THE RESPONSE OF MAIZE PHASEOLUS INTERCROPPING TO APPLIED NITROGEN ON OXISOLS IN NORTHERN ZAMBIA/

Experiments were carried out on two Oxisol series over two seasons. In addition to sole crops of maize and beans at their recommended optimu m densities, there were four intercropping systems representing all co mbinations of 100% or 50% of the sole crop density of each crop. Nitro gen at 0, 30, 60, 90 or 120 kg/ha was applied along the maize rows in the sole maize and the intercropping systems. The maize showed a good response to nitrogen in the sole crop and in all intercropping systems . Beans in intercropping also showed a good response as a result of th e nitrogen applied to maize, an effect attributed to the poor nodulati on of the crop on the acid soils. There was evidence of only slight co mpetition from the beans on the maize at no nitrogen, but at higher le vels of nitrogen the increased bean growth depressed maize yields by u p to 30%. At low nitrogen levels beans were highly suppressed by the m aize, but at the highest nitrogen levels bean yields approached or exc eeded the yield of the sole beans. LERs were well above 1 for all inte rcropping systems (overall mean 1.46), indicating large yield advantag es for intercropping. Contrary to most other cereal/legume studies, LE Rs increased with an increase in the level of nitrogen; means over the four intercropping systems were 1.27, 1.36, 1.41, 1.55 and 1.69 for t he increasing levels of nitrogen. Maize being the more important crop in northern Zambia, it is reasoned that farmers are likely to assess i ntercropping in terms of how growing beans with maize compares with gr owing maize on its own. Although there was evidence of a slight decrea se in maize yield due to intercropping at no nitrogen, the maize yield in intercropping with nitrogen applied was always well above the basi c maize sole crop yield at no nitrogen, despite some yield loss due to competition from the beans. For any level of nitrogen used, returns t o the cost of nitrogen and the overall net returns were greater from i ntercropping than from sole maize. It is concluded that, whatever leve l of nitrogen the farmer may adopt, the economics of sole maize are im proved by adding a bean intercrop. (C) 1998 Elsevier Science B.V.