Vergara - 1976 - Physiological and morphological adaptability of ri

NITROGEN sssmnsr: 0F lure m raoiatrat. t'or\'l)l'1‘loNs 523
Groin yield ( t/M t
4
i974‘ D9)’ fl-Lfi‘ I973 “QTH]
I
3 .. _
<
2 ..
o-o 2 ,4_o+ mu “can;
| - .1. No weeding -
°—— I I l I
0 so IOO I50 O 3O so %
Nitrogen opplbdtlqltlnl
10. Integrated effects of nitrogen and hand Weeding
(HW) on the grain yield of IRZU under irrigated conditions
at Sta. Cruz and Kapalangan. Nueva Ecija. Philip
pines. 1973 wet and I974 dry seasons (source of data:
IRRI agricultural economics department).
experiments conducted in farmers“ fields by the IRRI Agricultural Economics
Department. The average of data from two locations showed that nitrogen responses
of [R20 during the I973 wet season and l9?4 dry season were greater
with weed control than without weed control (Fig. l0) The results are simiiar
to those obtained under experimental conditions at the IRRI farm (De Datta
and Sharma. 1968'. Gomez. 1974, unpublished). Results from farmers field
experiments indicate. however. that weeding caused insignificant differences in
nitrogen response between dry and wet seasons.
Insect control
Insects do far more damage to rice in the tropics than in the temperate regions.
In experiments conducted at the IRRI farm in 1973, there were more insects,
particularly brown planthtipper (Nilaparvata lugens). in the wet season than in
the dry season. In the wet season. brown hopper-susceptible varieties 1R8 and
IRZU ivere completely killed WIthOUl. protection with insecticides at both levels
of nitrogen (Fig ll). With insecticide protection, IRZU yielded over 2 l/ha in the
dry season and none in the w=et season. In both seasons brown hopper-resistant
line IRl56l—22S—3 gave about 3 t/ha grain yield WtlhOtlt insecticide and nitrogen
applications, and had higher yields With insecticide and nitrogen applications.
With or without protection from insect damage. grain yields with added nitrogen
wcrc higher in the dry than in the wet season (Fig. 1 l).
Faun-level data collected in Laguna by Gomez (1974, unpublished) shoived
that IRl56l—228—3 gave a greater nitrogen response with a high level of insect
control than with a low level.