Optimizing Fertilizer Use and Planting Density for Lowland Rice Production in Agrivoltaic Systems

The agrivoltaic system (AVS) is an emerging agroecosystem that integrates food production with photovoltaic energy generation. However, there is little information on suitable cereal cropping practices for the AVS. Our objective was to clarify the effects of fertilizer rate and planting density on crop growth, grain yield, and grain quality of lowland rice in the AVS. On-farm experiments were conducted in Japan during summer (May to September) for 3 years. We compared two fertilizer rates (standard and low) and three planting densities (low, standard, and high) between the control and AVS. In the AVS, low fertilization did not reduce yield (6.5 t ha −1 ) compared with standard fertilization (6.2 t ha −1 ). The N balance in the AVS (i.e. N inputs from fertilizers – N content in the grains) under low fertilization was similar to that in the control under standard fertilization. The AVS did not reduce rice quality in any treatment or year. Meanwhile, high planting density significantly increased the panicle number in both the control and AVS, but did not increase yield. Our results suggest that fertilizer inputs can be reduced moderately (by 20%) for lowland rice under the AVS. This does not reduce grain yield or grain quality, and it reduces the risk of crop lodging. Crop management for conventional agroecosystems is not always efficient for the AVS. The development of AVS-specific cereal cropping guidelines will be urgently needed to promote the system’s introduction.