A thermal time analysis of ageing of maize (Zea mays L.) seed can account for reduced germination in hot moist soil

After sowing into moist soil, maize seed imbibe although the soil moisture content may be too low to permit seedling emergence. The hypothesis tested here is that in such circumstances, and especially at high temperature, the seed age in the soil with the result that when the moisture restriction is subsequently removed, germination and seedling emergence are reduced. First, maize seed were artificially deteriorated in the laboratory at four elevated moisture and five constant temperature regimes for four different periods in order to determine the effect of ageing on radicle and coleoptil e emergence. Next, the responses when seed were deteriorated at alternating temperatures were shown to be the same when the temperature exposure was e xpressed as thermal time. A base temperature for thermal ageing time was es timated as about 30 degrees C, Finally, when four Sri Lankan maize cultivar s were sown in soil, the seed imbibed and experienced temperatures above 30 degrees C with the result that final seedling emergence was reduced. The e ffect of ageing in the soil appeared greater than that in the laboratory be cause the moisture content of seed in the soil was not constant but increas ing. (C) 1999 Published by Elsevier Science B.V. All rights reserved.