Dynamics of Soil Microbial Biomass and Water-Soluble Organic C in Breton L After 50 Years of Cropping to Two Rotations

Abstract

Amounts and turnover rates of biomass and water-soluble organic C (WSOC) were measured at the Breton plots where records of long-term management of a Gray Luvisolic soil are available. Plots (control, manure, and NPKS) which had been cropped to either a wheat-fallow or a wheat-oats-barley-forage-forage rotation for 50 yr were sampled 13 times during 1981 and 1982. Biomass C and flush of microbial N were measured using the chloroform fumigation technique. Long-term crop yields were used to derive C supply to the plots. Regression analyses were used to relate seasonal fluctuations in environmental conditions to biomass and WSOC dynamics. Reinoculation with soil was unnecessary but Lysobacter sp. formed a greater proportion of isolates following incubation of fumigated soil than of unfumigated samples. Reinoculation with Lysobacter sp. is suggested to provide a more standardized biological assay. The 5-yr rotation contained 38% more N but 117% more microbial N than did the 2-yr rotation, and manured treatments contained twice as much microbial N as did NPKS or control plots. A management effect on soil organic matter quality is indicated. Averge turnover rates of biomass were 0.2–3.9 yr−1; being 1.5–2 times faster in the 2-yr rotation than in the 5-yr rotation. Replenishment of the WSOC component would have to occur 26–39 times yr−1 to supply microbial turnover. Most of the biomass must be dormant because annual C inputs are two orders of magnitude less than maintenance energy requirements. Seasonal variations in biomass were most consistently related to losses during desiccation and regrowth upon moistening. Regrowth appears to be at the expense of native soil organic matter. Management practices and environmental conditions therefore affect amount of organic matter by controlling both input of C and biomass turnover. Key words: Crop rotations, Luvisol, organic matter, biomass, soluble C, Breton plots

Biomassa microbiana e sua atividade em solos sob diferentes sistemas de preparo e sucessão de culturas

“…Essas variações podem estar relacionadas com o manejo do solo, como monocultura e rotação, que apresentaram, respectivamente, valores de 1,8 e 2,25% (Insam et al, 1989) ou 2,3 e 2,9% (Anderson & Domsch, 1989). Entretanto, para outros autores, essas relações estariam entre 1,8 e 2,1%, para parcelas cultivadas com monoculturas permanentes (Brookes et al, 1984), entre 2,5 e 3,3%, para áreas com rotação de culturas permanentes (McGill et al, 1986).…”

Ideas and perspectives: Strengthening the biogeosciences in environmental research networks

“…Longterm agricultural experiments were initiated, motivated by the prospects that agricultural science might increase and sustain crop yields (Rossiter, 1975). Examples include the Park Grass experiment in England, begun in 1856 to quantify how hayfields respond to soil amendments (an experiment that Tilman et al (1994) called the world's "most long-term ecological study"), and the Lethbridge and Breton plots in Alberta, Canada (established 1910 and 1930, respectively) to test the conversion of native prairie grasslands to cultivation-based agriculture and rotations (McGill et al, 1986). Long-term agricultural field studies spread to the developing world, for example, to China, India, and Pakistan (Tirol-Padre and Ladha, 2006), where today many dozens of long-term field experiments are used by scientists to test relationships between soil, management, and yields in intensively managed rice, Oryza spp.…”

Effect of legume-based cropping systems on nitrogen mineralization potential of Vertisol

“…The relation between cropping systems and the quantity and quality of soil organic matter has been inferred from studies of chemical and biological soil parameters (Birch and * ICRISAT JA (1638) ** FAX no corresponding author: +9140 241239 Dougall, 1967;Campbell et al, 1991;Wani et al, 1994a). Recently, measurements of microbial biomass (McGill et al, 1986;Wani et al, 1994b), potentially mineralizable N(No) and mineralizable C (Stanford and Smith, 1972;Wani et al, 1994a) have been used to monitor biologically meaningful changes in the quantity and quality of soil organic matter. Some increases in soil organic matter content and N mineralization potential of Gray Luvisols have been attributed to perennial forages and legumes grown in rotations with cereals (Campbell et al, 1991;Poyser et al, 1957;Wani et al, 1994a).…”