Rotating wheat with other crops is a common practice in the Willamette Valley of
western Oregon. Depending upon previous crop and soil type, current N fertilizer
recommendations for wheat in the Willamette Valley vary widely. Excessive fertilizer
poses environmental risk, whereas lower N inputs than required by the crop represent
economic losses to growers. Growers and their advisors face the challenge to minimize
the environmental risk, and at the same time to maintain or increase economic returns.
Questions are often raised concerning the efficient use of N fertilizer and accurately
predicting the amount of N needed by wheat following different crops.
The first study measured growth, N uptake and N use efficiency (NUE) of winter
wheat grown after either a legume or oat for three years. In all three growing seasons,
winter wheat showed higher biomass, N uptake and NUE when grown after a legume
than after oat. The contribution of legume was evident before the wheat was fertilized in
spring, indicating that legume N had mineralized in fall or winter.
Contribution of soil N to wheat suggested that fertilizer N can be reduced by 44 kg N ha�����
if a legume is grown previously. Nitrogen use efficiency estimated 50 to 70 days after N
application by isotopic method (24 to 94%) was comparable with that estimated simply
by difference (21 to 94%) at the same time.
The second study predicted gross mineralization rates using analytical models.
Comparable N mineralization was predicted by a model assuming remineralization and a
model assuming no remineralization, suggesting that remineralization was negligible. In
the spring, mineralization-immobilization turnover was at a lower pace than expected in
both rotations. In two growing seasons, gross mineralization rates were higher where the
previous crop was legume (0.37 to 0.74 kg����� ha����� day�����) as compared to where oat was
grown previously (0.14 to 0.6 kg����� ha����� day). Negative net mineralization indicated that
fertilizer N was immobilized in the oat-wheat rotation.
The third study evaluated calibration and digestion techniques used to determine
elemental concentration in grasses. Use of a dry ashed standard to calibrate the ICP
spectrometer generated highly variable calibration curves and was not a viable calibration
method. Good agreement was found between chemical and microwave digested
standards. Dry ashing resulted in considerable S and Mn losses, whereas, perchloric acid
digestion and microwave digestion showed similar results. Our study suggests that if
routine analysis are to be performed for macro nutrients or involve trace level work, the
best method is microwave digestion with chemical standard calibration of ICP
spectrometer. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33521 |
| Date | 06 April 1999 |
| Creators | Qureshi, Maqsood Hassan |
| Contributors | Christensen, Neil W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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