Tom Forge

Effects of organic mulches on soil microfauna in the root zone of apple: implications for nutrient fluxes and functional diversity of the soil food web

A variety of organic materials (e.g. composts, paper recycling wastes, hay) can be used as in-row mulches in perennial horticultural cropping systems such as high density apple orchards. As organic materials with variable properties, such mulches can be expected to have variable effects on structure of the soil food web and mineralisation of N and P in the root zone. The overall objectives of this study were to: (1) assess the effects of a selection of organic mulches on the abundance of protozoa and nematode trophic groups; (2) use the model of Hunt et al. [Biol. Fertil. Soils 3 (1987) 393] to assess the implications of changes in microfaunal abundance for microbial turnover and N mineralisation; and (3) determine effects of the mulches on nematode indicators of increased microbial production/turnover and functional diversity of the soil food web. Organic mulch treatments commenced in 1994 and included shredded office paper, municipal biosolids, shredded paper applied over municipal biosolids, shredded paper applied over municipal compost, alfalfa hay, and black polyethylene fabric. The control was conventional tree-row weed management with glyphosate. Biosolids and municipal compost treatments were re-applied in 1997. Protozoan abundance was determined in 1998, 1999 and 2000. Nematode community structure was assessed in 1998, 1999, and twice in 2000. Nematode community parameters evaluated included: abundance of bacterivorous, fungivorous, omnivorous and predacious nematodes; abundance of the root-lesion nematode, Pratylenchus penetrans; absolute and relative abundances of enrichment opportunist nematodes (Rhabditidae+Diplogasteridae+Panagrolaimidae); Simpson’s diversity; evenness; and the indices of nematode community enrichment (EI) and structure (SI) described by Ferris et al. [Appl. Soil Ecol. 18 (2001) 13]. Measurements of the abundance of enrichment opportunists and the EI were evaluated as indicators of enhanced nutrient fluxes. Diversity and the SI were evaluated as indicators of changes in functional diversity of the soil food web. The abundance of protozoa and bacterivorous nematodes, and estimated fluxes of N and P through the microfauna, were greater under all combinations of biosolids or municipal compost and shredded paper than under the control and plastic mulch. The abundance of enrichment opportunist nematodes and the EI were also consistently greater under combinations of biosolids or municipal compost and shredded paper. The abundance of enrichment opportunists and EI were both also correlated with leaf P, providing additional evidence to support the use of these parameters as indicators of enhanced turnover of microbial biomass and nutrients. The SI was greatest under shredded paper and shredded paper applied over municipal compost, and least under municipal biosolids and alfalfa hay. Population densities of P. penetrans were reduced under shredded paper mulch relative to the control and biosolids alone.

Biosolids increase soil aggregation and protection of soil carbon five years after application on a crested wheatgrass pasture.

Biosolids application to rangelands and pastures recycles nutrients and organic matter back to soils. The effects of biosolids (20 and 60 dry Mg ha(-)(1)) and N+P fertilizer on soil aggregate stability, bulk density, aeration porosity, and total C and N of stable aggregates were evaluated 4 and 5 yr after surface application to a crested wheatgrass [Agropyron cristatum (L.) Gaertn.] pasture in the southern interior of British Columbia (BC). The experiment was established in 2001 in a randomized complete block design with four replications. The 60 Mg ha(-1) biosolids treatment (Bio 60) had a greater aggregate mean weight diameter (MWD) and proportion of water-stable soil aggregates > 1 mm relative to the control and fertilizer treatments. Temporal variation in aggregate stability was attributed to seasonal variations in soil water content. Surface application of 60 Mg ha(-1) of biosolids increased C concentrations within water-stable aggregates relative to the control from 29 to 104, 24 to 79, and 12 to 38 g kg(-1) for the 2 to 6, 1 to 2, and 0.25 to 1 mm size fractions, respectively. The concentration of N within aggregates increased in similar proportions to C. Neither soil bulk density, nor aeration porosity were affected by biosolids application. Increased aggregation and the accumulation of soil C within aggregates following biosolids application creates a potential for better soil C storage, soil water retention, nutrient availability, and ultimately the overall health of semiarid perennial pastures.

Suitable orchard floor management strategies in organic apple orchards that augment soil organic matter and maintain tree performance

AimsOrganically-certified orchard floor management was assessed for its ability to improve soil fertility and biological activity and apple orchard performance.Methods‘Ambrosia’/B9 apple was maintained for the first six growing seasons with four orchard floor treatments, including 1) annual compost application; 2) in-row application of mown alfalfa grown between the rows; 3) bark mulch plus in-row application of mown hay; and 4) black plastic mulch.ResultsSoil collected from 0 to 10 cm indicated high soil organic matter and exchangeable K were measurable for all treatments by the second year. After 6 years, highest organic matter, total-, particulate- and mineral–C were associated with soil beneath the bark mulch treatment which also had most vigorous trees, decreased leaf N and elevated leaf P and K. Addition of alfalfa and bark mulch were equally effective at maintaining high exchangeable K and soil phosphatase enzymes, high total and particulate-N by the fourth year.ConclusionsDespite measurable improvements in soil properties among treatments, fruit yield and quality were minimally affected by management implying no limitations to adoption of any of the assessed strategies.

Organic fruit production in British Columbia

British Columbia has climatic conditions suitable for the production of a wide range of high-value fruit crops, and has the highest rate of increase of organic production in Canada. This review assesses the current status of organic fruit production using a case study of the three most valuable fruit crops currently grown: apple (Malus × domestica Borkh.), grape (Vitis vinifera L.) and high bush blueberry (Vaccinium corybosum L.). The review emphasizes the current status of organically acceptable management of crop resources and crop protection from insects and diseases. Central to organic production are soil management strategies designed to maintain soil fertility and increase soil biological activity and biodiversity by increasing soil organic matter content. Composts and organic amendments that require vigilant testing of their variable and often lower nutrient content are substituted for the chemical fertilizers of conventional production. Increased effort to manage vegetation within and between plan...

Organic mulches influence population densities of root-lesion nematodes, soil health indicators, and root growth of red raspberry

The root-lesion nematode Pratylenchus penetrans is a pathogen of red raspberry (Rubus idaeus). A field experiment was initiated in 2003 to determine the effects of organic mulches of two different composts, broiler manure, and shredded paper co-applied with broiler manure, on (i) the abundance of P. penetrans, (ii) free-living nematodes as indicators of soil food web structure, and (iii) root biomass and early productivity of ‘Malahat’ red raspberry. The organic mulches were applied each year at rates estimated to provide the 1.5 m wide root zone strip with approximately 133 kg·ha–1 of potentially available nitrogen. The nonmulched control was fertilized each year with urea at 133 kg N·ha–1. Soil samples were taken from the root zone for root biomass and nematode analyses at five dates during the 2005 and 2006 growing seasons. Population densities of P. penetrans in soil were lower and root biomass was greater under one of the composts and the shredded paper - broiler manure mulch relative to the nonmulched treatment. Fine root biomass was negatively correlated with P. penetrans per gram root. The abundance of omnivorous and predacious nematodes was negatively correlated with P. penetrans population densities and positively correlated with root biomass. The data are consistent with our hypothesis that organic mulches increase soil food web structure and the abundance of nematode antagonists (e.g., predacious nematodes), resulting in reduced crop damage by P. penetrans. However, we cannot rule out the possibility that the improved raspberry root growth and primocane productivity was the result of beneficial changes in soil chemical properties, such as increases in exchangeable calcium and pH.

Effects of aeration, molasses, kelp, compost type, and carrot juice on the growth of Escherichia coli in compost teas

Growth of a nonpathogenic E. coli strain (K12- MG1655, ATCC 700926) in aerated and nonaerated compost teas containing molasses, kelp and carrot juice was examined. Teas were prepared using four different compost types that had undetectable levels of indigenous E. coli. Three of the composts were produced by turn pile windrow composting method using dairy, swine and horse manure as feedstock, while the fourth, a vermicompost, was produced by feeding separated dairy solids to worms Eisenia feotida. Molasses and kelp enhanced the growth of E. coli in inoculated teas and the E. coli density was positively correlated with nutrient concentrations ranging from 0.1 to 8.0 g/L. Irrespective of the presence of molasses and kelp, E. coli was not detected in noninoculated teas. Even though E. coli is a facultative anaerobe, its growth was significantly higher in nonaerated teas than in aerated teas. Without aeration, dissolved oxygen in teas declined rapidly and fell below 0.1 mg/L within 20 h, whereas continuous aeration at 0.8 L/min maintained an aerobic condition (> 5 mg/L dissolved oxygen) in teas during the 48 h brewing period. The pH values of nonaerated teas were significantly lower than those of aerated teas and were always slightly acidic. E. coli growth in different compost types was significantly different. The density of E. coli was lowest in teas made with vermicompost and highest in teas made with swine manure compost. E. coli proliferations in both aerated and nonaerated swine manure compost teas were inhibited by carrot juice. Carrot juice lowered dissolved oxygen in aerated teas. The total bacterial densities in noninoculated compost teas were not reduced by carrot juice.

Nutritional implications of biosolids and paper mulch applications in high density apple orchards

A field experiment was designed to assess the effects on tree nutrition of surface application of municipal biosolids and shredded paper mulch, which have previously been reported to improve the performance of high-density apples despite wide differences in nutrient content. The experiment involved four treatments which included two levels (with or without) of two organic amendments, shredded paper mulch and Greater Vancouver Regional District (GVRD) municipal biosolids. Treatments were established over a 2 m wide strip centred on the tree row in a high-density (3700 trees ha-1) Golden Delicious (Malus × domestica Borkh.) orchard in the year of planting (1997) and maintained until 2004. GVRD-biosolids was applied at 40 t ha-1 (DW) in 1997 and 20.3 t ha-1 (DW) in 2001 potentially supplying larger amounts of all plant nutrients (N, P, K, Mg, Zn, Cu and Mn) except Ca than the paper mulch. All trees received standard commercial treatments of drip fertigation of 30 g N tree-1 yr-1 and 20 g P tree-1 in the esta...

Using C. elegans Forward and Reverse Genetics to Identify New Compounds with Anthelmintic Activity

Background The lack of new anthelmintic agents is of growing concern because it affects human health and our food supply, as both livestock and plants are affected. Two principal factors contribute to this problem. First, nematode resistance to anthelmintic drugs is increasing worldwide and second, many effective nematicides pose environmental hazards. In this paper we address this problem by deploying a high throughput screening platform for anthelmintic drug discovery using the nematode Caenorhabditis elegans as a surrogate for infectious nematodes. This method offers the possibility of identifying new anthelmintics in a cost-effective and timely manner. Methods/Principal findings Using our high throughput screening platform we have identified 14 new potential anthelmintics by screening more than 26,000 compounds from the Chembridge and Maybridge chemical libraries. Using phylogenetic profiling we identified a subset of the 14 compounds as potential anthelmintics based on the relative sensitivity of C. elegans when compared to yeast and mammalian cells in culture. We showed that a subset of these compounds might employ mechanisms distinct from currently used anthelmintics by testing diverse drug resistant strains of C. elegans. One of these newly identified compounds targets mitochondrial complex II, and we used structural analysis of the target to suggest how differential binding of this compound may account for its different effects in nematodes versus mammalian cells. Conclusions/Significance The challenge of anthelmintic drug discovery is exacerbated by several factors; including, 1) the biochemical similarity between host and parasite genomes, 2) the geographic location of parasitic nematodes and 3) the rapid development of resistance. Accordingly, an approach that can screen large compound collections rapidly is required. C. elegans as a surrogate parasite offers the ability to screen compounds rapidly and, equally importantly, with specificity, thus reducing the potential toxicity of these compounds to the host and the environment. We believe this approach will help to replenish the pipeline of potential nematicides.

Effects of nitrogen rate and application method on early production and fruit quality in highbush blueberry

Ehret, D. L., Frey, B., Forge, T., Helmer, T., Bryla, D. R. and Zebarth, B. J. 2014. Effects of nitrogen rate and application method on early production and fruit quality in highbush blueberry. Can. J. Plant Sci. 94: 1165–1179. Proper nitrogen (N) fertilizer management of highbush blueberry (Vaccinium corymbosum L.) is of major importance in south-coastal British Columbia, but little information is available. A field study was conducted to examine the effects of N rate and method of application on growth, yield, and fruit quality in highbush blueberry during the first 4 yr after planting in south-coastal BC. Nitrogen was applied at 0–150% of current production guide rates either with three equal applications of broadcast granular ammonium sulphate each spring or by fertigation through the drip irrigation system with 10 equal applications of liquid ammonium sulphate injected every 2 wk from early spring to late summer each year. Yield increased with increasing N rate during the second and third years of fruit production. The yield response as well as flower number and plant size were greater with fertigation than with broadcast fertilizers. Fruit firmness also increased consistently with increased N rates, while fruit size either increased or decreased, depending on year. There were no effects of N on fruit oxygen radical absorbance capacity (ORAC), titratable acidity, or soluble solids. However, the composition of fruit anthocyanins changed, with concentrations of seven anthocyanins decreasing, and three others increasing, with N rate. In 2 of 3 yr, total anthocyanin concentration was greater in fertigated than in broadcast treatments. Soil ammonium and nitrate concentrations increased with N rate, but only soil nitrate differed between the two application methods. Soil nitrate was higher with fertigation than with granular fertilizers, particularly at the end of the season and when greater rates of N were applied. In summary, fertigation produced more shoot growth and greater yields with less N than broadcast applications of fertilizer.

Host status and damage potential of Paratrichodorus renifer and Pratylenchus penetrans (Nematoda) to blueberry (Vaccinium spp.)

Abstract Stubby root nematodes (Paratrichodorus species) and root lesion nematodes (Pratylenchus species) have been found in root zone soil of blueberry plants in most blueberry-growing regions of North America. Relatively little is known, however, of the reproductive potential and damage caused by these nematodes to blueberry. We performed controlled inoculation studies in a greenhouse in order to assess population growth and damage caused by Paratrichodorus renifer and Pratylenchus penetrans on a range of blueberry cultivars, including representatives of Vaccinium corymbosum (four cultivars), V. angustifolium (one cultivar) and V. ashei (one cultivar). All tested blueberry cultivars were considered good hosts to P. renifer (reproduction factor (RF) values > 1.0) except V. ashei ‘Powderblue’ which was considered a poor host (RF = 0.2 and 0.1 for trials 1 and 2, respectively). Paratrichodorus renifer reduced root biomass of susceptible blueberry cultivars; however, this effect was not consistent across trials. Pratylenchus penetrans did not reproduce on any blueberry cultivars under greenhouse conditions. Population growth and damage caused by P. renifer on V. corymbosum × angustifolium ‘Chippewa’ was assessed using field microplots. Paratrichodorus renifer reduced berry yield, canopy volume and top dry weights two years after inoculation by 40, 25 and 25%, respectively. Our results clearly indicate that P. renifer population densities increase on V. corymbosum and V. angustifolium and the nematode is potentially damaging to blueberry.