Recommendations (Horticultural Crops)

The RECOMMENDATIONS section gives you the bottom line: how much fertilizer or lime should you apply for optimum production of your crop.  This may be the only part of the Soil Test Report that some people are concerned about. 

The first line of the RECOMMENDATIONS section gives the cropping history.  The Grapes Report shows Crop Before Last: Grapes and Last Crop: Grapes, which tells you that this is an established planting.  This is important information for making recommendations, because established perennial crop fertilizer recommendations are different than they are for new plantings.  The Vegetables Report shows Crop Before Last: Sweet Corn and Last Crop: Cabbage.  Cropping history is important for making nitrogen recommendations because crops like peas, snap beans, alfalfa, and clover in the rotation will provide some nitrogen for the following crop Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota.

The first box on the left side gives the “Crop and Yield Goal”.  The crop is Grapes, of course, on one report and on the Vegetables Report there are three crops listed: Sweet Corn, Cabbage, and Tomatoes.  For sweet corn, a yield goal of 8 tons/acre is given.  Yield goal is one of the factors used in determining N, P, and K fertilizer rates for some crops such as potatoes, snap beans, and sweet corn.  Recommendations for many other vegetable and fruit crops are based on a single “approximate yield goal”.  These can be found in Nutrient Management for Commercial Fruit & Vegetable Crops in Minnesota.  The “Crop and Yield Goal” box also gives a list of pertinent Comments and Notes following the label Comments.  In the Grapes Report, numbers 3, 18, 24, 50, 53, and 64 are specified.  In the Vegetables Report, numbers 4, 5, and 18 are specified for sweet corn and 18, 50, and 57 for both cabbage and tomatoes. We will discuss these Comments and Notes in the next section.

The next column to the right of “Crop and Yield Goal” is labeled “Method” and gives two application options for the recommendations that follow: “Broadcast” and “Row/Drill”.  Broadcast refers to spreading fertilizer or lime on the surface of the soil.  For annual crops this is done before planting and the fertilizer or lime is incorporated with subsequent tillage.  Shallow incorporation is also possible for some perennial crops that have cultivated inter-row spaces.  Row/Drill refers to methods of placing fertilizer close to the seed at planting as is done for some annual vegetable crops.  Row placement means that fertilizer is placed in a “starter” band that is traditionally about two inches to the side and two inches below the seed.  Drill application means that fertilizer is applied along with small grain seed.  This approach is generally not relevant to the crops we are discussing here.

The following column is labeled “Lime #ENP/A” and in the Grapes example the recommended rate is 2500 pounds of ENP per acre using a broadcast application.  Lime is recommended for grapes because the soil pH is less than 6.0.  ENP stands for Effective Neutralizing Power.  Giving the lime recommendation in units of ENP provides a uniform way of expressing the lime requirement, because there are a variety of liming materials on the market that differ in purity, particle size distribution, and neutralizing capacity.  The analysis on the label of a liming material will tell you the pounds of ENP per ton of the product.  Crops differ in their optimum pH and liming rates differ accordingly.  For Grapes, the lime requirement is designed to raise soil pH to 6.0.  For the three vegetable crops in this example, no lime is recommended because the soil pH is already 7.6.  For more information on liming and liming materials, see the University of Minnesota Extension publications Lime Needs in Minnesota and Liming Materials for Minnesota Soils.

After lime is the “N lb/A” (pounds of nitrogen per acre) column. For Grapes, the nitrogen recommendation is to broadcast 30 lb/acre. On the Vegetables Report the recommendations are: Sweet Corn – 150 lb/acre broadcast, Cabbage – 180 lb/acre broadcast, and Tomatoes – 130 lb/acre broadcast.  The next two columns in the RECOMMENDATIONS section are labeled “P2O5 lb/A” and “K2O lb/A”.  These give the fertilizer recommendations for phosphate and potash. Phosphate (P2O5) and potash (K2O) are the terms and chemical formulas used to express the amount of phosphorus and potassium in fertilizer recommendations.  The phosphate recommendations are 0 lb/acre for Grapes (since the soil test level was very high), 60 lb/acre broadcast or 35 lb/acre in the row for Sweet Corn, 150 lb/acre broadcast for Cabbage, and 150 lb/acre broadcast for Tomatoes.  As described in the RESULTS section, phosphate recommendations for the Vegetables are based on the Olsen Phosphorus test.  Potash recommendations are 100 lb/acre broadcast for Grapes,100 lb/acre broadcast or 40 lb/acre in the row for Sweet Corn, 200 lb/acre broadcast for Cabbage, and 200 lb/acre broadcast for Tomatoes.

The recommendations for Sweet Corn show that Row application of phosphate and potash permits the use of lower rates which will result in equivalent yields compared to higher rates of Broadcast application.  The effectiveness of reduced rates for row application has not been demonstrated for other vegetable crops.  Row applications may be recommended as the most efficient method (such as for phosphate fertilization of potatoes), but recommended rates for row application will not necessarily be lower than broadcast recommendations.

Following the primary macronutrients (N-P-K) are recommendations for secondary macronutrients and micronutrients.  Zinc, calcium, and magnesium were tested for Grapes and no additional nutrients were tested for the Vegetable crops.  Recommendations for Grapes are to broadcast 10 lb Zn/acre and 50 lb Mg/acre.  No additional calcium is required.