The conventional method for the determination of the organic matter content of diets and faeces is by ashing the sample at 550 °C (A.O.A.C, 1965)

Organic matter (O.M.) = dry matter (D.M.)–ash.

If the sample contains calcium carbonate, then some of this carbonate will be converted to oxide (Vogel, 1951) and the weight of carbon dioxide evolved will be calculated as organic matter. The amount of carbonate converted will be dependent upon the temperature at which the sample is ashed and the duration of the ashing process. We have found (Ørskov, Hovell & Allen, 1966; Hovell & Greenhalgh, 1972) that when calcium salts of volatile fatty acids are included in diets given to sheep, most of the calcium is excreted in the faeces as carbonate, and since apparent digestibility is the difference between the amounts of nutrient ingested and excreted, the estimation of the apparent digestibility of organic matter will be in error if no correction is made for the high calcium carbonate content of the faeces. For example, a diet which contained 9·2% of calcium acetate had a true organic matterapparent digestibility of 86·8%. Had no correction been made this would have been estimated as 84·9%.

Seven soil conditioners added to a sandy clay soil at Saxmundham did not benefit sugar-beet seedling emergence in four experiments in 3 years. In microplots at Broom's Barn free draining peat and sandy loam gave consistently more seedlings than limestone loam or flinty loam. In the laboratory, for each of three soil types, emergence was maximal only for a small soil moisture range and decreased rapidly when soils became drier or wetter. This suggests that conditioners which increase water-holding capacity should be tested on sandy loams rather than clay soils and that seed-bed preparation on heavier soils should seek to aerate the soil.