MICROBIAL RESPIRATION, MAIZE (<i>Zea mays</i> L.) GROWTH AND NITROGEN UPTAKE AS AFFECTED BY COWDUNG AND AMMONIUM SULFATE APPLICATIONS

Abstract

Top soil sample (0-15 cm) of Iwo series (Oxic Tropudalf) was amended with three rates each of cowdung (0, 5 and 10 g kg-1) and N (0, 25 and 50 mg kg-1)in a 3x3 factorial combination. These rates were equivalent to 0, 12, and 24 t ha-1 and 0, 60, and 120 kg N ha-1, respectively. In the laboratory, cumulative amounts of CO2 evolved up to the end of 8 and 16 weeks of incubation at 30oC were determined using the static CO2 absorption method. Two consecutive 8-week croppings of maize (Zea mays L.) were made in the greenhouse in plastic pots containing 4 kg of soil. At the end of each cropping, pH, plant heights, dry matter yield, tissue N and N uptake were determined. Carbon dioxide evolved and soil pH were significantly increased over the control with cowdung in the presence or absence of (NH4)2SO4 notwithstanding. Microbial activity in the cowdung, N and manure-N treatments were stimulated over the control by factors of 2.45-3.82, 1.50-2.82 and 2.64-4.67 respectively. Except at the end of the 2nd cropping for dry matter yield, plant height and dry matter yields were not significantly different at the end of both croppings. Tissue N content and N uptake increased with the rate of cowdung applied alone but decreased as N rate increased. Microbial respiration was significantly correlated (r=0.70*) with tissue N content and pH (r=0.88**) at the end of the 1st and 2nd croppings respectively. The results indicate that applied N was immobilized in the presence of cowdung throughout the two cropping periods. There was no advantage to plant dry matter accumulation of co-applying cowdung and (NH4)2SO4 at rates higher than 5 g kg-1 and 25 mg N kg-1respectively. It is suggested that cowdung and (NH4)2SO4 should be applied to the plant banded separately and not mixed together. Nigerian Journal of Soil Science Vol.4 2003: 16-24