The use of nitrogen 15 in nitrogen immobilization studies in the soil 2. effect of the mode of placement of straw with respect to nitrogen fertilizer on immobilization of the added nitrogen
Msumali, G.P.; Racz, G.J.
East African Agricultural and Forestry Journal 43(3): 232-237
Straw [from wheat stubble] applied at 1% soil (wt/wt basis) was either mixed with the soil (with fertilizer N mixed or banded) or the straw was banded in the soil (with the same methods of fertilizer placement). The soil was incubated at room temperature, samples taken after specified intervals for the determination of the mineral forms of N (NH4+, NO3- and NO2-) and a mass spectrometry determination of N15 excess for determining percent N retained in the soil after extraction of the mineral forms. Nitrite-N tended to accumulate in soil not treated with straw when fertilizer was banded. Percent recovery of mineral N (ratio of sum of NH4+, NO3- and NO2-) to added NH4+-N did not vary with incubation time, possibly due to biological interchange of N. The mode of placement of straw did not affect recovery. Percent recovery was low where fertilizer was banded, possibly because of gaseous losses due to chemo-denitrification. N15 data indicated that greater immobilization occurred when both straw and fertilizer were mixed with the soil, but less N was immobilized when fertilizer was banded. The mode of straw placement did not affect the extent of immobilization. The extent of biological immobilization of fertilizer N is determined mainly by the method of fertilizer placement rather than the placement of the crop residues which enhance immobilization.