The Importance of Root Interactions in Field Bean/Triticale Intercrops

Abstract

To highlight the contribution of belowground interactions to biomass and N and P yields, field bean and triticale were grown in a P-poor soil as sole crops and as replacement intercrops at two N levels. The shoots were always in contact, while the roots of adjacent rows were free to interact or were completely separated. This allowed simultaneous testing the intraspecific and interspecific competition between rows, which to our knowledge has not been studied before. Root biomass, distribution in soil, morphometry, and functional traits were determined, together with the nodule number and biomass. The Land Equivalent Ratio for shoot biomass and N and P yield were higher than 1 when roots were in contact, and markedly lower when they were separated. This demonstrates the positive contribution of root interactions, which in field bean, consisted of increased root elongation without changes in biomass and nutrient status; in triticale, of increased N and P uptake efficiency and reduced biomass partitioning to roots. The soil-plant processes underlying intercrop advantage led to complementarity in N sources with low N inputs and facilitated N and P uptake with high N inputs, which demonstrates that intercropping could be profitable in both low and high input agriculture.

Keywords: N level; P facilitation; field bean; intercrops; legume/cereal; nodule; root interactions; root morphometry; soil enzyme activity; triticale.

Figure 1

Shoot (a) and root (b) biomass of field bean, as affected by the Crop system × Row contact interaction (shoot) and by the Crop system × N level × Row contact interaction (root). SC, sole crop; IC, intercrop. Values are means of two N levels and three replicates (shoot) and of three replicates (root). In each figure, bars with different letters indicate that the corresponding means are significantly different at P < 0.05, Tukey’s test.

Figure 2

Root biomass density in soil of field bean (a) and triticale (b), as affected by the Crop system × Row contact × Soil depth interaction. SC, sole crop; IC, intercrop. Values are the mean of two nitrogen rates and three replicates. Within each figure, bars with different letters indicate that the corresponding means are significantly different at P < 0.05, Tukey’s test.

Figure 3

Nodule parameters (a–c) and nodule:root ratios (d–f) as affected by the Crop system × N level × Row contact interaction. SC, sole crop; IC, intercrop. Values are the mean of three replicates. In each figure, bars with different letters indicate that the corresponding means are significantly different at P < 0.05, Tukey’s test.

Figure 4

Nitrogen (a) and phosphorus (b) uptake efficiency per unit of root surface in field bean, as affected by the Crop system × N level × Row contact interaction. SC, sole crop; IC, intercrop. Values are the mean of three replicates. In each figure, bars with different letters indicate that the corresponding means are significantly different at P < 0.05, Tukey’s test.

Figure 5

Shoot (a) and root (b) biomass and root:shoot ratio (c) of triticale, as affected by the Crop system × N level × Row contact interaction SC, sole crop; IC, intercrop. Values are means three replicates. In each figure, bars with different letters indicate that the corresponding means are significantly different at P < 0.05, Tukey’s test.

Figure 6

Nitrogen (NUEuS, a) and phosphorus (PUEuS, b) uptake efficiency per unit of root surface in triticale, as affected by the Crop system × N level × Row contact interaction. SC, sole crop; IC, intercrop. Values are the mean of three replicates. In each figure, bars with different letters indicate that the corresponding means are significantly different at P < 0.05, Tukey’s test.

Figure 7

Air minimum and maximum temperatures and rainfall over the growing season 2018.

Figure 8

Schematic representation of the plant arrangement in sole crops and intercrops to give Aerial (a) and Full row contacts (b). Triticale (o); field bean (●).

Figure 9

Growth boxes of Full (a, left) and Aerial (b, right) treatments; side front removal from a growth box at harvest (b); a soil column during (c) and after excavation (d).