In the 1960s and 1970s there was great emphasis on selecting simple laboratory methods to estimate the potentially available soil N that could be routinely used as a method for the N recommendations systems (Keeney and Breniner, 1966; Stanford and Smith, 1976). Many chemical extractants were investigated (acids alkali, salts, water…) as possible tools for assessing how much N may be mineralized, varying the concentration of the extractant, temperature and time of extractions

Arrobas, Margarida

Fonseca, Telmo

Parada, Maria João

Rodrigues, M.A.

Biblioteca Digital do IPB

I I I I I I , I PROCEEDINGS OF Agro201 0 the Xlth ESA Congress ·August 29th - September·3rd, 2010 Montpellier, France I I ~ I ' I Chair • J. Wery, Montpellier SupAgro, France ESA President Scientific Committee • S. Asseng, CSIRO, Australia • J.M. Barbier, INRA Montpellier, UMR Innovation, France • M. Benoit, INRA Mirecourt, dpt SAD, France • J.E Bergez, INRA Toulouse, UMR Agir, France • J. Boiffin, IN RA Angers, AFA, France • P. Carberry, CSIRO, Australia • J.L. Chotte, IRD Montpelller, UMR EcoSol, France • 0. Christen, Martin Luther University, Halle-Wittenberg, Germany • M. Donatelli, ESA secretary, JRC and CRA, Italy • T. Dore, AgroParisTech-INRA/EA, France • C. Gary, INRA Montpellier, UMR System, France • M. Genard, INRA Avignon, UR PSH, France • P. Gregory, SCRI, United Kingdom • D. Habash, Rothamsted Research, United Kingdom • G. Hammer, APSRU, Australia • P. Hlnslnger, INRA Montpellier, UMR EcoSol, France • B.Hubert, Agropolis International, France • J. Jones, University of Florida,USA • J.D. Lebreton, CNRS Montpellier, IFR MEB, France AGRU POLIS D INTERN;(TIONAL agropolis fondat ion .. . . • F. Lescouret, INRA Avignon, UR PSH, France • R. Ufran, IN RA Montpellier, UMR Lameta, France • E. Malezieux, CIRAD Montpellier, France ' F. Maraux, CIRAD Montpellier, France • M. M orison, IN RA Grignon, France • N. Munier-Jollain, INRA Dijon-INRA/EA, France • M.L. Navas, Montpellier SupAgro, UMR CEFE, France • 8. Ney, AgroParisTech & Academie de !'Agriculture, Paris, France • J. Porter, University of Copenhagen, Denmark • F. Tardieu, INRA Montpellier, IFR Daphne, France • M. Van lttersum, WUR and Seamless, The Netherlands Organizing Committee ················· ·· ·· ···· ·· ··············· ··· ··· ········ ···· ·· • I. Bastie, Montpellier SupAgro • B. Cabantous, Agropolls International • C. Jacquet, CIRAD • F. Lava!, Montpellier SupAgro • E. Mignard, INRA • A. Perrin, Montpellier SupAgro • C. Picard, INRA • P. Prevost, Montpellier SupAgro - AFA • S. Renoir, CIRAD • M. Salas, Agropolis International • I. Slllli-Touzi, Montpellier SupAgro • N. Villemejeanne, Agropolis International Cl'rad •Uillj~ IN?A IH~DJ® II"""'P"m .. : ltl!lll 1 '"'""''d"'"'""'' li J Agro pour la dheloppe:Mtnt -I I Agro 2010, the XI ESA Congress, Montpel/ier Effect of sampling date on chemical indices of the mineralizable nitrogen in soil Fonseca T., Arrobas M., Joao Parada M., Angelo Rodrigues M. Mountain Research Center- ESA, Institute Politecruco de Braganr;a Campus de Sta Apol6nia, ap. 1172, 5301-855 Braganr;a, Portugal; *email: marrobas@sipb.pt In the 1960s and 1970s there was great emphasis on selecting simple laboratory methods to estimate ihe potentially available soil N that could be routinely used as a method for the N recommendations systems (Keeney and Bremner, 1966; Stanford and Smith, 1976). Many chemical extractants were investigated (acids, alkali, salts, water, ... ) as possible tools for assessing how much N may be mineralized, varying the concentration of the extractant, temperature and time of extractions. The results were usually related to N mineralized in laboratory incubations or with N recovered in field orops. Similar methodologies were also used to predict the N mineralized from organic substrates (manures, sewage sludge, ... ). In the following 1980s and 1990s, the published work was still . dominated by optimism, with the researchers finding good relationships between chemical indices and plant available N (Gianello and Bremner, 1986). However, after decades of searching for a rapid method to estimate the N mineralization capacity of soil there are still no con~istent recommendations. Many conflicting results have been appearing in the literature after a general inability of the following researchers to replicate the positive results however found (Wang et al., iOO!). One possible source of error could be the time of soil sampling. It would be expected that the most labile fraction of organic N, which plays a prominent role as a source of substrate for N mineralization, varies over the year due to debris deposition and root death. In this work the effect of sampling date on N extracted by several chemical methods was investigated in three different agrosystems: an intensive grazed pasture rich in legs; a rainfed olive orchard, the ground of which was managed by a simple application of glyphosate in April; and an intensive cropping system based on 1\vo silage crops per year (small grains from October to May, and maize from May to October). Materials and Methods The chemical extraction methods used in this work were essentially the same as reported by Sharifi et al. (2007) and Soon et al. (2007). Extractable NH4-N and NOrN (KC!Nmin) were determined from 10 g of soil and 40 mL 2M KC! shaken for 1 hour. The suspension was thereafter filtered through a Whatman #42 filter paper. The concentrations of~-N and N0 3-N in the extracts were determined by UV-vis. spectrophotometry. Hot KC! extractable NH4-N (HKCI~ l was determined by heating (1 00 oq 5 g of soil and 20 mL of 2.M KC! for 4 hours in a digestion block. Thereafter the tubes were removed and allowed to cool and the extract filtered through a Whatman #42. Hydrolysable NH4-N (Hyd~ l was obtained by subtracting initial NH4-N from hot KC! extractable NH4-N. The ultraviolet absorbance ofNaHC03 extracts were prepared by shaking 2.5 g soil with 0.01 mol L·' NaHC03 for 15 min. The suspension was filtered through a Whatrnan #42. The ultraviolet absorbance of the extracts was measured at 205 (Abs205) and 260 (Abs260) nm. Kjeldahl N (Kjel-N) was determined after the digestion of 1 g of soil with H2S04 and selenium as the catalytic agent in a heated (400°C) aluminium digestion block. After cooling, the suspension was distilled with alkali and the NH4+-N in the digest was titrated with HCI in a Kjeltec Auto 1030 Analyzer. Soil samples were provided from an intensive grazed pasture (sampled 10 times ·throughout the year); a rainfed olive orchard (sampled in October and May); and an intensive · cropping system based on small grains and maize (sampled in October and May) grown for silage. Results and discussions -The indices based on the UV absorbance at 205 and 260 nm appear very stable over time in all the agrosystems, without significant differences between sampling dates (table 1). Mineral-N released by cold KC! was significantly different between dates of sampling in the winter cereals-maize system and in the grazed pasture. The instability of the inorganic N fraction in soils is well-known and it may decrease quickly due to plant uptake, biological immobilization or by being lost from the 247 Agro 2010, the XI ESA Congress, Montpellier soil. A rapid increase of the mineral N in the soil is also possible when a net N mineralization occurs and there are no favorable conditions for crop uptake or N lost from the soil. NH/ released by hot KCI was significantly different among sampling dates in t11e olive orchard and also in the pasture The HydNH4 + followed the same pattern. In spite of there being no clear reference in the literature~ to which organic fraction is preferentially released by saline KC! solutions, it seems that HydNH/ is readily dependent on soil conditions at the time of sampling. In the pasture the higher values seern to be found in the autunm and early spring. Probably root activity together with microbial activity which are dependent of environmental variables, were the main factors influencing the NH} hydrolyzed by saline KCI solutions. The same seems to be true for the olive orchard, with the root activity in May (olive and weeds) promoting the presence of easily hydrolysable organic compounds. Table l . N mineralization indices for different soil sampling dates of the agrosystems maize/winter cereals for silage, olive orchard and S!:azed 12asture. Kjel-N KClNmin HKCINH/ HydNl{.' Crop Date Abs205 Abs260 (g kg-1) ----------- (mg NH4-N kg"1) -----··-· Maize 15-0ct-08 1.52 a 0.4Ia 0.75 a 22.52 a 11.25 a 6.15 a 22-Mny-09 1.62 a O.S i n 0.73 a 18.38 b 10.70 a 4.20a Olive 26-Sep-08 1.76 n 0.4ia 0.70 a 27.74 a 8.67 b 3.60 b 15-May-08 1.48a 0.47 n 0.6211 28.51 a 17.00 a 7.73 a 08-0ct-07 1.56 a 0.51 n 0.39 a 15.57 abc 10.10 ab 3.70 n 08-Nov-07 1.56 a 0.60 n 0.45 a 13.63 e 10.40 ab 3.50 a 17-Dez-07 L39a 0.47 a 0.42 n 17.88 abc 12.38 ab 1.65 abe 23-Jnn-08 1.78 a 0.64 a 0.42 a 18.78ab 12.20 ab 1.10 be Pasture 17-Mar-08 l.43a 0.53 a 0.38 a 16.93 nbc 13.80 a 2.95 nb 18-Abr-08 1.38 a 0.49 n 0.38 a 15.29 be 10.70 ab 1.30 be 04-Jun-08 1.54 n 0.63 n 0.42 a 16.98 nbe 11.65 ab 0.55 c 26-Jun-08 1.82 a 0.62 a 0.37 a 18.85 ab 10.40 ab 0.60 c 19-Ago-08 1.74 a 0.56 n 0.40 a 17.62 abe 9.00b 2.60 nbc 01-0et-08 1.57 a 0.48 a 0.42 a 21.24 n 10.78 ab 1.28 be Within each agrosystem means followed by the same letter in the colunms are not statistically different by Tukey-Kramer HSD test (u < 0.05). Conclusion The results showed that the sampling date may influence the N mineralization indices obtained by chemical extractions, at least when KCI was used as the extracting agent. Thus, it seems that the soil sampling date should be specified in the standard procedures of each method that presents promising results to be adopted in a Lab as a routine procedure. References Gianello, C., and Bremner, J.M. 1986. A simple chemical method of assessing potentially available organic nitrogen in soiL Commun. Soil Sci. Plant Anal. 17: 195-214. Kceney, D.R., and Bremner, J.M. 1966. Comparison and evaluation of laboratory methods of obtaining an index of soil nitrogen availability. Agron. J. 58: 498-503. Sharifi, M., Zebarth, B.J., Burton, D.L., Grant C.A., Cooper J.M. 2007. Evaluation of some indices of potentially mineralizable nitrogen in soil. Soil Sci. Soc. Am. J. 71, 1233-1239. Soon, Y.K., Haq, A., Arshad, M.A. 2007. Sensitivity of nitrogen mineralization indicators to crop and soil management. Commun Soil Sci Plant Anal 38, 2029-2043. Stanford, G., and Smith, S.J. 1976. Estimating potentially mineralizable soil nitrogen from a chemical index of soi l nitrogen availability. Soil Sci. 122: 71-76. Wang, W., Smith, C.J., Chalk, P.M., and Chen, D. 2001. Evaluating chemical and physical indices of nitrogen mineralization capacity with an unequivocal reference. Soil Sci. Soc. Am. J. 65: 368-376. 248 p SI s (I R n 

Effect of sampling date on chemical indices of the mineralizable nitrogen in soil

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Effect of sampling date on chemical indices of the mineralizable nitrogen in soil

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