ARS | Publication request: Soil Phosphorus Distribution in a Crop Production System with Long-term Compost Amendment

Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: February 17, 2010
Publication Date: August 6, 2010
Citation: Bortolon, L., Kovar, J.L., Cambardella, C.A., Singer, J.W., Gianello, C. 2010. Soil Phosphorus Distribution in a Crop Production System with Long-term Compost Amendment. In: Gilkes, R.J. and Prakongkep, N. (ed). Proceedings of the 19th World Congress Soil Science, August 1-6, 2010, Brisbane, Australia. ISBN 978-0-646-53783-2. DVD.

Interpretive Summary: Phosphorus (P) fertilizer is essential for maintaining high yields of agronomic crops. Organic amendments, such as manure and compost, are an economical alternative to commercial fertilizers for supplying P to crops. To better understand how plants capture P from soil amended with compost, rather than fertilizer, we should know how plant-available P is distributed in the topsoil. In this study, we evaluated P distribution in soil either with or without compost application in a corn-soybean-wheat/clover cropping system managed with intensive, moderate, or no tillage since 1988. We found that long-term compost application increased all P forms in the soil profile, especially the types of P most susceptible to loss by leaching and runoff. We also found that tillage affected P distribution more than the type of crop that was grown, and that less tillage meant that more P remained in topsoil layers where root activity is higher. These results should be of value to commercial growers and conservationists, as well as the organic farming community.

Technical Abstract: Excessive fertilization with inorganic or organic phosphorus (P) amendments, such as compost, increases the risk of P losses to surface waters. To properly manage fertilizer amendments, an understanding of P distribution in soil is essential. The objective of this research was to evaluate P distribution in soil with and without long-term compost amendment in a maize (Zea mays L.)-soybean (Glycine max L. Merr.)-wheat (Triticum aestivum L.)/clover (Trifolium repens L.) crop rotation managed with moldboard plow (MP), chisel plow (CT), or no-tillage (NT), with all phases present each year since 1988. Soil (Clarion silt loam and Canisteo silty clay loam) samples were collected in 2007 from three depth increments (0-7.5; 7.5-15; 15-30 cm) of each plot. Water-extractable P, Bray-1 extractable P, total P, and degree of P saturation (DPS) were determined from subsamples. Long-term compost application increased all P forms in the soil profile. The low C:P ratio of the compost likely increased soil P mineralization, leading to the differences we measured. The intensity of tillage affected all measures of P in the surface soil more than the crop that was grown. Water-extractable P was higher in the CT and NT treatments relative to the MP treatment, and tended to be higher following soybean. Similar results were found for Bray 1 P and total P. Compost applications can increase soil P, mainly P forms most susceptible to losses, thereby increasing the risk of P losses by leaching and runoff. Conservation tillage can reduce P leaching by keeping P in topsoil layers where root activity is higher. To decrease the risk of P losses from these cropping systems, compost applications should be P based.