The survival and recovery of perennial forage grass species during periods of drought or waterlogging can be influenced by ecological niches within landscapes at the toposequence scale and implementing management practices that reduce plant stress during these periods. This study aimed to generate evidence for assessing the validity of toposequence-based recommendations for the optimal positioning of forage species within farms in sandy landscapes in upland Cambodia.
From 2018 to 2022, fields in either upper or lower parts of toposequences were sown to Paspalum atratum cv. Terenos (Paspalum) or Urochloa hybrid cv. Mulato II in Samroung Tong District, Kampong Speu Province. Biomass cuts were measured every 45 days. Volumetric soil water was measured by Diviner 2000 at 10 cm increments to 1.6 m depth, coinciding with each biomass measurement. All toposequence by forage treatment combinations were analysed for trends in mean biomass production and profile soil water content.
Wet and waterlogged conditions were more frequent in lower field positions. However, during extreme dry periods profile, soil water conditions were similar in both landscape positions. The ecological niche concept was supported in this study, as Paspalum production was not limited in lower fields due to wet and waterlogged conditions. However, Paspalum production was restricted in upper field positions during drought periods. In contrast, Mulato II maintained a more consistent biomass production than Paspalum in upper field positions in drought conditions.
The onset of rainfall in the March to April period was found to be critical to the recovery of biomass production after the dry season. This indicates that after the dry down of the soil profile from December, irrigation will be critical until the onset of the early wet season to refill the upper soil profile (50 cm) to supply the majority of roots with water.