Coffee performs better than amomum as a candidate in the rubber agroforestry system: Insights from water relations

Abstract

Rubber (Hevea brasiliensis) plantations have been facing a double challenge of land degradation and seasonal drought in Southeast Asia. Various cash crops are recently interplanted with rubber trees to face these issues. However, the water relations between rubber trees and the intercrops remain poorly understood. This study aims to evaluate the influences of three cash intercrops, namely two herbaceous plants (Amomum villosum and Alpinia oxyphylla) and a woody beverage (Coffea arabica), on rubber water utilization through both spatial and temporal scales. We investigated the plant water-absorption dynamics, root biomass, and intrinsic water use efficiency (WUEi) throughout a whole year (2017–2018). The results showed that rubber trees (43.5 ± 2.6%) and intercrops (69.1 ± 3.2%) highly depended on soil water from the 0–20 cm depths. An interspecific water competition occurred in all the rubber-based agroforestry practices, because of their similar water source and root distribution in the vertical soil profiles. Overall, the WUEi of rubber trees was relatively higher during the dry season (δ13C: −30.79 ± 1.12‰) compared to the rainy season (δ13C: −31.65 ± 0.99‰). Coffee (C. arabica) better facilitated the soil water availability than the other intercrops, suggesting its suitability as an intercrop for rubber trees. Alpinia-oxyphylla (A. oxyphylla) played a moderate role on soil water retention. Amomum (A. villosum), however, aggravated the soil water deficit in the agroforestry practice. Given the differences in water relations to rubber trees, the introduction of woody crops rather than herbaceous crops can improve the resistance of rubber plantation to the frequent drought stress in this region.