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Fluid Journal : Early Spring 2012
Early Spring 2012 The Fluid Journal 10 • Continued losses through leaching and erosion of topsoil. Consequently, S has emerged as a major limiting factor in many cropping systems (Figures 1a and b). Behavior. Sulfur behaves similarly to N in the soil. It is readily mobile and becomes plant available through mineralization of organic matter. Sulfur mineralization rates are highest when soil water content is greater than 60 percent of field capacity, and soil temperature is in the range of 68° to 104°F. Under optimum soil temperature and moisture conditions, a significant amount of sulfate can be mineralized in a short period of time. Sulfate concentrations are usually lowest in the early spring due to leaching and slow mineralization rates. Sulfur distribution varies with landscape position. Sulfur deficiencies are most often observed on hilltop and side slope positions, especially on eroded, coarse- textured soils. Deficiencies are less common in lower landscape positions Summary: Sulfur (S) is a critical nutrient for crops, particularly canola, pulses, and forage legumes, such as alfalfa. Management of S fertility offers much flexibility, with the availability of several sources. Timing and placement of S can be managed to effectively provide the S needed by the crop. If a deficiency exists and a response is required during the growing season after application, a sulfate source should be used to ensure that S deficiency does not limit yield potential. Elemental sources may have a role in long-term rotational planning. Fertilizer management, however, is only one part of a management system designed to optimize the overall efficiency and profitability of a farming operation. By balancing fertilizer management with the various economic, logistic, and personal considerations in the entire production system, decisions can be made that fit the individual farm. It is a critical nutrient for crops as part of an overall management system. Don’t Overlook Sulfur In Crop Management The Fluid Journal • Ofﬁcial Journal of the Fluid Fertilizer Foundation • Early Spring 2012 • Vol. 20, No. 2, Issue# 76 Drs. Cynthia Grant and John Kovar Sulfur is an essential plant nutrient. It is required by plants in amounts similar to phosphorus (P). Thus, it is grouped with nitrogen (N), potassium (K), and P as the fourth major plant nutrient. Plants lacking essential nutrients have poor growth, low yield, and inferior quality. In plants and animals, S functions like N in that it becomes part of their structure. As a component of amino acids, S is important in protein synthesis, both for protein quality and quantity. It is also involved in N metabolism, photosynthesis, and in the synthesis of oils in oilseed crops, such as canola. Sulfur deficiencies are becoming more prevalent due to: • Decreasing aerial deposition of S as a result of clean air legislation • An increase in the use of high analysis fertilizers with little S • Decreased use of S-containing pesticides • Greater S removals with ever- increasing crop yields with medium- to heavy-textured soils high in organic matter. It is not unusual to find both high soil S concentrations and plant S deficiencies in the same field. Deficiency symptoms. Sulfur deficiency symptoms include reduced plant growth and chlorosis of the younger leaves, beginning with interveinal yellowing that gradually spreads over the entire leaf area. Sulfur is relatively immobile in the plant, so deficiency symptoms tend to occur first in younger leaves. As the deficiency becomes more severe, leaf cupping and a more erect leaf structure are often observed, especially in canola. Plants are small, grow slowly, and maturity may be delayed. Plants may flower, but have reduced seed set as is the case for canola, lentils, and alfalfa. Under mild to moderate S deficiency, visual symptoms may not always be a reliable indicator. Photos of S deficiency symptoms are available from many sources, including printed works and online sources. +S -S Figure 1a: Sulfur fertilizer response in corn.
Late Spring 2012