Interactions between N supply and N uptake by perennial ryegrass, 15N recovery and soil pH for four acid Scottish soils

Logan, K.A.B.; Thomas, R.J.

Interactions between N supply and N uptake by perennial ryegrass, 15N recovery and soil pH for four acid Scottish soils

1999

Logan, K.A.B. | Thomas, R.J.

The effects of NH4(+)-N, NO3(-)-N or urea-N addition on N uptake by perennial ryegrass (Lolium perenne), 15N recovery and pH of four limed and unlimed soils were determined in a pot experiment over 10 weeks. The best form of N in terms of herbage N uptake and fertilizer recovery differed between the soils. Recovery of applied 15N in herbage was greatest for the soil with the lowest pH and highest organic matter content, and overall recovery in the soil-plant system was influenced more by soil type than by N form. There was always an apparent mineralization of soil N when perennial ryegrass was present. Soil pH changes ranged from +0(.)11 to -0(.)58 units for the unlimed soils and from +0(.)03 to -1(.)06 units for the limed soils. The use of NO3(-)-N rather than NH4(+)-N or urea-N avoided further acidification. Lime increased herbage N only from the soils with the lowest pH values. Although the acidifying effect of NH4(+)-fertilizer was alleviated, Liming may increase nitrification and possibly N loss via denitrification and/or leaching in the field. The major influence of soil type on herbage N uptake, pH response to the treatments and fertilizer recoveries implies that liming and fertilizer N management decisions should consider soil characteristics, such as organic matter, clay contents and pH.

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