Availability of Rock Phosphate as Measured by an Acid Tolerant Pasture Grass and Extractable Phosphorus¹

Abstract

As agricultural development intensifies in tropical countries and as costs of superphosphate production increase, the need for further evaluation of rock phosphates has become apparent. An acid tolerant pasture grass (Brachiaria decumbens Stapf.) was used to evaluate the initial and residual (3 years) availability of P from several phosphate materials. A field study was conducted on a Typic Haplustox of the Cerrado of Central Brazil. Initial availability of P supplied as normal superphosphate, Hyperphosphate, Thermalphosphate, and North Carolina rock phosphate was similar when the soils were not limed (pH = 4.3, Al = 1.4 meq/100g). Where lime had been added and pH was increased to 5.4 the P in Hyperphosphate and N.C. rock phosphate was initially less available than P added as superphosphate and Thermalphosphate. After 10 months of contact, lime no longer significantly depressed P availability in these relatively soluble rock phosphates as measured by forage dry weight. The P in the other phosphate rock of low citric acid solubility, Araxá, was virtually unavailable during the 3 months after application. However, within 13 months, maximum forage yields were attained where this material had been applied to unlimed soil and at 25 months maximum yields were obtained on both limed and unlimed soil. Higher rates of Araxá material were required to obtain maximum yields than with normal superphosphate. Forage yields were 2 to 4 times greater where superphosphate was surface applied each year than where similar amounts were incorporated prior to planting. A comparison of extractant methods for soil P indicated that highly acidic extractants (e.g., 0.05 N HC1 + 0.025 N H2SO4) overestimated available P where rock phosphate had been applied. Where superphosphate or rock phosphate had been applied, P availability was better assessed by extractants such as 0.5 M NaHCO3 and Bray 1. The results emphasize the need to supplement laboratory and short‐term studies with long‐term evaluations of P materials with acid tolerant perennial crop species available in tropical countries.

Fontes, doses e extratores de fósforo em alfafa e centrosema

“…Segundo Yost et al (1982), a alta solubilidade em água acarreta maior absorção nos primeiros cortes, e maior fixação no solo, nos demais.…”

Avaliação do fosfato natural de Gafsa para recuperação de pastagem degradada em latossolo vermelho-escuro

“…Uma das alternativas para reduzir custos pode ser a utilização de fosfatos naturais para aplicação direta nas pastagens (Yost et al, 1982;Sanzonowicz & Goedert, 1986).…”

“…Avaliações do fosfato natural de Gafsa finamente moído (85% passando na peneira com malhas de 0,075 mm), feitas com gramíneas forrageiras tropicais, em experimentos de longa duração, mostraram que sua eficiência agronômica foi próxima à dos fosfatos hidrossolúveis, quando incorporado a solos ácidos, anteriormente sob savana (León & Fenster, 1980) ou cerrado (Yost et al, 1982;Goedert & Lobato, 1984;Sanzonowicz et al, 1987).…”

Cultivo de melão orgânico: fosfatos naturais como fontes alternativas de fósforo

“…Como a grande maioria dos FNs do Brasil não é de origem sedimentar, eles geralmente têm apresentado resultados de baixa eficiência agronômica (Yost et al, 1982;Oliveira et al,1984;Goedert & Lobato, 1984;León et al, 1986;Sanzonowicz & Goedert, 1986;Sanzonowicz et al, 1987). FNs de Gafsa, da Tunísia, Arad, de Israel, Carolina do Norte, dos Estados Unidos, todos de origem sedimentar, são mais eficientes em suprir P para plantas de ciclo curto, por apresentar um teor de P 2 O 5 solúvel em ácido cítrico igual ou superior a 30% do teor total de P 2 O 5 , assim como os termofosfatos, que apresentam resultados semelhantes aos fosfatos solúveis (Yost et al, 1982;Oliveira et al, 1984;Goedert & Lobato, 1984;Sanzonowicz et al, 1987;Braga et al, 1991;Choudhary et al, 1994).…”

“…FNs de Gafsa, da Tunísia, Arad, de Israel, Carolina do Norte, dos Estados Unidos, todos de origem sedimentar, são mais eficientes em suprir P para plantas de ciclo curto, por apresentar um teor de P 2 O 5 solúvel em ácido cítrico igual ou superior a 30% do teor total de P 2 O 5 , assim como os termofosfatos, que apresentam resultados semelhantes aos fosfatos solúveis (Yost et al, 1982;Oliveira et al, 1984;Goedert & Lobato, 1984;Sanzonowicz et al, 1987;Braga et al, 1991;Choudhary et al, 1994).…”