Mulch Layer Research Articles

Reduction of crop contamination by soil resuspension within the 30-km zone of the Chernobyl nuclear power plant.

A field experiment was conducted within the 30-km zone of the Chernobyl Nuclear Power Plant to analyze whether the application of mulching reduced resuspension of 137Cs contaminated soil in oat (Avena sativa) crops. In 1993, we applied a mulch treatment at a dose of 200 g m(-2), and soil resuspension was measured by estimating soil loadings onto plant surfaces from Ti concentrations in plants. In 1994, two mulch doses were applied, 200 and 50 g m(-2), and we estimated the contribution of soil resuspension by using artificial resuspension collection devices (ARC). In the 1993 experiment between 4.6 and 34.4% of the plant's total 137Cs contamination was attributed to external soil contamination. The mean amount of soil-derived 137Cs attached to vegetation was 124.7 Bq kg(-1)(plant) in control plots and 53.7 Bq kg(-1)(plant) in mulched plots. In the 1994 experiment, covering the soil with a mulch layer decreased the radiocesium content in ARC by about 70%. Results obtained in these experiments suggest that soil resuspension was a significant mechanism for plant contamination and that mulching was effective in reducing that contamination.

Mulch decomposition impedes recovery of net carbon sink function in a restored peatland

With the increase in the drainage and extraction of peat for horticultural, agricultural and energy purposes worldwide, there is an increased pressure to restore hydrological conditions essential to the re-establishment of Sphagnum mosses and, therefore, carbon sequestration. Measurements of ecosystem CO2 were conducted at a recently restored vacuum harvested bog in Eastern Québec, Canada. The peatland was restored by blocking the drainage networks to return optimal water table positions for the growth of Sphagnum mosses and the spreading of a dense straw mulch layer to reduce evaporative losses and stabilize the surface for the moss re-growth. However, the return of the moss species is a gradual process and previous studies have suggested that initially the carbon loss from the system actually increase as the mulch decomposes. We examined old and new mulch CO2 production in lab incubations and scaled these results to the ecosystem level in order to determine if mulch decomposition is impeding the net carbon sink function of this peatland. At mean growing season temperatures fresh mulch was observed to release 151.5 μmol CO2 g−1 per day, while older mulch released 145 μmol CO2 g−1 per day. Furthermore, under moist conditions the CO2 release increased for all mulches. However, contrary to most assumptions, Q10 values for all mulches decreased with increasing temperatures and were greater for older mulch than for fresh. Thus, in the short term, the application of a surface straw mulch layer can have significant effects on the carbon balance of a restored peatland. Due to the decomposition of this mulch layer over the first several seasons of restoration, the peatland became a larger source of CO2, despite the increase in production of a re-emerging vegetation layer.

A comparison of conventional and alternative understory management practices for apple production: multi-trophic effects

Modification of the soil for agricultural production is commonly studied as it relates to plant health and productivity, but the implications at other trophic levels are often over-looked. This study addressed the effects of orchard understory management at several trophic levels to understand potential impacts on the whole system. The soil in a newly planted Golden Delicious apple ( Malus domestica Bork.) orchard was modified with four treatments: (1) mulch layer of composted poultry manure, (2) mulch layer of synthetic fiber, (3) conventional herbicide, and (4) hand-weeded control. These treatments were evaluated for their impact on edaphic and arboreal arthropods, substrate microclimate and weed growth, and apple tree vigor during the first year of growth (1998). Understory treatment affected edaphic arthropods at three trophic levels: detritivore, herbivore, and predator. Compost mulch significantly increased both edaphic detritivores and predators. Edaphic herbivores were less abundant in plots treated with synthetic mulch. No effect was found for arboreal herbivores, but aphidophagous Aphidoletes aphidimyza (Cecidomyiidae) larvae were more abundant on trees in compost-treated plots. Host-plant growth and leaf quality (% N) were also affected by soil management, with a higher average trunk diameter and lower average leaf nitrogen (%) in compost-treated plots, despite equivalent N-input in all four treatments. Both mulches (compost and synthetic) resulted in lower soil temperatures and higher soil moistures and suppressed weed growth 10-fold better than either conventional herbicide or hand weeding. The results indicate that soil modification affects organisms at several trophic levels, and therefore, could hold important implications for the orchard ecosystem as a whole. Overall, mulching with composted manure benefited the whole orchard system the most and was superior to conventional herbicide as an understory management practice.

Changes in Chemical Components of Leaf Litter of Ginkgo Biloba during Mulching

The biological decomposition and chemical changes of leaf litter of Ginkgo biloba both at the surface and bottom layers were studied for 1 year. The changes in components such as the yields of 80% ethanol and water extractives, neutral sugars, uronic acids, Klason residues, acid-soluble phenolics, ash, nitrogen, and carbon were investigated. There were great drops of the yields of 80% ethanol extractives and water extractives in both surface and bottom mulch layers. Klason residues and sugars were the major components of the solid residues. The Klason residues lost 2.2% and 30.5% of their initial mass at the surface and bottom layers, respectively, during mulching. The total losses of the neutral sugars were 71.6% at the surface layer and 89.3% at the bottom layer. These results implied that the Klason residues were the most important inner component restraining the decomposition of the leaf litter of G. biloba and all analyzed cell wall components at the bottom layer had faster decomposition rates than those at the surface layer. Nitrogen content increased during one year of mulching, while changes in carbon contents were less than 1% throughout experiment.

Smoke, Mulch, and Seed Broadcasting Effects on Woodland Restoration in Western Australia

AbstractSmoke, canopy‐derived mulch, and broadcast seeds were used to maximize the establishment of Banksia woodland species in sand quarries in Western Australia. Smoke, particularly aerosol smoke, had a positive effect on total seedling recruitment. Pre‐mined (woodland) sites showed a 42‐fold increase in total germinants and a 3‐fold increase in the number of species with aerosol smoke application. Post‐mined (restored) sites showed only a 3.6‐fold increase in total germinants and a 1.4‐fold increase in the number of species. Two water‐based smoke chemicals, DC10 (pH 4.5) and SC63 (pH 2.5), increased seedling recruitment at both sites but were not as effective in stimulating recruitment as aerosol smoke. Neither of the chemicals were effective in significantly increasing species richness. Application of aerosol smoke directly to seeds as a pretreatment before broadcasting had no effect on seedling recruitment. Broadcasting of seeds onto restoration sites significantly increased seedling abundance and richness. Application of a single layer of mulch from the canopy vegetation after seed broadcasting gave optimum seedling recruitment. Two layers of mulch significantly reduced recruitment, as did applying mulch before seed broadcasting. For broad‐scale restoration, the application of smoke on newly restored sites would be more effectively achieved using smoke water sprayed over the soil surface. Species that do not recruit from replaced topsoil could be effectively recovered from broadcast seed rather than from mulch.

Immature Compost Suppresses Weed Growth Under Greenhouse Conditions

The influence of immature municipal solid waste-biosolids composts on emergence and mean days to emergence (MDE) of several weed species was evaluated in a pot trial under greenhouse conditions. The experiment consisted of placing a 7.5 cm deep layer of three-day-old immature compost, a mature and stable compost, an artificial medium or control sand as a mulch on ivyleaf morning glory seeds. Immature three-day-old compost decreased percentage emergence, shoot and root dry weight, and increased MDE of ivyleaf morning glory. In an experiment with eight-week-old immature compost utilizing mulching depths of 2.5, 5, 7.5, 10 cm and the untreated control on seeds of three weed species, common purslane did not emerge under any of the immature compost treatments. The MDE of ivyleaf morning glory and barnyard grass increased linearly as immature compost depths increased. Next, eight economically important weed species were sown in pots with either mature or immature (eight-week-old) compost utilizing mulching depths of 2.5 and 10 cm, in addition to an untreated control. Control pots yielded higher percentages of emergence than compost treatments for all species evaluated. Common purslane, large crabgrass, pig-weed, Florida beggarweed, and dichondra did not emerge through a 10-cm deep layer of mature compost mulch, or 2.5 or 10 cm deep layer of immature mulch. Significant compost maturity/depth interactions were observed for percent emergence on common purslane, ground cherry, large crabgrass, Florida beggarweed, and ivyleaf morning glory. A thinner layer was required to suppress germination using immature eight-week-old compost as compared to mature and stable compost. Immature (three-day or eight-week-old) compost containing acetic acid concentrations of 2474 and 1776 mg.kg−1 respectively reduced percentage emergence of several economically important weed species. These studies suggest that immature composts can be used to control weeds under conditions where spatial separation is maintained between the crop and the compost and phytotoxic fermentation products do not affect the health of the mulched plants and where odors associated with such partially stabilized products do not pose problems.

Soil Moisture Regime Changes in Tephra‐Mulched Soils

Large areas of the Canarian archipelago are catalogued as aridic according to U.S. soil taxonomy. A traditional system of cultivation, based on the application of a mulch layer of tephra, is widely practiced. The objective of this work is to compare the classification of soils with and without mulch using U. S. soil taxonomy, and illustrate the problems in estimating the soil moisture regime on the basis of meteorological data. In this study the moisture regime of a natural soil and an adjacent soil mulched with a 12‐cm layer of basaltic tephra was characterized on the basis of gravimetric moisture measurements, taken over a period of >1 yr, at 10‐cm intervals to a depth of 1 m. The moisture regime of the soil was also estimated using meteorological data. Results obtained for the natural, nonmulched soil using measured values and those estimated from atmospheric data are very similar, and both indicate an aridic soil moisture regime. The difference with the soil covered with basaltic tephra is noteworthy. In the latter case, the soil remained moist throughout the year, representing a udic moisture regime. This noteworthy difference is reflected in the classification of the soils: Aridisols in the first case and Inceptisols in the second. A proposal is made to include mulching with tephra as a cultural practice along with irrigation and fallowing in the definition of the classes of soil moisture regimes in U.S. soil taxonomy. This would prevent the practice of mulching with tephra from changing the soil order placement in U.S. soil taxonomy.

Cold climate wetlands: design and performance

Constructed wetlands are gaining widespread use as a simple, low cost means of wastewater treatment. Introduction of constructed wetlands technology into the northern United States has been limited by the ability of conventional wetland systems to operate without freezing during the winter. A design approach using subsurface-flow constructed wetlands covered with an insulating mulch layer has been demonstrated to prevent freezing. However, introduction of a mulch layer will affect oxygen transfer rates, pollutant removal performance, and plant establishment. These factors must be addressed for successful application of constructed wetlands technology in cold climates.

Association of Cellulytic Enzyme Activities in Eucalyptus Mulches with Biological Control of Phytophthora cinnamomi

ABSTRACT A series of samples were taken from mulched and unmulched trees starting at the surface of mulch or soil to a 15 cm soil depth, forming a vertical transect. Saprophytic fungi isolated from the soil samples on rose bengal medium and surveyed visually were most abundant in mulches and at the interface of mulch and soil (P < 0.05). Microbial activity as assayed by the hydrolysis of fluorescein diacetate was significantly greater in mulch layers than in soils. Cellulase and laminarinase enzyme activities were greatest in upper mulch layers and rapidly decreased in soil layers (P < 0.05). Enzyme activities against Phytophthora cinnamomi cell walls were significantly greater in mulch than in soil layers. When Phytophthora cinnamomi was incubated in situ at the various transect depths, it was most frequently lysed at the interface between soil and mulch (P < 0.001). Roots that grew in mulch layers were significantly less infected with Phytophthora cinnamomi than roots formed in soil layers. In mulched soil, roots were commonly formed at the mulch-soil interface where Phytophthora populations were reduced, whereas roots in unmulched soil were numerous at the 7.5 cm depth where Phytophthora cinnamomi was prevalent. Enzyme activities were significantly and positively correlated with each other, microbial activity, and saprophytic fungal populations, but significantly and negatively correlated with Phytophthora recovery.

Mulching With Composted MSW for Biological Control Of Weeds in Vegetable Crops

Compost maturity is one of several issues that the composting industry must face as it attempts to provide a high quality product to the agricultural community. In this paper, we examine the potential for using immature compost prepared from a mixture of municipal solid waste (MSW) and biosolids as a mulch for control of weeds in vegetable crop row-alleys. Two field experiments were conducted with 4 and 8-week-old composts in the fall of 1995 and the spring of 1996. The 4-week-old compost was applied to mulching depths of 3.8 (68 t dry weight .ha−1), 7.5 (135 t dry weight .ha−1), 11.3 (203 t dry weight .ha−1), and 15 cm (270 t dry weight .ha−1) in the fall, and at 2.0 (35 t dry weight .ha−1), 3.8, 7.5, and 11.3 cm depths in the spring. Other treatments were paraquat applied at 0.6 kg.ha−1 and an untreated control. All treatments were applied in row-alleys between raised, polyethylene-covered soil beds. The 8-week-old compost was applied to depths of 3.8, 7.5, 11.3, and 15 cm in fall and to depths of 2.0, 3.8, 7.5 and 11.3 cm in the spring. Untreated alleys served as controls. In the fall 1995 experiment under low weed pressures, the 4-week-old compost applied to 7.5 cm or greater depths completely inhibited weed germination and growth for 240 days after treatment. In the spring 1996 experiment, 4-week-old compost completely inhibited weed germination and growth for only 65 days if applied to a depth of 7.5 cm or deeper due to higher prevailing weed pressures, particularly due to yellow nutsedge (Cyperus esculentus L.). In the same spring experiment, a 50 % reduction in percentage weed cover was obtained for 240 days with a 11.25 cm deep layer of mulch compared to the control. In the fall 1995 experiment, 8-week-old compost applied at 7.5 cm or depths completely inhibited weed germination and growth for 240 days. In the spring 1996 experiment, 8-week-old compost applied as a 11.25 cm mulch reduced percent weed cover as compared to the control up to 240 days. In general, weed cover and weed dry weight decreased linearly as the depth of the mulch increased.Under these immature composts, inhibition of germination or subsequent weed growth may have been due to both the physical effects of the mulch and the concentrations of phytotoxic fatty acids during the first few days after mulches were applied. At the time of mulching with the 4-week old compost, acetic acid was present at a concentration of 1221 mg.kg−1 in the fall mulch, and at 4128 mg.kg−1 in the spring mulch. The same concentrations in the 8-week-old compost for the fall and spring mulches were 1118 mg.kg−1 and 3113 mg.kg−1, respectively. In conclusion, immature compost may provide an effective alternative weed control method for row-alleys in vegetable crop production systems. During these experiments, it was observed that man-made contaminants such as glass, hard and soft plastics in the composts were esthetically unacceptable and potentially posed hazards to field workers.

Heat and water exchanges of fallow land covered with a plant-residue mulch layer: a modelling study using the three year MUREX data set

The MUREX (Monitoring the Usable Soil Reservoir Experimentally) experiment was conducted on fallow land in the Southwest of France. A three year continuous data set, including climatic variables, energy fluxes, surface water content, soil moisture profiles, surface and soil temperature, and evolution of vegetation characteristics was collected. The field possessed a plant-residue mulch layer, formed naturally by the accumulation of decaying and dead biomass. The three-year data set was used to analyse and model the long-term water and heat exchanges of the field using the SiSPAT (Simple Soil Plant Atmosphere Transfer) model. The original version was modified to take into account heat and water transfer within the plant-residue mulch layer. The 1995 data set was used for calibration of unmeasured parameters. Years 1996 and 1997 were used for validation of the approach, using the same parameter set obtained in 1995. Model results and observations were in good agreement for the three years when the plant-residue (mulch) layer effect was considered. The model properly reproduced contrasting responses to different rainfall conditions. Model simulations were used to understand some physical processes modified by the mulch layer. A decrease of 5–10% of annual total evaporation was obtained, as compared to the residue free case, associated with a decrease in soil evaporation and increase of transpiration. The decrease in soil evaporation was responsible for higher surface soil moisture. Daily soil and air temperature profiles were shown to be considerably modified by the mulch layer, an inversion occurring within the mulch, leading to colder averages and a smaller amplitude for soil temperature.

Laboratory study of biological retention for urban stormwater management.

Urban stormwater runoff contains a broad range of pollutants that are transported to natural water systems. A practice known as biological retention (bioretention) has been suggested to manage stormwater runoff from small, developed areas. Bioretention facilities consist of porous soil, a topping layer of hardwood mulch, and a variety of different plant species. A detailed study of the characteristics and performance of bioretention systems for the removal of several heavy metals (copper, lead, and zinc) and nutrients (phosphorus, total Kjeldahl nitrogen [TKN], ammonium, and nitrate) from a synthetic urban stormwater runoff was completed using batch and column adsorption studies along with pilot-scale laboratory systems. The roles of the soil, mulch, and plants in the removal of heavy metals and nutrients were evaluated to estimate the treatment capacity of laboratory bioretention systems. Reductions in concentrations of all metals were excellent (> 90%) with specific metal removals of 15 to 145 mg/m2 per event. Moderate reductions of TKN, ammonium, and phosphorus levels were found (60 to 80%). Little nitrate was removed, and nitrate production was noted in several cases. The importance of the mulch layer in metal removal was identified. Overall results support the use of bioretention as a stormwater best management practice and indicate the need for further research and development.

Rainfall interception loss by pebble mulch in the semiarid region of China

Pebble mulches have been used to conserve soil moisture in the semiarid regions of China for over 300 years. However, little work has been carried out on rainfall interception loss by a pebble mulch layer. A field study was conducted to measure interception loss by pebble mulches during individual rainfall events, determine the rainfall-storage capacity of pebble mulch, and discuss the relationships between interception and rainfall parameters. The study showed that pebble size could affect interception loss. A 5 cm-thick pebble mulch layer, with pebbles 7.5–14.0 cm in the long dimension and 5.0–9.0 cm in the short dimension (larger pebble), had a saturation value of 0.281 mm, an average interception of 0.481 mm, and an average percentage interception of 11.5% during individual rainfall events. In contrast, a similar layer, with pebbles 2.0–6.5 cm in the long dimension and 2.0–6.0 cm in the short dimension (smaller pebble), had a saturation value of 0.526 mm, and an average interception of 0.742 mm, or 17.4% gross rainfall per storm. The correlation between interception by pebble mulch and gross rainfall was poor. The proportion of gross rainfall intercepted by pebble mulch tended to decrease as gross rainfall increased. The reduction in percentage was very marked for rains over 10 mm. Interception showed a tendency to decline with increasing rain intensity ( I 30). There was a broad variability in interception for intensities under 6 mm h −1. Interception tended to remain constant at about 0.25 mm for larger pebble and 0.40 mm for smaller pebble when intensity was over 6 mm h −1. Antecedent water content of pebble before a storm significantly affected interception loss, with about 50% interception occurring in the initial stage of a rainfall event. Rainfall duration and wind factors should, therefore, also be considered in future interception analysis.

Modelling heat and water exchanges of fallow land covered with plant-residue mulch

To document the long-term energy and water budget of a fallow land, a complete dataset was collected in the south-west of France. It included climatic data, surface fluxes, vegetation evolution and soil moisture monitoring. The soil hydrodynamic and thermal properties were also determined in situ and through laboratory measurements. The experiment was conducted during 3 years (1995–1997) on a 20 ha field. A natural plant-residue mulch layer was constantly covering the field. Its thickness artificially increased in June 1995 when the farmer unexpectedly cut the grass and left the residue on the ground. Two versions of the simple soil plant atmosphere transfer (SiSPAT) model were compared using the 1995 dataset: the original version which did not take into account the mulch layer; and a modified version where explicit modelling of the mulch was included (SiSPAT-mulch). The prediction of soil temperature, surface fluxes and surface soil moisture was improved when considering a mulch layer. Annual surface evaporation was divided by a factor two to four and transpiration increased by 30–50% when considering the mulch layer. Annual total evaporation decreases by 4–10% according to mulch characteristics, leading to a better simulation of the annual and daily water balance of the site. A sensitivity analysis investigated the robustness of these results and possible causes of inaccuracies on half hour values.

Reducing tillage intensity — a review of results from a long-term study in Germany

This paper reviews research performed at the Justus-Liebig-University of Giessen, Germany into the impact of different tillage systems on soil properties and quality. The impact of intensive soil tillage treatments on several soil properties was described by means of selected data obtained through long-term interdisciplinary research. The experiments were based on comparative application (long-term, up to 18 years investigations) of the respective tillage options on different soils (e.g. Eutric Cambisol, Eutric Fluvisol) ranging in texture from sand to a silt loam. These soils are located at five field sites with different crop rotations in the central German state of Hesse. Tillage intensity of the systems was considered to decrease in the following sequence: Conventional plough tillage (CT), reduced tillage (RT), and no-tillage (NT). For elucidating the impact of tillage intensity, the tillage extremes CT and NT were compared. Physical conditions of soil as influenced by the application of RT were considered to be intermediate between CT and NT. In general, bulk density in the upper layer of NT soils was increased, resulting in a decrease in the amount of coarse pores, and a lower saturated hydraulic conductivity when compared with the CT and RT soils. Surface cover by crop residues and higher aggregate stability under NT protected soil fertility by avoiding surface sealing and erosion. Lateral losses of herbicides were also reduced under NT conditions, whereas the susceptibility for preferential vertical transport of herbicides needs further evaluation. Accumulation of organic matter and nutrients near the soil surface under NT and RT were favorable consequences of not inverting the soil and by maintaining a mulch layer on the surface. Those improvements were associated with enhanced biological activities in NT and RT topsoils. Increased earthworm activity in NT treatments was associated with a system of continuous macropores which improved water infiltration rates. Earthworms support decomposition and incorporation of straw. Soils which have not been tilled for many years were more resistant to vehicle passage; consequently, the compaction by traffic was lower. Penetration resistance curves indicate that a uniformly stable structure had developed over the years in NT soils. Overall, the results show that RT and NT were beneficial to the investigated soil properties. If crop rotation, machinery, and plant protection are well adapted for the introduction of conservation tillage, these systems may replace conventional ploughing systems in many cases in German agriculture.

Carbon flux in a subalpine spruce-fir forest: pulse release from Hylocomium splendens feather-moss mats

Mature subalpine spruce-fir forests in western Alberta are often characterized by extensive feather-moss mat coverage of the forest floor surface. The ecosystem role of these mats has been described as one of a nutrient sink because of their ability to assimilate solutes from throughflow solutions and their role as a catchment area for litterfall and detritus. These bryophyte mats are subject to recurring episodes of wetting and drying during the summer months. We examined the potential for pulse release to throughflow solution of previously sequestered carbon held by Hylocomium splendens (Hedw.) B.S.G. During rehydration, pulse release, measured as total organic carbon (TOC), reached 1544 mg·m-2. At a stand level basis this represents up to 15 kg·ha-1 pulse release of readily soluble carbon from the live green layer of H. splendens moss mats during each rewetting event. Control throughflow collectors, where moss mats were replaced by an inert mulch layer, indicated that from 23 to 75% of this pulse release originated in the moss mats. High intensity rain events resulted in larger net TOC and K release, as did a pretreatment history of rapid drying of H. splendens fronds. These findings suggest that feather-moss mats may function, in part, as ecosystem capacitors, sequestering nutrients and carbon at low concentrations from atmospheric sources, which are later released at higher concentrations during rewetting events.Key words: bryophyte, pulse release, carbon cycling, moss, nutrient cycling, montane forest.

Distribution patterns of the litter macrofauna in agroforestry and monoculture plantations in central Amazonia as affected by plant species and management

Within heterogeneous land-use systems such as agroforestry or mixed tree crop plantations, the different morphological and physiological characteristics of the plants, together with their species-specific management, lead to a mosaic of different living conditions for the litter fauna. This may, in turn, influence the processes of decomposition and nutrient cycling and, thus, the growth-conditions of the plants. We studied the effect of different plant species on the litter macrofauna by collecting macro-invertebrates in the litter layer of an agroforestry system composed of four regionally important tree crop species in central Amazonia: cupuaçu ( Theobroma grandiflorum), annatto ( Bixa orellana), Brazil nut ( Bertholletia excelsa) and peach palm ( Bactris gasipaes), with the leguminous cover crop Pueraria phaseoloides and spontaneous grasses as soil cover. The agroforestry system was studied at two fertilisation levels and was compared with a peach palm monoculture. We found invertebrates belonging to 18 orders and 44 families. The number of fauna individuals per unit area differed significantly between plant species within the agroforestry system. Both the number of individuals and the faunal biomass increased linearly with litter dry matter per unit area. The Shannon–Wiener index of family diversity showed a non-linear increase with increasing sampling area and litter mass in the samples, approaching saturation values between 2 and 2.5. The highest faunal abundance and diversity was found in the litter of the peach palm monoculture, apparently due to the stable and protected habitat provided by the fleshy offshoot remains from the palm harvests. The two fertiliser levels only differed with respect to two invertebrate groups, snails and isopods. The results indicate that the creation of a litter and/or mulch layer of at least 3 Mg ha −1, but preferably 6 Mg ha −1 and the association of tree and cover crop species whose litter has a favourable effect on the fauna with species whose litter has a less favourable effect are suitable management tools for the conservation of an abundant and diverse litter fauna in plantations and agroforestry systems of the humid tropics.

The Effect of Varying Cultural Practices on the Location of Mycorrhizal Infection within the Rhizosphere of Highbush Blueberry Plants

Previous experiments in the laboratory and the field have suggested that location of mycorrhizal infection within the rhizosphere of blueberry plants may depend on cultural practices that are being used. Furthermore, we have observed that rapidly growing roots, whether in solution culture or within petri dishes, appear to be less likely to become infected when inoculated. A preliminary experiment found higher levels of mycorrhizal infection in roots growing at a 5-cm depth of soil compared to roots growing just under the mulch layer. To further test this hypothesis, an experiment was designed to evaluate the infection intensity of highbush blueberry plants (Vaccinium corymbosum L.) at different locations within the rhizosphere on plants growing under varying cultural practices. Cultural practices included mulching (mulch vs. no mulch) and nitrogen level (0 and 120 g ammonium sulfate/plant). Four-year-old `Bluecrop' highbush blueberry plants subjected to these treatments were arranged in a complete factorial design with six replications at the Russell E. Larson Agricultural Research Center at Rock Springs, Pa. Mycorrhizal infection intensity was evaluated from roots sampled nondestructively using a 2.5 cm soil corer at the interface of the mulch and soil, and at soil depths of 3 and 15 cm from two locations 15 cm from the crown of each plant. Results will be discussed.

Weed Control Consideration in Compost Production and Use

A rapid increase in municipal solid waste (MSW) production (2 kg/person per day), combined with a decreasing number of operating landfills, has increased waste disposal costs. Composting MSW can be an alternative method of waste disposal to traditional landfilling or incineration. Weed control methods using waste materials such as bark, straw, and sawdust were used in commercial crop production for many years before the advent of chemical weed control. Weed growth suppression by mulching can often be almost as effective as conventional herbicides. A 10 to 15 cm-deep mulch layer is needed to completely discourage weed growth in these systems, and best results are obtained with composted materials. In recent years, composts made from a large variety of waste materials have become available on a commercial scale. Preliminary investigations into the use of MSW compost as a weed control agent have shown that compost, especially in an immature state, applied to row crop middles reduced weed growth due to its high concentration of acetic, propionic, and butyric acids. Subsequently, compost can be incorporated into the soil for the following growing season to potentially improve soil physical and chemical properties. Integrated pest management programs that incorporate biological control should be adopted wherever possible because some weed species with persistent seeds can escape chemical control.

Packing Summer Fallow in the Pacific Northwest: Agronomic Benefits and Environmental Concerns

AbstractWinter wheat (Triticum aestivum L.) is sown as deep as 20 cm below the summer fallow soil surface in dry years in the semiarid Pacific Northwest (PNW). Many growers pack the summer fallow mulch in late August before seeding winter wheat to improve stand establishment. But packing may increase blowing dust, which is a major soil loss and air quality concern. A 2‐yr study was conducted on two silt loam soil types in 280 mm and 230 mm average annual precipitation zones in eastern Washington to determine the agronomic benefits and potential wind erosion hazards associated with packing. Packing a loose, thick surface mulch increased soil bulk density (BD) between the 5‐ to 12‐cm depth. This significantly benefited wheat seedling emergence and stand establishment, which subsequently increased grain yield 9% over nonpacked plots. But packing a soil with a thin mulch layer overlying a high BD tillage pan had no effect on soil BD, wheat seedling emergence, or grain yield. Packing rendered the soil more vulnerable to wind erosion at both locations by reducing soil clod mass 55% and surface residue 38% compared with not packing. There are agronomic benefits from packing summer fallow mulch before seeding, but packing should be practiced judiciously, and not considered when surface residue or soil clods are lacking. This is especially true for poorly aggregated coarse‐textured soils where soil structure is difficult to maintain.