Effect of Season and N Source on Brachiaria humidicola and Panicum maximum Growth Performance and Biological Nitrification Inhibition in Rhizoshepe soil

Abstract

Two weeks old B. humidicola (CIAT 679) and P. maximum (CIAT 16028) seedlings were transplanted into 200 g portions of two Japanese soil types, viz, Andisol and Terrace yellow in cellophane pots with basal perforation covered with filter paper. The experiment included three N sources (100 ppm N03- as KN03, 100 ppm NH/ as [NH4hS04 and minus N), two plant types and control (B. humidicola, P. maximum and no plant) and the two soil types in a 3 x 3 x 2 factorial in a completely randomized design with 4 replicates in the greenhouse. The experiment was conducted in summer (June - August, 2007) and repeated in winter (November, 2007 - January, 2008). The plant shoots were harvested after three months of growth, weighed fresh, oven-dried, analyzed chemically and nutrient uptake determined. The roots in the potted soils were removed and 5 g equivalent dry weight of each were added to 0.6-mL mixing solution (120 mg N kg-1 soil) in 6 replicates, incubated at 30DC and N02-, NO-3 and NH4 - N contents determined at 1, 3, 7, 14, 28 and 56 days incubation. Data were analyzed by ANOVA at P~5%. The results showed that N supplied either as N03- or NH4 significantly (p~0.05) increased fresh (58.4 - 98.5%) and dry matter yields (62.6 - 100%) of the plants over the control in summer, with a similar trend in winter. Plant yields and nutrient uptake were significantly higher in summer than in winter. Nitrification was significantly reduced in B. humidicola rhizosphere soils than in P. maximum in summer but as high as or higher than P. maximum in winter due to slow growth and low activity status of exudates released. Nitrification was .greater in Andisol than Terrace yellow soil. It was concluded that season and inherent soil properties significantly influenced the growth performance of B. humidicola, nutrient uptake, root exudates release and their functioning in nitrification in soils.

Additional keywords: Animal nutrition, crop yield, forage quality, N loss, pasture grass, soil fertility.