Vergara - 1976 - Physiological and morphological adaptability of ri

516 CLIMXFE AND RICE
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Nitrogen applied (kq/l-nl
3. Etleets of nitrogen levels on grain yield ofIR20 at Sta.
Cruz and Kapalangan. Nueva Eeija. Philippines. I973 wet
and I974 dry seasons (source of data: IRRI agricultural
economics department).
solar energy during the dry‘ season over that in the wet season was not reflected
in the nitrogen response.
Experiments conducted in a farmer's field in Nueva Eeija by the IRRI Agricultural
Eeonomies Department during the I973 wet season demonstrated that
nitrogen response in irrigated rice is greater than that in rainfed rice (Fig. 3).
Soils in the rainfed area were generally poorer and might have contributed to
nitrogen response lower than that in the irrigated area.
Similarly, a recent survey’ made by the Agricultural Economies group at
IRRI (Anden and Barker, 1973) reported that ltitrogeit a11d water levels were
the two major factors constraining yields of rice in some Asian countries.
Seasonal effects on varietal reactions t0 disease and insects
During the past few years. fertilizer experiments have been conducted in both dry
and wet seasons at the IRRI farm. at the Maligaya Rice Research and Training
Center in Central Luzon. at the Bicol Rice and Corn Experiment Station in the
Bicol region, and at the Visayas Rice Experiment Station in the Visayas region.
The out-station experiments were conducted in etioperatitin with the Philippine
Bureau of Plant Industry" (BPI). There were five nitrogen levels at the IRRI
farm. and six at the BPI stations. Figures 4 and 5 show average nitrogen response
(for the period between 1968 and 1973) of 1R8 and IRZO, modern varieties bred
by IRRI. and Peta. a traditional variety" from the Philippines bred in Indonesia,
In general the experiments were conducted with optimum moisture supply and
under good management. However. those at IRRI were more closely" supervised
than those at the BPI stations.