Observational data on dry matter accumulation (DMA) and dry matter partitioning (DMP) from the experiment of maize sown on four different dates in a normal year (2012) and three drought years (2014, 2015, 2018) were analyzed to assess the impact of drought and the sowing date on DMA and DMP in different above-ground organs. The phenology of maize was more closely related to the sowing date than to drought. In the normal year, the amount of dry matter in different organs differed slightly among sowing dates, except for those at maturity, and increased linearly after jointing: the dry matter of leaves and stalks increased rapidly before tasselling and the milk stage, respectively, and both increased slowly thereafter, whereas the dry matter of the ears increased linearly. In the drought years, DMA was more sensitive to precipitation relative to the normal year and was affected by the sowing date and drought. Specifically, drought lowered the dry matter of the above-ground organs to varying degrees and accentuated that variation in crops sown on different dates. From the view of DMP, a mild drought lowers the stalk DMP rate but increases the rate in ears. The more severe the drought, the smaller the DMP rate in ears and the stronger the inhibition of the transfer of dry matter from stalk to ears, as well as the more significant difference in the DMP pattern among the sowing dates. High temperatures and drought had a significant synergistic effect on DMAs in all the organs relative to that of drought alone, reversely having an inappreciable impact on the DMP pattern. During the three growth periods, namely jointing to tasselling, tasselling to the milk stage, and the milk stage to maturity, DMA during any two adjacent periods had a clear complementary effect, especially before and after tasselling. Dry matters of the above-ground parts in aggregate, of the stalk and of the ears, at the milk and maturity stages were negatively correlated to the degree of drought, and the maximum correlation was for the ears.

Roots are an important water transport pathway between soil and plant. Root water uptake (RWU) plays a key role in water and heat exchange between plants and the atmosphere. Inaccurate RWU schemes in land surface models are one crucial reason for decreased model performance. Despite some types of RWU functions being adopted in land surface models, none have been certified as suitable for maize farmland ecosystems. Based on 2007–2009 data observed at the maize agroecosystem field station in Jinzhou, China, the RWU function and root distribution (RD) in the Common Land Model (CoLM) were optimized and the effects of the optimizations on model performance were compared. Results showed that RD parameters calculated with root length density were more practical relative to root biomass in reflecting soil water availability, and they improved the simulation accuracy for water and heat fluxes. The modified RWU function also played a significant role in optimizing the simulation of water and heat fluxes. Similarly, the respective and integrated roles of two optimization schemes in improving CoLM performance were significant during continuous non-precipitation days, especially during the key water requirement period of maize. Notably, the improvements were restrained within a threshold of soil water content, and the optimizations were inoperative outside this threshold. Thus, the optimized RWU function and the revised RD introduced into the CoLM model are applicable for simulation of water and heat fluxes for maize farmland ecosystems in arid areas.