Evaluation of an undisturbed-soil incubation method as an index of soil nitrogen availability in a limed and non-limed soil

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<ul><li><p>This article was downloaded by: [Memorial University of Newfoundland]On: 06 October 2014, At: 07:37Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>South African Journal of Plant and SoilPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tjps20</p><p>Evaluation of an undisturbed-soil incubation methodas an index of soil nitrogen availability in a limedand non-limed soilP. J. Raath a &amp; D. Saayman ba Nietvoorbij Institute for Viticulture and Oenology, Agricultural Research Council ,Private Bag X5026, Stellenbosch , 7599 , Republic of South Africab Department of Soil and Agricultural Water Science , University of Stellenbosch ,Stellenbosch , 7600 , Republic of South AfricaPublished online: 15 Jan 2013.</p><p>To cite this article: P. J. Raath &amp; D. Saayman (1996) Evaluation of an undisturbed-soil incubation method as an indexof soil nitrogen availability in a limed and non-limed soil, South African Journal of Plant and Soil, 13:2, 35-41, DOI:10.1080/02571862.1996.10634372</p><p>To link to this article: http://dx.doi.org/10.1080/02571862.1996.10634372</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (the Content) containedin the publications on our platform. However, Taylor &amp; Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purposeof the Content. Any opinions and views expressed in this publication are the opinions and views of theauthors, and are not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Content should notbe relied upon and should be independently verified with primary sources of information. Taylor and Francisshall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, andother liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relationto or arising out of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms &amp; Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions</p><p>http://www.tandfonline.com/loi/tjps20http://www.tandfonline.com/action/showCitFormats?doi=10.1080/02571862.1996.10634372http://dx.doi.org/10.1080/02571862.1996.10634372http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions</p></li><li><p>S. Afr. J. Plant Soil 1996, 13(2) </p><p>Evaluation of an undisturbed-soil incubation method as an index of soil nitrogen availability in a limed and non-limed soif </p><p>P.J. Raath* Nietvoorbij Institute for Viticulture and Oenology, Agricultural Research Council, Private Bag X5026, Stellenbosch 7599, </p><p>Republic of South Africa </p><p>D. Saayman Department of Soil and Agricultural Water Science, University of Stellenbosch, Stellenbosch 7600, Republic of South Africa </p><p>Accepted 4 December 1995 </p><p>Nitrogen mineralization potentials were determined using an undisturbed-soil incubation procedure. The pur-pose of this study was to evaluate the above-mentioned method as an index of soil nitrogen availability. Undis-turbed soil samples (0-150 and 150-300 mm) of a limed (pH 7.3) and an. equivalent non-limed (pH 4.9) soil were incubated at 30C and field water capacity. After every consecutive 10-day period, four samples of each treatment/depth combination were removed, dried and analysed for mineral N content. This was conducted over a period of 60 days. Distinction was made between changes in NH: and NO; contents of the incubated soil, assuming the NO; release represented N release from the soil due to high nitrification rates. The release of NO; was depicted by a straight-line regression, where the slope was equal to the rate constant of mineralization (k). The mineralization potential (No) was assumed to be the maximum mineral N content obtained in the soil during incubation. Comparing the amount of CO2 that evolved per unit NO; released, it was found that the min-eralizing microbial activity was lower, but more efficient in releasing N at pH 7.3 than at pH 4.9. Both ammonifi-cation and nitrification proved to be pH-sensitive processes. Although unsatisfactory for making fertilizer recommendations, the total N content of the soil was found to be a good indication of its N mineralization potn-tial. The method used in this study gave no indication of the fraction of No that is released during the different seasons. The use of undisturbed samples makes this method cumbersome because of the large number of samples needed to accommodate a large spatial variability component. </p><p>Stikstofmineralisasiepotensiaal is ondersoek deur gebruik te maak van 'n onversteurde grondinkubasietegniek. Die doel van hierdie studie was om laasgenoemde tegniek te evalueer as 'n indeks van die stikstoflewerings-vermoe van grond. Onversteurde grondmonsters (0-150 en 150-300 mm) van 'n bekalkte (pH 7.3) en ooreen-stemmende onbekalkte (pH 4.9) kontrole-grond is by 30C en veldwaterkapasiteit ge'inkubeer. Na elke opeenvolgende peri ode van 10 dae is vier monsters, verteenwoordigend van elke behandelinglgronddiepte-kombinasie, verwyder, gedroog en geanaliseer vir minerale N-inhoud. Dit is oor 'n periode van 60 dae gedoen. Onderskeid is tussen die veranderinge van die ge'inkubeerde grond se NH: - en NO; - inhoude gemaak. Die NO; - vrystelling is as verteenwoordigend van die N-vrystelling in die grond aanvaar weens die hoe nitrifikasie-tempo's wat verkry is. Dit is deur 'n reguitlynregressie voorgestel waarvan die helling gelyk was aan die miner-alisasiekonstante (k). Die maksimum minerale N-inhoud wat in die grond tydens inkubasie waargeneem is, is aanvaar om gelyk aan die mineralisasie-potensiaal (No) te wees. Waar die hoeveelheid CO2-vrystelling per een-heid vrygestelde NO; in ag geneem is, is gevind dat die mineraliserende mikrobe-aktiwiteit laer, maar meer effektief ten opsipte van N-vrystelling was by pH 7.3 as by pH 4.9 grond. Ammonifikasie blyk ook, tesame met nitrifikasie, 'n pH-sensitiewe proses te wees. Hoewel totale N-inhoude van die grond 'n onbetroubare riglyn vir N-vrystelling in die grond was, om as riglyn vir bemestingsaanbevelings te dien, gee dit 'n goeie indikasie van die grond se N-mineralisasiepotensiaal. Die inkubasiemetode wat in hierdie studie gevolg is, gee geen aandui-ding van die fraksie van No wat tydens die verskillende seisoene vrygestel word nie. Die gebruik van onver-steurde monsters maak hierdie metode omslagtig as gevolg van die groot hoeveelheid monsters wat nodig is om die groot ruimtelike variasie te akkommodeer. </p><p>Keywords: Incubation, limed soil, mineral nitrogen, nitrogen mineralization potential, nitrogen release rate </p><p>*To whom correspondence should be addressed tpart of an M.Sc. (Agric.) dissertation to be submitted by the senior author to the University of Stellenbosch </p><p>35 </p><p>Introduction </p><p>Soil acidity is often regarded as a factor which restricts the rate at which organic N is converted to mineral N (Harmsen &amp; van Schreven, 1955). Other evidence, however, indicates that soil acidity has no negative effect on the mineralization of organic N (Thompson, Black &amp; Zoellner, 1954). According to Nyborg &amp; Hoyt (1978), Black (1956) suggested that when acid soils are limed, a portion of the soil organic matter </p><p>becomes more susceptible to mineralization, but after this portion has been decomposed, the rate of mineralization returns to near its original level, despite an altered composi-tion of the soil microbial population. </p><p>Nitrification, in particular, is sensitive to soil acidity (Harmsen &amp; van Schreven, 1955). Nyborg &amp; Hoyt (1978) found that liming of soil stimulates the activity of nitrifying bacteria. With time, however, bacterial adaptation occurred, </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Mem</p><p>oria</p><p>l Uni</p><p>vers</p><p>ity o</p><p>f N</p><p>ewfo</p><p>undl</p><p>and]</p><p> at 0</p><p>7:37</p><p> 06 </p><p>Oct</p><p>ober</p><p> 201</p><p>4 </p></li><li><p>36 </p><p>and no difference was obtained between the activities of nitri-fying bacteria in soils limed to different pH values. During incubation of disturbed soil, liming increased nitrification such that practically all NH: - N in the limed samples was nitrified during the incubation period (Lyngstad, 1992). The effect of liming also decreased from the first year until it finally disappeared after the sixth year. In a loam soil, liming hardly had any effect, while in a -clay loam soil, rich in organic matter, liming significantly increased the mineraliza-tion rate and the effect lasted for several years. Further liming of acid, organic soils may result in large amounts of N being mineralized, causing luxurious consumption of N by crops, while in mineral soils with little organic matter, liming can seldom replace fertilizer application. It is therefore difficult to predict the effect of liming on N mineralization since many divergent results for different soils have been obtained (Lyngstad, 1992). </p><p>Several studies to evaluate N mineralization were based on laboratory or field incubation of disturbed soil samples (Stan-ford &amp; Smith, 1972; Smith, Young &amp; Miller, 1977; Campbell, lame &amp; Winkleman, 1984). Raison, Connel &amp; Khanna (1987), Cabrera &amp; Kissel (1988), Hadas et al. (1989) and Sierra (1992) found that N mineralization of undisturbed and disturbed samples were not in good agreement. N mineraliza-tion was higher in disturbed, incubated soil samples than in the undisturbed samples, for every incubation period. </p><p>It is well known that handling and disturbance of soil sam-ples influences the amount of N mineralized during incuba-tion experiments. Soudi, Sbai &amp; Chiang (1990) reported an initial flush of extractable inorganic N in disturbed samples, followed by a fairly constant rate of mineralization for the soil types and depths they investigated. They attributed this flush to the drying of samples before incubation. Gambiagi, Rimolo &amp; Pirolo (1993) attributed the effect of drying, lead-ing to higher rates of N evolution, to the death of bacteria and their subsequent mineralization by surviving bacteria. In addi-tion, sieving exposed physically protected organic matter located in small pores of loam and clay soils to the minerali-zation processes (Craswell &amp; Waring, 1972; Hassink et al., 1993). Apart from the effect of sieving and drying on the N mineralization rate in soil, Cabrera &amp; Kissel (1988) suspected that the CaCl z or KCI, used for leaching soil after successive incubation periods, might influence microbial activity nega-tively. On the other hand, removal of mineral N from the soil might stimulate mineralization, which is a concentration-dependent process (Cabrera &amp; Kissel, 1988). They therefore suggested that undisturbed soil samples be used for incuba-tion in order to better depict field conditions. </p><p>Berthold (1991) suggested an incubation method where undisturbed soil samples were incubated at field water capac-ity at SoC, lSoC and 3SoC, respectively. The nett N minerali-zation at SoC and lSoC was described by a linear regression: N(t) = bt + a, where N(t) is nitrogen mineralized over time t, b is mineralization rate (the slope of the regression), and a is the amount of mineral N at t == 0, i.e. the mineral N in the soil before the commencement of incubation. </p><p>From N release data obtained during soil incubation at 3SC, Berthold (1991) showed that the mineralization poten-tial (No) of a soil and its mineralization rate constant (k) can be calculated according to the method described by Stanford </p><p>S. Afr. Tydskr. Plant Grond 1996, 13(2) </p><p>&amp; Smith (1972). They assumed that N mineralization follows first-order kinetics which can be described by the equation: dNldt = -kN where N is the concentration of mineralizable substrate, k is the rate constant of mineralization and t is time. </p><p>Nyborg &amp; Hoyt (1978) felt that in the light of the important role nitrification plays in the mineralization process, studies of the effect of liming on this pH-sensitive process were necessary. Since Nyborg &amp; Hoyt (1978) observed a doubling in the amount of N mineralized during incubation after soil was limed to pH 6.7, our study involved the use of limed and non-limed soil from an existing trial, to evaluate the method of Berthold (1991) as a possible index for accurate estimates of the No of vineyard soils in the Western Cape. </p><p>Materials and Methods </p><p>Treatments, soil sampling and analyses </p><p>Soil from a five-year-old liming trial, laid out on a yellow-brown, well-drained, medium-textured soil of the Clovelly form (Soil Classification Working Group, 1991), at Nietvoor-bij, Stellenbosch, was used. Disturbed and undisturbed soil samples were taken at random from the non-replicated treat-ments which consisted of non-limed soil (pH 4.9) and a soil that had received 108 ton ha J lime (pH 7.3). The disturbed samples were used for determining the pH, organic carbon (C) and total nitrogen (N) contents of the soil as well as its particle size distribution. Soil pH was measured in 1 M KCI using a soil: solution ratio of 1: 2.S. Organic C was deter-mined using the Walkley-Black method as described by Bar-nard et al. (1990), and total N was measured using a Perkin Elmer 2410N nitrogen analyzer. The particle size distribution of the soil was determined using standard Nietvoorbij sieve and hydrometer methods. The field water capacity (FWC), bulk density and water content of the soil were also deter-mined. </p><p>Incubation studies </p><p>A slight adaptation of the method described by Berthold (1991) was used. During the rainy season (June, 1992), 96 undisturbed samples were taken from the limed soil and from the non-limed control soil at depths of 0-1S0 mm and ISO-300 mm (Table 1), using pre-weighed brass rings of SO-mm inner diameter and 30-mm length. After weighing the soil-filled cylinders, the volume of water needed to bring the soil in the cylinders to FWC was added. In addition to the undis-turbed samples for experimental purposes, four samples of each soil and depth were taken, air dried and analysed to determine the initial mineral N content in the soil before incu-bation. The incubations were repeated in 1993 using the method outlined above, but included an additional step where the soils were dried overnight at 60C before incubation. </p><p>For each soil and depth, the cylinders with undisturbed soil at FWC were incubated for a period of 60 days at 30C. This was done by placing the samples on plastic trays, which were stacked such that free movement of air was not restricted. Each stack was then placed in a 200-dm3 plastic container (large enough to prevent the development of anaerobic condi-tions) with a loosely fitting lid. The containers were kept in an air-conditioned room. To minimize evaporation from the soil in...</p></li></ul>

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