Apple trees in garden-orchard system improve soil quality and yield of organic radish preceded by lettuce

Maintaining healthy soil is a major challenge in agriculture. Tree-based intercropping is very promising to ensure high production and conserve soil quality, as shown in agroforestry systems. Trees improve soil fertility through the input of organic matter by litterfall and root turnover, which enhance the soil microbial activity. This study aims to evaluate the effects of apple trees (Malus × domestica Borkh. ‘Golden Delicious’) on soil qualities and their potential to improve the yield of an unfertilized organic radish crop (Raphanus sativus L. ‘Ostergruss’). From June to August 2020, we compared the soil properties and the yield of radish beds located either at 1.5 m (B1) or at 5 m (C) from a row of 20-year-old apple trees. Litterfall, soil organic matter, and soil bulk density were measured on each bed. To characterize the effects of apple trees on soil microbial activities biodegradation capacity, we assessed the decomposition rates of the previous crop residues (lettuce roots - Lactuca sativa L. ‘Olana’) on each bed using 5 mm-mesh litterbags buried at 15 cm depth. N mineralization rate was measured in situ using PVC tubes. Apple tree litterfall enriched the 0-30 cm soil layer in organic matter (45 g kg-1 soil DW on B1 vs. 35 g kg-1 soil DW on C). Soil bulk density was significantly lower on B1 (1.2 g cm-3) than on C (1.5 g cm-3). Furthermore, the decomposition rate of lettuce roots was faster on B1 than on C: on B1, 50% of the initial dry mass was decomposed in two weeks and 65% after one month compared to only 35 and 48% on C bed, respectively. We also observed that net N mineralization rate was up to twice as high on B1 than on C. Consequently, soil NO3- content in the 0-30 cm layer was significantly higher on B1. Yield of radish was significantly higher on B1 due to higher soil mineral nitrogen content and lower soil bulk density. Our results suggest that fruit tree-based intercropping is a promising option for ensuring both soil quality and productivity of organic root vegetable crops.

Toky Ramananjatovo won the ISHS Young Minds Award for the best oral presentation at the International Symposium on Plant Nutrition, Fertilization, Soil Management at IHC2022 in France in August 2022.

Toky Ramananjatovo, L'Institut Agro Rennes-Angers, 2 Rue André le Notre, 49000 Angers, France, e-mail: tokyramananjatovo@gmail.com

The article is available in Chronica Horticulturae