Optimizing arrangement and density in maize and alfalfa intercropping and the reduced incidence of the invasive fall armyworm (Spodoptera frugiperda) in southern China

Abstract

Maize and alfalfa intercropping has yield advantages and is an important cropping system. However, the row arrangement and density design of narrow-strip intercropping systems require improvement for the synergistic production of maize and alfalfa with higher yield advantages. Moreover, whether this system is adequate for pest control is unclear. In this study, a three-year field experiment was conducted at Yunnan in southwestern China. Using monocultures of maize and alfalfa as controls (CK), the experimental design comprised intercropping with three row arrangements: 2M2A (two maize rows with two alfalfa rows); 1M3A (one maize row with three alfalfa rows); and 2M3A (two maize rows with three alfalfa rows) under low density with a replacement design and high density with an additive design for the maize density. The growth and yield of maize and alfalfa were measured; the total and partial land equivalent ratio, overyielding of intercropping, and the competition ratio of crops were evaluated. Moreover, the incidence of the invasive fall armyworm ( Spodoptera frugiperda , a major agricultural pest) was investigated. Maize and alfalfa intercropping produced a yield advantage, with 1.31 being the highest land equivalent ratio. The yield was affected by planting row arrangement and maize density. The land equivalent ratio of 1M3A was significantly higher than that of 2M2A and 2M3A by 20% and 18%, respectively. A high maize density with additive design increased the land equivalent ratio by 8% compared with a low maize density with replacement design; the maize had a competitive advantage in intercropping; the row arrangement significantly affected the alfalfa yield but not the maize yield, while a high maize density with additive design slightly increased maize yield compared with a low maize density with replacement design, but had no significant effect on alfalfa yield. In addition, compared with sole maize cropping, intercropping significantly reduced the incidence of the invasive fall armyworm by 80%. These findings suggested that increasing the alfalfa row number and maize density improved the land equivalent ratio for narrow-strip intercropping, and that the 1M3A arrangement under high maize density with an additive design synergistically produced maize and alfalfa. Importantly, the results also suggest that maize and alfalfa intercropping has the potential to ecologically control the incidence of the fall armyworm for the sustainable production of maize. • Low alfalfa production should be increased in narrow-strip intercropping with maize. • Optimizing arrangement and density increased both the alfalfa and maize yield. • One high density maize with three alfalfa rows was recommended for application. • Intercropped alfalfa reduced the incidence of invasive fall armyworm on maize.