Growth and Symbiotic Activities of Cowpea Cultivars in Sole and Binary Cultures with Maize

摘要

Nitrogen is a major limiting plant nutrient in cereal production in smallholder farming systems in the Limpopo Province of South Africa and the practice of intercropping the cereal with legumes is usually proposed to enhance nitrogen nutrition in the system. The benefit of symbiotic nitrogen fixation in intercropping systems has, however, been variable over diverse environments and needs further clarification. Alternate intercropping studies of maize and four distinct cowpea cultivars were conducted in 1998/99 and 1999/2000 at Syferkuil and Thabina/Dan in the Limpopo Province to determine the effect of the system on growth, nodulation, N_2 fixation and nitrogen uptake of the component crops. Maize dry-matter accumulation was generally not influenced by intercropping and nitrogen uptake of intercropped maize was only improved relative to the sole culture maize at Syferkuil in 1999/2000. On average, the amount of nitrogen fixed by the cowpea cultivars was higher in the intercropped cowpea than the sole crops, except in 1999/2000 at Syferkuil, where the amount fixed was 8.6% higher in the sole than the intercropped cowpea. The amount of nitrogen fixed by the legumes ranged from 20 to 69 kg N/ha and 87 to 217 kg N/ha at Syferkuil in 1998/99 and 1999/2000, respectively, whereas at Thabina/ Dan, the range was 103 to 175 kg N/ha and 83 to 147 kg N/ha, in 1998/99 and 1999/2000, respectively. Nodule formation differed among the cowpea cultivars tested, with the long-season cowpea cultivars generally producing heavier nodules at both locations in the two growing seasons. The different performance of the cowpea cultivars in nitrogen fixation at the two locations emphasises the importance of the environment on symbiotic nitrogen fixation activities in cowpea.