Proceedings of the Fifth Asian Regional Maize Workshop - Search ...

Early rainy season plantings have a higher risk of drought damage. In 1987, Tawatchai at a7.
evaluated the drought tolerance of 40 corn varieties by calculating harvest index, and reported
that Hercules 31 and Hercules 40 gave the highest yields under both drought stress and good water
conditions.
A summary of our results on trials planted during 1991-1993, follows:
1. Varietal i~roveMent. Most of the improved varieties evaluated had higher grain yields than
the checks. Highest yield was found in single cross hybrids. KS 5, the best open pollinated
variety, yielded as much as the commercial hybrids SUWan 3101 and car.633 and it was significantly
higher than Suwan 2602, Pac.9715 and OK 211-
2. Population density. Results showed that when plant densities were over 53,333 p1ants/ha,
yield tended to increase but there was a decrease in ears/plant and ear weight. Higher plant
densities increased yield significantly with appropriate times and rates of fertilizer.
3. Forage use. The new open pollinated variety Suwan 5 was tested for forage yield under high
population density. Times for best silage and grain yield were 90 and 115 days after planting,
respectively.
4. Removal of leaves. Results indicated that at anthesis stage, the removal of leaves above and
below the ear, and total removal of the leaves, caused 42, 22, and 93.4~ yield loss, respectively.
Removing the tops at 2, 3, and 4 weeks after silking also significantly reduced the yield.
5. Fertility: Studies on response of corn to nitrogen fertilizer and ability for N-P-K uptake
indicated that grain yield and biomass increased considerably with up to 80 kg N/ha. Higher
levels (160 kg N) did not increase the biomass, and only slightly increased yield. The response
of harvest index was not uniform with increasing rates of N. Nitrogen fertilization increased
yields of grain N, P, and K. The effect of increasing rates of N on P and K concentrations in
the grains was different. Total uptake of N and P increased to 160 kg N, and K up to 80 kg N.
The N harvest index was slightly affected by N fertilization, whereas the K harvest index tended
to increase, and the P harvest index increased with increasing rates of N. The weights of N, P,
and K in the kernel remained stable or increased slightly with increasing rates of N fertilizer.
Fertilizer trials indicated that varieties differed in their response to various fertilizer
formulations. The variety Across 8328 C3, tolerant to low n stress yielded significantly higher
than the original Across 8328 CO.
6. D~t: Drought stress at pref10wering stage caused an increase of ASI value, reduction in
plant height and ears/plant as well as ear and grain weights. Under rainfed conditions, both
CIMMYT germp1asm and Thai improved germp1asm had lower grain yields than when under irrigated
conditions being reduced by 44.9 and 25.~ respectively. Response of various corn varieties
tested at different stages of growth indicated that yield was significantly correlated to a
drought index at any stage of development.
144