The quantitative assessment of certain fertilizer management practices in the field

The direct measurement of uptake of nutrient from the fertilizer using labelled fertilizers is the best way to assess the effect of fertilizer management practices in the field. This is demonstrated by examples from field experiments on various crops. Fertilizer source, placement, timing, comparisons and the effect of cultural practices on uptake of fertilizer nutrient can be quantitatively measured. When the fertilizer source can not be labelled such as with natural materials (e.g. bone phosphates, rock phosphates and atmospheric N2 fixed by N2 fixation, etc.) a method is described which makes use of a treatment standard with labelled fertilizer to assess the amount of nutrient taken up from these source in field experiments. (author)