Optimization of intercropping for biomass production

Background and Objective

The integration of lupins with high biomass potential into new cultivation systems will enable the development of ecosystem services of leguminous crops for energy crop cultivation in the planned project.

Approach

New intercropping systems with maize and the integration of a new leguminous crop such as Andean Lupins (Lupinus mutabilis Sweet.) or of white lupin (L. albus) and oat with high biomass potential was the focus of this joint project of Julius Kuehn-Institute, University Rostock and Thünen Institute. The aim of the multi-site field trials was to promote biodiversity in the agricultural landscape and other positive traits belonging to the ecosystem services with consistently high yields for biogas production.

The development of an intercropping system of Andean Lupin and maize has to be based on a knowledge-based combination of plant genetic resources or varieties of Andean lupin on the one hand and on the testing of phenologically different maize varieties on the other. Therefore, 7 resp. 12 Andean lupins were tested in 3 environments in the years 2019-2021, each with 2 maize testers. In a second experiment, 7 maize varieties, each with 2 Andean lupins, were examined for their intercropping suitability at two locations over the same three-year period. In a corresponding approach, 4 white lupin varieties were evaluated with 4 oat species resp. varieties over 3 years at 4 locations for their suitability in the intercropping system.

In all intercropping trials, we determined parameters such as total dry-matter yield (DMY_t), lupin and maize dry matter yield and their share of DMY_t. In addition, the ensilability and silage quality were evaluated and the biogas and methane yield were examined using batch and continuous tests.

In the part of the sub-project of the Thünen Institute, additional field trials were conducted on row width and seed density of Andean lupins in mixed cultivation of Andean lupins and maize as well as with white lupin and oats to determine the optimal seed density ratio in a replacement design. Furthermore, studies were carried out at the Trenthorst site on the N_min contents, the infiltration capacity and the N₂ fixation of Andean lupins and white lupins.

Results

The results showed similar or partly significant lower total dry matter yields for the intercropping systems of Andean lupin and maize compared to maize in pure stand. While the different maize varieties had no effect on the DMY_t and the DMY of maize in the mixtures, the Andean lupins showed some significant differences with regard to the DMY of Andean lupin in the mixtures. We identified suitable lines of Andean lupins, two of them showed significantly higher DMY of lupin in the mixtures in 8 and 7 out of 9 environments, respectively.

All the tested mixtures with white lupin and oats produced a lower biomass DM-yield than expected. In the performance test, two mixtures performed better than the averaged yield of the pure stands after series calculations taking 10 environments into account.

The results of the sub-project of the Thünen Institute showed that a seed rate of 10 seeds m^-2 Andean lupin in combination with 8 seeds m^-2 maize and a row width of 37.5 cm is recommended.

Both intercropping systems had an influence on root stratification, which reduced water withdrawal from the soil. The mixtures of white lupin and oats showed a positive below-ground interaction with uniform rooting of the soil space, while this was not the case for the mixtures of Andean lupine and maize, suggesting a negative interaction, which could also explain the lower land use efficiency.

In the replacement trial, the mixtures of white lupin and oats showed higher yields compared to the pure stands. In terms to achieve a combination of good weed suppression and the highest possible yields, a mixture with 50% of each of the mixture partners in the sowing mixture is recommended. Differences between the variety combination of white lupin and oats were also observed.

The N₂ fixation in the pure stands was higher for white lupin than for Andean lupin and was significantly reduced in mixed cultivation compared to pure stand.