Effects Of Organic Matter Addition Research Articles

Effects of Organic Matter Addition on Soil Carbon Contents, CO2 Emissions, and Bacterial Compositions in a Paddy Field in South China

Increasing soil organic carbon (SOC) contents and reducing carbon dioxide (CO2) emissions in paddy soil fields can result in positive impacts on climate change mitigation and soil quality. However, SOC accumulation and its microbial driving factors under enhanced fertilization strategies (e.g., organic matter application) are still unclear. Therefore, we investigated the effects of organic matter addition on SOC variations, CO2 fluxes, and their relationships with soil bacterial compositions and functions through a 6-year fertilizer experiment in rice fields involving two fertilization types, namely chemical fertilizer (NPK) and chemical fertilizer combined with organic matter (NPK+OM). The results showed significantly higher and lower SOC contents (p < 0.05) in the 10–20 cm soil layer under the NPK+OM treatment before rice transplanting and after rice harvest, respectively, than those under the NPK treatment. The lower SOC contents after rice harvest might be due to the great nutrient consumption, resulting in higher rice yields in the NPK+OM than those in the NPK treatment by 6.68 to 32.35%. Compared with NPK, NPK+OM reduced the in-situ CO2 fluxes by 38.70–118.59%. However, the ex-situ SOC mineralization rates were not affected by NPK+OM in the 0–10 and 10–20 cm soil layers. The 16S rRNA sequence indicated a significant increase in the abundance of non-singleton amplicon sequence variants (ASVs) in the NPK+OM treatment scenario compared to those in the NPK treatment scenario. The top three most important soil bacterial phylum influenced by NPK+OM were LCP-89, BRC1, and Rokubacteria in April, as well as Firmicutes, Nitrospinae, and BRC1 in July. Soil Actinobacteria was negatively correlated with the SOC contents in April and July. The results of the present study demonstrate the economic and ecological benefits of the organic matter addition in rice production, as well as the contribution of soil bacteria to SOC accumulation and CO2 emission reduction.

Reduction in acidity and heavy metal concentrations of acid mine drainage with organic matter and coal fly ash treatments in two different reclaimed-mining soils

Organic matter (OM) has a very crucial role in the management of acid mine drainage (AMD) using a passive treatment system, although information on the use of this system in different reclaimed-mining soils (RMS) is very limited. Therefore, this study aimed to determine the effect of adding OM to RMS with different characteristics. It was carried out by adding only OM or in combination with coal fly ash (CFA) to two RMS with different characteristics (Palam and Cempaka Soils) and quartz sand (control) in a batch reactor experiment. This was followed by the incubation of the mixture of soil/quartz-OM or soil/quartz-OM-CFA at 60% water holding capacity for 15 days. After incubation, AMD slowly flowed into the reactor, and its pH in the reactor was monitored every day for 30 days, while the concentrations of Fe (iron), Al (aluminum), and Mn (manganese) were measured on the 30th day. The results showed that the application of OM on Palam Soil only increased AMD pH by 0.38 units, while Cempaka Soil and quartz sand increased by 4.83 and 5.36 units, respectively. The addition of OM to Cempaka Soil and quartz sand also showed a higher reduction in heavy metals concentration in AMD than those in Palam Soil. It was also discovered that the application of OM combined with CFA led to a higher improvement in AMD quality than only using OM. This study demonstrated that the effect of OM addition on increasing pH and decreasing metal concentration on AAT management with the passive treatment system is controlled by soil characteristics.

Effects of Organic Matter Addition on Soil Quality in Sustainable Agriculture

Effects of Organic Matter Addition on Soil Quality in Sustainable Agriculture

Effects of organic matter addition on the stoichiometric homeostasis of soil microbes in Pinus tabuliformis forest in Taiyue Mountain, China.

In Taiyue Mountain of Shanxi Province, five types of organic matter, i.e., biochar, maize straw, leaves of Quercus mongolica and Pinus tabuliformis, and sawdust of wood stem, were separately added to the soils of a P. tabuliformis forest. Nutrient content, enzyme activity, and microbial biomass were analyzed to elucidate the characteristics of soil ecoenzymatic stoichiometry and the element homeostasis of soil microorganisms. The results showed that the addition of woody sawdust significantly increased soil nitrogen and phosphorus content by 17.1% and 37.6%, and enhanced carbon, nitrogen, and phosphorus contents of soil microbial biomass by 118.0%, 41.0%, and 176.6%, respectively. The activities of carbon-, nitrogen- and phosphorus-targeting enzymes (i.e., β-1, 4-glucosaminosidase, β-1,4-N-acetylglucosaminosidase, leucine aminopeptidase and acid phosphatase) generally increased with the C:N of the added organic matter (biochar<Q. mongolica leaf< P. tabuliformis leaf < maize straw < woody sawdust). This indicated that ecoenzymatic stoichiometry was controlled by soil nutrient content and micro-bial biomass. The limitation of soil microbial growth by phosphorus was not alleviated after the addition of different organic matters, as indicated by the results of enzymatic ratio and its vector value. Soil microbial biomass carbon and nitrogen contents and their stoichiometry (C:N, C:P, N:P) were homeostatic, whereas the microbial biomass phosphorus content fluctuated slightly. The stabilities of microbial element contents and their proportion were mainly ascribed to the allocation of extracellular enzyme production. The susceptibility of soil microbial biomass phosphorus to the addition of organic matter indicated phosphorus limitation of microbial growth.

Effect of organic matter addition on the solubility of arsenic in soil and uptake by rice: a field-scale study

Effect of organic matter addition on the solubility of arsenic in soil and uptake by rice: a field-scale study

Effects of organic matter addition on chronically hydrocarbon-contaminated soil.

Soil is the recipient of organic pollutants as a consequence of anthropogenic activities. Hydrocarbons are contaminants that pose a risk to human and environmental health. Bioremediation of aging contaminated soils is a challenge due to the low biodegradability of contaminants as a result of their interaction with the soil matrix. The aim of this work was to evaluate the effect of both composting and the addition of mature compost on a soil chronically contaminated with hydrocarbons, focusing mainly on the recovery of soil functions and transformations of the soil matrix as well as microbial community shifts. The initial pollution level was 214ppm of polycyclic aromatic hydrocarbons (PAHs) and 2500ppm of aliphatic hydrocarbons (AHs). Composting and compost addition produced changes on soil matrix that promoted the release of PAHs (5.7 and 15 % respectively) but not the net PAH elimination. Interestingly, composting stimulated AHs elimination (about 24 %). The lack of PAHs elimination could be attributed to the insufficient PAHs content to stimulate the microbial degrading capacity, and the preferential consumption of easily absorbed C sources by the bacterial community. Despite the low PAH catabolic potential of the aging soil, metabolic shift was driven by the addition of organic matter, which could be monitored by the ratio of Proteobacteria to Actinobacteria combined with E4/E6 ratio. Regarding the quality of the soil, the nutrients provided by the exogenous organic matter contributed to the recovery of the global functions and species diversity of the soil along with the reduction of phytotoxicity.

Biophysical potential of organic cropping practices as a sustainable alternative in Switzerland

Little is known about the potential of adopting organic farming at regional scales for mitigating agricultural greenhouse gas (GHG) emissions. We simulated the effect of organic matter addition (manure and compost) on all cropland soils in Switzerland, with reduced tillage and winter cover cropping in combination. The DayCent model was run for the period 1991–2013 by accounting for factors such as soils, land use, and climate to evaluate alternative practices. Converting conventional cropping with only chemical fertilizers to organic cropping led to a regional mitigation in soil GHG emissions by 0.34–1.10 Mg CO2-eq ha−1 yr−1. Soil organic C (SOC) stocks increased by 104–259 kg C ha−1 yr−1, accounting for 86–100% of the GHG mitigation. Adopting organic practices with reduced tillage or cover cropping increased SOC stocks up to 433 kg C ha−1 yr−1. Our results suggest that the alternative practices could reverse C decline in conventional soils, predicted to be −241 kg C ha−1 yr−1. Organic practices combined with reduced tillage or cover cropping had varying effects on N2O emissions, ranging from a mean decrease of −0.60 kg N ha−1 yr−1 to an increase of 0.29 kg N ha−1 yr−1. Model results suggest the need to deliver mitigation that is more permanent with the careful combination of alternative practices. Also, risks such as increased N2O emission, especially when using organic amendments with high N decomposition potential, and yield penalty must be managed.

Use of biogas solid residue from anaerobic digestion as an effective amendment to remediate Cr(VI)-contaminated soils.

Chromium (Cr) is one of the most common metal pollutants and has thus attracted considerable attention. In this study, we investigated the potential use of biogas solid residue (BSR) from anaerobic digestion as an effective amendment to decrease the bioavailability of Cr in Cr(VI)-polluted soil using pot experiments. Compared to the no-addition treatment, the addition of BSR (treatments-50, 100, and 150gkg-1 soil) increased the soil nutrient levels, microbial diversity and activities, and decreased the redox potential (Eh). BSR treatment of Cr(VI)-contaminated soil caused a reduction in soil Cr(VI) concentration (16.6-52.1%) and the exchangeable Cr proportion (15.2-52.4%), thereby decreasing the available Cr for uptake by plants. BSR treatments resulted in a reduction in the Cr contents of the roots and aboveground biomass of pakchoi plants. The Cr(VI) content in treated soils decreased with increasing BSR addition, with 150gkg-1 being the most efficient application. The relative abundance of Cr-reducing groups, such as Pseudomonas, Microbacterium, and Bacillus, increased with the increase in BSR application. The enhancement of soil Cr(VI) immobilization by the addition of the BSR was mostly attributed to the simultaneous effect of organic matter addition, stimulation of microorganisms, and reduced Eh value. Organic matter contributed more to the variation in Cr. The presence of BSR decreased the bioavailability of Cr in the soil and, therefore, lowered the potential mobilization of Cr(VI) from the soils. Our results demonstrated that BSR application may offer a potentially promising solution for enhancing agricultural production in Cr-contaminated soils.

Restoration of Cordgrass Salt Marshes: Limited Effects of Organic Matter Additions on Nitrogen Fixation

The extensive loss of tidal marsh habitat surrounding the San Francisco Bay has led to numerous restoration projects to restore ecosystem function. Native cordgrass (Spartina foliosa) is important for sediment accumulation and nesting habitat for endangered California Ridgway’s Rail (Rallus obsoletus obsoletus), and because salt marshes are typically nitrogen-limited ecosystems, previous restoration studies in California have used nitrogen fertilizers to increase plant growth. This study compared the use of two low-nitrogen, high-carbon fertilizers (Macrosystis pyrifera (kelp) and sodium alginate) to stimulate N2-fixing bacteria inhabiting the S. foliosa rhizosphere in a historic and recently restored marsh in San Francisco Bay. Alginate increased N2-fixation, though there was no observed S. foliosa growth response. Kelp suppressed N2-fixation, and increased the foliar nitrogen content of Salicornia pacifica in mixed Spartina-Salicornia stands. The restored marsh had less than 0.5 μM phosphate in porewaters, suggesting phosphorus, not nitrogen, limits S. foliosa growth in this marsh. Alginate increased rates of N2-fixation and may promote plant growth in marshes exhibiting nitrogen limitation. Phosphate limitation was a surprise considering numerous previous studies indicate nitrogen as the primary limiting nutrient of tidal marsh plants. We recommend first assessing nutrient stoichiometry when considering manipulations to promote plant growth in restored marshes.

Effects of organic matter addition on methylmercury formation in capped and uncapped marine sediments

In situ subaqueous capping (ISC) of contaminated marine sediments is frequently proposed as a feasible and effective mitigation option. However, though effective in isolating mercury species migration into overlying water, capping can also alter the location and extent of biogeochemical zones and potentially enhance methylmercury (MeHg) formation in Hg-contaminated marine sediments. We carried out a boxcosm study to investigate whether the addition of organic carbon (OC) to Hg-contaminated marine sediments beneath an in situ cap would initiate and/or enhance MeHg formation of the inorganic Hg present. The study was motivated by ongoing efforts to remediate ca. 30,000 m2 of Hg-contaminated seabed sediments from a Hg spill from the U864 WWII submarine wreck. By the time of sinking, the submarine is assumed to have been holding a cargo of ca. 65 tons of liquid Hg. Natural organic matter and petroleum hydrocarbons from fuels and lubricants in the wreck are potential sources of organic carbon that could potentially fuel MeHg formation beneath a future cap. The results of our study clearly demonstrated that introduction of algae OC to Hg-contaminated sediments, triggered high rates of MeHg production as long a there was sufficient OC. Thus, MeHg production was limited by the amount of organic carbon available. The study results also confirmed that, within the six-month duration of the study and in the absence of bioturbating fauna, a 3-cm sediment clay cap could effectively reduce fluxes of Hg species to the overlying water and isolate the Hg-contaminated sediments from direct surficial deposition of organic matter that could potentially fuel methylation.

Arsenic(V) adsorption-desorption in agricultural and mine soils: Effects of organic matter addition and phosphate competition

High total and bioavailable concentrations of As in soils represent a potential risk for groundwater contamination and entry in the food chain. The use of organic amendments in the remediation of As-contaminated soils has been found to produce distinct effects on the solubility of As in the soil. Therefore, knowledge about As adsorption-desorption processes that govern its solubility in soil is of relevance in order to predict the behaviour of this element during these processes. In this paper, the objective was to determine As adsorption and desorption in four different soils, with and without compost addition, and also in competition with phosphate, through the determination of sorption isotherms. Batch experiments were carried out using three soils affected differently by previous mining activity of the Sierra Minera of La Unión-Cartagena (SE Spain) and an agricultural soil from Segovia province (central Spain). Adsorption was higher in the mining soils (and highest in the acidic one) than in the agricultural soils, although the latter were not affected negatively by organic matter or phosphate competition for sorption sites. The results show that As adsorption in most soils, both with and without compost, fitted better a multimolecular layer model (Freundlich), whereas As adsorption in competition with P fitted a monolayer model (Langmuir). Moreover, the use of compost and phosphate reduced the adsorption of As in the mining soils, while in the agricultural soils compost increased their low adsorption capacity. Therefore, the use of compost can be a good option to favour As immobilisation in soils of low adsorption, but knowledge of the soil composition will be crucial to predict the effects of organic amendments on As solubility in soils and its associated environmental risk.

Maize productivity dynamics in response to mineral nutrient additions and legacy organic soil inputs of contrasting quality

Residual effects of organic inputs of contrasting quality on maize productivity were investigated as a function of soil degradation in the highlands of western Kenya. Tithonia (Tithonia diversifolia (Hemsl.) A. Gray) green manure, cypress sawdust (Cupressus lusitanica Mill.), and biochar made from eucalyptus wood (Eucalyptus saligna Sm.) were applied at a rate of 6tCha−1 for three cropping seasons, both with and without mineral fertilizer additions (120kgNha−1, 100kgKha−1, 100kgPha−1). Maize grain yield was monitored for six years beyond the initial organic matter additions. During the years when amendments were added, tithonia applications resulted in the greatest yield increases, between 153 and 183% more than the unamended control in comparison to increases by136% with biochar and by 107% with sawdust additions. In contrast to application of tithonia, peak yields with sawdust or biochar in most cases occurred 1–2 years after additions had ended. Yet during the same period, yields in fields that had previously received tithonia were on average still 71% of peak yields. Four years later, yields declined to between 28 and 22% of peak yields, whereas yields after biochar and sawdust applications declined to between 57 and 25% of peak values. Six years after organic matter additions ended, maize yields were not significantly different irrespective of additions of the quality of organic amendments. The data indicate that yield responds in the short-term to input quality and specifically the amount of applied N; while the residual effects of organic matter additions on yield dynamics may relate more to legacy effects of high crop residue return, input C quality and increasing soil C.

Addition of organic matter influences pH changes in reduced and oxidised acid sulfate soils

Acid sulfate soils (ASS) are wide-spread in coastal and inland wetlands. When sulfidic ASS are exposed to oxygen, sulfuric acid is generated which can threaten wetlands and surrounding ecosystems. Organic matter plays an important role in ASS, as energy source for sulfate reducing bacteria during submergence and by stimulating competition for oxygen between oxidation of iron sulfide and utilisation by decomposers during dry periods. The aim of this study was to assess the effect of organic matter addition, as a potential management strategy, on pH changes in ASS in submerged and dry periods. Three ASS, namely sulfuric, hypersulfidic and hyposulfidic soils, collected from one profile in a wetland were used unamended or amended with 10gCkg−1 as finely ground wheat straw. The soils were exposed to a submerged (wet) period, a dry period, followed by another wet period. In the first wet period (10weeks), the pH increased only in the amended soils, which was accompanied by a strong decrease in redox potential. To investigate the effect of water content during the dry period on pH, the soils were rapidly dried to 40, 60, 80 or 100% of water holding capacity (WHC) at the start of the dry period. This water content was maintained during the dry period. The pH decrease during the 10week dry period was greater in amended than in unamended soils and greater at 60, 80 or 100% than at 40% of WHC. At the end of the dry period, the pH was higher in amended than in unamended soils and greater at 40% of WHC than at the higher water contents. In the second wet period (16weeks), the pH increased only in the amended soils. The pH increase was accompanied by a decrease in redox potential in the amended soils. The water content in the previous dry period did not influence pH in the second wet period in the unamended soils, but in the amended soils, the pH was higher in soils previously maintained at 40% of WHC than that maintained at higher water contents. At the end of the second wet period, the pH was higher in amended than in unamended soils. This study shows the ameliorative effect of organic matter addition in ASS. Organic matter addition can improve energy supply for sulfate reducers which results in an increase in pH during the wet period and lead to a higher pH in the oxidation period. The smaller pH increase and redox potential decrease in amended soils in the second compared to the first wet period suggest that OM decomposition was lower in the second wet period likely because rapidly decomposable compounds had been utilised in the previous wet and dry periods and only recalcitrant OM remained. Therefore OM may have to be added repeatedly for sustained amelioration of ASS.

Effects of organic matter addition on phosphorus availability to flooded and nonflooded rice in a P‐deficient tropical soil: a greenhouse study

AbstractAddition of organic matter (OM) to flooded soils stimulates reductive dissolution of Fe(III) minerals, thereby mobilizing associated phosphate (P). Hence, OM management has the potential to overcome P deficiency. This study assessed if OM applications increases soil or mineral fertilizer P availability to rice under anaerobic (flooded) condition and if that effect is different relative to that in aerobic (nonflooded) soils. Rice was grown in P‐deficient soil treated with combinations of addition of mineral P (0, 26 mg P/kg), OM (0, ~9 g OM/kg as rice straw + cattle manure) and water treatments (flooded vs nonflooded) in a factorial pot experiment. The OM was either freshly added just before flooding or incubated moist in soil for 6 months prior to flooding; blanket N and K was added in all treatments. Fresh addition of OM promoted reductive dissolution of Fe(III) minerals in flooded soils, whereas no such effect was found when OM had been incubated for 6 months before flooding. Yield and shoot P uptake largely increased with mineral P addition in all soils, whereas OM addition increased yield and P uptake only in flooded soils following fresh OM addition. The combination of mineral P and OM gave the largest yield and P uptake. Addition of OM just prior to soil flooding increased P uptake but was insufficient to overcome P deficiency in the absence of mineral P. Larger applications of OM are unlikely to be more successful in flooded soils due to side effects, such as Fe toxicity.

Phytoremediation of a soil contaminated by heavy metals and boron using castor oil plants and organic matter amendments

Phytoremediation is a sound alternative to soil decontamination, as it has lower costs and is more environmentally friendly than other practices. The need to handle contaminated biomass after harvesting and the search for new renewable energy sources have shifted research interests from typical edible or scenic plant species to those that can be used to produce biofuels. The castor oil plant (Ricinus communis L.) is a fast growing plant with high biomass production and is a potential phytoaccumulator of several metals. In recent years, the federal government of Brazil has encouraged castor oil plant cultivation for biodiesel and bioethanol production. The aim of the present work was to evaluate the phytoextraction potential of R. communis L. and the effect of organic matter addition (peat vs. filter cake) to a soil contaminated with scrap metal residue containing heavy metals and boron. The experiment consisted of a completely randomized block design with two organic matter sources and four rates of amendment (0, 20, 40 and 80Mgha−1 organic carbon). Treatments were replicated three times. The castor oil plants were harvested 74days after sowing. No accumulation of Cr, Ni, Cd, Cu, Pb or Zn was observed in the plants, but the concentration of B increased to 626mgkg−1 upon filter cake addition in castor oil shoots. Peat addition reduced by 2.7years the time needed for removal of 50% of soil B content compared to the treatment with no organic matter addition. The transfer factor and transference index values obtained for B with castor oil plants in the present study were comparable to those obtained for hyperaccumulator species. Although our results are promising, further studies should be conducted to prove the usefulness of plants grown in contaminated areas for remediation purposes and for biofuel production.

Organic Matter and Barium Absorption by Plant Species Grown in an Area Polluted with Scrap Metal Residue

The effect of organic matter addition on Ba availability toHelianthus annuusL.,Raphanus sativusL., andRicinus communisL. grown on a Neossolo Litólico Chernossólico fragmentário (pH 7.5), contaminated with scrap residue was evaluated. Four rates (0, 20, 40, and 80 Mg ha−1, organic carbon basis) of peat or sugar cane filter, with three replicates, were tested. Plant species were grown until the flowering stage. No effect of organic matter addition to soil on dry matter yield of oilseed radish shoots was observed, but there was an increase in sunflower and castor oil plant shoots when sugar cane filter cake was used. The average Ba transferred from roots to shoots was more than 89% for oilseed radish, 71% for castor oil plants, and 59% for sunflowers. Organic matter treatments were not efficient in reducing Ba availability due to soil liming.

Contribution of bait to lobster production in an oligotrophic marine ecosystem as determined using a mass balance model

The fishery for the western rock lobster ( Panulirus cygnus) in Western Australia is Australia's largest trap-based fishery, deploying 8.8 million pot lifts, landing on average 11,000 tonnes of lobster and using approximately 14,000 tonnes of bait annually. A mass balance model was constructed to determine the potential contribution of this bait to the diet of western rock lobsters. Bait is potentially a significant subsidy given the oligotrophic nature of Western Australia's marine environment. The mass balance model was constructed on the principle that the biomass of the lobster population reflects the difference between inputs (growth, immigration) and outputs (natural and fishing mortality and emigration). Biomass calculated using this approach was within 7% of biomass calculated from independent estimates based on depletion analysis, indicating the model is robust. The food required to explain observed growth was then calculated, allowing the potential contribution of bait to lobster diet to be assessed. The abundance of natural diet items on the benthos was sufficient to explain the observed growth of lobsters, with bait contributing a maximum of 13% of lobster food requirements over the whole ecosystem. This contribution of bait will differ spatially and temporally reflecting uneven distribution of fishing effort and may be as high as 35% during some months of the fishing season, a result consistent with dietary studies based on stable isotopes. Given observed effects of organic matter addition on ecosystem processes as observed in trawl fisheries and aquaculture operations, it is likely that the effects of bait addition on ecosystem function are more widespread than lobster production.

Effect of soil covering on nitrogen availability of vineyards soils in Champagne area

&lt;p style="text-align: justify;"&gt;We studied the effect of soil cover (bare soil, mulch of barks or composted organic materials, grass cover) on soil N dynamics in various experimental vineyards located in Champagne area (France). Soil cores were sampled periodically to measure water and mineral N in soil profile during autumn and winter. These measurements were used in a simple dynamic model (LIXIM) to calculate nitrate leaching and N mineralization. N mineralization potential of soils were also determined in laboratory incubations in controlled conditions. In most sites, soil inorganic N contents (0-75 cm) varied between 20 and 60 kg N ha-1, depending of the season. Soil inorganic N in plots receiving barks or composted barks or covered with grass did not differ significantly from control plots. Higher amounts of inorganic N were found in soils amended with refuse compost, peat or mixed compost (barks + farmyard manure) or composted farmyard manure. The model indicated that N leached varied from 8 to 77 kg N ha-1 and that the mean nitrate concentration in drained water was less than 50 mg NO3- L-1 except for plots receiving refuse compost or bark + farmyard manure compost. The calculated N mineralization varied from 9 to 45 kg N ha-1 over the autumn-winter period, i.e. 118 to 182 days. The N mineralization rate (Vp), expressed per 'normalised day' i.e. day at 15°C and field capacity, varied from 0.15 to 0.82 kg N ha-1 nd-1, including all sites and experimental treatments. Effect of organic matter addition on Vp was only observed for long-term experimental sites where large amounts of organic nitrogen had been added to soil using peat, refuse compost or compost mixtures with barks and farmyard manure. The Vp values measured in laboratory incubations showed the same trends and were in the same order of magnitude than those calculated with LIXIM model using in situ data. In average, the values measured in laboratory incubations underestimated the actual N mineralization in field conditions. The model was used to predict N mineralization and inorganic N in soil during the vegetative period using Vp values. It allowed to estimate the N uptake by vine: 10 ± 5 kg N ha-1 at flowering and 57 ± 5 kg N ha-1 over the whole growing period. These results show that soil N availability was sufficient to feed the vine during the whole growing period and that no inorganic N fertilisation was necessary, even in the grass covered soil. In this soil, water availability is probably the limiting factor when depressive effects are observed. On the long-term, it is necessary to manage the amount and quality of added organic matter since organic inputs may modify N availability and therefore vine behaviour, wine quality and environmental risks.&lt;/p&gt;

Effect of organic matter addition to the pen surface and pen cleaning frequency on nitrogen mass balance in open feedlots.

Three finishing trials were conducted to determine the effects of dietary manipulation and management on N losses from open feedlots. In each experiment, 96 steers were assigned randomly to 12 nutrient balance pens. In Trial 1, calves were fed for 180 d during the winter/spring months; in Trial 2, yearlings were fed for 132 d in the summer. In Trials 1 and 2, N losses from pens were compared directly by adding OM to the pen surface or indirectly by feeding digestible ingredients designed to increase OM excretion. The dietary treatment (BRAN) included 30% corn bran (DM basis) replacing dry-rolled corn. Pens where OM was directly added received sawdust applications (SAWDUST) at a rate to match OM excretion from the BRAN diet. These two treatments were compared with a conventional, 75% dry-rolled corn diet (CON). Because CON and SAWDUST diets were identical, performance for both treatments was similar during Trials 1 and 2. The BRAN diet decreased (P < 0.10) gain efficiency during Trials 1 and 2 by 9.5% relative to CON. Fecal N excretion was greater (P < 0.01) for calves and yearlings when BRAN was fed compared with CON. Adding OM to the pen surface increased (P < 0.01) the amount of N in manure removed from pens and reduced (P < 0.10) N losses in Trial 1. Nitrogen losses were not significantly different among treatments in Trial 2. In Trial 3, calves were fed for 166 d during the winter/spring months. A 2 x 2 factorial design was used to evaluate pen cleaning frequency and diets similar to CON and BRAN. Pens were either cleaned monthly or once at the end of the feeding period. Daily DMI was greater (P = 0.01) and ADG was lower (P < 0.01) when cattle were fed BRAN compared with CON. Responses from all three trials indicate a negative effect of BRAN on gain efficiency. Dietary treatment and cleaning frequency interacted for N balance in the feedlot. Nitrogen losses decreased and manure N increased (P < 0.10) for cattle fed BRAN compared with CON when pens were cleaned monthly. Feeding BRAN did not affect total manure N, but resulted in higher N losses when pens were cleaned only once. For all trials, BRAN increased the amount of N remaining in composted manure. Adding OM to pen surfaces and/or cleaning pens more frequently may decrease N losses from open feedlot pens and from compost, although responses seem influenced by ambient temperature or season.

Geoecological alteration of surface soils by the Hawaiiansilversword (Argyroxiphium sandwicense DC.) inHaleakala's crater, Maui

The geoecological effects of organic matter addition to soil byHawaiian silverswords (Argyroxiphium sandwicense DC.,Asteraceae) in Haleakala's crater (Maui) are examined. Sets of 12 surfacesoil samples were gathered in three positions: bare soils; under the crowncanopy of adjacent live plants; and below dead, withered rosettes. Silverswordstanding litter and live foliage were also collected. Several physical andchemical properties were investigated. Bare soils were coarse and exceptionallylow in chemical nutrients and water-holding capacity. Litter addition belowsilverswords altered all properties except particle-size distribution; soilsunder dead rosettes became modified more strongly than those below live plants.While rosettes grow, standing litter is tightly preserved, thus only smallamounts of organic matter are added to soil. When plants die, a substantialinflux of litter is released in a short period (7 to 9 years average); thisraises the C and N content, C/N ratios, exchangeable nutrient levels (Ca, Mg,K, P) and cation exchange capacity of soil. Physical properties, such as color,bulk density and porosity are also greatly affected; as a result, soilwater-retention at field capacity nearly doubles under withering plants. Soiltemperatures (5 cm depth) at noon were ∼18.1 °C lower beneath silversword canopies(18.5 °C mean) than in contiguous bare soils(36.6 °C). This cooling may result in lower evaporationand further conservation of soil moisture, thus increased seedgermination. Nutrient-retention strategies may have evolved in the semelparousArgyroxiphium to help it cope with the harsh,drought-prone soils and unpredictable climate of Haleakala. Silverswordflowering results in a tremendous seed output, but the plant needs to ensurethat some seeds – which have limited dispersal capability – willgerminate, and thus provides a nutrient-rich, water-retaining substrate moresuitable for seedling establishment than bare soils. Through itsself-regulating influence on underlying soils,Argyroxiphium affects both soil formation and its ownregeneration in Haleakala.