Vergara - 1976 - Physiological and morphological adaptability of ri

528 CLlls-LATT-l AND RICE
Table 1. Mechanical and chemical analyses o1‘ soils from different experimental sites of
upland rice Vflfllly trlal. 1973 wat season.
Mechanical
analysis:
lRRl Batangas N Ecila Negros Occ. Cam. Sur
Block H Stu. Tomes Maligaya La Granja Pili
Sand [%) 20.9 33.4 35.9 45.2 21.8
Silt {$6} 32.7 34.2 32 3 23.1 2B 4
Clay (a; 46.4 32.4 31a 31.7 49.5
50" IEXTUYB Illa)! clay loam clay loam sandy clay loam clay
Chem/cal analysis
pH [1 1) 5.4 5.1 6.7 5.8 4.9
Total N(%] 0.15 012 U U9 0.14 0.23
Organic matter ['16) 2.8 1.9 1.3 13 43
Available F‘ {ppm} 1.3 12.5 160 2610 Z14
CEC {meqltDflg soil) 32 26 25 26 33
In many deep-water rice areas. rice is seeded on dry soil and grown under upland
conditions for several weeks until heaw rains flood the fields to as mueh
as several meters deep. Therefore. deep-water rices or progenies derived from
them should have some drought tolerance (Dc Datta and Beaehell, 1972).
The crop seeded May 3] received the most solar energy during the ripening
period, while the crop seeded July 23 received the least (De Datta and Beachell,
1972). The low grain yield for the crop seeded July 23 may have been partly
caused by the low solar energy during the ripening period. At no time were soil
moisture tensions higher than 33 eb. Therefore. none of the crops suffered from
soil-moisture stress.
At Maligava, IRS produced consistently higher grain yields under upland
conditions than the upland variety‘, M1—48._ and the early-maturing line, IR579-
48-2. Except for the crops seeded on July 2 and July l7. the nitrogen response of
1R5 was almost linear up to I20 kg N/ha. The highest grain yield, 7 t/ha, was
obtained with [RS seeded on July 17. This yield is probably) close to the upper
limit for IRS during the wet season when the total solar energy during the ripening
period seldom exceeds 16.5 kcal/sc] cm (De Datta and Beachell, I972).
Similarly. during the 1971 wet season, two high-yielding lowland varieties.
IR24 and IRS. consistently outyielded Ml—48 at both Maligaya and at La
(Jrania experiment stations of the Bureau of Plant Industry‘. Low yields and poor
nitrogen response at La Granja are attributed to two reasons. Solar energy
values at La Granja were slightly lovrer than those at Maligaya. Although rainfall
was adequate during the crop season. the soil is more coarse-textured at the
La Granja station than at the IRRI farm and the MaIlgay-‘a station (Table I).
During the 1971 wet season. the soil-moisture tensions at the La Granja station
were often higher than 33 ch. The crop planted on May 2] suffered from
moisture stress during the booting stage. For the June l7 seeding, moisture
tensions were high during the vegetative and heading stages of the crop. while
plants seeded on July l2 experienced stress during the vegetative and panicle
initiation stages. As a result of moisture stress, the grain yields at the I.a (‘rranja
station were low (De Datta et al., 1974).