Different Rates of Urea as Nitrogen Fertilizer Affect Root and Stalk Rot Diseases of Maize in South West Nigeria

Aside from increasing the yield of crops, it is well known that application of fertilizers, especially Nitrogen, to soil has many other positive and negative effects. One of such effects include increasing or decreasing disease expression and/or severity. Information about the effect of continuous application of Nitrogen fertilizers to important cereals such as maize, in areas where local farmers have low access to information and technology, might go a long way in helping stakeholders to manage diseases. Two commonly cultivated maize cultivars, DMRE–Y and DMR–LSR-W, were planted in a randomized complete block design, first in Abeokuta (early cropping season of year 2000) and then in Ago-lwoye (early cropping season of year 2001) to evaluate the effect of increasing rates of Nitrogen fertilizer (in form of urea) application on stalk rot disease caused by Macrophomina phaseolina and root rot disease caused by Fusarium moniliforme.
Increasing rate of Nitrogen application led to a significant increase in the severity of these diseases with the highest disease expression at 300 kg N ha-1. Although the reactions of the two cultivars were similar, DMRE-Y was found to be more susceptible to these rots than DMR-LSR-W. Simple linear regression analysis indicated a very strong positive relationship between N rates and average disease index. A two year pooled index for DMRE-Y cultivar gave correlation coefficient values 0.9997 and 0.9844 for stalk and root rots respectively while for DMR-LSR-W cultivars, the values were 0.9933 and 0.9815 for stalk and root rots respectively.
Increasing rates of urea increased the grain yield but had diverse effects on yield components. The rates had no effect on plant height and ear length but considerably increased the kernel row and kernel weight. It, however, reduced days to 50% tasseling of maize crops.