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Reaction of Fertilizer and Liquid Manure Phosphorus with Soil Aggregates and Sediment Phosphorus Enrichment¹

ABSTRACT

Phosphorus enrichment ratios (PER) were estimated for sediment from six runoff events from plots that had been under one of three management systems for at least 5 yr: no-till (NT), no-till manured (NTM), and fall plowed manured (FPM). Sodium bicarbonate-extractable P enrichment ratios (Ext-PER) in sediment were 2.15, 1.30, and 1.10 for NT, NTM, and FPM treatments, respectively. The higher Ext-PER on the NT treatment could not be explained solely by a higher clay enrichment.

A laboratory experiment was conducted to test three hypotheses developed to explain the difference in Ext-PER values. Phosphorus in the form of either inorganic salt (KH₂PO₄) or liquid poultry manure (chicken, Gallus gallus domesticus) was added to soil at rates up to 400 mg P kg^–1. Soils were passed through 7-d wetting and drying cycles for 235 d and sampled periodically. Most of the added P from both the manure and inorganic P treatment was associated with the clay fraction. The proportion of P that was desorbable increased as the amount of P added increased. This may, in part, explain the lower Ext-PER on the manured plots, which had a greater amount of P added. Manure increased water stability of soil aggregates. In addition, the Ext-P concentration in water-stable aggregates from the manure treatment increased with increasing aggregate size, whereas the inorganic P source had no effect. Manure did not alter the size distribution of dry-sieved aggregates, but Ext-P was increased to a greater extent in the larger aggregates, indicating that there was a preferential sorption of manure P by larger-sized aggregates. This conclusion was supported by results from a small field trial. The preferential sorption of P from liquid manure by larger, more stable aggregates may result in a lower Ext-PER in sediment from manured fields.

Key Words: no-till • aggregate size • phosphorus adsorption • aggregate stability

¹ Contribution from the Dep. of Land Resource Science, Univ. of Guelph, Canada. This research was funded, in part, by the Ontario Ministry of Agriculture and Food.

² Formerly graduate research assistant, currently soil physicist, Dep. of Soils, Punjab Agric. Univ., Ludhiana, India, and professors of soil science, respectively.

Received for publication May 4, 1984.