Effects of plant density on intercropped wheat and field beans in an organic farming system

Abstract

In field trials in 1987\88 near Pangbourne, England, wheat (Triticum aestivum) and field beans (Vicia faba) were grown in an organic farming system as sole crops and additive intercrops. The sole crops were grown at 25, 50, 75, 100 and 150 % of the recommended density (RD) for conventionally grown crops. The intercrops consisted of all density combinations of wheat and beans from 25 to 100 % RD in a factorial experiment. The grain yield of sole cropped wheat and beans increased significantly as their density was increased. The highest yield of both was achieved at 100 % RD, indicating that the conventional recommendation was the optimum when applied to organically grown crops. Land equivalent ratio (LER) values for the intercrops were significantly greater than 1n0 when the wheat was sown at 5 % RD and beans at 50 % RD. The highest LER of 1n29 was achieved when wheat and beans were both sown at 75 % RD. There was resource complementarity, expressed as relative yield total (RYT) 1n0, in all of the density combinations. There was a significant decrease in resource complementarity with increasing wheat and bean density. The nitrogen content of the wheat grain and whole plant biomass was significantly increased when the density of beans in the intercrops was increased ; this was reflected in a significant increase in grain protein at harvest. The total amount of N accumulated by the wheat, however, decreased with increasing bean density due to a reduction in the biomass of wheat. Beans also showed a significant increase in %N as the density of the other component increased and a decrease in total N accumulation due to reduced biomass. All of the intercrops accumulated more N than the sole cropped wheat, but did not exceed that accumulated by sole-cropped beans. The biomass of weeds was greater under beans than under wheat. Weed biomass in intercrops was significantly reduced when the density of wheat and beans was increased, resulting in a lower weed biomass in the intercrops than was achieved in either the sole cropped wheat or beans. The N content of weeds was significantly reduced with increasing wheat density but was significantly increased with increasing bean density. The total amount of N accumulated by weeds per unit area was reduced significantly by increasing the density of both components. The levels of disease on the wheat were low, but mildew (Erysiphe graminis) increased significantly as bean density increased. The incidence of chocolate spot (Botrytis fabae) increased significantly with increased bean density. The experiment demonstrated that it was possible to harvest the crop with a combine harvester and the wheat and beans can be planted separately mechanically, therefore this system is suited to mechanized agricultural systems.

Competition between triticale (Triticosecale Witt.) and field beans (Vicia faba var. minor L.) in additive intercrops

“…Different findings have been reported by Haymes and Lee (1999) who observed yield benefit when field beans was sown in the intercrop at 100% and wheat at 50% of recommended pure stand density or the species were sown in the intercrop at 100% of their recommended pure stand densities. Bulson et al (1997) noted the highest yield advantage of wheat-field beans intercrop when both components were sown at 75% of recommended pure stand density. Unlike the experiment reported here both studies were conducted in more productive soil conditions that were suitable for both crops.…”

“…According to Austin et al (1988) It means the competing species use partially different growing resources or utilize the same resources but more efficiently due to differences in plant architecture, physiology or growing cycle (Bulson et al 1997). If there is no competition between species RYT = 2.0.…”

Ecological principles underlying the increase of productivity achieved by cereal-grain legume intercrops in organic farming. A review

“…Intercrops can potentially reduce weeds, diseases and pests (Trenbath 1993;Altieri 1999) often regarded as determinant factors influencing crop production (Liebman 1988;White and Scott 1991;Liebman and Dyck 1993;Midmore 1993;Bulson et al 1997;Liebman and Davis 2000;HauggaardNielsen et al 2001b). In particular, grain legumes, such as peas (P. sativum L.), are known to be weak competitors against weeds when grown as the sole crop (Wall et al 1991;Townley-Smith and Wright 1994;Mcdonald 2003), and weed infestations have been shown to severely limit the N nutrition and grain yield of organically grown grain legumes (Corre-Hellou and Crozat 2005).…”

Effect of cowpea (Vigna unguiculata) intercropping on weed biomass and maize (Zea mays) yield

“…For instance, Bulson et al (1997) found that weed biomass was significantly reduced when the densities of wheat (Triticum aestivum L.) and field bean (Vicia faba L.) intercrops were increased; and Arce et al (2009) showed that soybean seeding rates (24Á42 seeds/m 2 ) were inversely related to weed biomass. Increased seeding rates lead to quicker canopy closure, increased crop interference and greater weed suppression, resulting in increased yields (Olsen et al 2006;Kolb et al 2012).…”