The CERES-Wheat Crop Growth and Development model treats temperature,
nitrogen and water stresses as limiting factors. For each day the model calculates a
stress index for temperature, N and water, compares the magnitude of the indices,
and then adjusts the calculated daily potential growth using the index of the most
severe stress, while ignoring the other stresses. Under the conditions in Oregon,
however, mild N and water stress will often be present together in about equal degree
of stress. Some published results suggest that both stresses affect growth and yield
under those conditions. Therefore, this work was undertaken to evaluate the
combined effects of N and water stress on growth and development of wheat
(Triticum aestivum L.). To make such an evaluation one must be able to control both
N and water supplies to the plant and the response of the plant to these two variables
must be measured at different growth stages. A system of imposing controlled plant
water stress developed by Snow and Tingey (1985) was adapted and evaluated for its
potential to impose controlled levels of both N and water stress to single wheat
plants. Using a 12 mmol N and 4 cm pathlength as optimum N and water supply
treatment, 2 mmol N and 12 cm pathlength and a 1 bar standard ceramic disc in the
floral foam column as N and water stress treatments during tillering resulted in 15 %
reduction in tillers/plant for limits to the N supply alone, a 39 % reduction for limits
to the water supply alone, and a 52 % reduction when both stresses were imposed
simultaneously. There was no effect of N or water supply treatments on the leaf
appearance rate on the main stem, a measure of the rate of progress toward
flowering. Both N and water supplies had a strong effect on tillers/plant which, in
turn, affected plant biomass and its constituent parts. The effects were independent,
suggesting that, to accurately model the wheat canopy development when both mild N
and water stresses are present, both stresses must be considered. A 'law of
minimum' concept as currently used in the CERES-Wheat model would not be an
accurate model for the process of tillering. In an experiment where stress was
imposed during flowering and grain-filling, the grain yield/plant varied significantly
with both N and water supplies. The interaction between N and water treatments on
grain yield was also significant and was due primarily to their significant interaction
on mean kernel weight. The major determinant of grain yield was tillers/plant at
harvest. Both N and water supplies affected kernels/ear and N stress caused a
reduction of 12% in both fertile spikelets/ear and kernels/fertile spikelet. At an
optimum water supply, the difference between the effect of optimum and medium N
supply on grain yield was not significant but yield in low N supply was reduced by
54%. In the medium water supply, the grain yield at both medium and low N
treatments were significantly lower than at optimum N supply. There was no
significant difference in yield between N supply treatments in the low water supply
treatments. Thus, under severe water stress, a 'law of minimum' concept appeared to
be valid, but under less severe stress both N and water supply affected grain yield.
The data on leaf water potential and leaf temperature showed that plants in low water
supply treatments maintained consistently lower leaf water potential and higher leaf
temperature than in optimum water supply treatment. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36819 |
| Date | 11 September 1992 |
| Creators | Ashraf, Muhammad, 1952- |
| Contributors | Bolton, Floyd E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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