Nitrogen effect on weed management in rice in a tropical forest-savanna transition zone of Nigeria

Abstract

ABSTRACT Weed interference and poor soil fertility in rice (Oryza sativa L.) reduce grain yield and economic returns. Field experiments were, therefore, conducted to evaluate the effect of nitrogen (N) and weed-management using manual weeding (MW), herbicide and their combination in upland rice. Increasing N application rate from 0 to 60 and 60 to 90 kg ha−1 resulted in significant increase in weed density and biomass when weeds were controlled with either two MWs or butachlor applied alone at 2 kg ha-1. However, when weeds were controlled with butachlor plus a MW weed density and biomass remained statistically the same with 0, 60 and 90 kg N ha−1. Increasing N application rate to 90 kg ha−1 significantly increased rice grain yield (5.1 t ha−1), similar to the weed-free check (5.2 t ha−1) when the weeds were controlled by butachlor plus a MW. However, under poor weed management (two MWs (2.8 t ha−1) and butachlor applied alone (2.9 t ha−1)), the response was observed only from 0 to 60 kg N ha−1. Increasing N application from 60 to 90 kg ha−1 in plots with two MWs or butachlor applied alone did not increase rice yield but rather increased weed density and biomass. The results showed that N application at 90 kg ha−1 has the potential to increase weed competition if weeds are not adequately controlled. With adequate weed control using butachlor plus MW, however, application of 90 kg N ha−1 provided higher rice grain yield than 0 and 60 kg N ha−1.