Rainfall, temperature, and solar radiation are important climate factors, which determine crop growth, development and yield from instantaneous to decadal scales. We propose to identify year patterns of climate impact on yield on the basis of rain and non‐rain weather. There are inter‐related impacts of climatic factors on crop production within a specific pattern. Historical wheat yield data in Queensland during 1889–2004 were used. The influence of meteorological conditions on wheat yields was derived from statistical yield data which were detrended by 9‐year‐smoothing averages to remove the effects of technological improvements on wheat yields over time. Climate affects crop growth and development differently over different growth stages. Therefore, we considered the climate effects at both vegetative and reproductive stages (before and after flowering date, respectively) on yield. Cluster analysis was employed to identify the year patterns of climate impact. Five patterns were significantly classified. Precipitation during the vegetative stage was the dominant and beneficial factor for wheat yields while increasing maximum temperature had a negative influence. Crop yields were strongly dependent on solar radiation under normal rainfall conditions. As the effect of rainfall on soil water is relatively long‐lasting, its beneficial effect in vegetative stage was higher than its effect during the reproductive stage. The Agricultural Production Systems sIMulator (APSIM) was evaluated using long‐term historical data to determine whether the model could reasonably simulate effects of climate factors for each year pattern. The model provided good estimates of wheat yield when conditions resulted in medium yield levels, however, in extremely low or high yield years, corresponding to extremely low or high precipitation in the vegetative stage, the model tended to underestimate or overestimate. Under high growing season precipitation, simulations responded more favourably to reproductive stage rainfall than measured yields.

Rice Oryza sativa L. development-and also its response to climatic change-is mainly determined by temperature and photoperiod. An experiment was conducted to study the influence of meteorological factors on growth and development of hybrid rice in South China, in which seeds were sown at different sites at different dates in the spring. The 29 experimental sites were spread over a large area, with latitudes from 21°39' to 34°16' N and altitudes from 1 to 1862 m above sea level. It was found that the length of the growth period at low latitudes (21 to 25°N) was mainly determined by temperature and showed a single-peaked curve with an optimum temperature at about 25.7°C. The temperature response of development is almost linear at high latitudes (25 to 35°N), but the dependence is not as close and significant as that at low latitude, due to longer daylength and its higher variation. A phenological-simulation model with a biological basis was used to simulate the developmental stages of rice in South China. It described both thermal sensitivity and photoperiodism using nonlinear equations. The model was validated by data of sowing-date experiments carried out at different geographical sites, and then was applied to evaluate changes in the length of the rice-growth period in response to climate warming during the period from 1951 to 2006. Because there was significant warming, and the length of the growth period was sensitive to this change over the Yunnan-Guizhou Plateau, the length of the growth period was narrowed by 6 to 14 d (comparing 1990 to 2006 with 1951 to 1989), whereas it was shortened by 1 to 2 d in most low plain areas in South China. The probability of serious temperature related crop failure will increase if planting of a latematurity variety is adopted in high altitude areas.

Mass and energy fluxes between the atmosphere and vegetation are driven by meteorological variables, and controlled by plant water status, which may change more markedly diurnally than soil water. We tested the hypothesis that integration of dynamic changes in leaf water potential may improve the simulation of CO 2 and water fluxes over a wheat canopy. Simulation of leaf water potential was integrated into a comprehensive model (the ChinaAgrosys) of heat, water and CO 2 fluxes and crop growth. Photosynthesis from individual leaves was integrated to the canopy by taking into consideration the attenuation of radiation when penetrating the canopy. Transpiration was calculated with the Shuttleworth-Wallace model in which canopy resistance was taken as a link between energy balance and physiological regulation. A revised version of the Ball-Woodrow-Berry stomatal model was applied to produce a new canopy resistance model, which was validated against measured CO 2 and water vapour fluxes over winter wheat fields in Yucheng (36 • 57 N, 116 • 36 E, 28 m above sea level) in the North China Plain during 1997, 2001 and 2004. Leaf water potential played an important role in causing stomatal conductance to fall at midday, which caused diurnal changes in photosynthesis and transpiration. Changes in soil water potential were less important. Inclusion of the dynamics of leaf water potential can improve the precision of the simulation of CO 2 and water vapour fluxes, especially in the afternoon under water stress conditions.

ABSTRACT. Deficit irrigation has been shown to increase crop water use efficiency (WUE) under certain conditions, even