Agriculture Reference
In-Depth Information
Upland rice
300 mg N kg
-1
0 mg N kg
-1
BRA 02601
FIGURE 3.14
(
See color insert.
) Growth of upland rice genotype BRA 02601 at low and high N levels. Half
of the N was applied at sowing and the remaining half at the active tillering growth stage.
sufficient, and toxic levels of plant nutrients reported that N is nontoxic element. As a general rule,
micronutrients are more toxic to plants when absorbed in excess than macronutrients. Nutrient toxicity
symptoms first appear on the older leaves and spread to other parts of the plant if excess absorption
persists for a longer duration. Nutrient toxicity symptoms in plants can appear easily in solution culture
when applied in excess. However, under field conditions, it rarely happens, especially with macronu-
trients, including N. Excess nitrate-N reduced root growth, especially secondary roots, and increased
fibrous root hair growth in sorghum (Clark, 1993). Excess N in plants may cause excessive vegetative
growth, flowering may be delayed, and the grain set and yield are reduced.
Seedling injury has been reported for seed-placed urea at rates as low as 40 kg N ha
−1
for bar-
ley (Grant and Bailey, 1999; O'Donovan et al., 2008). Furthermore, seed-placed rates above 28 kg
Upland rice
0 mg N kg
-1
300 mg N kg
-1
BRA 02535
FIGURE 3.15
Root growth of upland rice genotype BRA 02535 at low and high N levels. Half of the N was
applied at sowing and the remaining half at the active tillering growth stage.
