Nutrient Release Rates Research Articles

Maize Residue Interaction with High Quality Organic Materials: Effects on Decomposition and Nutrient Release Dynamics

The application of organic materials with wide carbon-to-nitrogen (C-to-N) ratios is known to cause initial immobilization of nutrients, unless N fertilizers are applied. In Sub-Saharan Africa, regular application of mineral fertilizers with organic residues is seldom practiced due to several socioeconomic constraints. In the present study, we assessed the biomass qualities of Zea mays, Tithonia diversifolia and Vicia faba and evaluated whether delayed decomposition and nutrient release of low quality residues will improve when mixed with high quality residues. Our hypothesis was that high quality organic residues have high N supply capabilities to improve decomposition and nutrient release of low quality materials when mixed together. Compared with V. faba and T. diversifolia biomasses, Z. mays residue was found to be relatively poor in quality as a result of its relatively low N concentration (10.8 g/kg) and wider C-to-N ratio (37.2:1). The assessment on biomass quality was consistent with the results on decomposition. After one week, 42 % of Z. mays residues had decomposed compared with more than 90 % of T. diversifolia and V. faba residues. Further, the decomposition and N release rate of Z. mays tripled when mixed with either T. diversifolia or V. faba biomass. In this study, the initial N, C, lignin, C-to-N ratio, lignin-to-N ratio and (lignin + polyphenol)/N ratio of the residues were useful indicators of degradability and nutrient release based on significant (P < 0.005) correlations. The study found that mixing Z. mays residue with either T. diversifolia or V. faba green biomass improved the N composition and C-to-N ratio of the mixture, which accounted for the improved decomposition and nutrient release rates of Z. mays residues in the mixture compared with sole Z. mays treatment. Our study therefore suggested that in places where inorganic fertilizers are limited, T. diversifolia and V. faba residues could be viable sources of N for improved decomposition and nutrient release of low quality residues.

Macro‐ and micronutrient‐release characteristics of three polymer‐coated fertilizers: Theory and measurements

AbstractIn spite of several published studies we have an incomplete understanding of the ion‐release mechanisms and characteristics of polymer‐coated fertilizers (PCF). Here we extend current conceptual models describing release mechanisms and describe the critical effects of substrate moisture and temperature on macro‐ and micronutrient release of three PCF types: Polyon®, Nutricote®, and Osmocote®. Nutrient release was quantified at weekly intervals for up to 300 d from 5°C to 40°C in water and chemically inert sand, substrates that allowed release quantification without confounding effects of ion sorption/desorption. At least two release‐timeframe formulations of each PCF type were studied and all products had similar nutrient concentrations to allow isolation of the effect of coating technology. Contrary to several studies, our data and model indicate that there is no significant difference in nutrient‐release rates in water and a moist, solid substrate. This means that release rates determined in water can be used to model bio‐available nutrient concentrations in moist soil or soilless media where sorption/desorption properties alter concentrations after release. Across all PCF, the nutrients most affected by temperature were typically N, K, B, Cu, and Zn, while the least affected were P, Mg, and Fe. We also found consistent differences among the coating technologies. Osmocote fertilizers released faster than specified at both high and low temperatures. Nutricote had relatively steady release rates over time and a nonlinear response to temperature. Polyon released more slowly than specified but replicate samples were highly uniform.

Predicting sediment phosphorus release rates using landuse and water-quality data

We developed a series of models using landuse and water-quality variables to predict sediment P release rates under anoxic conditions in reservoirs. We collected sediment cores from 17 reservoirs in the Central Plains region of the USA, and we measured nutrient release rates under anoxic conditions in laboratory incubation studies. We used corresponding landuse and water-quality data from the reservoirs to develop regression models for predicting P release rates. We used variables that relate directly to trophic state, including % cropland in the watershed, which explained the greatest amount of variation in release rates. P release rates tended to be higher in reservoirs that had greater % cropland in the watersheds. We developed additional predictive models using surface total P concentrations and Secchi disk depths. Trophic state was also a good predictor of release rates because more P was released from hypereutrophic reservoirs than from mesotrophic or eutrophic reservoirs. The median release rates for reservoirs representing different trophic state classes (e.g., mesotrophic, eutrophic, and hypereutrophic) were very similar to those previously reported for natural lakes. Our models can be used to predict sediment release rates in individual reservoirs of concern or to screen a large number of reservoirs to help direct resources to those systems that are most vulnerable to internal loading. Models based on landuse characteristics are particularly valuable because these data can be obtained from computer-based assessments and do not require labor-intensive field sampling.

Produção, decomposição e ciclagem de nutrientes em resíduos de crotalária e milheto, cultivados solteiros e consorciados

O objetivo deste trabalho foi avaliar a produção de fitomassa e as taxas de decomposição e liberação de macronutrientes e de silício, nos resíduos vegetais de crotalária (Crotalaria juncea) e milheto (Pennisetum glaucum), em cultivo solteiro e consorciado. Utilizou-se o delineamento em blocos ao acaso, com quatro repetições, em arranjo fatorial constituído por três tipos de cobertura vegetal - milheto, crotalária e consórcio entre as espécies - e seis épocas de coleta - 0, 18, 32, 46, 74 e 91 dias após o manejo (DAM). O milheto apresenta maior produção de matéria seca e acumula mais N, P, K, Mg, S, C e Si, enquanto a crotalária acumula maior quantidade de Ca. A fitomassa do milheto apresenta as maiores taxas de decomposição e de liberação de nutrientes. Essas taxas são mais intensas entre 0 e 18 DAM. Com o transcorrer do tempo, as relações C/N, C/P e C/S aumentam e a relação C/Si, bem como a taxa de decomposição da fitomassa, diminui. O potássio é o nutriente de liberação mais rápida, e o silício apresenta a menor taxa de liberação.

Kinetics of nutrient release from different organic residues using a laboratory system

Organic residues play a vital role in maintaining soil fertility in arid and semi-arid regions. Knowledge of the nutrient release from organic residues will help in optimizing nutrient efficiency in agricultural crop production systems. This study was conducted to assess the continuous release of phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) from eight different organic residues (sheep manure, beet, waste material, rape, poultry manure, sunflower, potato and garlic) using successive extractions with distilled water. The residues were shaken for 1 h and equilibrated for longer intervals (1, 3.5, 18, 42, 72, 192, 768, 1248, 1608, 1968 and 2328 h) with successive extractions. Cumulative nutrient release curves by different organic residues versus time showed an initial rapid phase followed by a slow phase. The average percentage of nutrients released and the average release rate of nutrients found using a power model was different and were in the order K > P > Ca > Mg and Ca > Mg > P > K, respectively. According to MINTEQ software, the partitioning of total P between HPO4 2− and H2PO4 − is sensitive to the type of organic residue. On average (pooled over all extractions), between 13% (rape) to 40% (poultry) and 27% (poultry manure) to 79% (beet) of total P in aqueous solutions present as HPO4 2− and H2PO4 −, respectively. Among the various organic residues and in the first stage of release, sunflower residue, beet residue, poultry manure and garlic residue had the highest rate constant for Ca, Mg, P and K, respectively, indicating the high potential availability of these nutrients in the early stage of application to soils.

Mass Transfer Model for Coated Urea Particle in Controlling-Release Process

Based on mass conservation and Fick’s diffusion law, a model for describing the nutrient release from coated urea particles was proposed. This model was verified by the release data of three novel paraffin- rosin coated urea in distilled water. The results indicate that the model is effective in describing and predicting the delivery behaviors for a diffusion-controlled coated- urea and their correlation coefficients R2 are 0.9976, 0.9973 and 0.9984, respectively. The model shows that the nutrient release rate for coated urea is direct proportion to effective diffusion coefficient Deff, inverse proportion to diameter’s square of urea granule and inverse proportion to the coating thickness.

Calcium, Magnesium, Sodium, and Potassium Release during Decomposition of Some Organic Residues

The use of organic residues might be appropriate in maintaining long-term nutrient requirements of crops. We investigated under laboratory conditions the dynamics of calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and potassium (K+) release during decomposition of eight plant residues and two manures over 12 weeks of incubation at 25 ○C. During the processes of decomposition, these nutrients were extracted by 0.1 M sulfuric acid (H2SO4). The release rate of nutrients for residues was best estimated by the exponential model. There were differences in the rates at which release took place between residues and nutrients. In general, release patterns of nutrients with time for all residues were similar in shape, and two regions could be distinguished: a first one during the first 4 weeks of incubation, corresponding to faster release of nutrients, and a second for longer incubation times (weeks 5–12), when the release of nutrients was slower. A 71% loss of K+ was found after 1 week for vegetable waste and only 43% loss of Na+ for rape. Generally, based on release rate (% week–1), nutrient release from residues was in the order K+ (–0.363) > Na+ (–0.344) > Mg2+ (–0.327) > Ca2+ (–0.280). The release rate of nutrients was significantly correlated with their residue content. Our results suggest that the use of organic residues as a source for short- and long-term nutrients supply for crops should be encouraged. The quick release of K+ and Na+ may pose a high risk of K+ and Na+ losses in sandy soils with low cation exchange capacity.

Photodegradation for Nutrient Management in the Dry Tropics

Nutrient limitation in agriculture is a big problem in many tropical areas. Much research has focused on the optimal use of crop residues in agriculture. Recent work indicates that plant residue decomposition rates, including nutrient release rates can be increased by pre-exposure to sunlight. This has potential as a technology to manipulate nutrient release from residues to match crop demands. The possible development and use of this technology is discussed. There is some evidence that this could increase emissions of trace gases, but the increase is thought to be small. Research needs are discussed.

Produção e ciclagem de nutrientes por plantas de cobertura nas culturas de arroz de terras altas e de soja

As plantas de cobertura em sistema de plantio direto pode contribuir na formação de palhada e ciclagem de nutrientes para as culturas em sucessão. O objetivo deste trabalho foi avaliar a produção de matéria seca e ciclagem de nutrientes por plantas de cobertura semeadas em safrinha no desempenho do arroz de terras altas e da soja semeados em rotação, em sistemas plantio direto e preparo convencional, em Latossolo Vermelho do município de Rio Verde, Goiás. O estudo foi realizado no período de abril de 2008 a abril de 2010. Utilizou-se o delineamento em faixas com fatorial 2 x 5 com quatro repetições. Nas faixas horizontais foram testados os dois sistemas de manejo do solo (plantio direto e convencional) e nas faixas verticais, as plantas de cobertura. As avaliações de matéria seca, taxa de cobertura do solo e ciclagem de nutrientes foram realizadas apenas nos tratamentos plantio direto, em que as parcelas foram subdivididas em seis épocas de coletas de matéria seca após a dessecação das plantas de cobertura, o que ocorreu aos 0, 15, 30, 60, 90 e 120 dias a partir da dessecação de manejo das plantas de cobertura, perfazendo um fatorial 5 x 6. As plantas de cobertura, semeadas em safrinha, foram as seguintes: Brachiaria brizantha, B. ruziziensis, Pennisetum glaucum e B. ruziziensis + Cajanus cajan e o pousio. Avaliaram-se a produção de matéria seca, a taxa de cobertura do solo, o acúmulo e liberação de nutrientes pelas plantas de cobertura e a produtividade do arroz na safra 2008/09 e da soja na safra 2009/10, semeados em rotação. As espécies B. ruziziensis e B. ruziziensis + C. cajan destacaram-se na produção de matéria seca, taxa de cobertura do solo e acúmulo de nutrientes no final do período de entressafra. Os nutrientes com mais acúmulos nas matérias secas foram N e K, e as maiores taxas de liberação no solo foram observadas nos elementos K e P. As maiores produtividades de arroz sob plantio direto foram obtidas sobre palhadas de P. glaucum e B. ruziziensis, enquanto a cultura da soja não apresentou diferenças em sua produtividade nos tratamentos estudados.

Decomposição e liberação de nutrientes de coquetéis vegetais para utilização no Semiárido brasileiro

A decomposicao e liberacao de nutrientes de residuos vegetais podem assumir importante papel no manejo da fertilidade dos solos da regiao semiarida. Portanto, o presente estudo teve por objetivo avaliar a taxa de decomposicao da materia seca (MS) e liberacao de carbono (C) e nutrientes de coqueteis vegetais no Semiarido brasileiro. O experimento foi conduzido em casa de vegetacao, no periodo de novembro de 2007 a junho de 2008, com coqueteis vegetais compostos por especies de leguminosas (L) (calopogonio, Crotalaria juncea, Crotalaria spectabilis, feijao de porco, guandu, lab-lab) e nao leguminosas (NL) (gergelim, girassol, mamona, milheto e sorgo), combinados nos seguintes tratamentos: T1 - 100% NL; T2 - 100% L; T3 - 75% L e 25% NL; T 4 - 50% L e 50% NL; T5 - 25% L e 75% NL. As taxas de decomposicao da MS e liberacao dos nutrientes foram monitoradas por meio de coleta dos residuos, realizadas aos 8; 15; 30; 60; 90; 120; 150; 180 e 210 dias apos o inicio do experimento. Utilizou-se o delineamento experimental em blocos casualizados com tres repeticoes. Os coqueteis apresentaram taxas de decomposicao de MS e liberacao de nutrientes semelhantes, exceto para Ca, Cu e Mn, em que os coqueteis compostos com predominância de especies NL apresentaram liberacao mais rapida. A partir da media dos valores de k para todos os coqueteis estabeleceu-se a seguinte ordem de liberacao de macronutrientes: K > N > Ca > Mg > P e de micronutrientes: Fe > Mn > Cu > Zn > B.

Injection Molding Preparation and Film Formation Performance of Powders-Modified Polyethylene Biomass Carrier for Aerobic Process

A simple injection molding process was proposed for manufacturing polyethylene (PE) biofilm carrier composited with various powder additives including hydroxyapatite (HAP), starch, bagasse, activated carbon(AC) and magnetic powder(MP) as slow-released nutrients in wastewater biological treatment. The powders were also responsible for improving the hydrophilicity and biomass affinity of the carrier. Pre-attachment between powders and PE particle may achieve great improvement in flow ability of particle-powder mixture during injection molding process. The slow release rate of nutrients (mainly water-soluble starch) from the modified carrier to wastewater can be controlled by the amount of bagasse and activated carbon supplemented in the carrier. The contact angle of a water droplet on the polyethylene surface decreased from 80° to 59° after modification, and the period of biofilm formation on the modified carrier with acclimated sludge reduced from 7 days (on PE carrier without additives) to 4 days. The amount of attached biomass on the modified carrier was also found about twice as that on the common PE carrier. The strength performance test demonstrated the capability of long-term operation for the modified carrier in practical application.

Seasonal variability in nutrient regeneration by mussel Mytilus edulis rope culture in oligotrophic systems

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 431:137-149 (2011) - DOI: https://doi.org/10.3354/meps09095 Seasonal variability in nutrient regeneration by mussel Mytilus edulis rope culture in oligotrophic systems Henrice M. Jansen1,2,3,*, Øivind Strand1, Tore Strohmeier1, Cathinka Krogness1, Marc Verdegem3, Aad Smaal2,3 1Institute of Marine Research, Nordnesgaten 50, 5817 Bergen, Norway 2Wageningen IMARES–Institute for Marine Resources and Ecosystem Studies, Korringaweg 5, 4401 NT Yerseke, The Netherlands 3Department of Aquaculture and Fisheries, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands *Email: henrice.jansen@imr.no ABSTRACT: Blue mussel Mytilus edulis cultures contribute to nutrient cycling in coastal ecosystems. Mussel populations filter particulate nutrients from the water column and inorganic nutrients are regenerated by excretion of metabolic wastes and decomposition of (pseudo-)faeces. The objective of this study was to determine the intra-annual variability in nutrient regeneration by mussel rope cultures in oligotrophic fjord systems. In situ respiration and nutrient uptake and release rates of 1 m mussel ropes were measured using 250 l pelagic chambers. There was a 20-fold difference between winter and summer respiration and nutrient release rates. Inorganic nitrogen release ranged from 50 to 1000 µmol h–1 per meter rope. These variations were mainly related to mussel growth but were also related to changes in water temperature and biofouling biomass (organisms that colonized the mussel ropes). In total 24 genera of fouling organisms were observed, diversity increased over time (ranging from 2 to 12 genera m–1), and fouling biomass was mainly characterised by ascidians (max. 37 ± 14 g m–1). However, mussels dominated the culture ropes, representing >90% of total faunal biomass. The amount of organic material associated with the ropes was stable (6.9 ± 0.3 g m–1). At the scale of one mussel farm, nutrient regeneration by mussel rope cultures increased inorganic nitrogen concentrations by 20% and inorganic phosphorus concentrations by 5% during summer conditions. During winter, there was no significant effect of mussel cultures on the inorganic nutrient pools. Nutrient regeneration by mussel cultures also affected stoichiometry as nutrients were excreted in dissimilar proportions (nitrogen > phosphate > silicate). The increased nutrient availability may contribute to primary production, especially in nutrient-limited (oligotrophic) fjord ecosystems. However, fjord-scale effects are largely dependent on hydrographic conditions of the fjord system. KEY WORDS: Nutrient dynamics · Respiration · In situ · Suspended mussel culture · Biofouling · Pelagic chamber Full text in pdf format PreviousNextCite this article as: Jansen HM, Strand Ø, Strohmeier T, Krogness C, Verdegem M, Smaal A (2011) Seasonal variability in nutrient regeneration by mussel Mytilus edulis rope culture in oligotrophic systems. Mar Ecol Prog Ser 431:137-149. https://doi.org/10.3354/meps09095 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 431. Online publication date: June 09, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

UVB exposure does not accelerate rates of litter decomposition in a semi-arid riparian ecosystem

Abstract Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decomposition in a Tamarix -invaded riparian ecosystem during the establishment of an insect biological control agent in northern Nevada. Feeding by the northern tamarisk beetle ( Diorhabda carinulata ) on Tamarix spp. trees leads to altered leaf litter quality and increased exposure to solar UVB radiation from canopy opening. In addition, we examined the dynamics of litter decomposition of the invasive exotic Lepidium latifolium , because it is well-situated to invade beetle-infested Tamarix sites. Three leaf litter types (natural Tamarix , beetle-affected Tamarix , and L. latifolium ) differing in substrate quality were decomposed in litterbags for one year in the field. Litterbags were subjected to one of three treatments: (1) Ambient UVB or (2) Reduced UVB (where UVB was manipulated by using clear plastic films that transmit or block UVB), and (3) No Cover (a control used to test for the effect of using the plastic films, i.e. a cover effect). Results showed a large cover effect on rates of decomposition and nutrient release, and our findings suggested that frequent cycles of freeze–thaw, and possibly rainfall intensity, influenced decomposition at this site. Contrary to our expectations, greater UVB exposure did not result in faster rates of decomposition. Greater UVB exposure resulted in decreased rates of decomposition and P release for the lower quality litter and no change in rates of decomposition and nutrient release for the two higher quality litter types, possibly due to a negative effect of UVB on soil microbes. Among litter types, rates of decomposition and net release of N and P followed this ranking: L. latifolium > beetle-affected Tamarix > natural Tamarix . Altered nutrient dynamics with beetle introduction as well as the rapid decomposition rates exhibited by L. latifolium are consistent with vulnerability to secondary invasion. In this desert ecosystem, decomposition and nutrient release were strongly affected by litter type and much less so by UVB exposure.

Decomposition and nutrient release of leguminous plants in coffee agroforestry systems

Leguminous plants used as green manure are an important nutrient source for coffee plantations, especially for soils with low nutrient levels. Field experiments were conducted in the Zona da Mata of Minas Gerais State, Brazil to evaluate the decomposition and nutrient release rates of four leguminous species used as green manures (Arachis pintoi, Calopogonium mucunoides, Stizolobium aterrimum and Stylosanthes guianensis) in a coffee agroforestry system under two different climate conditions. The initial N contents in plant residues varied from 25.7 to 37.0 g kg-1 and P from 2.4 to 3.0 g kg-1. The lignin/N, lignin/polyphenol and (lignin+polyphenol)/N ratios were low in all residues studied. Mass loss rates were highest in the first 15 days, when 25 % of the residues were decomposed. From 15 to 30 days, the decomposition rate decreased on both farms. On the farm in Pedra Dourada (PD), the decomposition constant k increased in the order C. mucunoides &lt; S. aterrimum &lt; S. guianensis &lt; A. pintoi. On the farm in Araponga (ARA), there was no difference in the decomposition rate among leguminous plants. The N release rates varied from 0.0036 to 0.0096 d-1. Around 32 % of the total N content in the plant material was released in the first 15 days. In ARA, the N concentration in the S. aterrimum residues was always significantly higher than in the other residues. At the end of 360 days, the N released was 78 % in ARA and 89 % in PD of the initial content. Phosphorus was the most rapidly released nutrient (k values from 0.0165 to 0.0394 d-1). Residue decomposition and nutrient release did not correlate with initial residue chemistry and biochemistry, but differences in climatic conditions between the two study sites modified the decomposition rate constants.

A Rapid Technique for Prediction of Nutrient Release from Polymer Coated Controlled Release Fertilizers

Controlled release fertilizers (CRF) are produced with different rates and durations of nutrient release to cater to different crops with wide ranges of nutrient requirements. A rapid technique is needed to verify the label specifications of nutrient release rate and duration. Polymer-coated urea (PCU) (43% nitrogen [N]) and polymer-coated N, phosphorus (P), potassium (K) (PC_NPK; 14-14-14) fertilizer products were used in this study. Soil incubation of the above CRF products at 25℃ showed that 63.6% to 70.8% of total N was released over 220 days (d). At 100℃ in water 100% of N release occurred in about 168 to 216 hours (h). Regression equations were developed for cumulative nutrient release as a function of release time separately at 25℃ and 100℃. Using the above regressions, the release duration for a given percent nutrient release at each temperature was calculated. These values were then used to establish a relationship between the release duration at 25℃ as a function of that at 100℃. This relationship is useful to predict the release duration at 25℃ of an unknown CRF product by conducting a rapid release test in water at 100℃. This study demonstrated that a rapid nutrient release test at 100℃ successfully predicted nutrient release rate and duration at 25℃, for polymer coated fertilizers. Therefore, this rapid test can be used to verify the label release rate and duration of most CRF products.

Decomposition and nutrient release patterns of the leaf biomass of the wild sunflower (Tithonia diversifolia): a comparative study with four leguminous agroforestry species

The selection and use of appropriate plant materials to maintain a sufficiently high nutrient supply to meet crop needs remains a major challenge of nutrient management under low input systems. Therefore, research on plant biomass quality as it relates to decomposition and nutrient release has become imperative. This research was conducted at the Agroforestry Research Station of the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana to determine the decomposition and nutrient release patterns of Tithonia diversifolia, a rarely used non-traditional species but of research interest in soil fertility improvement practices in Ghana. The decomposition and nutrient release patterns of T. diversifolia was compared with Sennaspectabilis, Gliricidia sepium, Leucaena leucocephala and Acacia auriculiformis which are commonly used in biomass transfer systems. Results of the study confirmed significantly high N, P, K concentrations in T. diversifolia comparable to levels recorded for the four leguminous species. In addition, T. diversifolia recorded the highest percent decomposition and nutrient release rates which differed significantly (P < 0.05) from rates of the four leguminous species. It was apparent from the study that decomposition and nutrient release rates of species are related to quality of leaf material. Phosphorus and Mg concentration in particular were most influential in decomposition and nutrient release based on significant results. For this reason, it would be imperative to consider the concentrations of P and Mg among other factors in selecting high quality plant materials for green manuring.

Macro-invertebrates accelerate litter decomposition and nutrient release in a Hawaiian rainforest

Macro-invertebrates (>2 mm in size) can play a key role in litter decomposition by influencing litter chemistry and other components of the decomposer community, thus affecting rates of decomposition, nutrient release, and primary production. However, in many ecosystems the influences of macro-invertebrates on key ecosystem processes have not been adequately addressed. We investigated the influence of the macro-invertebrate community in litter decomposition and the cycling of nutrients in a young rainforest site on the island of Hawaii by using litter bags with and without 2.5 cm holes to allow or prevent access by macro-invertebrates. Presence of macro-invertebrates increased rates of litter decomposition by 16.9% and rates of nutrient release for N and Mn by 33.2% and 30.3%, respectively. Macro-invertebrate activity thus has a major impact on N release accounting for 3.32 kg/ha/yr. This internal ecosystem transfer of N from the litter is greater than estimates of nitrogen inputs from rain water, dry deposition, volcanic sources, atmospheric dust, and nitrogen fixation for this ecosystem. These findings demonstrate that improved knowledge of the ecosystem effects of macro-invertebrates is necessary to understand how ecosystems function.

Carbon and Nitrogen Mineralization and Persistence of Organic Residues under Conservation and Conventional Tillage

A combination of high biomass cover crops with organic mulches may be an option for no‐till vegetable production, but information on mineralization rates from these residues is lacking. The objective of this study was to assess nutrient release rates and persistence from mimosa (Albizia julibrissin Durazz.), lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don], oat (Avena sativa L.) straw, and soybean [Glycine max (L.) Merr.] residues under conventional and conservation tillage. The experiment was conducted in Tallassee, AL using litterbag methodology in a split‐plot design (main plots: two tillage systems; subplots: four residue types). Comparison of rate constants showed that labile portions of residues was more affected by tillage than recalcitrant portions. In spring, mimosa residue contained 78 kg N ha−1 when buried the previous fall, compared to 123 kg N ha−1 when surface placed; soybean residue showed similar results (39 vs. 72 kg N ha−1, respectively). Results were similar for lespedeza (72 vs. 101 kg N ha−1, respectively), but not for oat straw (24 vs. 26 kg N ha−1, respectively). After 1 yr, surface placed mimosa residue mineralized 33% of initial N compared to 71% when buried, while surface placed lespedeza mineralized 36% of initial N compared to 64% when buried. Soybean residue mineralized N quickly regardless of placement (73 vs. 87%, respectively). This study demonstrates that cut‐and‐carry mulches may be used under conservation tillage for the enhancement of soil organic matter (SOM), soil organic carbon (SOC), and soil N status.

Long-term changes in lake sediments and their infl uences on lake water quality in Japanese shallow lakes

In order to elucidate the nutrient dynamics in lakes with special reference to sediments, the changes in vertical distributions of sediment nutrients over 20 years were analyzed with the aid of sediment dating at the centers of two shallow, eutrophic lakes in Japan, i.e. Lakes Kasumigaura and Suwa. Peaks of 137 Cs and apparent density gave estimated sedimentation rates of around 1 and 2 kg m -2 y -1 in Lakes Kasumigaura and Suwa, respectively. Slight decreases of TP and TN contents (0.07 and 0.63 mg g -1 for TP and TN, respectively, in Lake Kasumigaura and 0.90 mg g -1 for TN in Lake Suwa) were observed by comparison between the cores obtained around 1980 and those of recent years except for a considerable decrease in TP in Lake Suwa (1.0 mg g -1 ). This decrease probably came from the higher percentage of easily releasable phosphorus in the past sediments of Lake Suwa. Using the TP and TN increases in lake waters during summer, the averaged nutrient release rates were estimated to be within the ranges of those observed by laboratory core experiments and by measuring the vertical profiles of interstitial concentrations except for a smaller estimation of TN in Lake Kasumigaura. On the other hand, the nutrient release rates were also determined using the long-term changes in sediment nutrient contents. The estimated rates were a little lower than the rates determined by the method using the increase in lake nutrient concentrations other than the higher ones for TP in Lake Suwa, which were originally based on the higher percentage of easily releasable phosphorus as mentioned above. Net sedimentation rates for 24 years in Lake Kasumigaura and those for 26 years in Lake Suwa calculated as the sum of new sedimentation and changes in old sediments during these periods were compared with the net input loads based on the per capita/exporting method. In the case ofTP, we observed a fairly good agreement because of its conservation, whereas the residuals were larger for TN due to denitrification in the overlying waters of sediments. The rates estimated from the imbalances in TN were in the ranges of the measured denitrification rates in laboratory tests with the sediments. Thus, the information on the long-term changes in sediment nutrients could provide the average rates of these fundamental processes in lake environments.

Litter quality and decomposition of Vitis vinifera L. residues under organic and conventional farming systems

In viticulture, residue decomposition may be important in terms of fertilization, due to the low grapevine nutritional demands. Grapevine residue quality, mass loss and nutrient release rates were studied in an organic (Vorg) and a conventional vineyard (Vconv) for 19-months. Leaf and cane residues of the Vorg (Lorg, Corg) and of Vconv (Lconv, Cconv) were buried in litterbags in both vineyards. Lorg contained in mg g −1 526 C, 14.7 N, 1.2 P and 5.4 K; Lconv 509 C, 17.9 N, 1 P and 7.3 K; Corg 556 C, 5.7 N, 1.4 P and 6.9 K; Cconv 554 C, 7.6 N, 0.9 P and 7.7 K. Mean mass loss and N, P and K release rates ( k′ = k × 10 5) were higher in leaf ( k′ = 543, 541, 448, 725) than in cane residues ( k′ = 146, 90, 136, 494). In Vorg, mass loss and N, P and K release rates were higher in Lconv ( k′ = 904, 748, 630, 1287) than in Lorg ( k′ = 293, 357, 336, 502). For Lorg, mass loss and N release rates and for Corg mass loss rate were lower in Vorg ( k′ = 293, 357, 102) than in Vconv ( k′ = 537, 541, 218). For Lconv, mass loss and N and K release rates were lower in Vconv ( k′ = 440, 518, 557) than in Vorg ( k′ = 904, 748, 1287). Incorporation of plant residues in Vconv allowed reductions of nutrient applications of 25, 2 and 21 kg ha −1 y −1 of N, P and K, respectively; in Vorg nutrient applications reduced by 7, 1, 5.5 kg ha −1 y −1.