Border-row proportion determines strength of interspecific interactions and crop yields in maize/peanut strip intercropping

Abstract

Strip intercropping enables increases in yields and ecological services in agriculture. Crop yields of species grown in strip intercropping are often related to the yield responses (increases or decreases) in the outer rows of the strips: the border rows. This suggests that the yield response can be modulated by changing the proportion of border rows in the field. Here we studied the relationship between component species yields and proportion of border rows in strip intercrops of maize (Zea mays L.) and peanut (Arachis hypogaea Linn.). We tested four different intercrops with equal proportions of maize and peanut but a different number of rows per strip: M2P2 (2 rows maize intercropped with 2 rows peanut), M4P4, M6P6, M8P8, and sole maize (SM) and sole peanut (SP). The border-row proportions were 1, 0.5, 0.33 and 0.25 for the intercropping M2P2 to M8P8, respectively, and 0 for the pure stands. Yield responded positively to the proportion of border rows for maize, but negatively for peanut, confirming the dominance of maize in this system. Kernel number per ear of maize and pod number per plant of peanut were the main yield components that responded to the border-row proportion. Across three years, relative maize yield (yield in intercropping divided by yield in monoculture), varied from 0.76 in M2P2 to 0.56 in M8P8, while relative peanut yield varied from 0.19 in M2P2 to 0.39 in M8P8. Relative yield total was not significantly different from one in any of the mixtures. Yield of intercropped maize in border rows was 48% higher than in inner rows and the sole crop, in part due to a significantly higher kernel number per ear (13%). Yield of intercropped peanut in border rows was on average 29% lower than in inner rows and 48% lower than in sole peanut. Yield responses in border rows were independent from the border-row proportion. The results show that relative crop yields responded strongly to variation in border-row proportion resulting from variation in strip width from 1 to 4 m. Strip width thus provides a mechanism to control the strength of interspecific plant interactions and relative yields in strip intercropping.

Does reduced intraspecific competition of the dominant species in intercrops allow for a higher population density?

“…Peanut, on the other hand, improves available nitrogen in the soil of maize, as peanut is able to fix the atmospheric N 2 with rhizobia (Inal & Gunes, 2008). Previous studies on maize and peanut intercropping did not show a significant improvement on yield in semi‐arid environment (Wang et al., 2020; Zhang et al., 2020). We hypothesized that increasing the plant density of maize, a major contributor to yield advantage in the intercropping, might enhance the land productivity.…”

“…The main disadvantage for farming is the shortage of adapted machinery and related additional labor costs. The widen the crop strips, such as four rows maize with four rows peanut or six rows maize with six rows peanut, might also be reasonable configurations when take machinery into account (Wang et al., 2020). It is necessary and important to use optimal plant densities in the pure stand when calculating the LER of intercropping.…”

“…This intercropping advantage occurs when interspecific competition is weaker than intraspecific competition or mutual facilitation between component crops (Hauggaard‐Nielsen et al., 2001a, 2001b; Snaydon & Satorre, 1989). The species, which is more competitive, always capture more resources to produce greater biomass and grain yield in intercropping compared with its sole cropping (Wang et al., 2020). The species, which is less competitive, often be suppressed and display a yield reduction under the competition with dominant crops (Zhang et al., 2020).…”

Strip-width determines competitive strengths and grain yields of intercrop species in relay intercropping system

“…These include the benefits of mutual interactions between adjacent allospecific plants, e. g., facilitation in water and nutrient uptake, which are maximized 3 , 4 . Several studies tested wider-strip widths and revealed that intercropping systems with wider-strips of 3 m 5 , 3.1 m 6 , 3.3 m 7 , 3.4 m 8 , and 6 m 9 achieved the highest LER compared to narrow-strips. Therefore, intercropping of crops with larger operating strips would be easier to manage with existing farm machinery, and it will produce high profits for farmers.…”

Species patch size at seeding affects the productivity of mixed legume-grass communities

“…Neighboring species show a strong interaction when individuals are more densely packed (Kennedy et al, 2002;Rayburn and Schupp., 2013). In mixed cropping systems, intercropping primarily utilizes the advantages of species interactions by adjusting the planting distances between species (Ma et al, 2007;Wang et al, 2020). Because species interactions can be controlled by the sizes of conspecific patches at seeding, it is possible to test the association of neighbor-effect intensity with the scale of facilitation or competition in plant communities and further quantify the intensity of negative and positive plant interactions.…”