Vergara - 1976 - Physiological and morphological adaptability of ri

NITROGEN RESPONSE OF RICE IN 'I'ROPIC.»’\I. ("()NDI'I'I()NS 5I7
Grub yield one)
8
on stAso/v .7 ncr ssasav
Solar radiation
IRZOI I6 I Kool/sqcml
IRS (no.2 Kcot/sqcml
Peta l I63 Kcol/sqem)
2_
‘a
Solcrmdmim 1‘
IRZOIZZZKrd/sqcni] ‘-, '1'--.,__
RGIZIBKwI/sqcm} 1 ‘v
Peta (216 Kml/sqeml
Peto-"%_
.'o,u"‘
l | | | r t t t I
Q%@9Q m|5o03o6090|20|50
Nitroqanuppllodlhqlhul
4. Effects of nitrogen levels on grain yield of 1R8. IR20.
and Peta. IRRI. 1968-73. 1968 and 1969 dry seasons:
0. 3D. 60. 90. and 120 kg N~'ha; I968 wet season: 0. 20.
40. 60. and 80 kg Xilia; 1969 wet season: 0. 25. 50. 75.
and I00 kg Nlha.
Response to nitrogen was markedly dilTerent between the dry and wet seasons.
The difference can be explained by the level of solar energy during these seasons.
Effect of plant type on nitrogen response W35 also obvious. Modern varieties,
1R8 and IR20, consistently’ gave higher nitrogen response than Peta in any
season and at all locations (Fig. 4 and 5).
Between the drf; and wet seasons, however. response to nitrogen in 1R8 and
IRZU varied from location to location’ ilhe variation can he explained by reactions
to diseases and insects
At IRRI. there was less problem with disease in the dry season than in the
wet season and as a result. nitrogen response of 1R8 and IRZU followed closely
the yjield potential of these two varieties. IRZO gave higher response to N in the
wet season because of higher disease and insect resistance than IRS (Fig. 4).
Under disease-free conditions. such as in the drjv season in Maligaya and dry
and wet seasons ill Bicol. nitrogen responses of IR8 were higher than those of
IR20, following the genetic potential ofthese xiarieties (Fig. S). In the wet season.