STUDIES ON THE DECOMPOSITION OF PLANT MATERIAL IN SOIL. V. THE EFFECTS OF PLANT COVER AND SOIL TYPE ON THE LOSS OF CARBON FROM14C LABELLED RYEGRASS DECOMPOSING UNDER FIELD CONDITIONS |
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Authors: | D S JENKINSON |
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Institution: | Rothamsted Experimental Station, Harpenden, Herts. AL5 2JQ |
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Abstract: | Ryegrass uniformly labelled with 1 4C was allowed to decompose for 10 years under field conditions in a range of contrasting soils. The amount of organic matter already in a soil had no effect on the retention of labelled C by that soil, nor had a variation in soil pH of from 4.9 to 8.1. Decomposition was initially slower in a strongly acid soil (pH 3.7) but by the end of 5 years the difference between this soil and the others had almost disappeared. The more clay in a soil, the greater the retention of labelled C over the whole 10 year period; this was true of both strongly acid and near-neutral soils. More labelled organic matter was leached from a soil containing 7.6% clay than from one with 17.5% clay, but the amount thus lost was insufficient to account for the difference in retention of C by the two soils. The decomposition of labelled plant material was faster in bare soil than in soil growing grass but the ‘protection’ thus given to the labelled C by the growing grass ended when the grass was removed. In bare soil about one third of the labelled ryegrass C was left after one year but thereafter decomposition became very much slower and about one eighth of the labelled C still remained in the soil after 10 years. The decay curve can be represented by a two compartment model, in which about 70% of the ryegrass C decomposed by a first order process of half life 0.25 years and the remainder by a similar process of half-life 8 years. |
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