Evaluating pea and barley cultivars for complementarity in intercropping at different levels of soil N availability

Two field experiments were carried out on a temperate sandy loam using six pea (Pisum sativum L.) and five spring barley (Hordeum vulgare L.) cultivar s to determine cultivar complementarity in the intercrop for grain yield, d ry matter production and nitrogen (N) acquisition. Crops were grown with or without the supply of 40 or 50 kg N ha(-1) in the two experiments. Cultiva rs were grown as sole crops (SC) and as mixed intercrops (IC) using a repla cement design (50:50). The land equivalent ratio (LER), which is defined as the relative land area under SC that is required to produce the yields ach ieved in intercropping, were used to compare cultivar performance in interc ropping relative to sole cropping. Barley was the stronger competitor in the intercrops and as a result barley grain yield and nitrogen uptake in IC were similar to SC. The per plant pe a grain production and aboveground N accumulation in IC were reduced to les s than half compared to SC pea plants due to competitive interactions. Application of N caused a dynamic change in the intercrop composition. Comp etition from barley increased with N application and the pea contribution t o the combined intercrop grain yield decreased. The LER values showed that in the intercrop plant growth resources were used on average 20% more effic ient without N application and 5-10% more efficient with N application. The choice of pea cultivar in the intercrop influenced the intercrop perfor mance to a larger degree than the choice of barley cultivar. Furthermore, p ea cultivar x cropping systems interactions was observed, indicating that c ultivars performed differently in sole and intercrops. An indeterminate pea cultivar competed strongly with barley causing a greater proportion of pea s in the intercrop yield, but caused a reduced N uptake and yield of barley . Determinate peas with normal leaves caused the highest degree of compleme ntary use of N sources by allowing barley to exploit the soil N sources eff iciently, while they contribute with fixed N-2. However, difference in perf ormance among cultivars was observed. Using the indeterminate pea cultivar combined IC grain yield was in general lower than the greatest sole crop yi eld and vice versa for the determinate pea cultivars. Up to 22% (LER = 1.22 ) greater combined IC grain yield was observed in several mixtures using de terminate pea cultivars. From the present study, it is was concluded that there is a need for breedi ng suitable pea cultivars for intercropping purposes, since cultivars bred for sole cropping may not be the types, which are the most suitable for int ercropping. For optimized N-use in pea-barley intercrops it is concluded th at important traits for the intercropped pea are: (1) determinate growth, ( 2) a medium competitive root system for soil inorganic N and other nutrient s during early growth, (3) high light absorption capacity by peas growing u nderneath the canopy of the higher barley component and (4) early establish ment of symbiotic NZ fixation to support a high growth rate during early gr owth stages. Fertilized pea-barley intercrops gave a 15% higher net income than fertiliz ed barley sole cropping and is regarded as a better safeguard for the farme r's earnings compared to pea sole cropping known for variable yields and po or competitive ability towards weeds. (C) 2001 Published by Elsevier Scienc e B.V.