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Fertility Management

Nutrient management planning considers crop nutrient inputs to resemble money budgets. You must know two things:

  • What you have
  • What you need

Determining what you have simply requires using a well-designed soil testing program to determine the current soil fertility status. The absolute number given for P or K per acre is usually not the most important information given on the report. There will be an index value for the mineral nutrients which is very important. These indices are usually very low, low, medium, or high. Some laboratories are beginning to use the term "adequate" to describe the medium or high indices.

An index of high (or sometimes very high) for a nutrient indicates it is very unlikely plants would benefit from the application of additional nutrient. On the other end of the scale, a very low index for soil supplied P or K indicates a growing crop would likely have a measurable response to addition of the nutrient.

What you need is determined by realistic personal assessment of a farming operation. It is not possible to underestimate the value of record-keeping in nutrient management. Yield history and management level should provide a reasonable starting point to project future yields. With realistic yield goals, it is possible, using resources available from farm advisors, to estimate nutrient requirements of any future crop.

It is important to make the difference between nutrient uptake and removal. Plants utilize nutrients throughout their entire system from the roots to the pollen. This is not all removed by crop harvest and remains in the field. As much as 45 percent of some crops' (non-root or tuber crops) biomass actually may be below ground.

Another consideration in nutrient removal is the mode of harvest. For example, most forage crops have substantial quantities of K in the leaves and stems, thus K fertility must be monitored closely when hay is harvested and hauled from the field.

It is impossible to balance crop nutrients inputs and outputs to absolute accuracy, but a "virtual" balance can be calculated. Once this balance is determined, application of either purchased fertilizer or on-farm animal manures should follow best management practices (BMP's).

BMP's are:

  • simple
  • economical
  • common-sense
  • doable
  • proven

It is simple to illustrate these points with one example. When applying chicken litter near a small stream, simply drive far enough away from the water that no litter goes into it. It's a simple practice, it's cheap, it's doable, and it is well-proven that buffer zones of no application reduce off-site movement of nutrients. And it's all common sense.

Soil Fertility Best Management Practices

  • Use soil testing to assess fertility status.
  • Use common-sense, attainable yield goals.
  • Determine nutrient and moisture content of manure.
  • Base nutrient applications (either manures or purchased fertilizer) on crop needs as determined by the soil test.
  • Rotate fields receiving manure to avoid nutrient buildup and maximize nutrient utilization.
  • Use only sufficient fertilizer required for attainable crop yield goals.
  • Incorporate fertilizer and manure when possible.
  • Calibrate all application equipment.
  • Avoid applying fertilizer, or manure, on wet soils to minimize compaction, runoff and leaching/denitrification.
  • Avoid applying fertilizers and manure near streams, ponds, or other water bodies.
  • Use grass filter strips along ditches and waterways to reduce soil erosion, runoff and nutrient losses.
  • Time applications to when nutrients are needed by the crop as possible.
  • Utilize fall cover crops to minimize soil erosion and runoff and to maximize nutrient utilization from manure applications.


Extension Soils/Fertilization publications
Soil Testing for the Farmer
Cotton Fertility
Soybeans -- Liming and Fertilization
Nitrogen in Mississippi Soils
Phosphorus in Mississippi Soils
Managing Animal Wastes
You and Animal Wastes


Other Soil Information

Natural Resources Conservation Service
Land Application of Animal Wastes
American Society of Agronomy
Soil and Water Conservation Society
Conservation Tillage Information Center
National Cotton Council
United Soybean Board
National Corn Growers Association
The International Plant Nutrition Institute
The Fertilizer Institute
Environmental Working Group
Fertilizer Management

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Publication Number: IS372
Publication Number: P1466
Publication Number: IS894
Publication Number: IS0871


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Portrait of Dr. Larry Oldham
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Soil Health, Soil Fertility, Nutrient Management, Soil Conservation and Management, Certified Cr