Importance of rapid canopy closure for wheat production in a temperate sub-humid environment: experimentation and simulation

Rapid canopy closure (RCC) is one of the physiological attributes that may enhance genetic yield potential of wheat (Triticum aestivum L.), particularly in a short growing season. The objectives of this study were (1) examination of the interrelationships among RCC-related traits and grain yield under rainfed conditions in a temperate sub-humid environment, and (2) quantitative evaluation of the value of RCC to wheat production in the environment. Canopy development before closing is described by an exponential equation, Y = alpha(L) exp(beta(L)t), where y is the crop leaf area index (LAI), t the thermal time, alpha(L) the LAI at the beginning of the exponential growth and beta(L) the relative growth rate of LAI (m(2) m(-2) degreesC d(-1)). Field experiment results, using 13 wheat cultivars, showed that exponential phase of canopy development can be divided into two sections; an early section during which canopy dry weight and LAI are highly related to alpha(L), and a second section where crop dry weight and LAI are highly dependent on beta(L). Grain weight had a positive effect on alpha(L) parameter and canopy dry weight and LAI during early section of exponential phase. In cultivars with high grain yield, canopy dry weight and LAI were also higher during exponential phase of canopy development. High grain yield was related to higher beta(L) but not with alpha(L). There was genotypic difference for RCC parameters, alpha(L), and beta(L), indicating the possibility of genetic improvement for these traits. However, a negative correlation (-0.69, P < 0.01) observed between the parameters may reduce gain from a higher beta(L) Simulation analysis was performed for four hypothetical and standard (Zagros) cultivars using a modified SUCROS 1-Wheat model to explore possible long-term yield consequences of RCC. These four cultivars were created based on observed variation and association between the parameters in the field experiment. Results showed that attempts to increase RCC and thereby yield through greater beta(L) would be more beneficial than alpha(L). Twenty percent increase in beta(L) caused yield gain of 7-10% for irrigation conditions and 13-18% for tainted conditions, depending to the values of alphaL compared to yield gain of 3 and 5% resulted from a 20% greater alpha(L) under irrigated and rainfed conditions, respectively. Sensitivity tests with decreased alpha(L) and beta(L) showed that a large-decrease in grain yield is obtained for 20 and 40% lower alpha(L) and beta(L). Hence, it was concluded that in locations with non-optimum agronomic management affecting RCC, yield increase has to be obtained firstly by improvement of agronomic measures. The implications for other environments and future research needs are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.