EFFECTS OF TEMPERATURE AND PHOTOPERIOD ON PHENOLOGY AS A GUIDE TO THESELECTION OF ANNUAL LEGUME COVER AND GREEN MANURE CROPS FOR HILLSIDE FARMING SYSTEMS

The effects of temperature and photoperiod on times from sowing to flo wering and maturity in a range of multi-purpose leguminous cover crop species have been investigated in controlled environments in order to quantify the photothermal coefficients which determine their potential environmental adaptation. Six genotypes representing six tropical or subtropical species were grown in 12 environments comprising all combi nations of mean diurnal temperatures of 17, 22 and 27 degrees C and ph otoperiods of 11.5, 12.5, 13.5 and 14.5 h day(-1). Another six genotyp es representing five temperate species were grown in nine environments comprising all combinations of 17, 22, and 27 degrees C and photoperi ods of 12.5, 13.5 and 14.5 h day(-1). For all tropical and subtropical species, the warmest temperature combined with the shortest photoperi od hastened flowering and fruit maturity. However, except for Lupinus mutabilis which was photoperiod-insensitive, all temperate species bot h flowered and matured sooner at the warmest temperatures combined wit h the longest photoperiod. These photothermal responses in phenologica l development were amenable to modelling. Times to flowering were sati sfactorily described using a general triple plane rate model. Rates of progress from first flowering to first mature pod were also satisfact orily modelled using temperature alone as the independent variable. Th ese photothermal and thermal relations have identified considerable in ter-specific differences in phenological responses to environment. The relations can now be applied to reveal the relative suitabilities of these diverse species as potential cover crops across hillside environ ments throughout the tropics and subtropics. (C) 1998 Elsevier Science B.V. All rights reserved.