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

A.
1991-1993.
Rachain Thiraporn !I
Introduction.
Maize (Zea mays L.) is an important feed grain mostly produced in the North, northeast, and
central regions of Thailand. More than two thirds of the production is used domestically by feed
industries, and the rest is exported accounting for 7~ of the world market. Maize exports
contribute substantially to foreign exchange earnings of the country (Office of Agric. Economics,
1992). In recent years, rapid expansion of the livestock industry has triggered an increased
demand for maize affecting the exports of the grain.
However, the gross production of maize is still below the amount targeted by the National
Economic and Social Development Plan. Agronomic research to increase productivity in farmers'
fields is important to raise the national economic level.
Previous studies reported that the appropriate planting rate of 3 corn varieties, Guatemala
CMS-PB 5, Puerto Rico Gp.1, and Veracruz 181 x Antigua Gp.2 grown in the early and late rainy
seasons, ranged from 6400-8500 plants/rai (OWaht et a7., 1970) (1 ha=6.25 rai). In 1971, OWaht at
a7. also reported that using 5 different densities ranging from 6,400 to 17,000 plants/rai of 5
corn varieties, the number of ears/plant showed a negative correlation with plant density.
Yields of all entries did not differ Within densities. However, treatments of 8,500 plants/rai
or more tended to yield lower. Supot et a7. (1971) studied the response to high plant density
(32,000 to 16,000 plants/rai) of 2 corn varieties, CUba 11 x Georgia Cow Corn-Prolific, and
Guatemala PB 8. It was found that the number of barren plants increased as the plant density
increased. Barreness in Guatemala PB 8 was nearly 1~ higher than in CUba 11 x Georgia Cow Corn­
Prolific. In 1982, SUpot et a7., studied the optimum density of SUWan 1 and SUWan 2301 planted
at various densities. Results indicated that the optimum planting rates of Suwan 1 and SUWan
2301 were 9,500 and 14,800 plants/rai, respectively, but grain yields from both planting rates
were not different from that of 8,500 plants/rai. In 1981 the Dept. of Agriculture, Ministry of
Agriculture and Cooperatives, recommended 7,000 and 8,500 plants/rai in low to , moderate soil
fertility, and 12,000 plants/rai in fertilized soil. SUpot et a7. reported that the optimum
density for growing corn for silage was 1-1.5 times higher than that for grain production.
Studies on the effects of various rates of nitrogen on corn yield and quality have also been
reported. In 1978, Thiraporn et a7. reported that six corn varieties planted at 0, 30, 40 and
80 kg N/rai at Farm Suwan showed different results of N-response which could be classified into 3
groups as low, medium, and high input varieties. Another unpublished report by Thiraporn on
N-use efficiency of 16 corn varieties indicated that selection under N-stress could improve the
yield response of low N selections such as Across 8328 C3, which yielded higher than the original
population Across 8328 CO. Feil et a7. (1992) stUdied N, P and K content of Suwan 2301 compared
with CPl. Both entries were grown in different N-fertilization treatments at Farm SUWan. The
results revealed that N-content in seed increased with N-fertilization. The response was higher
in SUWan 2301 than in CP 1. It was also found that with N levels of 80-160 kg N/ha the assimilation
of- P and K was more efficient than in low N. Thiraporn et a7. (1992) indicated that N
fertilization increased levels of N, P, and K in the grain.
There are three distinct maize growing seasons in Thailand. Each year, the rainy season
extends from March to November. Early rains generally begin in March and extend up to mid-June.
There is a dry spell during June to July, and the late rainy season extends from August to mid
OCtober. Corn and other rain-fed field crops are grown in the early and late rainy seasons.
!Ji Director, Inseechandrastitya Inst., Kasetsart Univ., Bangkhen, Bangkok 10900, Thailand.
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