Nitrogen, sulphur and carbon uptake from some nitrogenous fertilizers using ¹⁵N, ³⁵S and ¹³C as tracers

Abstract

1. Pot culture experiments are described comparing the recovery of nitrogen, and sulphur by the difference and ‘labelled atom’ methods and the recovery of carbon by the latter method. Italian ryegrass was used as the test crop with ammonium sulphate, calcium nitrate and urea as the fertilizers.2. The recovery of fertilizer nitrogen was less using the ‘labelled atom’ technique than the conventional difference method.3. The recovery of sulphur from ammonium sulphate ‘labelled’ with 35S was measured. It was considerably less than the nitrogen, but not inconsiderable especially as a basal dressing of ‘unlabelled’ K2SO4 was applied.4. Using urea ‘labelled’ with 13C there was no evidence that any of the carbon was in the ryegrass four weeks after application.

Interactions between fertilizer nitrogen and soil nitrogen—the so‐called ‘priming’ effect

“…Again, a positive AN1 is much more likely when fertilizer is added as labelled NH,-N than as NO,-N; labelled NO,-N will not cause an apparent AN1 by displacement or by pool substitution unless the soil NH,-N pool runs out or the soil becomes anaerobic. Most investigators who have compared NH,-N and NO,-N have observed larger ANIs with NH,-N than with NO,-N (Walker er al., 1956;Low & Piper, 1957;Rennie & Rennie, 1973;Steele et al, 1980). If an experiment shows that uptake of unlabelled soil N alters with addition of labelled fertilizer, or if fertilizer uptake efficiency as measured by recovery of I5N is not the same as when measured by the non-isotopic 'difference' method, it is prudent to see whether the results can be explained on the basis of an apparent ANI, before assuming that fertilizer N really changes the uptake of soil N. Small additions of highly-enriched 15N are particularly informative in this respect.…”

Fates and Use Efficiency of Nitrogen Fertilizer in Maize Cropping Systems and Their Responses to Technologies and Management Practices: A Global Analysis on Field 15N Tracer Studies

“…The 15 N tracer approach has been regularly used to track N fate since the mid‐twentieth century, which has greatly improved our understanding of N cycling (Low & Piper, 1957; Sharp et al., 1956). When applied in soil‐crop systems, 15 N tracers can identify contributions of indigenous soil‐N and exogenous fertilizer‐N to crop N uptake, allowing calculation of the direct proportion of N fertilizer absorbed by maize.…”

Interactions Between First and Second Applications of Fertilizer Nitrogen and Implications in Efficiency of Nitrogen Use

“…Fertilizer N and soil TV. Studies of N uptake in which labelled fertilizer N was used (2,11) show that heavy dressings of N can increase the availability of soil N, a phenomenon described as 'priming'. It is obvious that such 'priming' has occurred when the response as N uptake approaches or exceeds 1-0 kg N/kg N applied as fertilizer.…”