La biomasa microbiana como agente de las transformaciones de nitrogeno en el suelo tras el enterrado de la paja del cereal. [The microbial biomass as the agent of transformation of soil nitrogen after the incorporation of cereal straw.] PhD thesis, University of Madrid, Spain

F - Theses

Ocio, J. A. 1990. La biomasa microbiana como agente de las transformaciones de nitrogeno en el suelo tras el enterrado de la paja del cereal. [The microbial biomass as the agent of transformation of soil nitrogen after the incorporation of cereal straw.] PhD thesis, University of Madrid, Spain. F - Theses

AuthorsOcio, J. A.
Abstract

At present, the surplus straw fence1 is eliminated primarily by burning. However, this practice will probably be banned by the EEC in the near future. This places the buried straw as the most viable and practical alternative for the farmer to use the excess straw that is burned every year. Currently, there is some controversy about the negative and positive effects of buried straw in the dynamics of N in the soil. In this sense, it has been considered that the buried of the straw causes a significant immobilization of inorganic N, since the microbial biomass that develops has a great demand of N. This can, under certain circumstances, cause harmful effects in the next harvest . Another point of view is that the immobilization of inorganic N after the straw is buried is beneficial environmentally, since otherwise this N (in the form of nitrate) would be exposed to a serious risk of leaching during the autumn-winter when the demand of N for the harvest is very small or nil. The objective of this work was to study and clarify the effects of straw burial on N losses and mineralization-N immobilization processes, considering the microbial biomass as agent of the biochemical transformations of N in the soil. Initially, four methods of determining microbial biomass in soils containing recently added straw were compared. The methods were: fumigation incubation, fumigation extraction (FE), respiration induced by substrate and adenosine triphosphate (ATI '). It was concluded that the IT1 ': and ATI' methods are valid for determining biomass in soils containing recently added substrates (eg straw) in their active phase of decomposition. The FE method has been modified to allow the determination of the microbial biomass in soils with straw taken directly from the field, with a minimum preparation of the samples. These allowed us to study the short-term and seasonal variation of the microbial biomass of the soil after the straw was buried in field conditions. Burial of the straw caused a large and rapid increase in biomass, between 50 and 100 kg of microbial N / ha in 7 days. Subsequently, the biomass in soils with straw gradually decreased throughout the year. The fraction of the straw soluble in hot water contributed minimally to this increase. The contribution of the different sources of N (N straw, N fertilizer, N inorganic soil and N organic soil) to the increase of microbial N after the straw buried in field conditions was studied with isotopic techniques together with The FE method, using straw labeled with 15N and fertilizer marked with 15N. Approximately 50% of the increase in microbial N at 7 days came from the N of the same straw, around 20% of the fertilizer N and less than 5% of the inorganic N of the soil itself. (The greater immobilization of the N of the fertilizer with respect to the inorganic N of the soil itself was probably due to the fact that the N of the fertilizer was applied in the form of NH4NO3). This leaves approximately 25% of the increase in microbial N without justification. It is suggested that the organic N of the soil was the main alternative source of N, since it is unlikely that the fixation of N, contributed significantly. The burial of the straw (7.4 t / ha) reduced the winter losses of the added nitrogen fertilizer (30 kg N / ha) by about 8 kg N / ha in the first meter of the soil. By the technique of sampling tubes of the soil solution, it was estimated that the straw reduced nitrate leaching (from the fertilizer and from the soil itself) below 25 cm in about 30 kg N / ha in the same period. The availability of N for the plants in spring, in the first meter of the soil, was not affected by the straw buried in autumn. In addition, the content of inorganic N in the topsoil of the soils with straw was similar or slightly higher than that of those without straw from at least 111 days after burying. Therefore, it was concluded that the straw intercourse had no negative effects on the availability of N for the next harvest and significantly reduced N losses by leaching during the winter.

Year of Publication1990
Funder project or code14
Open accessPublished as non-open access
Collective titlePh. D. Thesis, Universidad Autonoma de Madrid, Spain

Permalink - https://repository.rothamsted.ac.uk/item/865v4/la-biomasa-microbiana-como-agente-de-las-transformaciones-de-nitrogeno-en-el-suelo-tras-el-enterrado-de-la-paja-del-cereal-the-microbial-biomass-as-the-agent-of-transformation-of-soil-nitrogen-after

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