Nitrogen management is important in determining cotton (Gossypium hirs
utum L.) yield and fiber quality. Plant tissue tests are often used to
estimate cotton N status and determine if further fertilization is ne
eded during the growing season. This study was conducted to examine th
e relationship between plant tissue tests of petiole NO3 concentration
and leaf N content and cotton performance as measured by vegetative g
rowth (i.e., leaf area) and bell load. Nitrogen rates of 0, 18, 36, 72
, and 144 mM N pot(-1) were applied at 2-wk intervals beginning 13 and
26 d after emergence in 1987 and 1988 through bell maturity to a gree
nhouse-grown cultivar, Stoneville 213. The strong relationship between
leaf N and leaf area and boll number (r(2) = 0.80 and r(2) = 0.89) 1
wk after first flower appearance suggests that the transition period b
etween vegetative and boll development is a critical time to assess co
tton's N status in relation to yield. Nitrogen deficits had little eff
ect on bell weight, boll period duration, and number of main stem node
s. Although boll weight decreased with increasing N deficit, final bol
l weight of the high-N plants were within 20% of the plants receiving
low N supply. The relationship between leaf N and petiole NO3 content,
was best described by Y = a + bX(C); however, with this function only
one-half of the variation in leaf N was accounted for by variation in
petiole NO3 content (r(2) = 0.48). Leaf area and boll number were poo
rly correlated with petiole NO3 content. Leaf N content was a better p
redictor of cotton vegetative growth (as indicated by LAI) and bell nu
mber than petiole NO3 content, particularly when measurements are made
1 wk after first flower