Soil Sulfur Cycling in Temperate Agricultural Systems
To avoid sulfur deficiency in agricultural crops, sulfur must be available in the required forms and quantities and in synchrony with plant demand. Soil sulfur exists in numerous forms, and its dynamics play an important role in the sulfur application to plants. Soil organic sulfur has been separated into broad—mostly chemically defined—fractions, reflecting land use and fertilizer practice, but these are of limited value for predicting plant availability. There are several reasons for this: (i) soil organic sulfur consists of a continuum of fractions with different timescales for mineralization; (ii) association to soil particles provides physical protection of soil organic sulfur against decomposition; and (iii) mineralization only constitutes 0.5 to 3% per year of the soil organic sulfur pool. The addition of organic material can build up soil organic sulfur and may contribute significantly to plant sulfur supply, depending on the carbon/sulfur (C/S) ratio of the added material. In animal manure, some of the sulfur is plant-available in the application year, but there is no indication that residual sulfur mineralizes more readily than the bulk of soil organic sulfur. For crops with a short growing season, mineralization of residual and soil organic sulfur may not be in synchrony with the demand and may even lead to increased leaching losses of sulfate on freely draining soils with high winter rainfall; although, some catch crops have demonstrated an ability to reduce sulfate leaching and increase synchrony with crop demand. The transient nature of plant-available sulfur makes soil sulfur testing a difficult task and often sulfur balance considerations provide a better background for fertilizer sulfur recommendations, keeping in mind that availability and synchrony is ignored using this approach.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2008. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, 5585 Guilford Road, Madison, WI 53711-5801, USA. Sulfur: A Missing Link between Soils, Crops, and Nutrition. Agronomy Monograph 50.