Yard Waste Compost Research Articles

Influence of compost application rate on nutrient and heavy metal mobility: Implications for stormwater management.

Amending soils with compost has become increasingly common in stormwater management practices. Compost can be a source and sink for nutrients and heavy metals, and it is important to understand the effect of compost on pollutant leaching under different hydrologic conditions. The objectives of this study were (a) to quantify the distribution coefficient (Kd ) of PO4 -P and metals (Cd, Cr, Cu, Ni, Pb, Zn) for compost-soil blends and (b) to examine how compost rate alters leaching patterns of nutrients (NH4 -N, NO3 -N, PO4 -P) and metals from compost-soil blends. Material consisted of a sandy loam subsoil, a yard-waste compost, and compost-soil blends at 20 or 50% compost by volume. Materials were tested in sorption-desorption experiments using simulated stormwater (SW); columns with the materials were also leached with either SW or deionized (DI) water. As compost rate increased, the Kd decreased for PO4 -P and Cr but increased for Cd, Cu, Ni, and Zn. The addition of compost reduced the sorption of PO4 -P and Cr, potentially making it a source of these pollutants. Simulated stormwater did not increase the amount of pollutants retained compared with DI water for compost blends, except for 100% compost columns. Nitrate was the only constituent that had a negative removal efficiency, suggesting the compost was a source of NO3 -N. Column media retained >70% of the metals from the added stormwater solution. These results suggest that yard-waste compost blends at ≤50% have the potential to retain certain pollutants from infiltrating stormwater, but this effect may decline after several storm events.

Compost applications increase bacterial community diversity in the apple rhizosphere

AbstractSustainable practices are key to the improvement of soil fertility and quality in apple (Malus × domestica Borkh.) orchards. Rootstock genotype and fertilizer inputs can alter soil biology, as well as aboveground traits including nutrient acquisition. In this study, a factorial design was used to assess the interaction between two apple rootstocks, ‘Geneva 41’ (‘G.41’) and ‘Malling 9’ (‘M.9’) with four fertilizer treatments [chicken‐litter compost, yardwaste compost, fertigation using Ca(NO3)2, and an unamended control]. The bacterial community in the rhizosphere was assessed for its impact on both plant and soil properties for each rootstock × fertilizer treatment combination. The bacterial community was dominated by Acidobacteria, Proteobacteria, and Planctomycetes, but Verrucomicrobia and Chloroflexi were the most responsive to the fertilizer treatments. The chicken litter and yardwaste treatments had a greater effect on bacterial community structure than the control. Yardwaste, in particular, was associated with increased relative abundance of Chloroflexi, which was correlated with soil nutrient concentrations. Malling 9 had a greater bacterial diversity than G.41, but the rootstock treatment had no independent effect on the rhizosphere community structure. There was, however, a strong interaction between the rootstock and fertilizer treatments. Carbon cycling was the most prominent functional change associated with the soil bacterial community. These results suggest that compost amendments have a more positive effect on soil bacterial activity and nutrient availability than Ca(NO3)2. Our work shows that waste‐stream amendments can lead to multiple positive responses, such as increasing aboveground tree biomass, thus potentially improving orchard productivity.

Different organic mulch materials affect the abundance of enchytraeids in an open-field experiment

Organic mulch may provide favourable soil conditions e.g. soil moisture or organic matter content, which may enhance the number of enchytraeids. However, there is no sufficient information about the relationship between plant-based mulch and this beneficial soil animal group. Therefore, an open-field experiment was conducted with tomato as a test plant to examine the effect of different types of organic mulch materials on the natural occurence of enchytraeids. Our study microplots received the following treatments: 1) yard-waste compost, 2) walnut leaf litter, 3) mixed leaf litter without walnut and 4) wheat straw. Control microplots were left unmulched. Randomized block design was used with eight replications to the treatments and four to the control. At the end of the growing season, three soil samples were taken from the root zone of each plant with a split soil corer, and enchytraeids were extracted by the wet funnel method. Living enchytraeids were counted under a dissecting microscope, and their density values were estimated. Worms were identified in five randomly selected samples of each treatment. In addition, soil moisture was determined by oven-drying as well. Mulch material types had significantly different effects on both Enchytraeid density and soil moisture. Under walnut leaf litter, mixed leaf litter and straw cover, higher numbers of individuals were found. In the case of soil moisture content, straw mulching had the highest value, while compost and uncovered surfaces the lowest. It appears that mulch materials serve as food source and provide favourable conditions for enchytraeid communities as well.

Compost and Biochar to Promote Soil Biological Activities under Sweet Potatoes Cultivation in a Subtropical Semiarid Region

South Texas is located in a subtropical semiarid climate, and due to high temperature and irregular precipitation, farmers opt to leave their fields fallow during the summer months jeopardizing overall soil health. We evaluated whether sweet potato (Ipomoea batatas) cultivation coupled with drip irrigation could restore soil biological activities compared with bare fallow. Additionally, because sweet potatoes have high demand of soil nutrients, especially potassium (K), we evaluated the nutrient supply of locally sourced soil amendments. Sweet potato was cultivated during summer 2018 in McAllen, Texas, under control (no fertilizer), NPK (synthetic fertilizer), RC (yard-waste compost), and AC (compost produced under an enhanced composting process), and biochar (gasified walnut shell at 900°C), each with three replicates. Soil amendments were applied at different amounts to result in a rate of 80 kg K ha−1. Soil biological indicators were microbial biomass phosphorous, phosphatase activity, and the rate of fluorescein diacetate hydrolysis (FDA). Available nitrogen, phosphorus, potassium, and sodium were also quantified. Aboveground biomass and storage root yield estimated sweet potato’s agronomic performance. Cultivation and irrigation stimulated soil enzyme activities and microbial biomass-phosphorous. Sweet potato yields were the highest in NPK treatment but still 2.8 times lower than variety’s potential yield. Storage root yield was inversely related to aboveground biomass, suggesting that growing conditions benefited the production of shoot versus roots. Both biochar and AC treatments stimulated FDA rates and K availability. Soil pH and sodium concentration increased in all treatments over the growing season, possibly due to river-sourced irrigation water. Together, these findings show that crop cultivation promoted soil biological activities and the maintenance of nutrient cycling, compared to bare-fallow conditions. For a better agronomic performance of sweet potato, it would be necessary to identify management practices that minimize increase in soil pH and salinity.

Winter cover crops increase readily decomposable soil carbon, but compost drives total soil carbon during eight years of intensive, organic vegetable production in California.

Maintaining soil organic carbon (SOC) in frequently tilled, intensive organic vegetable production systems is a challenge that is not well understood. Compost and cover crops are often used to add organic matter to the soil in these systems. Compost contributes relatively stabilized carbon (C) while cover crops provide readily degradable (labile) organic matter. Our objectives were to quantify C inputs, and to assess the effects of urban yard-waste compost, winter cover crop frequency and cover crop type on SOC and labile C stocks during eight years of intensive, organic production that usually included two vegetable crops per year in a long-term systems study in Salinas, California. Total C inputs from pelleted fertilizer, compost, vegetable transplant potting mix, vegetable residue and cover crops, including estimates of below ground inputs, ranged from 40 to 108 Mg ha-1 in the five systems evaluated. Following a rapid decline in SOC stocks in year 1, compost had the largest effect on SOC stocks increasing mean SOC over years 2 to 8 by an average of 9.4 Mg ha-1, while increased cover crop frequency (annual vs. quadrennial) led to an additional 3.4 Mg ha-1 increase. In contrast, cover cropping frequency had the largest effect on permanganate oxidizable labile C (POX-C), increasing POX-C by 26% after 8 years. Labile POX-C was well correlated with microbial biomass C and nitrogen. Compost had the greatest effect on total SOC stocks, while increasing cover crop frequency altered the composition of SOC by increasing the proportion of labile C. These results suggest that frequent winter cover cropping has a greater potential than compost to increase nutrient availability and vegetable yields in high-input, tillage intensive vegetable systems.

Evaluating anaerobic soil disinfestation and other biological soil management strategies for open-field tomato production in Florida

AbstractIn the search for alternative practices to chemical soil fumigation (CSF), anaerobic soil disinfestation (ASD) has proven to be a promising tool for soil-borne pest management and crop production improvement. The ASD treatment with composted poultry litter (CPL) and molasses (M, a labile carbon source) was identified as an effective approach for a biologically based soil disinfestation system in tomato (Solanum lycopersicum L.) production in Florida. However, environmental and food-safety concerns are associated with animal manure-based amendments, which led to the exploration of composted yard waste (CYW) as a potential substitute for CPL in ASD application. In this study, field trials were conducted in Citra and Immokalee, FL to examine the effects of ASD using CYW, CPL and M compared with a commercially available microbial amendment system on root-knot nematodes, weeds, fruit yield and quality of fresh-market tomato. Treatments included (1) ASD with CPL (11 Mg ha−1) and M (6.9 m3 ha−1) (ASD0.5), (2) ASD with CYW (26.9 Mg ha−1) and M (CYW1 + M), (3) ASD with CYW (13.5 Mg ha−1) and M (CYW0.5 + M), (4) Soil Symphony Amendment (SSA), (5) CYW (26.9 Mg ha−1) alone (CYW1) and (6) a combination of CYW1 + SSA, in comparison with (7) untreated control and (8) CSF (Pic-Clor 60 at 224 kg ha−1). Cumulative soil anaerobiosis was greater in ASD0.5 compared with all the other treatments. The root-knot nematode gall index ratings on the tomato crop were significantly lower in CSF, ASD0.5, CYW1 + M and CYW0.5 + M than untreated control in Citra. Although CYW1 and SSA alone had a moderately suppressive effect on weed coverage and root-knot nematodes, their positive impact on crop performance was limited when used alone. ASD0.5, CYW1 + M and CSF had significantly higher marketable and total fruit yields than untreated control in both locations, while all treatments showed promising results in the Immokalee trial in comparison with untreated control. In general, few differences in major fruit quality attributes were found. Although using CYW in ASD was not as effective as CPL in creating soil anaerobic conditions, the enhanced crop performance in CYW1 + M and CYW0.5 + M suggests the potential of using CYW as an alternative source of organic amendment in combination with M to achieve benefits similar to those obtained with CPL-based ASD.

Accelerating biodegradation of PLA using microbial consortium from dairy wastewater sludge combined with PLA-degrading bacterium

This work mainly aims to develop an efficient method for accelerating degradation of commercial polylactic acid beverage cups (cPLA). Ultraviolet (UV) irradiation was used to reduce the molecular weight of cPLA. The cPLA sheets were buried in soil amended with various sources of microbial consortium, including cow-manure compost, green yard-waste compost, and wastewater sludges from dairy, rice vermicelli and coconut milk factories. Interestingly, a complete degradation of cPLA sheets was found after 15 days of burial in the soil with dairy wastewater sludge, having high total nitrogen content. The dominant bacterial genus in the soil mixture of agricultural soil and dairy wastewater sludge was Actinomadura. In addition, there were the significant increases in the percentages of biodegradation and weight loss of cPLA and neat PLA (nPLA) in the soil with dairy wastewater sludge and Pseudomonas geniculata WS3, compared to the uninoculated control, indicating a synergistic action of the microbial consortium in sludge and P. geniculata WS3 on PLA biodegradability. The cPLA was more difficult to degrade than nPLA. In conclusion, UV-C irradiation of PLA followed by burying in a soil mixture of dairy wastewater sludge with P. geniculata WS3 inoculation is an efficient method for accelerating degradation of PLA waste.

Impact of Engineered Filter Bed Substrate Composition and Plants on Stormwater Remediation within a Rain Garden System1

Abstract Thirty-two rain-garden-engineered filter-bed substrates (EFBS) resulting from combinations of two substrate bases (sand and slate), two organic matter amendments [composted yard waste (CYW) and pine bark (PB)], two combination methods (banding and incorporation), and four combination amounts [2.5 cm/5%, 5.1 cm/10%, 7.6 cm/15%, and 10.2 cm/20% (by vol.)] were evaluated using three plant species (Betula nigra L. ‘Duraheat', Monarda fistulosa L. and Panicum virgatum L. ‘Shenandoah'). The impact of particle size distribution, saturated hydraulic conductivity (Ksat), volume of effluent, evapotranspiration, EFBS composition, and plant growth on water movement within a rain garden was determined. Sand EFBS maintained a numerically lower Ksat compared to slate EFBS regardless of composition. Using CYW and banding reduced effluent volume and increased evapotranspiration. Each EFBS was also evaluated for its ability to support plant growth and nutrient uptake. Shoot dry weight and shoot nutrient content (nitrogen and phosphorus) trends were similar and were highest for all species when grown in sand amended with banded CYW. Higher levels of total soluble nitrogen (TSN) were in the effluent from CYW compared to PB, regardless of substrate base. Sand generally had lower concentrations of TSN and PO4−3-P present in the effluent than slate. Index words: bioretention cell; saturated hydraulic conductivity (Ksat); effluent volume; effluent nutrient concentration; evapotranspiration; particle size distribution; total soluble nitrogen; ortho-phosphate; nitrate; ammonium. Species used in this study: ‘Duraheat' river birch (Betula nigra L.); wild bee balm (Monarda fistulosa L.); and ‘Shenandoah' switch grass (Panicum virgatum L.).

Enrichment of antibiotic resistance genes in soil receiving composts derived from swine manure, yard wastes, or food wastes, and evidence for multiyear persistence of swine Clostridium spp.

The impact of amendment with swine manure compost (SMC), yard waste compost (YWC), or food waste compost (FWC) on the abundance of antibiotic resistance genes in soil was evaluated. Following a commercial-scale application of the composts in a field experiment, soils were sampled periodically for a decade, and archived air-dried. Soil DNA was extracted and gene targets quantified by qPCR. Compared with untreated control soil, all 3 amendment types increased the abundance of gene targets for up to 4 years postapplication. The abundance of several gene targets was much higher in soil amended with SMC than in soil receiving either YWC or FWC. The gene target ermB remained higher in the SMC treatment for a decade postapplication. Clostridia were significantly more abundant in the SMC-amended soil throughout the decade following application. Eight percent of Clostridium spp. isolates from the SMC treatment carried ermB. Overall, addition of organic amendments to soils has the potential to increase the abundance of antibiotic resistance genes. Amendments of fecal origin, such as SMC, will in addition entrain bacteria carrying antibiotic resistance genes. Environmentally recalcitrant clostridia, and the antibiotic resistance genes that they carry, will persist for many years under field conditions following the application of SMC.

Alternative Fertility Management for Establishing New Apple Orchards in the Mid-Atlantic

In the Mid-Atlantic, mineral nitrogen (N) fertilizers are applied in high-density apple (Malus ×domestica Borkh.) orchards to increase tree vegetative growth and achieve earlier fruiting. However, when applied in excess of plant needs, N fertilizer applications are an unnecessary expense and may lead to N leaching and groundwater pollution. Therefore, it is necessary to develop orchard fertilization programs that simultaneously provide adequate crop nutrition and minimize N loss into the environment. Nitrogen was applied in each of 3 years to newly planted ‘Red Delicious cv Schlect’/‘M.26’ trees at 67 kg N/ha/year in six fertilizer treatments: 1) two equal applications of granular calcium nitrate [Ca(NO3)2]; 2) chicken litter compost; 3) yardwaste compost; 4) a combination of chicken litter compost and granular Ca(NO3)2 with equal amounts of N from each fertilizer; 5) a combination of yardwaste compost and granular Ca(NO3)2 with equal amounts of N from each fertilizer; and 6) fertigation which consisted of eight weekly applications of solubilized Ca(NO3)2. Nonfertilized trees served as the control. In the third year of this experiment, the two chicken litter compost treatments had the greatest soil extractable P, the yardwaste compost treatment had the greatest soil extractable K, both full-rate compost treatments had greater soil extractable Mg than the other treatments, and all four compost treatments had greater soil extractable Mn than the treatments without compost. The four compost treatments also had greater soil extractable Ca and B than treatments without compost. By the third year of the experiment, the four compost treatments also had greater soil organic matter (OM) and soil C (with the integrated chicken litter compost treatment having similar soil C to the other treatments). Potentially mineralizable nitrogen and soil microbial biomass were similar among the treatments over the course of this experiment. The full rate chicken litter compost treatment and both yardwaste compost treatments had greater soil microbial respiration in 2015. The fertigation treatment performed similarly to the treatment where Ca(NO3)2 was applied as a granular product to the soil. Treatment differences found for the soil properties did not translate to increased tree size or leaf N content, suggesting that the trees were able to acquire sufficient N from the soil under all of the treatments. Our results suggest that applying fertilizers to fine textured soil with relatively high OM may not increase apple tree growth or productivity within the first 3 years after planting. In addition, compost applications can improve many soil properties, but these differences may not result in improved orchard productivity within 3 years.

Cover cropping frequency is the main driver of soil microbial changes during six years of organic vegetable production

Soil microbes play a key role in soil health, and understanding the functional role of this living component of soil organic matter is critical to developing sustainable systems in major vegetable production regions like Salinas, California. Soil microbial community size and composition was evaluated after six years of commercial-scale production in five organic vegetable systems in a long-term systems experiment. All systems produced lettuce, and spinach or broccoli annually, and differed in yard-waste compost inputs (none or 15.2 Mg ha−1 year−1), winter cover crop frequency (annually or every 4th year), and cover crop type (legume-rye, mustard, or rye). The same levels of irrigation, and supplemental fertilizer were applied to all systems. Cumulative organic matter inputs from compost and cover crop shoots over the six years ranged from 7.4 to 136.8 Mg ha−1 and caused differences in microbial biomass C (MBC) and N (MBN), and soil organic C (SOC). MBC increased by 40 mg C kg−1 soil with compost and infrequent cover cropping, and to levels that were relatively high (200–250 mg C kg−1 soil) for a loamy sand soil in systems with annual cover cropping. Changes in SOC between systems were caused primarily by compost while changes in MBC and MBN were more related to cover cropping frequency. Fatty acid methyl ester (FAME) analysis revealed differences in microbial community structure that were consistent with differences between systems in MBC and MBN. Across systems, the ratio of fungal: bacterial FAME indicators decreased over time while indicators of invertebrates, and gram positive bacteria increased. High-throughput sequencing revealed relatively few differences in bacterial phyla between systems, but the increase in cropping intensity across all systems changed the relative abundance of some bacterial phyla (Bacteroidetes, Deinococcus-Thermus) and genera (Flavobacterium, Nocardioidetes). Cover crop type and frequency also influenced the abundance of two bacterial genera (Pseudomonas, Agromyces). These results provide evidence that carbon (C) inputs from frequent cover cropping are the primary driver of changes in the soil food web and soil health in high-input, tillage-intensive organic vegetable production systems.

Compost mulch no-tillage systems in organic vegetable production

With growing agricultural demands from both conventional and organic systems comes the need for sustainable practices to ensure long-term productivity. In Hungary small scale vegetable growers face challenges in producing their crops due to the lack of effective weed control practices and viable methods of sustainable soil fertility management based on local or regional soil amendment resources. There is a demand for cultural practices that reduce hand labor requirements and black plastic mulches whereas long-term productivity is held or increased. To identify effective alternative weed control and soil fertility management options for the management of intensive organic vegetable systems, our research focuses on the evaluation of compost and paper mulches, in conjunction with reduced-tillage practices. In 2015 determinate tomato (cv. Roma) is grown in five different soil treatments using yard waste compost (YWC) mulch and combination of YWC and paper mulch (PM) plus bare ground control under intensive and reduced tillage variants to evaluate their effectiveness on organic tomato marketable yield and weed suppression. Since most organic tomatoes at present are grown on small acreage in Hungary, and are direct-marketed, the application of organic mulches can be assumed financially feasible. Our results will show if the combination of organic mulching materials together with reduced tillage may be a viable option for organic vegetable growers. Keywords: alternative weed control, compost, compost mulch, paper mulch, organic, no tillage, vegetable, tomato

Assessment of Selected Bioretention Blends for Nutrient Retention Using Mesocosm Experiments

This study compares the performance of three bioretention media blends for N and P removal from simulated urban runoff in experimental mesocosms. TerraSolve, Biofilter, and "VT Mix" (Virginia Tech) were compared with and without vegetation at varying hydraulic residence times (HRTs). Adsorption isotherm experiments were also conducted. TerraSolve and VT Mix included water treatment residuals (WTRs), Biofilter and VT Mix included yard-waste compost (YWC), and TerraSolve included a mix of coir and peat. TerraSolve removed the highest amount of total P (>95%), which is attributed to the high quantity of WTRs. Results were similar for VT Mix, likely due to WTR content. Adsorption isotherms indicate a substantial difference due to this factor. Vegetative mesocosms were found to be less effective at P removal at an HRT of 6 to 12 h but not at an HRT of 24 h. VT Mix had the highest removal of total Kjeldahl nitrogen (TKN), significantly different than the other blends. Interactive effects with vegetation were observed, generally improving TKN removal at all HRTs, with the highest at 24 h. Substantial export of nutrients when using compost was not observed. The addition of YWC appeared to increase N removal, possibly by denitrification. It is recommended that bioretention media contain <10% fines, a source of amorphous Al for P adsorption, at least 3 to 5% total organic C in the form of a low P, relatively stable compost, and a minimum concentration of plant-available nutrients for establishment of vegetation. For systems that use HRT, optimum residence time is influenced by media composition.

Influence of compost source on corn grain yields, nitrous oxide and carbon dioxide emissions in southwestern Ontario

Drury, C. F., Reynolds, W. D., Yang, X. M., Tan, C. S., Guo, X., McKenney, D. J., Fleming, R. and Denholme, K. 2014. Influence of compost source on corn grain yields, nitrous oxide and carbon dioxide emissions in southwestern Ontario. Can. J. Soil Sci. 94: 347–355. The impacts of compost type on corn grain yields over 10 yr and N2O and CO2 emissions in the first 3 yr after compost application were evaluated on a Brookston clay loam soil in Woodslee, ON. The treatments included yard waste compost (YWC), kitchen food waste compost (FWC), and pig manure compost (PMC), which were applied once in the fall of 1998 to field plots at a rate of 75 Mg ha−1 (dry weight basis) and no further applications occurred thereafter as well as a fertilized control treatment. Large application rates were examined to see if the various compost sources could have a lasting effect on soil C storage, N2O and CO2 emissions and corn yields. Compost application significantly increased corn grain yields by 12.9 to 19.4% over 3 yr. However, after 10 yr, FWC was the only compost source which significantly increased yields by 11.3% compared with the fertilized control. Emissions of N2O and CO2 varied with compost type, soil water content and time. Greater N2O emissions occurred in 1999 from PMC (5.4 kg N ha−1) than YWC (2.7 kg N ha−1) and FWC (1.3 kg N ha−1); however, the N2O emissions from the PMC were less than from YWC and FWC in 2001. The 3-yr average N2O emissions were significantly greater with PMC (2.7 kg N ha−1) and YWC (2.5 kg N ha−1) compared with the control (1.5 kg N ha−1). Hence, the timing of N2O emissions varied by compost type, but the overall losses were similar as the higher N2O losses in the first year with PMC were offset by the reduced losses with PMC in the third year. Significantly more CO2 was produced from the FWC in 2000 and from PMC in 2001 than the control.

Organic carbon and nitrogen stocks in a clay loam soil 10 years after a single compost application

Yang, X., Reynolds, W. D., Drury, C. F., Fleming, R., Tan, C. S., Denholm, K. and Yang, J. 2014. Organic carbon and nitrogen stocks in a clay loam soil 10 years after a single compost application. Can. J. Soil Sci. 94: 357–363. Household food waste compost (FWC), yard waste compost (YWC) and pig manure plus wheat straw compost (PMC) were applied once in the fall of 1998 to a Brookston clay loam soil in southwestern Ontario to determine immediate and long-term effects of organic amendments on soil quality and productivity. In this report, we describe the residual effects of these single compost applications on soil organic carbon (SOC) and total soil nitrogen (TN) stocks 10 yr after compost addition (2009). FWC was applied at 75 Mg ha−1, 150 Mg ha−1 and 300 Mg ha−1, while YWC and PMC were applied at the single rate of 75 Mg ha−1. The 75 Mg ha−1 additions of YWC, PMC and FWC increased SOC in the top 30 cm relative to a control (no compost additions) by 12.3% (9.0 Mg ha−1), 16.6% (12.2 Mg ha−1) and 0%, respectively; and they increased TN relative to the control by 8.0% (0.53 Mg ha−1), 11.7% (0.77 Mg ha−1), and 0%, respectively. The 150 and 300 Mg ha−1 additions of FWC increased SOC in the top 30 cm by 13.0 and 24.7 Mg ha−1, respectively, and they increased TN by 0.93 and 1.70 Mg ha−1, respectively. These results indicate that increases in SOC and TN stocks accruing from a single compost addition can persist for at least a decade, but the degree of increase depends strongly on compost type and addition rate. It was concluded that high compost addition rates of FWC and/or addition of composts derived from recalcitrant organic materials may be a good strategy for achieving long-term carbon and nitrogen sequestration in the cool, humid fine-textured soils of southwestern Ontario.

Organic fertilizer effects on growth, crop yield, and soil microbial biomass indices in sole and intercropped peas and oats under organic farming conditions

In a field experiment, peas (Pisum sativum L.) and oats (Avena sativa L.) were grown as sole crops and intercrops, fertilized with horse manure and yard-waste compost derived from shrub and garden cuttings at 10tCha−1 each. The objectives were to compare the effects of these organic fertilizer and cropping system in organic farming on (a) yield of peas and oats, grown as the sole crop or intercropped, as well as N2 fixation and photosynthetic rates, (b) the yield of wheat as a succeeding crop, (c) microbial biomass indices in soil and roots, and (d) microbial activity estimated by the CO2 evolution rate in the field and the amount of organic fertilizers, recovered as particulate organic matter (POM). In general, organic fertilizer application improved nodule dry weight (DW), photosynthetic rates, N2 fixation, and N accumulation of peas as well as N concentration in oat grain. Averaged across fertilizer treatments, pea/oat intercropping significantly decreased nodule DW, N2 fixation and photosynthetic rate of peas by 14, 17, and 12%, respectively, and significantly increased the photosynthetic rate of oats by 20%. However, the land equivalent ratio (LER) of intercropped peas and oats exceeded 1.0, indicating a yield advantage over sole cropping. Soil microbial biomass was positively correlated with pea dry matter yields both in sole and intercropped systems. Organic fertilizers increased the contents of microbial biomass C, N, P, and fungal ergosterol in soil and CO2 production, whereas the cropping system had no effects on these microbial indices. According to the organic fertilizer recovered as POM, 70% (manure) and 64% (compost) of added C were decomposed, but only 39% (manure) and 13% (compost) could be attributed to CO2–C during a 101-day period. This indicated that horse manure was more readily available to soil microorganisms than compost, leading to increased grain yields of the succeeding winter wheat.

Respuesta de tomate (Solanum lycopersicum L.) a la fertilización con nitrógeno y aplicación de composta.

Por tres años se evaluaron los efectos de composta producida a partir de residuos vegetales y biosólidos, y de nitrógeno inorgánico en el crecimiento, rendimiento y calidad de fruta de tomate en las Subestaciones de Lajas (Typic Haplusterts) y Juana Díaz (Cumulic Haplustolls) (Subestación de Fortuna), Puerto Rico. En Fortuna, la aplicación de 50 t/ha aumentó el rendimiento sobre suelo sin enmendar pero una segunda aplicación de 50 y 100 t/ha redujo los rendimientos. No hubo un efecto residual de la composta en el tercer año. Los niveles de fertilización no incrementaron significativamente los rendimientos excepto en el tercer año, cuando los mayores rendimientos se obtuvieron con la aplicación de 75 kg N/ha en forma de fertilizante inorgánico. En Lajas, hubo respuesta a la fertilización inicial en uno de los dos sitios-años. La adición de composta no mejoró los rendimientos ni los componentes agronómicos del tomate. El uso del medidor de clorofila SPAD puede ser útil para la producción de tomate cultivado en bancos elevados, con plástico y riego por goteo porque los valores máximos de SPAD coincidieron con los mayores rendimientos obtenidos. La medida sirvió para evaluar el efecto de los tratamientos, aunque los resultados dependen de la variedad o híbrido utilizado. El nivel óptimo económico obtenido fue poco sensitivo a los precios de fertilizante y tomate seleccionado. El nivel óptimo de fertilización de N para obtener el 99% de rendimiento máximo fue 143 kg N/ha en áreas que recibieron aplicaciones iniciales de N en Lajas, y 165 kg N/ha en áreas con más de un año bajo el cultivo de tomate en Fortuna, con rendimientos cerca de 54 t/ha.

Laboratory Investigation of Rill Erosion on Compost Blankets under Concentrated Flow Conditions

A flume study was conducted using a soil, yard waste compost, and an erosion control compost to investigate the response to concentrated flow and determine if the shear stress model could be used to describe the response. Yard waste compost (YWC) and the bare Cecil soil (CS) control responded to concentrated laboratory runoff similarly in rill formation, and the shear stress model was useful in estimating sediment yields from both of these land covers. Results indicated that critical shear stress values for yard waste compost and Cecil soil were not significantly different. However, the erodibility of the soil was higher, resulting in increased solids loss, on the Cecil soil. Micro-dams, the main mechanism for limiting soil erosion for the compost, often occurred in the rills of the erosion control compost (ECC), causing the concentrated flow to infiltrate and fan out through the compost. Since flow could not be maintained in the rill, parameters for the stress model could not be determined for the erosion control compost.

Enzyme activities and heavy metals concentration in soil amended with sewage sludge

Municipal sewage sludge (MSS) and yard waste compost (YWC) provide amendments useful for improving soil structure and nutrient status. However, soil amendments contain heavy metals that may potentially affect soil microbes and the enzymes they produce. A field study was conducted using three soil managemet practices (MSS, YWC, and native soil). Broccoli (Brassica oleracea L.) seedlings were planted, and the activities of the enzymes hydrolyzing urea (urease), sucrose (invertase), and p-nitrophenyl phosphate (acid and alkaline phosphatase) were determined in spring and fall agricultural soil. The greater soil urease and invertase activities in spring soil amended with MSS provided evidence of increased soil microbial population. On the contrary, the application of YWC in spring did not alter soil urease or invertase activities to any appreciable extent. Overall acid and alkaline phosphatase were stimulated in soil amended with YWC. Nickel, Zn, and Cu increased in soil amended with MSS while, concentration of Pb increased after addition of YWC to native soil. Nickel and Pb were taken up by broccoli plants grown in MSS amended soil, but their concentration in broccoli heads were below the Codex Commission Allowable Limits.

Field Investigation of Compost Blankets for Erosion Control under Concentrated Flow Conditions

Compost blankets are recognized as an effective erosion control practice that has been utilized widely. While previous studies have proven that compost blankets can control erosion as well or better than traditional methods under normal rainfall and sheet flow conditions, little attention has been paid to how compost will respond to concentrated flow conditions. The objective of this research was to investigate erosion processes on compost blankets under concentrated flow conditions. Erosion control compost (ECC), yard waste compost (YWC), and a bare soil (BS, loam) were studied using four concentrated flow rates on 12.5% slope plots. Time to initiate discharge, flow velocity, solids concentration, and total loss of solids were measured. The erosion process and rill evolution under these conditions were observed and recorded. Results indicated that the time elapsed to commence discharge from compost plots was significantly longer than that from soil plots. Large amounts of inflow were able to infiltrate into the compost matrix and flow through it, leaving a smaller portion of surface flow on compost plots than on soil plots. Under high inflow rates (2.7 10-4 and 3.3 10-4 m3/s), solids loss from compost plots was significantly less than those from soil plots. Under a same inflow conditions, average solids concentrations were significantly lower on compost plots than on soil plots, as deposition occurred in compost rills. Deposited solids often formed micro-dams in the compost rills, which further promoted flow through the compost matrix and deposition of suspended particles. The formation of micro-dams in compost plots was an important mechanism in preventing soil erosion under concentrated flow conditions. Results of this study indicated that the erosion process on compost blankets may differ from classical shear-induced rill erosion on soil surfaces. Future work will investigate models that may be used to better understand and predict erosion of compost material under concentrated flow conditions.