Intercropping and fertilization strategies to progress sustainability of organic cabbage and beetroot production

Abstract

Sustainably increasing organic vegetable crop productivity is needed to meet growing demands, considering replacement of conventional animal manures with alternative fertilizers. We investigated the effects of intercropping (IC) and different organic fertilization strategies, and their interactions, on the plant-soil system. A 2-year IC field experiment with white cabbage and beetroot was conducted with two compost-supplemented fertilization strategies (animal-based AF+C; plant-based PF+C) and one control with pig slurry (CONT). Root growth was measured with the minirhizotron method. Overall productivity of intercropping (IC) was lower or similar to that of monocropping (MC) systems with a land equivalent ratio of 0.8 in 2018 and 1.0 in 2019. IC affected rooting intensity in only few soil layers: at harvest (2018), beetroot IC had higher rooting intensity compared to beetroot MC in 0.25–0.75 m soil layer. Mycorrhizal colonization of beetroot roots was increased by 37 % under IC. CONT crops had the highest yield and nitrogen (N) accumulation in 2018. In 2019, yield, N and phosphorous (P) accumulation and soil enzyme activity were higher in the PF+C and CONT conditions than with AF+C. Potential N mineralization was 24–37 % higher under PF+C compared to CONT and AF+C, whereas hot water extractable P was highest under animal-based fertilization strategies (CONT: 8.66 mg kg−1, AF+C: 8.56 mg kg−1) compared to PF+C: 7.99 mg kg−1. Benefits of productivity and N-use-efficiency from complementary root growth and resource use were not found in cabbage-beetroot IC. Instead, displacement of sowing/planting dates in the second year decided the dominating species, supported by mycorrhiza in beetroot. This management practice reduced the level of competition and increased the overall productivity of the IC system compared to 2018. The plant-based fertilization strategy had higher soil fertility as indicated by potential N mineralization and similar P use efficiency and can replace pig slurry. The methods of IC and fertilization strategy interacted only on potential N mineralization. Long-term improvements are expected with compost-supplemented fertilization strategies owing to their high organic carbon and N inputs.