The relative isotopic abundance (δC, δN) during composting of agricultural wastes in relation to compost quality and feedstock.

Variations in the relative isotopic abundance of C and N (δC and δN) were measured during the composting of different agricultural wastes using bench-scale bioreactors. Different mixtures of agricultural wastes (horse bedding manure + legume residues; dairy manure + jatropha mill cake; dairy manure + sugarcane residues; dairy manure alone) were used for aerobic-thermophilic composting. No significant differences were found between the δC values of the feedstock and the final compost, except for dairy manure + sugarcane residues (from initial ratio of -13.

Principles and limitations of stable isotopes in differentiating organic and conventional foodstuffs: 2. Animal products.

In this review, we examine the variation in stable isotope signatures of the lighter elements (δH, δC, δN, δO, and δS) of tissues and excreta of domesticated animals, the factors affecting the isotopic composition of animal tissues, and whether stable isotopes may be used to differentiate organic and conventional modes of animal husbandry. The main factors affecting the δC signatures of livestock are the C3/C4 composition of the diet, the relative digestibility of the diet components, metabolic turnover, tissue and compound specificity, growth rate, and animal age. δN signatures of sheep and cattle products have been related mainly to diet signatures, which are quite variable among farms and between years.

Identifying N fertilizer regime and vegetable production system in tropical Brazil using (15) N natural abundance.

Background: This study was conducted in areas of vegetable production in tropical Brazil, with the objectives of (i) measuring the variation in δ(15)  N in soils, organic N fertilizer sources and lettuce (Lactuca sativa L.) from different farming systems, (ii) measuring whether plant δ(15)  N can differentiate organic versus conventional lettuce and (iii) identifying the factors affecting lettuce δ(15)  N.

Results: Samples of soil, lettuce and organic inputs were taken from two organic, one conventional and one hydroponic farm.

13C isotopic fractionation during biodegradation of agricultural wastes.

Significant differences in δ(13)C signatures occur within and between plant tissues and their constituent biochemical entities, and also within and between heterotrophic bacteria and fungi and their metabolic products. Furthermore, (13)C isotopic fractionation occurs during the biodegradation of organic molecules as seen in the substrate, respired CO(2) and the microbial biomass, which could be related to substrate composition and/or microbial metabolism. The (13)C isotopic fractionation observed during the decomposition of a single defined C substrate appears to be due to the intra-molecular heterogeneity in (13)C in the substrate and to (13)C isotopic fractionation during microbial metabolism.

Principles and limitations of stable isotopes in differentiating organic and conventional foodstuffs: 1. Plant products.

Among the lighter elements having two or more stable isotopes (H, C, N, O, S), δ(15)N appears to be the most promising isotopic marker to differentiate plant products from conventional and organic farms. Organic plant products vary within a range of δ(15)N values of +0.3 to +14.