Biomass Productivity and Water Use Efficiency Are Elevated in Forage Crops Compared with Grain Crops in Hydrothermally Limited Areas

Insufficient precipitation and low temperatures can restrict grain yield but not necessarily vegetative growth in cold-arid regions. This indicates that forage production may be more suitable than grain cultivation in these environments while also meeting the increasing demand for livestock products. In this study, we compared the effects of cultivating forage maize (<i>Zea mays</i> L.) and forage oat (<i>Avena sativa</i> L.) with those of traditional grain crops, such as potato (<i>Solanum tuberosum</i> L.) and wheat (<i>Triticum aestivum</i> L.), in terms of aboveground biomass, crude protein yield, and water use efficiency (WUE). Across the four-year study, the results showed that aboveground biomass increased by 26-125% with oat (9.10 t ha^-1) and maize (13.7 t ha^-1) cultivation compared to potato (7.23 t ha^-1) or wheat (6.10 t ha^-1). Maize and potato exhibited greater biomass stability due to longer growing seasons and better synchronization with peak precipitation. In contrast, wheat and oat exhibited higher biomass variability, reflecting their susceptibility to early spring drought. Among the four crops analyzed, maize achieved the highest crude protein yield (1068 kg ha^-1) and WUE (31.9 kg biomass ha^-1 mm^-1), primarily due to its superior biomass production rather than its protein concentration or elevated soil water consumption. Therefore, cultivating forage crops with longer growth periods could effectively align water demand with seasonal precipitation, thereby improving biomass accumulation and WUE in hydrothermally limited regions.