Gypsum: A Novel Soil Amendment

Gypsum Increases Soil Calcium Availability

Calcium sulfate (Ca SO4), better known as gypsum, may prove to be a valuable soil amendment. Gypsum is available as the mined mineral of Ca SO4 2H2. Beneficial effects of gypsum have been demonstrated in field studies by G.K. Evanylo of the Eastern Shore Agricultural Experiment Station in Painter in Virginia. They report that gypsum increased rooting proliferation and alleviated drought stress in deep rooted crops such as alfalfa, and corn. They also found that as a result of applying 2.67 tons/acre of gypsum, subsoil nitrate concentration decreased as total N uptake by corn increased from 81 to 121 lbs/acre.

Gypsum has been shown to decrease Al activity in acid soils where Al and Mn concentrations can reach toxic levels. Although gypsum is not an inherently acid-neutralizing compound such as limestone, it is more efficient than limestone in providing Ca. Limestone produces cation exchange sites to which Ca binds, making the nutrient unavailable to plants. Unlike limestone, gypsum does not produce additional cation exchange sites which make Ca inaccessible to plants. Less gypsum is therefore required to raise the activity of Ca in soil than limestone. Due to its greater solubility than limestone, gypsum leaches easily through soils and increases Ca uniformly down the soil profile.

Gypsum is a crucial amendment in peanut production because of the critical role Ca plays in the development of this crop. Enhanced Ca uptake with gypsum application has been demonstrated to increase the quality of potato tubers, apples, and avacados. The beneficial effects of gypsum applications on subsoil acidity are likely to persist for at least six years.

G.K. Evanylo. 1989. Amelioration of Subsoil Acidity by Gypsum. The Vegetable Growers News 44 (2): 3-4.

For more information contact:

Dr. G.K. Evanylo
Eastern Shore Agricultural Experiment Station
Painter, Virginia

Gypsum Improves Water Infiltration Rate

If you have a problem with soil erosion in your fields you may find help from phosphogypsum. Phosphogypsum is a by-product of phosphorus fertilizer. It is 97% gypsum, but also contains trace amounts of: Mg SO4 (1%); P2O5 (0.6%); flourapatite and SiO2 (1.4%). A team of Israeli scientists conducted an experiment to understand the effect of PG on soil erosion in potato fields. Potato yields suffer when the ridges are destroyed by the high percentage of runoff found in potato fields, an effect which is confounded by the steep slope between the top of the ridge and the bottom of the furrow. The ridges need to be reconstructed several times during the rainy season, until the potato canopy can protect the soil surface.

Soil erosion and runoff often occur when a seal forms on the surface of the soil which prevents water infiltration. Seal formation on soil exposed to rainfall is due to two mechanisms: (1) the clay particles are physiochemically dispersed and clog pores beneath the surface, and (2) soil aggregates are broken-down due to the impact of raindrops, and contribute to the formation of the seal. As a result of runoff and erosion, water and fertilizer are lost and must be resupplied during the growing season. If seal formation were avoided, water infiltration would improve, and soil erosion prevented.

The researchers spread 10 tons per hectare of PG over the surface of the soil of a potato field. They also experimented with dyked furrows which they treated with PG. The field has a slope of 7%, and the slope between the top of the ridge and the bottom of the furrow is 65%. The scientists found that when PG is spread over the soil, it dissolves and releases electrolytes that prevent clay dispersion. By preventing clay dispersion, PG improved the permeability of the soil and increased the stability of aggregates at the soil surface. The infiltration rate of PG-treated plots tripled, runoff decreased by 50% , erosion was reduced by 60% on gentle slopes, and the soil loss from the ridges to the bottom of the furrows was reduced 20-fold.

Laboratory experiments using a rain simulator were conducted on soil at slopes of 5% and 25%. When the slope reached 25%, soil loss increased 7-fold in the control treatment, and only 2-fold in the PG plot, although increase in slope had little effect on the amount of runoff on either the PG-treated or control plots. The effect of PG was even more pronounced in the field experiments where soil losses from the ridges were 4.1 and 86 kgm -2 for the treated and control treatments, respectively. The PG treatment in the field was more efficient because of the steeper slope (65%) in the field, compared with (25%) in the laboratory.

The expenses for the application of 10 t per ha in the field were about $80. Transportation (100-km distance) was the major expense. While the beneficial effect of phosphogypsum is clear, the economy of using it must be considered for each site.

M. Agassi, I. Shainberg, D. Warrington, and M. Ben-Hur. 1989. Runoff and Erosion Control in Potato Fields. Soil Science, Vol.148, No. 2.

For more information contact:

M. Agassi
Soil erosion Research Station
Ruppin Inst.
P.O. Emeq Hefer 60960