PHOSPHOGYPSUM USES IN AGRICULTURE

Phosphogypsum (CaS04), a by -product of phosphoric acid production from rock phosphate is a potential source of calcium and sulfur for plants, as well as an ameliorant for alkaline and sodic soils. Phosphogypsum production worldwide exceeds 150 million Mg annually, with only about 4 percent being used in agriculture and industry and the rest being dumped into the ocean or stock piled as a waste. Florida leads in the production of phosphogypsum in the United States with an annual production of 33 million Mg and about 600 million Mg in stacks, and a projection of 1 billion Mg by the year 2000. This paper will discuss the various agronomic uses of phosphogypsum (i.e. source of nutrients for plants, conditioner for sodic soils, hard-setting clay soils and subsoil hardpans, and the acidifying benefits on high pH soils to help alleviate micronutrient deficiencies). This paper will also discuss any potential environmental hazards to be concerned with from using phosphogypsum in agricultur

Aplicação de gesso e calcário na recuperação de solos salino-sódicos do Estado de Pernambuco Application of gypsum and limestone in the reclamation of saline-sodic soils of the Pernambuco State

Experimento em colunas de solo foi conduzido, objetivando-se avaliar o efeito da aplicação de gesso e gesso + calcário, na recuperação de solos salino-sódicos do Perímetro Irrigado de Custódia, PE. Os tratamentos foram dispostos em um delineamento em blocos casualizados, com arranjo fatorial de quatro solos, dois métodos de aplicação de gesso e gesso + calcário (aplicados na superfície e incorporados aos primeiros 5 cm da coluna de solo), duas combinações dos corretivos (100% de gesso + 0% de calcário e 80% de gesso + 20% de calcário), calculados com base na necessidade de gesso dos solos, e quatro faixas de granulometria de gesso (2,0-1,0, 1,0-0,5, 0,5-0,3 e < 0,3 mm), com três repetições. A quantidade de gesso determinada em laboratório pelo método de Schoonover M-1, mostrou-se adequada no deslocamento do sódio trocável do complexo de troca. A eficiência do gesso e da mistura gesso + calcário na recuperação dos solos revelou-se superior quando os corretivos foram incorporados aos primeiros 5 cm das colunas de solo. Entre as granulometrias de gesso, as frações mais finas (0,5-0,3 mm e < 0,3 mm) apresentaram melhor desempenho na substituição do sódio trocável do complexo de troca.<br>An experiment was carried out in soil columns with the objective of evaluating the effect of application of gypsum and limestone on reclamation of the saline-sodic soils in the Irrigation district of Custódia, PE. The treatments were arranged in a randomized block design in a factorial scheme of four soils, two methods for applications of gypsum and gypsum plus limestone (applied on surface and incorporated into the first five cm of the soil column), two combinations of the chemical amendments (100% gypsum plus 0% limestone and 80% gypsum plus 20% limestone), calculated on the basis of gypsum requirement of soil and four granulometry gypsum strips (2.0-1.0; 1.0-0.5; 0.5-0.3 and < 0.3 mm) with three replications. The gypsum amount determined by the method of Schoonover M-1, under laboratory conditions, shows to be adequate in the displacement of the exchangeable sodium of the soil exchange complex. The efficiency of the gypsum as well as the gypsum plus lime mixture in reclamation of the soils shows to be superior, when the amendments are incorporated into the first 5 cm of the soil columns. Among the gypsum granulometry, the finest fractions, (0.5-0.3 mm and < 0.3 mm), presented better performance in replacing the exchangeable sodium of the exchange complex