Availability of mineralized N from microbial biomass and organic matter after drying and heating of grassland soils

Abstract

A dwarf bamboo-type grassland soil (Thick High-humic Andosol) was nitrogen-limited for grass despite the presence of a considerable amount of microbial biomass N. By either treatments of air-drying and subsequent heating, the content of mineral N in the soil was increased by 3.7 g N and 11.7 g N m -2, respectively, after a 55-day incubation period. The efficiency of mineralized N for growth of orchardgrass was compared with nitrate-N added just before cultivation. The dry matter content of the grass increased from 81.7 g (control) to 169 g and to 337 g m -2 in the dried and in the heated soils, respectively, when N application was omitted. Of the mineral N released by air-drying and heating of the soil, 84% and 77% were absorbed by the grass, and 30% and 20% was assumed to be derived from microbial biomass, respectively. In contrast the grass apparently absorbed 54-56% of the 5 g nitrate-N m -2 added to the control and the air-dried soils. It was also noted that fungal biomass N had decreased by 1.5-1.9 g m -2 in the control soil after addition of 10 g nitrate-N m -2.

Changes in heated and autoclaved forest soils of S.E. Australia. I. Carbon and nitrogen

“…West et al (1988) found that soil texture effects the rate of decline of microbial biomass C in air-dried soils, and Marshman & Marshall (198 1) reported that clay content may protect microbial cells from desiccation and predation. Microbial N is considered to be the main source of N mineralised after drying and heating in some soils (Marumoto et al 1982;Okano 1990). In this study, we found a good relationship (r;!…”

“…Marumoto et al (1982) reported that, in oven-dried (70 'C, 24 hours) and air-dried soils, approximately 77 and 55% respectively, of the N mineralised after remoistening and incubating came from the freshly-killed biomass. Lower values (20% and 30%, respectively) were reported by Okano ( 1990) from their data that microbial cells killed by soil desiccation contributed only a minor amount to the C and N mineralisation on rewetting and incubation. Microbial biomass decreased on autoclaving, and the values obtained were similar to those in soils heated to 120 "C (Fig.…”

“…An increase in mineralisation rate in heated soils suggests changes in the substrate quality and the fast recovery of the microbial populations. Several authors have reported increases in N mineralisation rate after fire or after drying and heating soils (Okano 1990;Singh et al 1991;Fenn et al 1993). …”

“…This carbon was easily mineralisable (Jenkinson 1966;White et al 1973;Okano 1990) and was respired within 30 days of incubation. Inoculation of soils stimulated respiration without any time lag in the development of microbial populations, which had otherwise occurred in heated soils.…”

Soil nitrogen contents and classification of selected post-fire sites in the sub-boreal spruce zone of central British Columbia.

“…Studies tend to show an immediate loss o f total nitrogen contents due to volatilization I I accom panied with an increase the concentrations o f available forms o f nitrogen which are mobilized from the burned woody plants, the forest floor litter, duff layer and the microbial biomass (Beese, 1992;Christensen, 1973;Curran, 1994;Feller, 1982;Kutiel and Naveh, 1987;Mroz e ra /., 1980;Okano, 1990; i W ells e t a i, 1979). A summary o f reported changes in nitrogen levels due to fire events are provided I from selected studies in Table 3.9.…”