Noeleen T. McDonald1, Miguel A. Dionisio2 and David P. Wall2

1, Agricultural Catchments Programme, Teagasc, Johnstown Castle, Co. Wexford, Republic. of Ireland.2,Teagasc, Crops Environmental and Land use Programme, Johnstown Castle, Co Wexford, Republic. of Ireland.

4. CONCLUSIONS

% Additional sieving oror ball-milling ofof a soil sample toto <1.5mmmm did notsignificantly improve the quantity ofof MNMN measured using the ISNT.

% Thehe maximum MNMN recovery (measured asas glucosamine-N)N) from atemperate soil using the ISNT method appears toto bebe achieved withinthe standard 5 hour period.

% However, 100% recovery ofof the spiked glucosamine-N was notachieved for this temperate grassland soil.

% Further studies investigating the recovery ofof MNMN for different soil typesusing ISNT, especially those with higher levels ofof soil organic matter arerecommended.

1. INTRODUCTION

e Thehe Illinois soil nitrogen (N) test (ISNT) has been proven toto provide arapid and reliable estimate ofof mineralizable N (MN) across a range ofoftemperate mineral soils (R(R2=0.6969, n=n=3535) (McDonald etet alal. 2014).

e ToTo date validation and modification ofof the ISNT method have mainlybeen conducted onon soils with relatively low organic matter and total Nconcentrations inin North America (Klapwyk & Ketterings, 2005; Spargo & Alley,

2008).

Study Objectives:

e Investigate ifif soil sample aggregate size (2mmmm vsvs. <1.5mm) can improvethe quantity ofof MNMN measured using the ISNT onon temperate soil types.

e Identify the appropriate time required toto maximize MNMN recovery using theISNT onon a representative temperate mineral soil type.

3. RESULTS

e Experiment 1:) There was a significant difference (p<0.0505) inin the concentration ofof

ISNT-N between the 3 temperate soil types ranging from 180 toto 429 mgmgkgkg-1.

) However, there was nono significant difference inin concentration ofof ISNT-Nbetween two sample aggregate sizes for each soil type. (Fig 1).

e Experiment 2:) Approximately three quarters ofof the spiked glucosamine-N (7676%) was

recovered within the first 3 hours during the standard ISNT diffusionmethod (Fig 2).

) Recovery ofof glucosamine-N plateaued after ~ 5 hours, however 100%recovery from this soil was not achieved after 6 hours (Fig 3).

noeleen.mcdonald@teagasc.ie

www.teagasc.ie/agcatchments

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2. METHODOLOGY

e Study was split into two investigate experimental studies.

e Experiment 1: Comparing ISNT-N yield from 2 different samplesieve sizes across 3 grassland mineral soil types.

) Soil was collected from a depth ofof 1010cmcm from three grassland sites ininIreland inin 2010 (Table 1 & see pictures).

) Soils were oven-dried atat 4040oC.) Sample aggregate size:

1.1. 2mmmm (sieved)2.2. <1.5mmmm (ball-milled)

) Mineralizable N measured using standard ISNT method (Klapwyk &

Ketterings, 2005) (See pictures).) Randomized complete block design (hotplate) with 6 replications ofof

each soil type X sample size.) Statistical analyses procedures were preformed using SAS.JMP v9.

e Experiment 2: Recovery ofof MN from a temperate mineral soil typeusing the standard ISNT method over a 6 hour period.

) For experiment 2, soil type from site B sieved atat 2mmmm was used.) Treatments:

1.1. Spiked soil with 1mlml ofof standard glucosamine solution2.2. Untreated soil

) Recovery ofof glucosamine-N & MNMN using the standard ISNT method(Klapwyk & Ketterings, 2005).

) Randomized complete block design (hotplate) with 7 replications ofofeach treatment.

) Mason Jars were removed from the hotplate atat 1 hourly intervals upup totothe 6thth hour.

) Statistical analyses procedures were preformed using SAS.JMP v9.

References:

e Klapwyk & Ketterings, 2005. SSSAJ. 6969:1129-1134.

e McDonald etet alal., 2014. SSSAJ. 7878:1052-1064.

e Spargo & Alley, 2008. SSSAJ. 7272:823-829.

Figure 1. Effect ofof sample size (i)<1.5mmmm and (ii) 2mmmm onon the meanconcentration ofof mineralizable N,N,asas measured byby the Illinois Soil Ntest (ISNT) across 3 soil types.(difference letters denotesignificant difference within soiltype) (p<0.0505).

Figure 2. Proportional recoveryofof the total glucosamine-N fromeach hour ofof the standard ISNTdiffusion incubation method.

Figure 3. Recovery ofofglucosamine-N during a 6 hourperiod ofof the standard ISNTdiffusion incubation. (error barsdenote std err).

Table 1. Soil classification, physical & chemical properties ofof three temperategrassland soils used inin experiment 1 and soil B for experiment 2.