Mineralization of Carbon and Nitrogen in Some New Zealand Allophanic Soils

Net soil nitrogen (N) mineralisation and its implications in soil under fallow and wheat were investigated in field and pot experiments. Wheat significantly enhanced net soil N mineralisation compared with that under fallow. In the field . . mineralisation depended on the stage of wheat growth, beginning only after sufficient root development had occurred, and continuing to the booting stage. However, it was not related to differences in soil heat accumulation and moisture content between fallow and wheat. Soil ammonium-N (NH 4-N) and nitrate-N (N0 3-N) levels under fallow followed a seasonal pattern, decreasing over the winter and early spring, and increasing over late spring and summer. There was no apparent lag in net soil N mineralisation under fallow in the spring compared with that under wheat. Total amounts of soil N mineralised over 9 months were 3.3 and 2.0% under fallow and wheat respectively. Mean rate of nitrification increased with increasing depth of soil sampled under fallow. Nitrifier numbers did not change over the same sampling period when large changes in NH 4-N and N0 3-N occurred, and thus nitrifier numbers do not provide a reliable estimate of NH 4-N formation. In growth cabinets, the response of microbial populations to some moisture treatments differed in soil under fallow and wheat. Increases in daytime temperature of 7°e from 17°e did not affect net soil N mineralisation. Under fallow, different sequences of fluctuating temperatures also showed no effect.

Section: M3contrasting

confidence: 70%

Nitrogen mineralisation in fallow and wheat soils under field and laboratory conditions

Hart¹,

Goh²,

Lüdecke³

1979

“…Perhaps it may be argued that the presence of allophane in some soils enables them to nitrify actively at low pH. Since allophanic soils are generally high in organic matter content (Broadbent et al 1964) the latter may also influence nitrification. Allison A similar series of experiments was carried out using synthetic allophane, bentonite, and kaolin.…”

Section: Resultsmentioning

confidence: 99%

Nitrification activities of some New Zealand soils and the effect of some clay types on nitrification

Sarathchandra

1978

Short-term nitrification actIvitIes (SNA) and the numbers of nitrifying bacteria in nine :\ew Zealand soils were examined. All the soils contained significant numbers of nitrifyinx bacteria (in the range IOL107/g). Nitrification activities of different soils were widely different, but no relationship was observed between SNA and the numbers of nitrifyin~ bacteria. Separation of a high nitrifYing soil into various size fractions did not affect the short-term nitrification activity. Although pure cultures of Nitrosomonas sp. failed to nitrify below pH 6.2, a colloid fraction separated from an allophanic soil was capable of nitrification at pH 5.5. Similarly Nitrosomonas sp. grown in the presence of laboratory synthesised allophane was able to oxidise ammonium to nitrate at pH 5.5.

“…Massive amounts of data are available on some aspects of N-mineralisation in arable soils. Most studies on N mineralisation have been carried out in the laboratory in the form of long term incubation studies (Broadbent et al 1964). Little or no information is available on the microbial populations and their activity during these incubation studies.…”

Section: Mineralisation Of Organic Nitrogenmentioning

confidence: 99%

“…Yellow-brown loams, on which some of the most productive pastures in New Zealand are located, are almost invariably associated with high levels of organic matter (Broadbent et al 1964). …”

Section: Mineralisation Of Organic Nitrogenmentioning

confidence: 99%

Nitrogen mineralisation and the activity and populations of microflora in a high producing yellow-brown loam under pasture

Sarathchandra

Upsdell

1981

At 25°C, optimum N-mineralisation in a topsoil sample from a yellow-brown loam under high-producing pasture was observed in the laboratory at 80% moisture (by weight). Populations of ammonium-oxidisingbacteria and moulds did ~ot orlTer significantly at soil moisture levels of 20%, 40%, 80%, and 140% by weight, but 20% moisture reduced the populations of total aerobic bacteria, gram negative bacteria, fluorescent PseuiIomonas spp., and nitrite-oxidising bacteria. Liming with Ca(OH)2 (equivalent to 2500 kg.ha-1 , pH 7.0) did not increase ~ mineralisation but increased C02 evolution. Liming also increased total aerobiC bacteria, gram negative bacteria, and the biomass carbon level.