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. For some people, this may be the only part of the Soil Test Report that they are concerned about. 

The first line of the RECOMMENDATIONS section gives the cropping history. In the Grapes Report it tells you& Crop Before Last: Grapes and Last Crop: Grapes, which tells you that this is an established planting. This is important information for the Soil Testing Laboratory to know, because for perennial crops fertilizer recommendations are different for established plantings than they are for new plantings. In the Vegetables Report it tells you Crop Before Last: Sweet Corn and Last Crop: Cabbage. Cropping history is important in determining nitrogen recommendations when a legume is included in the rotation, because crops like peas, snap beans, alfalfa, and clovers 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 that will be planted in this field: 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 after we go through the lime and fertilizer recommendations for Grapes and Vegetables.

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 row middles. Row/Drill refers to methods of placing fertilizer close to the seed at planting and it is practiced for some nutrients on 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. The term Drill means that fertilizer is applied along with small grain seed as it is planted with a grain drill, which is not relevant to the crops we are discussing here.

The following column is labeled “Lime #ENP/A” and in the Grapes Report 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. For all three vegetable crops no lime is recommended, because the soil pH is already 7.6. ENP stands for Effective Neutralizing Power. Giving the lime recommendation in ENP units provides a uniform way of expressing the lime requirement, because there are a variety of liming materials on the market that differ in their purity, their particle size distribution, and their neutralizing capacity in the soil. 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 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 label. 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 amounts 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 soil test measurement. 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 for this crop row application of phosphate and potash permits the use of lower rates that result in equivalent yields compared to higher rates of broadcast fertilizer. 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 are not lower than broadcast recommendations.

After the primary macronutrients NPK 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 calcium is required.