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Serial manure amendments : effects on soil properties and root rot of sweet cornCox, Bonnie S. Hoffman 14 June 2005 (has links)
The effect of serial (multiple-year) organic matter (OM) amendment on
soil properties has been described in some cropping systems, although less is
known about the effect of serially amended field soils on soil-borne plant diseases.
The objectives of this study were to describe the effects of the third and fourth
years of annual, serial amendment with dairy manure solids on 1) soil physical and
biological properties and 2) severity of sweet corn root rot. Plots were amended
with five rates of separated dairy manure solids annually for three years. In the
fourth year, plots were split and only half of each plot was re-amended. Soil
physical properties [bulk density, free and occluded particulate organic matter
(POM), soil water retention, total porosity, gravimetric moisture content] and
biological properties [microbial activity (as hydrolysis of fluorescein diacetate;
FDA) and microbial biomass-C] were assessed each year in all treatments. Root
rot severity was assessed in situ and in the greenhouse with multiple sweet corn
(Zea mays L. cv Golden Jubilee) bioassays conducted in the amended field soils.
Necrosis of the radicle and nodal roots was assessed when plants reached the 6-
leaf stage. Amendment rate was positively associated with increases in soil
properties that serve as indicators of soil quality, such as POM content, total
porosity, microbial biomass, and FDA activity. In the third year after amendment,
weak root rot suppression was observed in-field and was associated with FDA
activity. By the fourth year of serial amendment this trend was no longer evident,
however evidence from the high-rate treatment that was not re-amended (3HNRA)
pointed to an emerging suppressive mechanism that persisted up to 13
months after the third amendment. Factors that may be interacting over time to
generate observed disease suppression in these serially amended soils include:
short-term post-amendment microbiostasis, soil moisture retention, inoculum
potential, and a novel suppressive mechanism. / Graduation date: 2006
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Ion exchange membranes and agronomic responses as tools for assessing nutrient availabilitySalisbury, Steven Earl 13 July 1999 (has links)
Winter wheat is commonly grown in rotation with leguminous and non-leguminous
crops in the Willamette Valley. For agronomic, economic, and
environmental reasons it is important to understand the influence of previous crops on
availability of N and other nutrients.
Objectives of this study were: (1) to evaluate the effects of long-term rotations on
winter wheat response to N fertilizer, and (2) to evaluate the use of Plant Root
Simulator���(PRS) probes for measuring soil N mineralization and N availability to
winter wheat.
Field experiments were conducted over three growing seasons in plots of
`Stephens' soft white winter wheat at Hyslop farm. Plots receiving 0, 50, 100, 150 and
200 kg N ha����� at Feekes GS 4 were sampled to determine above ground N uptake, grain
yield, and grain protein. In spring 1998, PRS probes were placed in 0 kg N ha����� plots and
removed at one-week or two-week intervals. In autumn 1998, probes were placed in
unfertilized plots and removed at 1-week, 4-week, and 8-week intervals. Probes
measured the availability of NH������-N, NO������-N, K���, Ca�����, Mg�����, and P0��������-P.
Grain yield and N uptake were greater for wheat following clover as compared to
following oats. Three-year average fertilizer equivalent values calculated from N uptake
and grain yield data were 44.5 kg N h����� and 49.0 kg N h�����, respectively. The similarity
of these independent measurements suggest that differences in N availability were the
primary reason for the rotation effect.
PRS probes also detected rotational differences in N availability. Average N
recovered by probes sampled at 1-week intervals indicated that there was 63% as much
NO������-N available to wheat following oat as compared to clover. Wheat recovered 64% as
much N following oats as compared to clover. This suggests that PRS probes are an
effective method for predicting relative amounts of plant available N. PRS probes also
detected rotational differences in plant available potassium.
Agronomic responses are useful for assessing the availability of nutrients that are
limiting plant growth. PRS probes, on the other hand, are effective for assessing the
availability of both limiting and non-limiting nutrients. / Graduation date: 2000
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