Effect of K on nitrogen fixation of intercrop groundnut and the competition between intercrop groundnut and maize

Application of adequate level of K has shown to improve the competitive ability of the legume in legume/grass mixtures. However, the effect of K on the competitive ability of grain legumes in legume/cereal intercropping systems has not been adequately studied. Hence, studies were made to ascertain if the effects of K could be exploited in improving the performance of groundnut (Arachis hypogaea L.) cv. No. 45 when intercropped with maize (Zea mays L.) cv. Badra. The study was conducted at the Faculty of Agriculture, University of Ruhuna, Kamburupitiya, Sri Lanka in 1988 in basins filled with 36 kg of soil. It involved establishing maize and groundnut as monocrops and as intercrops at three K levels viz. 0, 20 and 40 mg of K kg^–1 of soil. Monocrop maize and groundnut had 2 and 5 plants/basin, respectively while the intercrop had 1 maize plant and 3 groundnut plants/basin. The soil used was Red Yellow Podzolic which was tagged by incorporating¹⁵N-labelled plant material. When grown as a monocrop, K had no effect on the percent N derived from atmosphere, amount of N₂ fixed, dry matter production, pod yield and total N content of groundnut. However, when intercropped with maize lack of K application affected the above parameters significantly which was overcome by improving K level. Thus, the optimum level of K for groundnut was greater when intercropped than monocropped. A significant interaction between K level and cropping system was evident with regard to N₂ fixation, pod yield and total dry matter production of groundnut. Intercrop maize derived 30–35% of its N content from the associated groundnut plants which amounted to 13–22 mg N/plant. The amount of N supplied by groundnut to associated maize plant was not affected by K level. It appears that there is scope for alleviating growth depression of the legume component in legume/cereal intercropping systems by developing appropriate K fertilizer practices.