Diversifying maize rotation with other industrial crops improves biomass yield and nitrogen uptake while showing variable effects on nitrate leaching

Crop rotation and diversification can alleviate the high nitrate leaching associated with maize (Zea mays L.) monoculture, without reducing yields. Prior research focused on maize-legume/cereal rotations, with limited exploration of rotations with industrial crops destined for biorefining. In 2012, four-year rotation systems were established on sandy soil in Denmark, consisting of maize, hemp (Cannabis sativa L.), beet (Beta vulgaris L.), and triticale (Triticosecale), organized into four sequences to ensure the occurrence of each crop in each year. The fallow periods in the rotations were covered with “secondary crops”- winter rye (Secale cereale L.), winter rape (Brassica napus L.), or grass-clover (Festuca rubra L. – Trifolium repens L.). Over two rotation cycles (eight years), we assessed the aboveground biomass dry matter, biomass nitrogen (N) uptake, and their stabilities of maize in rotations versus monoculture, alongside quantifications of nitrate leaching, and soil carbon (C) and N stocks up to 100 cm deep. In the first cycle, the aboveground biomass of maize in rotation (15.5 Mg ha−1) was 7% significantly lower than that in monoculture (16.6 Mg ha−1), but this difference disappeared in the second cycle (17 versus 16.5 Mg ha−1). The maize biomass N uptake in rotation (194.5 kg ha−1) was similar to that in monoculture (196.6 kg ha−1) in the first cycle and was significantly higher by 8% in the second cycle (195.5 versus 165.7 kg ha−1). Nitrate leaching varied interannually with precipitation and secondary crops. Higher rainfall increased nitrate leaching for both systems in cold months, while rotations had more leaching after irrigation in dry periods. Initially, diverse rotation halved nitrate leaching compared to monoculture, but increased at the onset of the second cycle when the preceding winter rape did not survive in the winter. Winter rye following maize reduced nitrate leaching, except when the preceding crop was grass-clover or poorly thriving winter rape. During the whole period, the rotation system increased soil C and N stocks at 0–100 cm depth. This study highlights the environmental and yield benefits of diversifying maize rotations, and the crucial role of secondary crop management to optimize maize rotation strategies.