Yield, its components and pest incidence in mixed intercropping of oats (Avena sativa) and field beans (Vicia faba)

Abstract

Abstract. Seed yields, yield components, pest incidence and damage were examined in two field experiments of mixed intercropping of oats (A vena saliva) with field beans (Vida faba) in Southern Finland in 1984.The stand types were monocrops and replacement series of mixtures with 2/3 and 1/3 or 1/3 and 2/3 of oats and beans, respectively, on plots treated or not treated with insecticide.In the first season when the overall performance of the crops was poor and the numbers of the main pest Rhopalosiphum padi (Horn., Aphididae) on oats low, the Land Equivalent Ratio (LER) index indicated an intercropping advantage in the bean yield and a disadvantage in the oat yield, the insecticide treatment having no effect on the overall nor on the relative performance of the component crops. The site used during the second season was of high fertility, thus favouring oats over beans. The LERs indicated no advantage or disadvantage in mixed cropping for either oats or beans when R. padi was not controlled. Spraying against R. padi improved the performance of oats, the mixture with 1/3 oats showing an advantage over the monocrop. Simultaneously, there were signs (p = 0.08) of a reduction in the relative performance of the beans. The indicative results support the hypothesis of interspecific dynamics in compensatory yielding as an element of improved reliability in intercropping.The yield components most sensitive to the change in cropping pattern were the number of panicles per plant in oats and the seed weight in beans, both increasing in the mixtures. Compared to known responses to stand density in monocrops, the beans responded to the mixed cropping in a more specific way than the oats.Mixed cropping increased the numbers of aphids in oats. There were signs of a reduced incidence, but not of a reduced average colony size, of Aphis fabae, and of a reduced rate of notching by Silona spp. weevils on beans in mixed cropping. The results for damage by the frit fly (Oscinella frit) were inconclusive.

Insect Numbers and Pest Damage in Intercrops vs. Monocrops

“…Mixed cropping with faba bean slightly delays the ripening of oats (Helenius & Ronni 1989), as can be seen already at flowering. This slowing of the development of oats in the mixtures may contribute to the indicated one-to two-day delay in reaching peak density for the populations of R. padi (Helenius 1989a).…”

“…Tillering was higher the lower the proportion and density of oats in the mixture (Helenius & Ronni 1989). Leaffstem ratio was not significantly affected, but in some cases, although not consistently, oats grew taller and accumulated more biomass in the mixtures than in the monocrop (Helenius 1990~).…”

“…In two of -the experiments an additional experimental factor was Downloaded by [Stockholm University Library] at 06:45 20 August 2015 the intensity of cereal aphid infestation at two levels: natural infestation that was not manipulated and low infestation caused by spraying with aphicide (Helenius & Ronni 1989. In three of the experiments an additional factor was activity abundance of epigeal predators which was manipulated by barriers and trenches (Helenius 1990b) (Table 1).…”

“…These are known as important mortality agents of cereal aphids in the region (Rautapaa 1976). The occurrence of pests other than cereal aphids was incidental (Helenius & Ronni 1989).…”

“…Also, the spatial distribution of the prey may greatly affect the predation rate (see Murdoch 1975, Andow & Risch 1985, for a discussion in the context of crop diversification). In the mixed crop habitat, the average distance between oat shoots (and even the absolute population density of plants (Helenius & Ronni 1989)) is decreased, and the distribution of R. padi among the shoots is more aggregated, as compared to the monocrop habitat: It follows that, in Research. Reviews, Practices and Technology a given prey density, in order to predate in the mixture at the same rate as in the monocrop, an option for a predator would be to in-' crease the velocity of the foraging movement.…”