Growth and productive responses of tropical grass Panicum maximum to nitrate and ammonium supply

This study was conducted to investigate growth response parameters and forage yield of Panicum maximum Jacq. plants supplied with nitrate (NO3-) and ammonium (NH4+) as N source in a nutrient solution. Six NO3- and NH4+ combinations were tested at the following proportions: 100-0, 85-15, 70-30, 55-45, 40-60 and 25-75%. Grass shoot (number of tillers and leaves and leaf surface area) and root (length and surface area) growth parameters and dry matter production exhibited highest values in P. maximum plants growing in the nutrient solution supplied with NO3-:NH4+ at the proportions ranging between approximately 70-30 and 55-45%. The use of NO3-:NH4+ mixture at the ratio of 55-45% instead of the NO3- solely as N source in the nutrient solution enhanced the production of tillers and leaves and the leaf area surface of P. maximum by about 30, 20 and 30%, respectively. Plants supplied with NO3- and NH4+ mixture (55-45%) showed an increased root length and root surface area by approximately two and six-fold, respectively, compared with P. maximum fertilized with NO3- exclusively in the growth medium. Supplying N in the nutrient solution as NO3- or NH4+ exceeding approximately 70 or 50%, respectively, caused a diminished P. maximum forage yield. Enhanced N-use efficiency associated with P. maximum plants supplied with a NO3- and NH4+ mixture in the growth medium supports the assumption that it is possible to increase plant production by managing N fertilization based on quality (N forms) of N fertilizers applied in pasture systems.