Organic compounds from plant extracts and their effect on soil phosphorus availability

Paulo Sergio Pavinato,Ciro Antonio Rosolem,Alexandre Merlin

doi:10.1590/s0100-204x2008001000017

Abstract

The objective of this work was to evaluate the effect of organic compounds from plant extracts of six species and phosphate fertilization on soil phosphorus availability. Pots of 30 cm height and 5 cm diameter were filled with Typic Hapludox. Each pot constituted a plot of a completely randomized design, in a 7x2 factorial arrangement, with four replicates. Aqueous extracts of black oat (Avena strigosa), radish (Raphanus sativus), corn (Zea mays), millet (Pennisetum glaucum), soybean (Glycine max), sorghum (Sorghum bicolor), and water, as control, were added in each plot, with or without soluble phosphate fertilization. After seven days of incubation, soil samples were taken from soil layers at various depths, and labile, moderately labile and nonlabile P fractions in the soil were analysed. Plant extracts led to an accumulation of inorganic phosphorus in labile and moderately labile fractions, mainly in the soil surface layer (0-5 cm). Radish, with a higher amount of malic acid and higher P content than other species, was the most efficient in increasing soil P availability.

Highlights

Tropical soils are generally very poor in available phosphorus (P), and adequate levels of this plant nutrient are essential for optimal grain yield
Considering that cover crops have different amounts of low-molecular-weight organic acids (LMWOA) which can be rapidly released to soil, after deposition (Stevenson, 1967; Franchini et al, 2003), the objective of this study was to evaluate the effects of organic compounds, present in plant extracts of six species, and phosphate fertilization on soil phosphorus availability
The amounts of K were high in all the plant extracts, and the amounts of Ca and Mg added via extracts were considered low, compared to the original soil contents

Summary

Introduction

Tropical soils are generally very poor in available phosphorus (P), and adequate levels of this plant nutrient are essential for optimal grain yield. The presence of organic compounds in rhizosphere may increase or decrease nutrient availability, depending on the characteristics of each organic compound and their interactions with the soil (Franchini et al, 2003; Moraes et al, 2007). The study of low-molecular-weight organic acids (LMWOA), and the ability of their carboxylate functional groups to interact with soil, by occupying anion adsorption sites and competing with phosphate, has an expressive importance to increase available P in soils (Guppy et al, 2005). PH change in rhizosphere and LMWOA presence may increase organic P solubility by complexing Fe and Al oxides, besides the competition for adsorption sites promoted by the carboxylate groups (Sposito, 1989; Jones, 1998)

Objectives

Methods

Results