Relationship between soil solution aluminium and low molecular weight organic acids in a conservation cropping system

2003

J. Agric. Sci.

The effects of additions of four organic amendments to an Oxisol on soil pH, exchangeable and soil solution Al, extractable P and maize growth were compared with those of lime and P in a glasshouse experiment. The organic amendments were: grass residues, household compost, filter cake (a waste product of sugar mills) and layer poultry manure and they were added at a rate equivalent to 20 t/ha with or without the addition of either lime (equivalent to 0, 5 or 10 t/ha) or P (equivalent to 0, 10 or 50 kg/ha). Lime applications to the control (unamended) treatment resulted in a marked reduction in exchangeable Al, and concentrations of total (AlT) and monomeric (Almono) Al in soil solution and the proportion of AlT present as Almono. In unlimed soils, amendment additions increased pH and decreased exchangeable Al in the order: poultry manure>filter cake>household compost>grass residues>control. The addition of all the organic amendments increased soil pH and reduced AlT and Almono to low concentrations regardless of whether lime was applied or not. As a result, there was no yield response to applied lime in any of the amended treatments. Olsen-extractable P concentrations in soils followed the order: poultry manure>filter cake>household compost>grass residues>control and there was no yield response to applied P for the poultry manure and filter cake treatments. The decrease in adsorption of subsequently added P induced by additions of organic amendments followed the order: poultry manure>household compost>filter cake>grass residues. It was concluded that the addition of organic amendments to acid soils is a practicable way of liming them and reducing the potential for Al toxicity and it can also reduce fertilizer P requirements.

Section: Resultsmentioning

confidence: 99%

A glasshouse evaluation of the comparative effects of organic amendments, lime and phosphate on alleviation of Al toxicity and P deficiency in an Oxisol

Mokolobate

2003

J. Agric. Sci.

“…We initially thought that the substantially greater organic matter content under trash retention would lead to decreased Al Mono concentrations in solution through complexation by soluble organic material (Haynes & Mokolobate, 2001). In a comparison of burning with stubble retention under wheat, Slattery & Morrison (1995) showed that stubble retention caused a decrease in the concentration of Al Mono and the proportion of Al T present as Al Mono as a result of complexation of Al Mono by organic ligands originating from the decomposing stubble. However, in this study trash retention caused a small net decrease in soil pH and increases in exchangeable acidity, exchangeable Al 3+ and Al T , and Al Mono in solution.…”

Section: Changes In Acidity and Cecmentioning

confidence: 99%

Changes in soil chemistry and aggregate stability induced by fertilizer applications, burning and trash retention on a long‐term sugarcane experiment in South Africa

Graham

European J Soil Science

Meyer

2002

109

Summary Throughout the world there is a trend towards retaining crop residues rather than burning them. For this reason, changes in soil chemistry and aggregation in a Vertisol induced by 59 years of burning or green cane harvesting with or without annual fertilizer applications were investigated. Crop residues were either burnt prior to harvest with the harvest residues raked off (R1), burnt prior to harvest with the harvest residues left on the soil surface (R2), or left unburnt with all the trash left on the soil surface (R3). Concentrations of organic C in the surface 10 cm of soil increased with fertilizer applications and with increasing amounts of crop residue returned in the order R1 < R2 < R3. Fertilizer applications caused an accumulation of residual P in both inorganic (Pi) and organic (Po) forms. A sequential P fractionation showed that fertilizer P accumulated in both labile and recalcitrant Pi and Po forms, and trash retention caused an accumulation of recalcitrant Po. Concentrations of K decreased in the unfertilized R1 and R2 treatments because K reserves were depleted. By contrast, there was an increase in the concentrations of K in the fertilized R3 treatment. The soil became more acid on the fertilized and, to a lesser extent, trash retention plots. We attribute this to nitrification and subsequent nitrate leaching. Acidification resulted in a loss of exchangeable Ca and Mg, a decrease in ECEC, and an increase in the concentrations of total and monomeric Al in soil solution, in exchangeable Al3+ and in the buffering reserve of non‐exchangeable Al associated with organic matter. Aggregate stability was increased by increasing crop residues but decreased by fertilizer applications. The decrease was attributed to an increase in the proportion of exchangeable cations present in monovalent form due to applications of fertilizer K and leaching of Ca and Mg. We conclude that trash retention and annual fertilizer applications have substantial long‐term effects on both organic matter status and soil pH and therefore on other soil chemical and physical properties.

“…The considerably greater concentrations of organic C present in soil solution after the addition of the poultry manure will also tend to maintain large concentrations of Al in soil solution in complexed form. Indeed, some other workers have shown that Al T in soil solution is unaffected or even increased during the decomposition of organic residues (Berek et al ., 1995; Slattery & Morrison, 1995). In such cases, Haynes & Mokolobate (2001) suggested that large quantities of soluble organic C present, originating from the decomposition of residues, complex with Al and maintain it in solution.…”

Section: Discussionmentioning

confidence: 99%

“…It has also been suggested that Al is complexed in solid phase by the decomposing residues, thereby reducing both exchangeable and soluble Al (Hoyt & Turner, 1975). In addition, soluble organic molecules produced during decomposition of the residues are believed to complex with monomeric Al in soil solution, thus rendering it non‐phytotoxic (Berek et al ., 1995; Slattery & Morrison, 1995).…”

Section: Introductionmentioning

confidence: 99%

Increases in pH and soluble salts influence the effect that additions of organic residues have on concentrations of exchangeable and soil solution aluminium

Mokolobate

European J Soil Science

2002

Summary It has been suggested that additions of organic residues to acid soils can ameliorate Al toxicity. For this reason the effects of additions of four organic residues to an acid soil on pH and exchangeable and soil solution Al were investigated. The residues were grass, household compost, filter cake (a waste product from sugar mills) and poultry manure, and they were added at rates equivalent to 10 and 20 t ha−1. Additions of residues increased soil pH measured in KCl (pH(KCl)) and decreased exchangeable Al3+ in the order poultry manure > filter cake > household compost > grass. The mechanism responsible for the increase in pH differed for the different residues. Poultry manure treatment resulted in lower soil pH measured in water (pH(water)) and larger concentrations of total (AlT) and monomeric (Almono) Al in soil solution than did filter cake. This was attributed to a soluble salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al3+ and H+ back into soil solution. The considerably larger concentrations of soluble C in soil solution originating from the poultry manure may also have maintained greater concentrations of Al in soluble complexed form. There was a significant negative correlation (r = −0.94) between pH(KCl) and exchangeable Al. Concentrations of AlT and Almono in soil solution were not closely related with pH or exchangeable Al. The results suggest that although additions of organic residues can increase soil pH and decrease Al solubility, increases in soluble salt and soluble C concentrations in soil solution can substantially modify these effects.