Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109711
07/10/97
Potato Fertilizer Recommendations Extension Bulletin E-2220, April 1990
Maurice L. Vitosh Extension Soil Specialist Department of Crop and Soil Sciences Manganese Recommendations
Manganese (Mn) deficiency in potatoes is most often associated with the lake-bed and organic soils of Michigan. The availability of Mn is largely determined by the soil pH. Therefore, Mn fertilizer applications should be based on soil pH and a Mn soil test. Manganese deficiency does not occur in mineral soils unless the soil pH is above 6.2. On organic soils, Mn deficiency is seldom found unless the soil pH is above 5.8. One ppm of 0.1 N HCl extractable Mn is normally sufficient for potatoes grown on acid sandy soils (soil pH). (See Table 5 for Mn recommendations based on the soil pH and Mn soil test level for mineral and organic soils.) As the soil pH increases, Mn availability rapidly decreases. Thus, higher soil test levels are needed at higher soil pH's to prevent a deficiency. Likewise, more Mn fertilizer is recommended at higher pH levels for a given Mn soil test level. ==================================================== Table 5. Manganese fertilizer recommendations for potatoes.
MINERAL SOILS
Soil test Soil pH
---------------------
6.0 6.5 7.0 7.5
---------------------------------
ppm lb Mn/acre
---------------------------------
4 0 3 6 9
8 0 0 4 8
12 0 0 3 6
16 0 0 0 5
20 0 0 0 3
24 0 0 0 2
28 0 0 0 0
ORGANIC SOILS
Soil test Soil pH
---------------------
5.8 6.2 6.6 7.0
---------------------------------
ppm lb Mn/acre
---------------------------------
4 0 5 8 11
8 0 3 7 10
12 0 2 6 9
16 0 0 4 8
20 0 0 3 6
24 0 0 2 5
28 0 0 0 4
32 0 0 0 3
36 0 0 0 2
40 0 0 0 0
====================================================
When Mn is needed, the best placement is in the
starter fertilizer banded at planting time.
Broadcast applications of Mn fertilizer are totally
ineffective. Foliar applications of Mn have been
successfully used to correct Mn deficiencies. Use 1
lb of Mn as manganese sulfate in a foliar
application when the plants are small and 2 lb on
larger plants. Several foliar applications of Mn may
be necessary to adequately correct a severe
deficiency. It is impractical to try to build up
soil test levels of Mn with Mn fertilizers. If Mn
deficiency occurs, it will be necessary to apply Mn
fertilizers every year unless the soil pH drops.
Manganese Fertilizer Sources
Only inorganic sources of Mn are recommended. Manganese chelates are ineffective on organic soils and usually too expensive to be used at the same rate as inorganic sources on mineral soils. They do not have greater availability than inorganic sources. Manganese sulfate is the most common source of Mn fertilizer. Granular manganese oxide is not recommended unless it has been finely ground. Soil Organic Matter, Legume and Manure Credits
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
The contribution of soil organic matter to plant nutrition should be taken into account to make accurate N recommendations. High organic matter soils will need less fertilizer N to obtain the same crop yield because they are capable of mineralizing more N than low organic matter soils. Michigan State University N fertilizer recommendations are based on soils with 0 to 4 percent organic matter. See Table I for suggested N credits for soil organic matter. ==================================================== Table I. Suggested nitrogen credit for various soil organic matter levels.
Soil organic matter Nitrogen credit* ----------------------------------------------- 0-4% - Mineral soils None
4-8% - Mineral soils 20-40 lb N/A >20% - Organic soils 40-80 lb N/A
*Subtract this amount of N from the recommended rate. The amount may be crop and yield dependent. ==================================================== Legumes have long been used in crop production systems to improve the fertility and filth of soils. The N supplied by legumes, which is due to a nitrogen fixation process in root nodules, needs to be credited to subsequent crops as a part of the nutrient management plan. A good stand of alfalfa will release more than 100 pounds of N per acre in the first year after being plowed or renovated. Other legumes, such as soybeans, red clover and sweet clover, also contribute to the available N supply, but the amount is usually less. The amount of credit given for legume N fixation depends on how long the legume has been growing and the density of the legume when killed by herbicide or tillage. See Table II for suggested N credits for previous crops. ==================================================== Table II. Nitrogen credits for corn based on the previous crop.
Previous crop Nitrogen Credit(1)
----------------------------------------------
-lb N/A
Corn and most other crops 0
Soybeans 30
Grass sod/pastures 40
Established forage legume(2) 40-140
40 + 20 * (plants/sq.ft.)
to a maximum of 140
Annual legume cover crop(3) 40
(1)Subtract this mount of N from the recommended rate. (2)Any legume established for more than one year. (3)Any legume or legume-grass mixture that has been established for less than one year. Nitrogen credit may be quite variable, depending on plant species, stand, growing conditions and date of destruction. Where legume growth is heavy following a small grain harvest, N credit may be considerably higher. ==================================================== Manure has long been recognized as a source of plant nutrients. All of the crop nutrient requirements can be met by manure if sufficient amounts are applied, but frequent applications of manure often result in a buildup of residual N and P. Extremely high soil P levels should be avoided, because runoff or erosion from this land can increase the risk of non-point source losses of P to lakes and streams. This leads to growth of unsightly weeds and aquatic plants in the water, increases the biological oxygen demand, and reduces both its recreational value and its ability to support fish and other desirable animals.
When manure or other biological (organic) materials are applied to cropland as nutrient sources, crop producers should follow the Michigan Right-to-Farm generally accepted agricultural and management practices (GAAMP). One set of GAAMP addresses manure management and utilization and a second set discusses nutrient utilization. Recommended practices include analyzing manure (or other organic material) to determine its nutrient content, knowing the rate of application, following fertilizer recommendations, implementing good soil and water conservation practices, and recordkeeping. Application of manure to frozen or snow-covered soils should be avoided or appropriate provisions must be made to ensure that manure is not lost to surface waters by runoff and erosion.