Phosphorus sources and fractions in an oxisol under no-tilled soybean

Abstract

Phosphorus dynamics in soil can be modified by the use of no-till systems. Brazilian farmers have applied phosphorus fertilizers onto the soil surface to optimize machine field operations despite the lack of research supporting this practice. An experiment was conducted to study the effects of the application of two P sources onto soil surface and soybean seed furrows. The treatments consisted either of the application or not of 80 kg ha -1 of total P 2 O 5 as natural reactive rock phosphate and superphosphate spread on the soil surface over the standing plant residues. At soybean planting, additional treatments (80 kg ha -1 of Natural Phosphate or Superphosphate) were applied at seed furrows. Soil was sampled down to 40 cm deep before soybean planting and after harvest. A control sample was taken from an adjacent non-cropped area. Phosphorus contents increased down to 40 cm after the soybean crop, and the increase was observed mainly in Ca-bound P and organic phosphorus. However, there was a decrease in Fe-bound P, showing that P availability to soybeans was likely related also to this fraction. Phosphorus fertilization with both phosphates decreased occluded P contents on the soil surface layer when compared with the non-cropped area. Key words: natural phosphate, phosphorus fertilizer, mineral phosphorus, organic phosphorus, phosphorus fractioning FONTES E FRAÇÕES DE FÓSFORO NUM LATOSSOLO SOB SEMEADURA DIRETA DE SOJARESUMO: A dinâmica do P no solo pode ser modificada em sistemas com semeadura direta. Os agricultores brasileiros vêm aplicando fósforo na superfície do solo para otimizar a operação de máquinas, embora não seja uma prática recomendada pela pesquisa. Foi conduzido um experimento para estudar os efeitos da aplicação de duas fontes de fósforo na superfície do solo e no sulco de semeadura da soja. Os tratamentos consistiram da aplicação ou não de 80 kg ha -1 de P total como fosfato natural reativo e superfosfato, aplicados na superfície do solo, sobre os resíduos da cultura anterior. Na semeadura da soja, tratamentos adicionais (80 kg ha -1 de fosfato natural ou superfosfato) foram aplicados ao sulco de semeadura. O solo foi amostrado até 40 cm de profundidade, antes da semeadura da soja e após a colheita. Uma amostra controle foi tomada de área adjacente, sem cultivo. Houve aumento nos teores de P até 40 cm de profundidade, após a colheita da soja, de modo que o aumento foi observado principalmente no P ligado ao Ca e no P orgânico. Entretanto houve decréscimo nos teores de P ligado ao Fe. A adubação com ambas as fontes de fosfato levaram a um decréscimo nos teores de P ocluso na superfície do solo quando comparada com a área sem cultivo. Palavras-chave: fosfato natural, fertilizante fosfatado, fósforo mineral, fósforo orgânico, fracionamento de fósforo

Congo grass grown in rotation with soybean affects phosphorus bound to soil carbon

“…Growing Congo grass increased soil available P as estimated by resin extraction at both soil depths when P fertilizers were applied. The buildup of available P in the topsoil by B. ruziziensis cropped under no-till supports the findings of several other studies, including other species (Galvani et al, 2008). This effect may result from the influence of organic acids on P sorption, since Brachiarias can exude citrate or oxalate (Watts & Evans, 2003;Louw-Gaume et al, 2010), and Congo grass was shown to decrease the soil maximum P adsorption capacity (Janegitz et al, 2013).…”

Phosphate fertilization and phosphorus forms in an Oxisol under no-till

“…Galvani et al (2008) also observed that P-Al contents, in an uncropped area down to 0.40 m deep, were larger than those in the cropped area.…”

Phosphorus fractions in sandy soils of vineyards in southern Brazil

“…Studies in Brazil have shown increasing organic P in the soil profile, especially in soils with phosphate fertilization under no tillage (Galvani et al, 2008;Oliboni & Rosolem, 2010). This can be partly explained by the absence of soil tilling over the years and crop litter deposition on the soil surface (Tokura et al, 2002).…”