An improved double-row rubber (Hevea brasiliensis) plantation system increases land use efficiency by allowing intercropping with yam bean, common bean, soybean, peanut, and coffee: A 17-year case study on Hainan Island, China

Light limitation has been a major constraint in maximizing land use via intercropping in conventional single-row rubber plantations. Based on a double-row rubber plantation established by using cordon rubber tree clone (CATAS 7-20-59) in 2002, a long-term field experiment was conducted to investigate whether land use efficiency could be increased by allowing intercropping with more crops in the lower strata. Although the double-row system produced significantly lower total rubber yield (12964 kg ha(-1)) compared with the single-row system (14455 kg ha(-1)) from 2010 to 2018, no difference in rubber yield per tree between the double-row and single-row systems was observed. Unlike single-row systems, the double-row system prevented the development of continuous heavy shade at tree maturity and permitted 2-4 h of direct sunlight to penetrate the lower strata, where companion crops were planted in 2014 and 2017. The photosynthetically active radiation ranged from 26 to 1815 mmol m(-2) s(-1) in the intercropped area in the double-row system, whereas it ranged from 12 to 450 mmol m(-2) s(-1) in the single-row system. Of the annual intercrops tested, yam bean produced the highest yield in comparison to its yield in monoculture (74.6% of that in monoculture), whereas peanut exhibited the lowest comparative yield potential (38.1% of that in monoculture). Compared with a typical yield of Robusta coffee in monocultures (1226.0 kg ha(-1)), the yield of intercropped Robusta coffee plants was 35.3% lower. The yield of intercropped Arabica coffee (1319.8 kg ha(-1)) was similar to that of monocultural Robusta coffee. Taken together, results demonstrate that double-row planting sufficiently improves soil-level light availability, thus allowing intercropping with more potential crops without loss in rubber yield per tree at maturity, as compared with single-row systems. (C) 2020 Published by Elsevier Ltd.