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Organic Materials Which Stabilize Natural Soil Aggregates¹

ABSTRACT

The effect of periodate followed by sodium borate treatment on the stabilities of prewet soil aggregates has been determined by a permeability technique and by wetsieving. The effect of periodate treatment depends on the history of the site, the depth, and the great soil group from which the sample is taken. The stabilities of aggregates from various Red Brown Earths were all reduced by periodate treatment. The reduction was small for samples from plots which had been under pasture for many years, but very large for samples which had been under pasture for 4 years or less, or which were continuously cropped. The stabilities of all subsurface samples of the Red Brown Earths were completely destroyed by periodate treatment. Aggregates taken from a Solonized Brown soil were much less sensitive to periodate treatment, and those taken from a Rendzina were with one exception unaffected. These soils contain free CaCO₃. It is probable that the most important function of the periodate treatment is to cause breakdown of the polysaccharides and polyuronides in the soil, and the results show that in cropped soils and soils under young pastures aggregate stability is primarily due to these materials. In soils under older pastures, or soils which contain free CaCO₃, other materials prevent aggregate breakdown.

¹ Contribution from the Department of Agricultural Chemistry, Waite Agr. Research Inst., University of Adelaide, South Australia.

² Lecturer in Soil Science, Junior Fulbright Fellow, and Reader in Soil Science, Department of Agricultural Chemistry, Waite Agr. Research Inst., Univ. of Adelaide, S. Australia. G. R. Lindstrom is now located at Sterling, Colo.

Received for publication September 5, 1961. Accepted for publication November 20, 1961.