Nitrification in soils after different periods of dryness

Abstract

It has been shown (Birch 1) that the longer a soil remains in an air-dry state the greater are the amounts of carbon and nitrogen mineralised on moistening it. These amounts were found to be a significant linear function of the log. of the time the soll was in a dry state prior to moistening. Even short periods in the dry state were sufficient to produce considerably greater amounts of mineral nitrogen, on moistening, than solls that had not been given a preliminary dryäng. Harpstead and Brage s have also reported recently that drying and storage of soils leads to a pronounced increase in their nitrifying ability, a result which they ascribe to changes in the relative numbers of various micro-organisms in the soll.The experiment from which the foregoing results were quoted is now complete and is described below. It shows the effect of different periods in the dry state on subsequent nitriIication in soils with carbon contents ranging from 1 to 7 per cent. The range of soils and drying periods covered are, it is hoped, sufficiently wide for the results to serve as a general guide in soil-nitrogen studies, particularly in countries with pronounced wet and dry seasons. The application of the results is discussed in some detail, particularly with respect to soll nitrogen. Brief reference is also made to carbon rundown in soils.

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

“…For example, water-extractable phosphorus is markedly influenced by even mild drying of soil. It has been known for some time that soil drying can render considerable concentrations of organic carbon soluble in water [54] and a similar effect was recently reported for phosphorus in a wide range of pasture soils from England and Wales [55]. In the latter study, 7 days air drying from approximate field moisture capacity at 30 • C increased concentrations of water-extractable organic phosphorus by up to 1900%.…”

Interactions between plant nutrients, water and carbon dioxide as factors limiting crop yields

“…The importance of this is considerable in those parts of the tropics with clearly defined wet and dry seasons. The classical studies of Birch (1958Birch ( , 1960 showed that the flush of mineral N at the start of the wet season in East Africa was a result of the population dynamics of the soil microbes. Immediately after rain, the young population increases rapidly, utilizing relatively easily decomposable materials.…”

Progressive development of a hydrologic and inorganic nitrogen conceptual model to improve the understanding of small Mediterranean catchments behaviour

“…The non-linear inorganic nitrogen behaviour led to include into the model scheme also other threshold mechanisms (U min , U nitr , U imm and U denitr ) in order to simulate soil processes 'pulse' behaviour, previously observed in several Mediterranean and semi-arid environments (Birch 1959(Birch , 1960(Birch , and 1964Mummey et al, 1994, Schiwinning et al 2004. The sensitivity analysis, generally pointed out that thresholds as influential on nitrogen simulation.…”

“…Simulated mineralization seems to be highest immediately after the summer drought period ( 'Birch effect', Birch 1959, 1960, and 1964, when the soil moisture content reaches approximately 50% of the soil field capacity.…”

“…Models based on a representation of temperate climates do not represent this rapid transition from dry to wet periods well. Birch (1959Birch ( , 1960Birch ( , and 1964 was one of the first to characterize the impacts of soil drying and wetting cycles on mineralization and nitrification, demonstrating that rapid mineralization follows rewetting of dry soil and that in continuously moist conditions there is a release of nitrogen, much of it as nitrate. Many other authors stressed the influence that wet-dry cycles have on microbial biomass (Van Gestel et al, 1993), denitrification (Mummey et al, 1994, Peterjohn andSchlesinger 1991) and ammonia volatilization (Heckathorn and Delucia, 1995).…”