Solar radiation utilization of five upland–paddy cropping systems in low-light regions promoted by diffuse radiation of paddy season

Abstract

Solar radiation affects crop productivity in farmland ecosystems. Global dimming has resulted in decreased incident global radiation over recent decades, with a huge subsequent effect on food security. Attempting to increasing utilization of radiation and production to increase output, especially in multiple cropping systems, is a significant problem in low-light regions. Here, five upland–paddy cropping systems were evaluated in a low-light region during 2016–2017 and 2017–2018: Garlic–rice (GR), wheat–rice (WR), broad bean–rice (BR), rapeseed–rice (RR), and potato–rice (PR). Solar radiation and crop-related indicators were investigated to determine radiation utilization. The results showed that annual global radiation was 4056.97. MJ·m−2 and 3985.43 MJ·m−2 in 2016–2017 and 2017–2018, respectively, 13.69%–26.25% of which was wasted during the fallow season. Furthermore, the seasonal distribution of global radiation was differed to study years. The ratio_dif in paddy season was greater than 75%, whereas in upland season was less than 55%. Additionally, the annual radiation utilization efficiency (RUE) values of the crops investigated in this study were 0.53%–0.80% and RUE during upland season were 0.30%–0.95%, compared to 0.99%–1.35% during paddy season. The ratio_dif during paddy season had a greater contribution to RUE than that of the upland season, whilst the ratio_dif had a positive relationship with RUE. Therefore, in the low light region the high radiation utilization of upland-paddy systems could primarily be attributed to the efficient utilization of diffuse radiation by rice, which had a high radiation interception, net photosynthesis and net assimilation rate. This increase in diffuse radiation will further promote the efficient use of radiation in low-light regions. Furthermore, planting the upland crops with long growth period (garlic) and high planting intensity (wheat and rapeseed) could take advantage of limited global radiation in low-light regions. Our study clarifies RUE magnitude and its causes in upland–paddy cropping systems in low-light regions, while also providing a theoretical reference for grain production prediction and crop RUE improvement within the context of global dimming.