A model is presented that dynamically estimates the radiocesium activity in herbage from readily available soil parameters. Three key properties underlying the bioavailability of radiocesium in soils were estimated in the model: the labile radiocesium distribution coefficient (k dl ), the solution K + concentration ([m K ]), and the radiocesium concentration factor (CF, Bq kg -1 plant/Bq dm -3 soil solution). These were determined as functions of the soil clay content and exchangeable K status. The effect of time on radiocesium fixation was described by two first-order decay equations. The model was initially parametrized using radiocesium uptake data from a ryegrass pot trial. Without further parameterization, the model was then tested for a wide range of soil and crop combinations using a database of published and unpublished information from a variety of sources and covering contamination time periods of 0.5-11 years. Model predictions of activity concentrations in crops were in generally good agreement with observed values.

A database of soil-to-plant transfer factors for radiocesium and radiostrontium has been compiled for arable crops from published and unpublished sources. The database is more extensive than previous compilations of data published by the International Union of Radioecologists, containing new information for Scandinavia and Greece in particular. It also contains ancillary data on important soil characteristics. The database is sub-divided into 28 soil-crop combinations, covering four soil types and seven crop groups. Statistical analyses showed that transfer factors for radiocesium could not generally be predicted as a function of climatic region, type of experiment, age of contamination, or soil characteristics. However, significant relationships accounting for more than 30% of the variability in transfer factor were identified between transfer factors for radiostrontium and soil pH/organic matter status for a few soil-crop combinations. Best estimate transfer factors for radiocesium and radiostrontium were calculated for 28 soil-crop combinations, based on their geometric means: only the edible parts were considered. To predict the likely value of future individual transfer factors, 95% confidence intervals were also derived. A comparison of best estimate transfer factors derived in this study with recommended values published by the International Union of Radioecologists in 1989 and 1992 was made for comparable soil-crop groupings. Whilst there were no significant differences between the best estimate values derived in this study and the 1992 data, radiological assessments that still use 1989 data may be unnecessarily cautious.

Field experiments were undertaken on two infertile and acidic soils in the semi-arid Mackenzie Basin, South Island, New Zealand, to determine the influence of fertiliser placement and rate of N application (0, 15, or row, respectively) but not when N was drilled 20 mm below the seed. Seedling numbers declined in all treatments over summer, and 32 weeks after sowing, numbers were only significantly lower when 30 kg ha -1 N was drilled with the seed (11.1 and 7.9 m -1 , respectively). Early seedling growth of legumes, apart from lupin, responded to N, the largest increases occurring where N was drilled with the seed. Although individual plant weight increases where N was drilled with the seed were still evident 32 weeks after sowing, legume DM yields were not significantly affected because of the lower establishment. Plant growth 32 weeks after sowing was affected by competition from existing vegetation, and increases in individual plant weight and legume DM yield from N occurred only where herbicide was applied. Basal superphosphate was more effective when it was drilled with rather than below the seed. The role of N fertiliser in the establishment of legumes overdrilled into low fertility situations is discussed.