F. L. Pfleger

Field responses to added organic matter, arbuscular mycorrhizal fungi, and fertilizer in reclamation of taconite iron ore tailing

A three season study was conducted to determine the effect of added composted yard waste, arbuscular mycorrhizal (AM) fungi, and fertilizer on plant cover, standing crop biomass, species composition, AM fungal infectivity and spore density in coarse taconite iron ore tailing plots seeded with a mixture of native prairie grasses. Plant cover and biomass, percent seeded species, mycorrhizal infectivity and spore density were greatly increased by additions of composted yard waste. After three seasons, total plant cover was also greater in plots with added fertilizer. Third season plant cover was also greater in plots amended with the higher rate (44.8 Mg ha−1) of compost than the moderate rate (22.4 Mg ha-1). Field inoculation with AM fungi also increased plant cover during the second season and infectivity during the first two seasons. Seeded native species, consisting mostly of the cover species Elymus canadensis, dominated plot vegetation during the second and third seasons. Dispersal of AM fungal propagules into nonmycorrhizal plots occurred rapidly and increased infectivity in compost-amended plots during the third season. In plots with less than 10% plant cover, AM fungal infectivity of inoculated plots was greatly reduced after the second season. The high level of plant cover and the trend of increasing proportion of mycorrhizal-dependent warm-season grasses, along with increases in infectivity, forecast the establishment of a sustainable native grass community that will meet reclamation goals.

Green manures of oat, rape and sweet corn for reducing common root rot in pea (Pisum sativum) caused by Aphanomyces euteiches

Green manure crops of sweet corn, soybean, alfalfa, snap bean, rape, pea and of the two oat cultivars ‘Dane’ and ‘Troy’ were incorporated into the same soil and containers in which the crop had grown for five weeks. The soil was then evaluated for suppression of common root rot (Aphanomyces euteiches) of pea grown in infested pasteurized and non-pasteurized soils in the greenhouse. Pea biomass reduction and a plant bioassay for A. euteiches were used to measure the green manure suppression of disease. Green manures of sweet corn cv.‘Jubilee’, oat cv.‘Troy’, and rape cv.‘Humus’ significantly reduced pea biomass losses over the non-amended control soil treatments. Oat cv.‘Troy’and sweet corn cv.‘Jubilee’ green manures significantly reduced inoculum density of A. euteiches over the corresponding fallow controls in inoculated pasteurized soil by 87% and 76%, respectively, and in inoculated non-pasteurized soil by 67% and 66%, respectively. Only the green manure of oat cv. ‘Troy’ reduced inoculum density significantly below fallow.

Host responses to AMF from plots differing in plant diversity

Increased plant species richness in a plant community leads to changes in the composition of the associated arbuscular-mycorrhizal fungal (AMF) community. We tested whether AMF from plots with increased plant diversity cause significant differences in the growth of Lespedeza capitata, Schizachyrium scoparium or Liatris aspera. Seedlings of each were transplanted into pasteurized soil inoculated with soil from their own monocultures, or from plots with one, seven, or 15 additional plant species. In addition, inocula from S. scoparium and L. capitata monocultures were tested for reciprocal growth effects. Inocula from plots containing the native tallgrass prairie species Lespedeza capitata showed increasing AMF species richness and spore density with increasing plant diversity; this was not true with plots containing Schizachyrium scopariumor Liatris aspera. All three species responded to AMF inoculation with increased growth and Cu concentrations, and lowered Mn concentrations compared to non-inoculated control plants. Increasing the plant diversity of the inoculum source-plots significantly affected plant weights of L. capitata, but not of the other two host plants. Both S. scoparium and L. capitata showed increases in growth with inoculum from S. scoparium monocultures compared to that from L. capitata monocultures. Spore density of inoculum source plots was associated with subsequent plant growth or nutrient content only in Lespedeza plots, which contained considerably fewer spores, plant cover, and root biomass in plots with lower plant diversity.

Evaluation of methods for estimating inoculum potential of Aphanomyces euteiches in soil

Three methods were evaluated for determining inoculum potential of Aphanomyces euteiches inoculum in soil and sand: rolled towel (RT), most probable number (MPN), and soil indexing (SI) bioassays. The RT and MPN bioassays were evaluated using clay loam, loam, and sand that were artificially infested with a series of oospore concentrations ranging from 2 to 500/g. Oospore numbers added to soil and estimated inoculum potential measured using the RT and MPN were highly correlated (r=0.99 and 0.85, respectively). These two bioassays, however, yielded highly variable results among replications, and inoculum potential estimates for sand and soil infested with equal numbers of oospores were dissimilar

Response ofBromus inermis inoculated withGlomus fasciculatum to potassium fertilization and drought stress

SummaryBromus inermis Leyss. was grown in a 2×2×2 factorial design using different levels of mycorrhizal inoculation (inoculated and noninoculated), soil water stress (Ψ1 or −0.8 MPa) and potassium (K) fertilization (0 or 150 ppm) as factors. Soil water stress and mycorrhizal inoculation significantly reduced plant top dry weight during the 18 week study. Chlamydospore production by the mycorrhizal symbiontGlomus fasciculatum (Thaxter sensu. Gerd.) Gerd. and Trappe was significantly reduced by soil water stress of −0.8 MPa. Potassium (K) fertilization did not significantly influence plant top growth or mycorrhizal colonization. However, foliar Ca and Mg were significantly lower in plants fertilized with K. Foliar Ca and Mg concentrations of P, K, N, Mn, Zn and Cu were significantly greater in drought stressed plants whereas Ca and Mg concentrations were significantly greater in well-watered plants.

Common root rot of pea (Pisum sativum L.): Oat pre-crop and traffic compaction effects in fine-textured mollisols

Common root rot of pea caused by Aphanomyces euteiches Drechs. is widespread and difficult to control. In many production areas, yearly losses have been estimated at 10% because of the disease. Cultural control is needed even when disease tolerant cultivars are planted. Soil compaction due to traffic is known to aggravate the disease. In a series of research studies in a heavily infested nursery and adjacent farm fields, it was shown that compaction aggravates the disease by decreasing drainage and thus providing more favourable soil water conditions for early infection of pea roots. Traffic compaction has also provided an adverse abiotic environment for plant stress due to poor aeration. A precrop of oat (Avena sativum L.), as a full-season or late-summer crop, suppressed the disease only if the oat residue was incorporated at a shallow depth late in the fall using a chisel. Incorporated oat residue reduced inoculum potential of A. euteiches above 10 cm when incorporated with a chisel and below 10 cm when incorporated with a moldboard plow. A rolled towel bioassay using a susceptible pea cultivar successfully estimated inoculum potential when the test soil was placed near the epicotyl of 7-day-old seedlings. Although A. euteiches is an aggressive disease, all of these findings focus on vulnerability during the infection process. These investigations were required to examine carefully the soil ecology pertaining to the host crop, the pathogen when in the saprophytic mode, and the host crop interaction with the pathogen.