37 mg g–1 DW, and a marked decrease in starch, from 59 mg g–1 DW to 8 mg g–1 DW. Seasonal variations in elemental content indicated developmental stage-related nutrient movement. During leaf development, all nutrients accumulated in leaves, with more than a 70% increase in N, K, Ca, Mg, S, B and Fe content. During fruit development, the foliar content of many nutrients decreased, suggesting fruit are a strong sink for essential elements, as well as carbohydrates. However, nutrient changes differed with the stage of fruit development. For example, foliar concentrations of Mg and Zn decreased by 23% and 24%, respectively during cotyledon formation; while P, K, S, B, Cu and Mn levels decreased during reserve accumulation by 4, 15, 7, 12, 8 and 10%, respectively. During the period leading-up to leaf abscission, leaf nutrient resorption was observed with decreased contents of N (6%), P (14%), K (7%), Ca (7%), Mg (10%) and S (3%). Pecan leaf expansion and fruit development are critical periods, when nutrient movement can be appreciable. Maintaining adequate fertility levels during developmental periods of high nutrient demand may be important to optimise tree function. Management practices that promote late-season leaf retention would prevent nutrient losses associated with premature defoliation.

Simulation of soil drying induced phosphorus deficiency and phosphorus mobilization as determinants of maize growth near tree lines on a Ferralsol

Understanding the effect trees have on the growth of crops requires an understanding of the multiple interacting processes that determine resource uptake by the crops. On a Ferralsol in sub-humid western Kenya maize ( Zea mays L.) growth was primarily limited by phosphorus availability. We observed that maize growth near grevillea ( Grevillea robusta A. Cunn.) tree lines was strongly reduced, while maize growth was slightly increased near cassia ( Cassia spectabilis DC (syn. Senna spectabilis, DC, H.S. Irwin and R.C. Barneby). This was contrary to expectations because grevillea has a relatively low nutrient demand while Cassia has a relatively high nutrient demand. We compared maize growth in an experiment with simulations using the mechanistic tree–crop interaction model WaNuLCAS. The model simulations showed that the measured 30–40% decrease in maize growth near the Grevillea tree line was due to 0.025 m 3 m −3 lower soil water contents (at mean levels of 0.35 m 3 m −3 and high pF). This was not due to direct water limitation. The lower soil water content caused decreased P diffusion to roots and a cumulative decrease in crop root-growth and a concomitant decrease in crop growth over time. Measured maize yield near Cassia was 115%, unaffected by trees. Model simulations predicted it should be reduced to 80% due to direct competition for P between tree and crop. This suggests that rhizosphere modifications measured near Cassia roots probably supplied P to the tree itself and also to the maize crop. On P-limiting tropical soils, it is important to prevent soil drying to avoid soil drying induced P deficiency. In these conditions tree species that are able to mobilize P can prevent competition with the crop and may even increase crop performance.

Irrigation Levels Affect Plant Growth and Fruit Yield of Drip-Irrigated Bell Pepper

Bell pepper (Capsicum annum L.) plants have a high demand for water and nutrients and are sensitive to water stress during the establishment period and fruit setting. High levels of irrigation are often applied in order to maximize yields. However, field observations suggest that excessive irrigations may negatively affect bell pepper plants. The objective was to evaluate the effects of irrigation rate on plant growth and fruit yield. The trial was conducted in Spring 2003 at the Coastal Plain Experiment Station, Tifton, Ga. Drip-irrigated bell pepper (`Stiletto') plants were grown on black plastic mulch in 1-m wide beds (1.8-m centers). Plants were irrigated with an amount of water that ranged from 33% to 167% the rate of evapotranspiration (ET), adjusted by crop stage of development. Soil moisture content (% by volume) over the season was continuously monitored with time domain reflectometry sensors connected to a datalogger. The results showed that the average soil moisture content for the season increased with increasing rates of irrigation. Vegetative top fresh wt. and marketable fruit yield were reduced at both, low (33% ET) and high (166% ET) rates of water application. However, irrigation rate had a stronger effect on fruit yield than on top fresh wt. Plants supplied with high irrigation rates appeared to be more chlorotic compared to plants irrigated at medium rates (100% ET). There was a tendency for higher incidences of soil borne diseases (Pythium sp., Phytophtora capsici) in plants receiving higher rates of irrigation. The conclusion is high irrigation rates (>166% ET) are not recommended since they waste water and may result in both, higher incidences of soil-borne diseases and reduced bell pepper yields.

Forest regrowth as the controlling factor of soil nutrient availability 75 years after fire in a deciduous forest of Southern Quebec

The effects of secondary succession on soil nutrient availability following fire in the 1920s was investigated in a hardwood forest of southern Quebec by correlation analyses between soil and solution chemistry, tree species composition, tree growth, litterfall nutrient fluxes and presence of charcoal monitored in six 300 m 2 plots between 1994 and 1998. The results suggests that the pioneer stand of largetooth aspen, paper birch and yellow birch that followed fire enriched the forest floor and upper mineral soil with its K-rich litter, but lowered solution NH4, NO3 and Mg concentrations through its high nutrient demand. High woody biomass primarily observed in the maple-dominated stands was associated with low exchangeable base cation concentrations in the forest floor, suggesting that nutrient immobilisation in trees is also a significant process leading to spatial variation in base cation availability in the forest floor. Finally, charcoal was positively correlated with exchangeable base cations in the forest floor which leads to believe that charcoal has a high affinity for base cations and that it can increase base cation availability decades after forest fire disturbance.

Silvicultural effects on the productivity and wood quality of eucalypt plantations

The productivity of most forest plantations is less than their physiological potential as defined by the prevailing climate, because the supply or capture of light, water and nutrients is less than optimal. However, maximum growth does not equate to maximum wood value. The silvicultural challenge is to design and use management regimes that achieve target growth rates and wood quality by manipulating resource supply, capture or use. It has been and remains possible to identify and ameliorate factors limiting growth, sometimes on a large scale, e.g. by soil cultivation, residue management, fertiliser, weed control, irrigation, coppice management, thinning and pruning. This review examines some of these silvicultural practices for eucalypt plantations. During the past two decades, an increase in research on silvicultural practices in relation to soil and plant processes has improved our understanding of their effects on tree growth and wood quality, and on non-wood values including the potential for adverse on- or off-site effects. Eucalypt silviculture usually targets high growth rates and short rotations. High growth rates, and to some extent low nutrient-use efficiencies of eucalypts, lead to high nutrient demand and a high potential for nutrient depletion if management does not facilitate nutrient conservation. A detailed examination of nutrient management is presented. We indicate how silvicultural information is incorporated into current empirical- and process-based systems of productivity prediction, and identify potential improvements to these models. Silvicultural options are included adequately in some empirical models, and some process-based productivity models adequately cater for pruning and thinning, but process-based predictions of other silvicultural options, e.g. cultivation, slash retention, fertiliser, weed control and pest management, remain in their infancy.

O consumo alimentar de gestantes adolescentes no Município do Rio de Janeiro

The increase in teenage pregnancy has been viewed with concern by public health experts. Food consumption to help maintain high nutrient demands has been identified as one of the most relevant components. This study aims to present the habitual consumption of food and energy-specific nutrients by pregnant adolescents. A total of 1,180 adolescent mothers were interviewed in maternity hospitals in the City of Rio de Janeiro, and a simplified questionnaire on semi-quantitative frequency of food consumption was applied. Lower consumption of fruit juice, vegetables, and fruits was observed among adolescent mothers over 15. Adolescent mothers classified in the lowest quartile of consumption lack the minimum recommended consumption of energy and nutrients. An inverse association was found between the number of household members and energy and nutrient consumption. Adolescent mothers who received dietary information and changed their eating habits during pregnancy showed better results concerning the consumption of energy and nutrients. Prenatal care was a key factor for improving the results of pregnancy, emphasizing the importance of providing dietary information.

Yield potential of chive: Effects of cultivar, plastic mulch and fertilisation

Chive is a perennial herb, growing also natural in Finland. Commercial production of the herb is very small in our country, but large amounts of chive are imported. This fact has aroused interest in investigating the opportunities of producing chive using modern cultivation techniques. Effects of cultivar, plastic mulch as ground cover and fertilisation on yield were studied in field experiments over three years. In the experiments, the most productive cultivars or populations (a Finnish population “Hankoniemi”, a Dutch population “Tavallinen” and a German cultivar ‘Grolau’) produced 10–20% higher yields than the less productive cultivars. There were no clear differences in the yield quality between the cultivars. Black plastic mulch was effective in increasing yield, controlling weeds and maintaining soil moisture. For fertilisation, the experiments revealed the high nutrient demand of chive. After the basic soil fertilisation, weekly fertigation with a NPK fertiliser at a higher nitrogen dose (10-15 kg ha -1 N per week) resulted in higher biomass production than fertigation with nitrogen alone and/or a half nitrogen dose. In the years following the planting, the annual uptakes in yield were 185-200 kg ha -1 for nitrogen, 17-20 kg ha -1 for phosphorus, and 120-140 kg ha -1 for potassium in the most intensively fertilised treatment producing the highest yield. The results show that chive is feasible for commercial production with modern cultivation techniques.;

Growth and Macronutrient Accumulation of Chasmanthium latifolium (Michx.) Yates and Hakonechloa macra Makino 'Aureola' in Response to Temperature

Optimum growing temperatures were determined for Hakonechloa macra Makino 'Aureola' and Chasmanthium latifolium (Michx.) Yates, two shade-tolerant ornamental grasses found naturally in regions differing in temperature conditions. Plants were grown in four growth chambers at average daily temperatures of 13, 19, 25, and 31 °C for 12 weeks. After the treatment period, plants were destructively harvested to quantify growth and shoot tissue concentrations of N, P, K, Ca, and Mg. Optimal growth occurred at an average daily temperature of 25 °C for both grasses, but Hakonechloa was better able to tolerate lower temperatures. Hakonechloa died at 31 °C, while Chasmanthium growth was only slightly reduced at this temperature. Nutrient concentrations in shoot tissue for both species increased with increasing temperatures up to the temperature supporting optimal growth. At 13 and 19 °C, the concentrations of most nutrients were higher for Hakonechloa than for Chasmanthium, possibly reflecting the greater growth (higher nutrient demand) of Hakonechloa at lower temperatures. When compared on a per plant basis at each grasses' optimum temperature for growth, Chasmanthium has a much greater demand for nutrients than Hakonechloa, reflecting the greater growth potential of Chasmanthium.

Arbuscular mycorrhizal colonization and growth of wild and cultivated lettuce in response to nitrogen and phosphorus

Lettuce ( Lactuca sativa) is a crop with high water and nutrient demand. Its nearest wild relative, Lactuca serriola, is tolerant of low moisture and nutrient-poor conditions. Due to selection in different types of environments, the two taxa may differ in response to mycorrhizal colonization. Pot experiments were used to determine if mycorrhizal colonization, growth, root allocation, and P and N tissue concentrations differed between the two Lactuca taxa when inoculated with Glomus intraradices. In Experiment 1, two levels of P [0 (P0) or 0.25 (P1) mmol P kg −1] were added to a sand/soil medium with and without G. intraradices at low N supply (0.89 mmol N kg −1) for 4 weeks. In Experiment 2, two levels of N [1.7 (N1) or 5.0 (N2) mmol N kg −1] were supplied to the same soils containing 0.25 (P1) mmol P kg −1, and plants were grown for 6 weeks. In Experiment 1, the two taxa had similar mycorrhizal colonization, and shoot and root dry weight. In Experiment 2, cultivated lettuce had slightly higher colonization and growth than wild lettuce. Mycorrhizal plants at N1 were small with high root allocation and colonization. Colonization decreased and growth increased at N2. In these experiments, no major difference in mycorrhizal response occurred between L. sativa and L. serriola. Use of wild lettuce for breeding improved cultivars of lettuce, will at least maintain any ability, to benefit from mycorrhizas, especially in farming systems with low P inputs.

Respostas de crescimento da pupunheira à adubação NPK

As palmeiras apresentam grande demanda por nutrientes. Por este motivo, o efeito da adubação NPK no crescimento de pupunheiras (Bactris gasipaes Kunth) foi estudado durante 30 meses (11/90 a 04/93) em experimento conduzido a campo em solo Aluvial álico (corrigido por meio de calagem) em Ubatuba, SP (clima "Cfa"). Utilizou-se o delineamento de blocos ao acaso, com uma repetição, em esquema fatorial fracionado (½ de 4³), com tratamentos dispostos em dois blocos, parcelas úteis de 24 plantas e bordaduras duplas ao redor. Foram testadas quatro doses de nitrogênio (0, 100, 200 e 400 kg ha-1 ano-1 de N), fósforo (0, 50, 100 e 200 kg ha-1 ano-1 de P2O5) e potássio (0, 50, 100 e 200 kg ha-1 ano-1 de K2O), aplicadas em faixa e divididas em cinco aplicações anuais, utilizando como fontes nitrocálcio, superfosfato triplo e cloreto de potássio. As plantas foram cultivadas no espaçamento de 2 × 1 m, e avaliadas periodicamente quanto ao diâmetro da haste principal, número de perfilhos e porcentagem de plantas perfilhadas. Em solo arenoso e de baixa fertilidade, a pupunheira apresenta resposta linear, positiva e significativa de crescimento às adubações com nitrogênio (N) e potássio (K) e ausência de resposta ao fósforo (P). As primeiras respostas significativas ocorreram três meses depois de iniciadas as adubações diferenciadas. Não houve interações significativas entre N, P e K. O crescimento máximo foi obtido com doses anuais de 400 kg de N, 0 kg de P2O5 e 200 kg de K2O por hectare.

Differences in the behaviour of high and low yielding dairy cows selected by genetic merit

The effects of high milk yields on the behaviour and welfare of the dairy cow are unclear. A high milk yield increases the need to consume sufficient fodder in an attempt to meet high nutrient demands. The failure to meet the demands may result in persistent hunger in the dairy cow having to modify her behaviour by employing various coping strategies. These modifications may help the cow overcome a state of hunger but at the expense of being unable to express other important behaviours. The objective of this study was therefore to determine whether the behaviour and welfare of the genetically high yielding dairy cow is being compromised by the increased nutritional demands of milk production, and to investigate the possibility that an increased amount of time spent in food-directed behaviours may have a detrimental effect on the time available to perform other important behaviours.

Effect of seeding osteoprogenitor cells as dense clusters on cell growth and differentiation.

One approach for forming tissue equivalents involves seeding of cells into porous scaffolds followed by culture in vitro. Within this paradigm, the strategy by which cells are initially seeded may dictate the ultimate properties of the tissue equivalent. In particular, low cell densities may suffer from poor intercellular communication, whereas high densities may result in an unfavorable microenvironment due to transport limitations. A third alternative is to seed cells as dense clusters, which might benefit from intercellular contact without the high nutrient demand. To test this approach, planar substrates were seeded with 10(4) osteoprogenitor marrow stromal cells either as a diffuse subconfluent dispersion (2.6 x 10(3) cells/cm(2)) or as a single dense cluster (8 x 10(4) cells/cm(2)). In this study, the densely clustered cells demonstrated significantly diminished cell growth and collagen synthesis. However, a significantly higher level of alkaline phosphatase activity--a measure of bone-forming potential--and moderately more mineralization were observed with these dense cultures. These findings show that clustering can enhance the differentiation phase while diminishing the proliferating phase of these diploid cells without requiring large cell numbers. Thus, this seeding strategy may improve the quality of engineered tissues.

Simultaneous, bidirectional translocation of 32P and 33P between wood blocks connected by mycelial cords of Hypholoma fasciculare

Summary Translocation of nutrients through fungal mycelia has mainly been viewed in terms of unidirectional movement from sources to sinks. This paper describes an experiment designed to test the possibility of bidirectional phosphorus transport in mycelial cords of the white rot fungus Hypholoma fasciculare growing in soil microcosms. A novel technique is described that uses the different energy spectra of the radioactive phosphorus isotopes 32 P and 33 P, in combination with nondestructive electronic autoradiography, to monitor the distribution of the two isotopes within single mycelial cord systems. The tracer isotopes were applied to pairs of wood blocks connected by mycelial cords, and isotope translocations were monitored during a 29‐d period. Significant amounts of phosphorus were transported in both directions simultaneously between the two colonized wood blocks. Simultaneous, bidirectional translocation of phosphorus occurs in mycelial cords of H. fasciculare . Such circulation of nutrients in fungal mycelia should equalize differences in nutrient concentrations in different parts of the mycelia, enabling net translocation of nutrients from areas of high nutrient availability to those of high nutrient demand.

Nitrate uptake ability by maize roots during and after drought stress

The effects of different intensities and durations of soil drought and re-watering on the nitrate uptake ability of maize roots were studied. Plants were grown in split-root containers with one part of the root system subjected to different intensities and durations of soil drought and re-watering while the other part of the root system was continuously watered to 23% (w/w) soil water content (70% water capacity). Experiments were performed in split-root containers to maintain a high growth rate, thus ensuring high nutrient demand of the shoot irrespective of the soil water regime. To avoid limitation of nitrate uptake by transport processes in the dry soil, and to ensure a uniform 14N/15N ratio at the root surface, 15N was applied to the roots by placing them into an aerated nutrient solution with 0.5 mM Ca(15NO3)2. Shoot elongation and biomass were only slightly affected by drought in one root compartment when the soil in the other root compartment was kept wet. Therefore, the growth-related nutrient demand of the shoot remained at a high level. At moderate levels of soil drought (10% w/w water content) the ability of the roots for N-uptake was not affected even after 10 d of drought. N-uptake ability was reduced to about 20% of the well-watered control only when the soil water content was decreased to 5%. Total soluble sugar content of the roots increased with increasing soil drought, indicating that low N-uptake ability of roots subjected to severe soil drought was not caused by low assimilate supply from the shoot. Nitrate uptake ability of roots maintained in very dry soil (5% soil water content w/w) even for a prolonged period of 8 d, recovered within 3 d following re-watering. Root growth increased one day after re-watering. A short-term experiment with excised roots formerly subjected to severe soil drought showed that nitrate uptake ability recovered in old and young root segments after 2 d of re-watering. Obviously, the increase in N-uptake ability after re-watering was caused not only by new root growth but also by recovery of the uptake ability of formerly stressed roots.

Evolution of nutritional support in acute pancreatitis.

Acute pancreatitis is a catabolic illness and patients with the severe form have high metabolic and nutrient demands. Artificial nutritional support should therefore be a logical component of treatment. This review examines the evidence in favour of initiating nutritional support in these patients and the effects of such support on the course of the disease. Medline and Science Citation Index searches were performed to locate English language publications on nutritional support in acute pancreatitis in the 25 years preceding December 1999. Manual cross-referencing was also carried out. Letters, editorials, older review articles and most case reports were excluded. There is no evidence that nutritional support in acute pancreatitis affects the underlying disease process, but it may prevent the associated undernutrition and starvation, supporting the patient while the disease continues and until normal and sufficient eating can be resumed. The safety and feasibility of enteral nutrition in acute pancreatitis have been established; enteral nutrition may even be superior to parenteral nutrition. Some patients, however, cannot tolerate enteral feeding and this route may not be practical in others. Parenteral nutrition still has a role, either on its own or in combination with the oral and enteral routes, depending on the stage of the illness and the clinical situation.

Impact of Agrobacterium tumefaciens-induced stem tumors on NO 3 − uptake in Ricinus communis

Developing tumors induced by Agrobacterium tumefaciens, strain C58, on stems of Ricinus communis L. var. gibsonii cv. Carmencita were shown to be strong metabolic sinks for sucrose and amino acids, thus causing higher nutrient demand in the host plant. However, NO 3 − uptake and, to a lesser extent, also H2PO 4 − uptake were strongly inhibited. Correspondingly, NO 3 − concentration was lower in tumorised than in the control plants. NO 3 − reductase activity was the same in both plant types, but it was completely suppressed in the tumors. The electrical membrane potential difference of root cells was unaffected in tumorised plants when soil-grown, but significantly lowered when grown hydroponically. Consistent with the low NO 3 − uptake rate, NO 3 − -dependent membrane depolarisation at the onset of NO 3 − /2H+-cotransport was nearly zero. In the phloem sap, sucrose and amino acid concentrations were considerably lower in tumorised than in control plants, and lower below than above the tumor. The qualitative pattern of amino acids of the phloem sap of stems was almost the same in tumorised and control plants. It is concluded that neither the overall amino acid concentration nor special amino acids nor ammonium in the transport phloem suppress NO 3 − uptake in the roots. Aminocyclopropane-carboxylate, the precursor of ethylene, which is produced in the tumors in high amounts, was low in the stems and the same in both plant types. Thus, ACC and ethylene were ruled out as directly interfering with nutrient uptake in the roots. Root morphology was strongly affected during tumor development. Root fresh weight decreased to 50% of the controls and lateral root development was almost completely prevented. This suggests that the high tumor ethylene production, together with an increasing concentration of phenolic compounds, severely inhibits the basipetal auxin flow to the roots. Auxin accumulation and retention was confirmed by specifically enhanced expression of the auxin-responsive promoter of the soybean gene GH3:GUS in tumors induced in transgenic Trifolium repens L. Hence, root development is poorer and anion uptake inhibited in tumorised plants. This may be aggravated by abscisic acid accumulation in the tumor and its basipetal export into the roots. Moreover, sucrose depletion of the sieve tubes leads to energy shortage at the root level for maintaining energy-dependent anion uptake.

The role of nutrients in decomposition of a thecate dinoflagellate

The decomposition of freeze‐dried whole cells and empty thecae of the dinoflagellate Peridinium gatunense Nygaard originating from dense blooms in Lake Kinneret (Israel) was followed experimentally under controlled conditions in the lab. The two materials (whole cells; empty thecae) were suspended in replicate bottles containing nutrient‐poor epilimnetic water from the lake. After 7 d, nutrients (N, P, and trace metals) were added to half the bottles. We followed the changes with time in dry weight, the dynamics of nutrients, microbial abundances and a range of microbial activities including leucine incorporation rates and activities of hydrolytic enzymes. Because of the low N and P content of thecae (C:N:P atomic ratios >3000:19:1) relative to protoplasts (276:51:1), the microbial utilization of thecae was expected to depend much more on the availability of external nutrient sources than the utilization of protoplasts. Indeed, decomposition of thecae did not occur in the absence of external nutrients but was rapid (1–2 d to their disappearance) after nutrients were added. In contrast, almost no stimulating effect of nutrient addition was observed for the decomposition of whole cells. The results suggest that intensive regenerative nutrient cycling or external nutrient inputs are a necessary precondition for an efficient trophic transfer of the energy stored in blooms of thecate dinoflagellates. The high nutrient demands of microbial degradation imply furthermore a competition for nutrients between heterotrophic degradative and phototrophic productive processes. Because of the generally assumed stronger competitive ability of heterotrophic bacteria, reduced primary production is expected as an indirect result of dinoflagellate bloom degradation. Indeed, reduced primary production is observed in Lake Kinneret every summer after the decline of the annual Peridinium bloom in June–July.

Nutrient use patterns in woody perennials: implications for increasing fertilizer efficiency in field-grown and landscape ornamentals

Timing nutrient application to periods of high nutrient demand could increase nutrient use efficiency and reduce the potential for fertilizer leaching or runoff. However, current recommendations for field nursery and landscape ornamentals (extension publications) suggest fertilizing in late fall and early spring despite research with perennial fruit crops that demonstrates low uptake potential during those times. Research is needed to resolve this apparent conflict. Application rates for woody ornamentals, established in the 1960s and 1970s, also need reexamination in the light of environmental concerns.

Nutrients limiting microbial growth in a tropical forest soil of Ghana under different management

Respiration profiles were analysed following addition of a carbon source (glucose), nitrogen (NH 4NO 3), and phosphorus (H 2PO 4 −/HPO 4 2−) to three different soils from the tropical forest belt of West Africa. In all stands (virgin forest, rubber, and cocoa plantation) microbial growth was limited by C whereas N did not limit growth in either C- or C+P-amended soil. The P-limitation indicated in C- as well as C+N-amended incubations was significant for virgin and cocoa soil. In soil from the cocoa stand, microbial growth started earlier when P was added together with C as compared to C-addition alone. This difference in timing of microbial growth caused by P-addition not observed in the other stands suggests that the microbial community in the cocoa soil differed functionally from that in the other soils in accordance with the high nutrient demand of cocoa as compared to rubber trees. The study therefore provides direct evidence for the P-limitation often claimed in tropical soils as opposed to a N-limitation found in temperate soils.