Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109708
07/10/97
Potato Fertilizer Recommendations Extension Bulletin E-2220, April 1990
Maurice L. Vitosh Extension Soil Specialist Department of Crop and Soil Sciences
Magnesium
Magnesium (Mg) deficiency is most likely to occur on acid, sandy soils or soils that have been limed with calcitic lime or marl. Potatoes are quite responsive to Mg, and growers should pay more attention to Mg soil test levels. Magnesium can also get out of balance with K Over-fertilization with K fertilizer can create a Mg deficiency.
The MSU fertilizer recommendation program uses three criteria to determine when to recommend Mg on mineral soils: (1) if the soil test level is below 75 lb per acre; (2) if K exceeds Mg (calculated as a percentage of the total exchangeable bases as indicated on your soil test); and, (3) if Mg represents less than 3 percent of the total exchangeable bases. When any of the three criteria indicates a need for Mg, you must then examine your soil's lime requirement. When lime is needed, the recommendation is to use dolomitic limestone to provide Mg. When no lime is called for, the recommendation is to use 50 to 100 lb of soluble Mg per acre broadcast or 10 to 20 lb per acre in the row at planting Magnesium sulfate (epsom salts), potassium-magnesium sulfate (Sul-Po-Mag or K-Mag), and finely ground magnesium oxide are all satisfactory Mg sources.
Magnesium may also be applied as a foliar spray, but soil applications are preferred to give season-long uptake. Suggested foliar rates per acre are 10 to 20 lb of magnesium sulfate in at least 30 gallons of water. Introduction
Nutrient Management to Protect Water Quality Extension Bulletin WQ-25, January 1996
Maurice L. Vitosh and Lee W. Jacobs Extension Soil Specialists Department of Crop and Soil Sciences Michigan State University
Considerable national attention is being given to nitrate nitrogen (N) contamination of groundwater and phosphorus (P) contamination of surface water. The source of this contamination is non-point in nature, meaning that it cannot be specifically identified. Agricultural practices, however, have been implicated as causing much of the non-point source contamination.
Water is the most common ingredient in all natural processes and is the medium for movement of nutrients away from the land surface. It is constantly being recycled from water surfaces and through plants to the atmosphere by evapotranspiration and back again to the earth's surface as precipitation to produce stream flow and groundwater flow on and within our land surface. As water moves through this cycle, it dissolves nutrients from soil minerals, crop residues, fertilizers, manures and other materials. Thus nutrients, like water, have their own natural cycle.
The earth contains an abundant supply of plant nutrients, but not all agricultural soils contain adequate nutrients for intensive crop production, particularly N. P and potassium (K). Fertilizers, manures and other organic materials are required to supplement nutrients supplied by the soil. All nutrients, whether they are synthetic or naturally occurring, can become mixed with surface water or groundwater by natural processes such as runoff and leaching. Therefore, proper management of all nutrients is crucial to protect surface and groundwater quality.
Managing the amount, form, placement and timing of nutrient applications is the only realistic and practical approach to minimizing the risk of surface and groundwater contamination. Education and demonstration programs are urgently needed to help producers become more aware of potential environmental problems and to get them to adopt best management practices. Other less desirable alternatives include legislative action and enforcement.
Crop producers need to develop a "whole-farm" nutrient management plan for their farms. They need to look at the entire farm operation, not just one field at a time. To develop a whole-farm nutrient plan, they should ask a number of questions: What nutrient inputs exist on the farm? Is the farm operation utilizing these inputs to their fullest potential? Where might the operation be overloading the nutrient cycle? What practices need more attention?
Crop producers should also understand how nutrient availability fluctuates from year to year. Nitrogen availability can fluctuate very rapidly and is greatly affected by seasonal weather conditions, whereas phosphorus availability fluctuates very little from year to year because it is largely controlled by soil pH, organic matter and insoluble forms of soil phosphorus. Potassium availability can fluctuate from season to season, depending on crop removal and the ability of the soil to supply potassium. Understanding how nutrient availabilities change with time can help crop producers do a better job of managing fertilizer nutrients.
The following management practices will help protect water quality. Crop producers are encouraged to follow as many of these practices as possible.