359-1 Soil Based N Tests: Accounting for Mineralised Soil N On Contrasting Irish Grassland Soils.



Wednesday, October 19, 2011: 8:05 AM
Henry Gonzalez Convention Center, Room 212A, Concourse Level

Noeleen T. McDonald1, Catherine J. Watson2, Ronnie J. Laughlin2, Stanly T. Lalor3, Nyncke J. Hoekstra3, Christopher T. Elliott4 and David P. Wall3, (1)Teagasc/Queens University Belfast, Wexford, Ireland
(2)Agri-Food and Biosciences Institute, Belfast, BT9 5PX, Northern Ireland
(3)Teagasc, Environmental Research Centre, Wexford, Ireland
(4)Institute of Agri-Food & Land Use, Queens University Belfast, Belfast, BT9 5AG, Northern Ireland
Current nitrogen (N) recommendations do not give credit for N released from the soil through N mineralisation (No), which can vary greatly for temperate grassland soils. Reductions in N input costs and losses of N to the environment could be achieved through better prediction of No in a soil. However, a reliable soil N testing procedure is needed. Many studies have emphasised the reliability of biological N tests (incubations) and have used these tests as standards for predicting No. However, these studies also note the time consuming nature of these tests (7-210 days) and the implications for routine soil analysis.

The objective of this study was to evaluate the ability of a range of rapid soil N tests to differentiate between soils and quantify No for a range of Irish grassland soils, by comparison with the standard 7 day anaerobic incubation method (AI-7).

A total of 37 soils were sampled (10cm depth) from sites representing a range of soils used for grassland production in Ireland. A range of physical, chemical and biological soil properties were determined through laboratory analysis for each soil. The biological standard AI-7 test was conducted to estimate No for all 37 soils. The rapid N tests evaluated included, (1) Cold and (2) Hot 2M KCl extractable nitrate (NO3--N), nitrite (NO2--N) and ammonium-N (NH4+-N); (3) Mild acid-oxidation yielding NH4+-N; (4) the Illinois soil N test (ISNT), measuring amino sugars & NH4+-N concentrations; and (5&6) Ultraviolet (UV) absorbance of 1M KCl filtered soil extract at 260nm and 210nm, respectively.

The 37 soils showed a large range in No from 92.17 to 723.08 mg NH4+-N kg-l. The ISNT had the strongest relationship (R2 0.69) with AI-7 values, followed by UV 260nm (R2 0.38), UV 210nm (R2 0.31) and hot 2M KCl (R2 0.24). There was no significant relationship between the acid oxidation test or the cold 2M KCl test and AI-7. The large range in soil No indicates the need to allow for this N in making fertiliser recommendations. These results and the potential techniques to quantify No for a range of soil types will be discussed in further detail in this paper.

See more from this Division: S04 Soil Fertility & Plant Nutrition
See more from this Session: Management Strategies to Improve Nutrient Use Efficiency: I