Effect of direct drilling and soil type on soil atmosphere composition

Abstract

A study of the soil atmosphere in soils ploughed and cultivated normally and under long-term direct drilling was made in two soil types throughout a two year period, 1973 to 1975. Probes were sited at two depths, 15 cm and 30 cm, in the two cultivation treatments, mou\board ploughing to a depth of 20 cm and no-tillage, and in plots with different soil types, a sandy loam (Macmerry series) and a sandy clay loam (W'inton series). Spring barley (cv Zephyr) was grown every year.

Soil atmosphere samples were withdrawn at weekly intervals and analysed by gas chromatography for carbon dioxide, oxygen, methane and ethylene.

The sites were sampled for moisture content, bulk density and temperature to aid the interpretation of the results.

In the first growing season the soil atmosphere had a higher carbon dioxide and lower oxygen percentage than in the second, this being related to a higher rainfall and temperature in the first season. Soil atmosphere composition was similar in the two winters. The methane component of the soil atmosphere declined throughout each growing season as soil moisture declined but levels were found to be higher in 1974- than 1973.

Ethylene was not detected regularly and not in any appreciable quantity. There was a greater incidence of detection from probes sited in no-tillage plots at a depth of 30 cm. Oxygen levels, as sampled, have little influence on ethylene in the soil atmosphere.

In a comparison between the treatments, no-tillage and ploughing, the carbon dioxide percentage of the soil atmosphere was always higher and the oxygen percentage lower, in the first growing season only, under no-tillage. This was related to a markedly lower air filled porosity in this treatment. Similarly in the first growing season differences in the soil atmosphere between soil types were seen with a higher carbon dioxide and lower oxygen percentage in the Winton soil. This soil was consistently lower in air filled porosity but only at the low levels found in the first, wetter, growing season was this difference reflected in the composition of the soil atmosphere. The soil atmosphere at 30 cm was higher in carbon dioxide and lover in oxygen than the soil atmosphere at 15 cm.

The soil was also sampled at monthly intervals for one year and incubated anaerobically in the laboratory. This showed that throughout the year the soil did have the capacity to produce ethylene.

PTFE tubing as a soil atmosphere sampling tool was investigated and shown to be successful.