Effects of Phosphorus Precipitation Chemicals on Characteristics and Agricultural Value of Municipal Sewage Sludges

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Abstract
In a two-year pot experiment with spring barley, Al sludge caused a decrease in grain yield compared to a P fertilized treatment without sludge on acid sandy clay soil only. Fe+Al sludge 2 and AVR sludge decreased the grain yield on organic soil, whereas Fe+Al sludge 1 sludge gave good results on all soils. Precipitated, quick lime stabilized sludges and Ca sludge were on a par with P fertilization. Increases in P, Ca, Al and Fe contents of sludge treated soils affected the element contents of grains less than the contents of straw. Sludges precipitated with Al and Fe increased the content of these elements in straw. The uptake of P by the total barley yield was highest when Fe+Al sludge 1 was applied, irrespective of soil type. P uptake was lowest with Al sludge on mineral soils and with Fe+Al sludge 2 on organic soil. Uptakes of Al and Fe were dependent on these elements being added in the soils with sludges. The proportion of grains on the total uptake of Al was about one-tenth and that of Fe about one-third.