The response of sweet potato (Ip < /em>omoea batatas (L.) Lamj plants cv. "Abees"
to water stress , imposed at vegetative growth ryvS,) or root enlargement ryvS2)
stages, under four varying N-fertilizer levels (0, 30, 60 and 90 kg N/fed.) and their
ointeraction effects were studied. Two field experiments were conducted during the
summer seasons of 2000 and 2001 at the Agricultural Experimental Station, Faculty of
Agriculture, Alexandria University.
The obtained results, in general, recorded significant decrements in all
vegetative growth characters of sweet potato plants, expressed as main stem length,
number of branches, leaf area and shoot dry weight as well as relative water content
(%) and leaf water potential. due to water stress at WS, and WS2. in both seasons,
compared with the unstressed plants ryvSo). On the other hand, N-fertilizatlon at all
applied levels gave significant increments in these characters, compared with
unfertilized plants, under all water stress conditions.
Results showed. also. significant decreases in the contents of photosynthetic
pigments (chI. a, band carotenoids ) and total carbohydrats and significant increases
in total soluble sugars as well as N, protein and proline contents of sweet potato
leaves, under WS, and WS2 , however , the application of N at 60 kg Nt fed.
significantly increased the contents of photosynthetic pigments, total carbohydrates,
and leaf water potential but significantly reduced total soluble sugars, N and protein as
well as proline contents, especially under WS, and WS2.
Tuberous root yield of sweet potato and average root number, per plant, as
well as quality characteristics of roots, expressed as average root weight, root length
and diameter and dry matter content (%) and also chemical composition of roots (total
carotene, reducing sugars, starch ,protein and minerals contents) were significantly
reduced under water stress conditions. However, the application of N up to 60 kg
Ntfed. significantly increased root yield, improved root quality and enhanced its
chemical composition and could overcome the adverse effects of water stress on
sweet potato productivity. -
It could be recommended the use of N-fertilizer at moderate levels to mitigate
the negative effect of water stress on sweet potato plants, on the other hand, N deficit
and high N levels should be avoid under water stress conditions.