Nitrogen mineralization: a review and meta‐analysis of the predictive value of soil tests

Abstract

Accurate estimation of mineralizable nitrogen (N) from soil organic matter is essential to improve fertilizer management in agricultural systems. Mineralizable N refers to the amount of N in soil that is released during a certain period (ranging from 1 week to the length of a growing season). It has been estimated from increases in inorganic N during incubation or from N uptake by plants grown in a greenhouse or field. Many chemical soil tests measuring extractable organic N (EON) fractions have been proposed to predict mineralizable N. We evaluated the predictive value of these soil tests, using 2068 observations from 218 papers. Meta-analysis was used to find the best soil test, to analyse differences between field and laboratory experiments, and to determine whether their predictive value is affected by extraction intensity (% of total soil N that is extracted). The concentration of EON was positively related to mineralizable N, explaining on average 47% of the variation. It did not, however, explain more of the variation than total N. Best predictions (57% < R 2 < 74%) were obtained when EON was extracted with hot CaCl 2 , acid KMnO 4 , acid K 2 Cr 2 O 7 , hot water or hot KCl. Extraction intensity was not related to the strength of the above-mentioned relationship. Predictions of mineralizable N were significantly worse when mineralization was measured in the field compared with measurements under controlled conditions. We found no evidence of a causal and direct relationship between EON and mineralizable N. Accuracy of soil testing may improve when the current 'single soil test approach' changes to a more complex approach, which includes different soil tests, soil properties and environmental conditions.

Soil Nitrogen Transformations and Availability in Upland Pine and Bottomland Alder Forests

“…N mineralization, the microbial conversion of organic N to inorganic N, has been intensively studied because it is believed to be the principal control of N availability to plants in terrestrial ecosystems [6]. Recent progress in the knowledge of and techniques related to organic N and the priming of rhizospheres for N availability has shaken the classical assumption that N mineralization dominates as the primary source of available N, [7][8][9][10]; nevertheless, in field N studies, N mineralization and other inorganic N indices remain meaningful standard measures which provide useful insight.…”

“…Environmental controls of N mineralization and availability, particularly temperature and soil moisture, have been investigated through a theoretical model [11], literature review [9,12], laboratory experiments [13][14][15], and field manipulations [16][17][18][19]. For example, soil moisture varies significantly in space and time, and affects various biogeochemical processes in different ways [20][21][22].…”

Nitrogen deposition and climate effects on soil nitrogen availability: Influences of habitat type and soil characteristics

“…Measurements of potentially mineralisable N seem likely to be more robust indicators of N 83 availability (Ros et al, 2011), for reasons explained below. 84…”

“…Agronomic researchers require measures of N availability to predict productivity (Ros et al, 2011). In 68 semi-natural systems, niche occupancy models that predict likely species occurrence in relation to 69 changing environmental factors (Latour and Reiling, 1993 Plant-available N is not straightforward to define or measure, and is thus a major source of uncertainty 75 in current ecosystem models (Wamelink et al, 2002).…”

Predicting soil nitrogen supply from soil properties

“…Numerous soil N availability indices have been proposed (Sharifi et al 2007a;Griffin 2008) based on either biological or chemical principles. While a number of N availability indices have shown promise, no single approach has been shown to be successful across soils, cropping systems and climatic zones (St. Luce et al 2011;Ros et al 2011) as a result of the complexity of controls on soil N mineralization (Schimel and Bennet 2004;St. Luce et al 2011).…”