Ha-1 Gypsum Research Articles

Gypsum amendment to soil can reduce selenium uptake by alfalfa grown in the presence of coal fly ash

Experiments in the field and greenhouse were conducted in the presence of coal fly ash to determine whether gypsum can reduce Se concentration in alfalfa (Medicago sativa L.). In the field experiment, conducted at a coal fly ash landfill, 11.2 t ha-1 gypsum was applied to soil as a top dressing to test the effect of gypsum in reducing selenium (Se) concentration in aboveground plant tissue. There were four treatment combinations of gypsum over a two year period, 1990 and 1991: (0, 0), (0, 11.2) (11.2, 0) and (11.2, 11.2). In 1991, the Se concentration was lower in alfalfa grown with gypsum regardless of whether the gypsum was applied in both years or in only one year, indicating that the effect of gypsum application in the first year persisted into the second year. Since there was no increase in aboveground biomass with added gypsum, differences in Se concentration reflect a competitive interaction between S and Se. In the greenhouse experiment, 12 soil treatments were tested: three levels of fly ash (0, 10 and 20%) in combination with each of four levels of gypsum (0, 2.5, 5, and 7.5%). The Se concentration in alfalfa grown in 10% fly ash declined linearly with increasing gypsum dose, resulting in a reduction in Se concentration of 0.04±0.02 μg g-1 for each 1% gypsum added for the first harvest and 0.06±0.03 μg g-1 for each 1% gypsum added in the second harvest. Based on these results, gypsum may prove useful as a management tool to reduce the uptake of Se by plants growing on coal fly ash landfills. ei]H Lambers

The effect of gypsum on cation exchange in two red duplex soils

Gypsum at rates of up to 15 t ha-1 was applied to the surface 10 cm of two red duplex soils in northern Victoria. At both sites, approximately five years after application, the following changes in soil properties were established: 1. Only when 15 t ha-1 of gypsum was applied was exchangeable sodium in the upper 25 cm significantly decreased. 2. Exchangeable magnesium was not decreased at depths greater than 15 cm. After five years only the 15 t ha-1 treatments still contained some undissolved gypsum in the A horizon. Of the gypsum that had dissolved, 53% had been involved in exchange. This represented an efficiency of exchange of 26-34%, based on the ratio of sodium replaced to calcium dissolved. At both sites over this five-year period, the mean solubility of gypsum from the 15 t ha-1 treatment was 120-130 mm of rainfall per t of gypsum.

Amelioration of structurally unstable grey soils in the north-western wheat belt of New South Wales

Methods of amelioration of structurally unstable grey clays were studied in field experiments conducted at three sites in the Gwydir Valley in northern New South Wales. A set of ameliorative treatments was established at each site in 1973, and a second set of treatments was established in 1974. Plots were sown with wheat each year until 1977 to study residual effects. In the first series of experiments, gypsum at 12.5 t ha-1 greatly increased wheat yields at all sites, with residual effects still strongly evident in 1977. The yield increases were commonly associated with reduced surface soil crust strength, increased wheat establishment, and increased stored soil water at sowing. Potassium sulphate at 3.75 t ha-1 and organic matter (chopped hay at 12 t ha-1) gave initial yield increases, but residual effects did not persist. Neither polyvinyl alcohol (200 kg ha-1) nor deep ploughing (to 25 cm) was successful as an ameliorant. In the second series of experiments, gypsum at 2.5 t ha-1 consistently increased wheat yields, with residual effects still evident in 1977, although yield increases were much less than those obtained with 12.5 t ha-1 gypsum in the first series of experiments. A crop of oats ploughed under was not a successful ameliorant, but calcium carbonate (5 t ha-1) showed some potential.

Effects of nitrogen and phosphorus fertilizers and gypsum on a Danthonia caespitosa-Stipa variabilis grassland. 2. Residual response

The residual effects of nitrogen and phosphorus fertilizers applied over four consecutive years and gypsum applied once only, were assessed over five years on a Danthonia caespitosa-Stipa variabilis grassland, growing on the semi-arid Riverine Plain of south-eastern Australia. Totals of 155 and 31 0 kg ha-1 of N, 100 and 200 kg ha-1 of P, and 3.34 and 6.68 t ha-1 of CaS0,. 2H2O had been added. The increase in dry matter production in response to nitrogen ceased one year after the last application of nitrogen fertilizer. After five years, grassland which had received 200 kg ha-1 of phosphorus and 6.68 t ha-1 of gypsum yielded 6500 kg ha-1 of dry matter, compared with 1300 kg ha-1 in the absence of fertilizers and gypsum. Legume growth was still suppressed five years after nitrogen fertilizer had been applied, but legumes increased production greatly in response to the previous phosphorus and phosphorus-gypsum treatments. Nitrogen content of the herbage averaged 2.1 per cent four years after the previous high level phosphorus treatment, compared with 1.6 per cent with the control after four years. It was unaffected by previous nitrogen fertilizer. Phosphorus content was reduced for the first three years after nitrogen fertilizer was last added, but was increased by phosphorus fertilizer to 0.28 per cent, compared with 0.1 8 per cent on the control, four years after phosphorus fertilizer was last added. Soil moisture characteristics, and total soil nitrogen and carbon showed no differences between treatments. The Truog phosphorus in the soil under the high phosphorus level decreased from 103 p.p.m. to 53 p.p.m., compared with the unaltered control level of 7 p.p.m, over the five year period.