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.