Sources of N uptake by wheat (Triticum aestivum L.) and N transformations in soil treated with a nitrification inhibitor (nitrapyrin)

Abstract

Rates of N uptake by spring wheat as ammonium and as nitrate, and rates of nitrification, gross N immobilization and gross N mineralization were measured in a pot experiment during 84 days of growth in a clay soil. Soil treatments included an unfertilized control and addition of 15NH4NO 3 or NHn~SNO3 in the absence and presence of N-serve 24E.Incorporation of ammonium into the soil organic N pool was considerably higher in the presence compared to the absence of nitrapyrin, but the processes contributing to this effect could not be positively identified. Both dry matter and grain yield as well as N uptake by wheat were enhanced in the presence of the inhibitor in N fertilized soil, despite the increased immobilization of N. On the other hand, inhibitor application had a detrimental effect on yield and N uptake by wheat in unfertilized soil.Both ammonium and nitrate forms of inorganic N were absorbed by wheat, but nitrate uptake was dominant in the absence of the inhibitor. The uptake of N as ammonium was higher and the uptake of N as nitrate was less, both in absolute and proportional terms, in the presence compared to the absence of inhibitor. In addition, the proportion of N taken up as ammonium was higher than the proportion of N as ammonium in the available N pool up to day 56 in the inhibitor treatment, which indicated a preference for ammonium uptake by wheat.Evidence was obtained which suggested that several factors may have contributed to the positive response of wheat to inhibitor application in N fertilized soil, including reduced N losses, higher gross N mineralization and a physiological response due to the proportional increase in uptake of inorganic N as ammonium.

Nitrapyrin addition mitigates nitrous oxide emissions and raises nitrogen use efficiency in plastic-film-mulched drip-fertigated cotton field

“…The yield in this study was lower than reported earlier [ 13 , 41 – 42 ]. Our findings were more similar to the report by Crawford and Chalk [ 43 ] who found that there was no significant difference in yield between fertilizer N plus nitrapyrin and N applied only. Under the tested condition of drip-irrigated plot with input of 225 kg N ha -1 , the relatively high NUE (>50%) was gained, and more importantly, nitrapyrin addition increased NUE by 10.7% ( P <0.05).…”

The effect of nitrification inhibitors in reducing nitrification and the ammonia oxidizer population in three contrasting soils

“…There was no effect on the rate of NH 4 + immobilization after inhibitor addition (Fig. 1), although the inhibitors blocked transformation of NH 4 + to NO 3 − supporting previous reports by Chalk (1990) and Crawford and Chalk (1993). In our study, soil pH might be a key factor influencing the effectiveness of DMPP and C 2 H 2 on nitrification; however, their effectiveness might also have been affected by other soil properties such as soil texture .…”

On inorganic N uptake by vascular plants: Can 15N tracer techniques resolve the NH4+ versus NO3− “preference” conundrum?

“…Over a period of 20 days it was estimated that 61% of plant N was taken up as NH 4 + . Crawford and Chalk (1993) found that the uptake of NH 4 + by wheat (U 1 ) during 0 to 20 days in a clay soil with high biological activity was less, both in absolute amounts and relative proportions, than the uptake of NO 3 − (U 2 + U 3 ) in paired pots, but when the nitrification inhibitor nitrapyrin was added with the fertilizer, uptake of NH 4 + increased and NO 3 − decreased, so that the relative proportions taken up by wheat were approximately equal. On the other hand, application of nitrapyrin to a pasture soil had little effect on the proportional uptake of NH 4 + and NO 3 − by perennial ryegrass, because the soil had a low nitrification capacity (Geens et al, 1991).…”

“…It is also possible to estimate U 2 from the data of Crawford and Chalk (1993) by using the difference in the uptake of N in ± inhibitor treatments. For example, U 2 = U n(−inhibitor) -U n(+inhibitor) = 50-31 = 19 mg N kg −1 soil.…”