Sulfur Nutrition and Food Security

Abstract

Food security is an issue that will continue to challenge agricultural production and the distribution of produce. While access to food has improved in the past couple of years the challenges of a changing climate, urbanization, and resource security will require attention to improving productivity within the current land resource. Fertilizers enable half the world's food to be produced. Sulfur is important as an essential plant nutrient that assists with both the quantity and the quality of a range of plant products. It is also critical for animal nutrition. In crops, nitrogen and sulfur nutrition are closely tied and changes in N/S ratio can result in changes in grain quality. This balance, along with the role of nitrogen and phosphorus, indicate that sulfur is a key part of a balanced plant nutrition program to meet future food security. Grains represent the major depletion of sulfur in a national sulfur audit, followed by livestock, and a national audit suggests an annual sulfur removal of 0.4 kg S ha(-1), similar to an audit from 1995. This is balanced by the input of sulfur containing fertilizer as well as the use of agricultural gypsum and manures and inputs from sulfur in irrigation water and the atmosphere. Much of the sulfur in soils is present in organic matter, which must be mineralized before plants can access it. Sulfate ions remain in soil solution and are readily leached, and with changing farming systems, the number of sulfur deficient soils is increasing. As a result, there has been a steady increase in the demand for sulfur for crop nutrition. There is a global supply of around 50 Mt of sulfur, with nearly all recovered from S-rich oil and gas with a growth of around 5% per annum predicted. 85% of sulfur is used for sulfuric acid production including the manufacture of a range of sulfur containing fertilizers such as ammonium sulfate and single superphosphate, although newer sulfur fortified products are entering the market. Attention to using the appropriate source of sulfur at the right rate and at the right time and place will be key strategies to help with sustainable food production now and in the future.