The semi-arid regions of the Pacific Northwest are
characterized by a high degree of annual temperature and
precipitation variation. As a result of this climatic
variation, dryland nitrogen fertilizer trials on fallow-
,wheat rotations typically demonstrate a variable response.
Wheat growers in the area must not only cope with this
climatic variation and its sundry effects upon their
livelihood, they must also make decisions regarding the
future level of anticipated climatic variation.
The specific objectives were to: 1) develop a climatically
responsive yield potential prediction model for soft
white winter wheat from historical data at the Sherman
Branch Experiment Station (Moro, OR); 2) modify this model
for use on commercial fields; 3) field simulate five fallow-crop
precipitation patterns characteristic of the variation
found in the Sherman county area of eastern Oregon in order
to test the yield potential model: 4) examine the effects of
precipitation variation on nitrogen fertilizer responses,
moisture storage and depletion and nitrogen mineralization;
and 5) establish a quantitative relationship between precipitation/
soil moisture and nitrate accumulation in both
the fallow and crop seasons.
Two interacting regression models were developed to
estimate grain yield levels in the 250-350 mm precipitation
zone of eastern Oregon. The first model estimates yield
potential from monthly precipitation and temperature values.
The second model estimates the percent grain reduction due
to delayed crop emergence. The grain yield model was
adapted to commercial fields using a Productivity Index
factor (PI). The PI is a measure of the productivity of
other locations in relation to the Sherman Branch Experiment
Station, using water-use-efficiency (WUE) as the basis
of comparison.
The field simulation of five fallow-crop precipitation
patterns demonstrated that the maximum grain yield response
occurred at 40 kg N (soil + fertilizer)/metric ton.
The grain yield model demonstrated a 15% level of
accuracy on a commercial field basis in both field trials
and a survey of past production levels (1972-1980).
It was hypothesized that the distribution of precipitation
in the fallow and crop periods had an effect on
both the amount and distribution of stored soil moisture.
The field simulation demonstrated that more soil moisture
was stored at the 90-240 cm depths by the patterns with
more fallow season precipitation when measured in March of
the crop year.
Soil moisture storage and storage efficiencies fluctuated
throughout the fallow and crop periods. At the
cessation of the winter precipitation season in both the
fallow and crop periods (March), the storage efficiency
was highest when low levels of precipitation occurred. At
this point in time, the mean crop period storage efficiency
was 10% below the mean fallow period storage efficiency
(34 and 44%, respectively) in both simulation studies.
Soil moisture, temperature and immobilization requirements
of crop residues interact to affect the net amount
of nitrogen mineralization. The mineralization model
proposed by Stanford and Smith (1972) was tested under
field conditions. When the nitrogen immobilization requirement
of the crop residues was included, the actual and predicted
values were in agreement at the close of the 1978
fallow period. A nitrogen deficit was predicted at the
0-30 cm depth at the close of the 1980 fallow; however, the
actual levels indicated a net accumulation of nitrate-nitrogen.
Crop season mineralization, inferred from Mitscherlick
and a-value extrapolations, in 1979 demonstrated that there
was a decreasing amount of net mineralization during the
crop season with increasing amounts of both fallow and crop
season precipitation. Crop season mineralization in 1980
indicated that there was no net accumulation of nitrogen,
rather a tie-up of 14 kg N/ha. This result reflects both
the unsatisfied immobilization requirement predicted for
the 1979 fallow season and crop season denitrification. / Graduation date: 1981
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37530 |
| Date | 16 February 1981 |
| Creators | Glenn, D. M. (David Michael) |
| Contributors | Bolton, Floyd E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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