Field Crops Research, 29 (1992) 163- ! 76 Elsevier Science Publishers B.V., Amsterdam 163 Modelling the fully expanded area of maize leaves B.A. Keating~,~ and B.M. Wafulab aACIAR/CSIRO Dryland Project. P.O. Box 41567, Nairobi, Kenya bKdRl, National DrylandFarming Research Centre-Katumani, Machakos, Kenya (Accepted 21 January 1991 ) ABSTRACT Keating, B.A. and Wafula, B.M., 1992. Modelling the fully expanded area of maize leaves. Field Crops Res., 29. i63-176. Crop simulation models used for research or management, frequently require the development of leaf area to be mathematically described. This work examined, for maize, the relationship between the fully expanded area-per-leaf a~d leaf position, in an attempt to identify appropriate functions for use in such models. The slightly skewed bell-shaped function of the form LA~= Ea*exp(a* (xn-Xo)2+b* (xn-Xo)3), was used to relate area-per-leaf (LAn) to leaf position (xn). Tihe amplitude oftbe curve (Yo) repre- sents the size of the largest leaf (at position Xo). Plants varied in total leaf number (TLNO) from 12 to 17 and this variation had a major bearing on the total leaf area per plant (TLA). Both ]to and Xo were linearly related to TLNO (r 2 of 0.94 and 0.99 respectively). The parameter which controls the width of the bell-shaped curve (a), was non-linearly related to TLNO (re=0.99), while the parame- ter that controls the degree of skewness (b), varied little with TLNO. Use of the bell-shaped curve in combination with the functions relating its parameters ( Yo, a, Xo) to TLNO, resulted in a root mean standard deviation (RMSD) of estimates of total leaf area per plant (TLA) of 176 cm" for plants varying in TLNO from 12 to 17 and in TLA from 2839 to 6925 cm2. Bell-shaped functions were successfully fitted to independent area-per-leaf data from plants whose TLNO ranged from 13 to 26. The parameters developed in this study allowed area-per-leaf an0 TLA to be modelled accurately when non-limiting cultural conditions maximized leaf size. Under such circumstances, the bell-shaped curve with parameters linked to TLNO was shown to be a simple and flexible model of the potential area of individual leaves in maize. Resource constraints (such as those that can develop under high plant population) were shown to limit leaf size to less than that predicted by this model. Future work needs to examine the use of the bell-shaped curve in a simulation model context to address these constraints. INTRODUCTION The biomass produced by a crop is a function of the accumulated radiation intercepted and the efficiency with which radiant energy is converted to dry matter (Monteith, 1977; Muchow, 1989). Intercepted radiation is in part a 'Present address: CSIRO, Division of Tropical Crops and Pastures, 306 Carmody Rd., St. Lu- cia, 4067, Brisbane, Australia. 0378-4290/92/$05.00 CO1992 Elsevier Science Publishers B.V. All fights reserved.