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1.This document is HS 743 (formerly Notes in Soil Science No. 32), one of a series by the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. D ate first printed: January, 1989. Revised: August, 1998. Please visit the FAIRS Web site at http://hammock.ifas.ufl.edu .The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide resea rch, educational information and other services only to individuals and institutions that function wit hout regard to race, color, sex, age, handicap, or national ori gin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of F ood and Agricultural Sciences / University of Florida / Christine Taylor Waddill, Dean2.G.J. Hochmuth, professor, Horticultural Sciences Department; and E.A. Hanlon, professor and center dir ector, SWFRECImmokalee, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.HS 743Calculating Fertilizer Rates for Vegetable Crops Grown in Raised-Bed Cultural Systems in Florida1 G. J. Hochmuth and E. A. Hanlon2Most people involved in agriculture recognize theregardless of the cultural practices such as bed spacing. term pounds per acre (lb/A) as a rate. This method ofThe purpose of this paper is to discuss an alternate expressing nutrient additions to the soil in order toexpression of fertilizer rates for several raised-bed obtain a positive crop response is the form in whichcropping systems used in Florida. most fertilizer recommendations are made. The University of Florida, Institute of Food and Agricultural Sciences Extension fertilizer recommendations are reported in terms of lb/A. The recommended fertilizer supplements the nutrition supplied from the soil, satisfying the nutrient requirement of the crop for that specific nutrient. This unit (lb/A) describes a weight (pounds) applied over a surface area (acre). The term was originally used to describe the process of applying an amendment over the entire surface of a field, a so-called broadcast application. The terminology is still used in modern agriculture to describe fertilizer rates. Exact placement of the fertilizer, either broadcast or band, is based upon IFAS research with each crop and is a necessary part of the fertilizer recommendation. However, confusion exists when the cropped portion of an acre is less than the complete acre; for example in production systems where a drainage ditch is used between one or more cropped polyethylene-mulched beds. In such a system, both the fertilizer and most of the root system are confined in the volume of soil forming the bed. Additional root confinement exists when subsurface irrigation is used in conjunction with the above cultural practice. When fertilizing vegetables, it is important to provide the correct concentration of fertilizer in the soilDefinitions of TermsReal-estate acre: Farm land (land area) that occupies an area of 43,560 sq ft. This term may also be called a "gross acre" and refers to the land area including all of the cropped land plus the land used for access roads and irrigation/drainage ditches.Cropped area: The portion of the real-estate acre used solely for crop production. Alternately, the cropped area is the land surface remaining after uncropped land, such as access roads and ditches, has been subtracted from the real-estate acre. If the entire acre is used for crop production, then the cropped area is equal to a real-estate acre. Otherwise, the cropped area is less than a real-estate acre.Linear bed foot: A linear distance of 1 ft measured along the planting bed. This term is abbreviated as "LBF." The total number of feet of bed in a planting system that are in the cropped area of the real-estate acre is expressed as linear bed feet per real-estate acre (LBF/A).
Calculatin g Fertilizer Rates for Ve g etable Crops Grown in Raised-Bed Cultural Systems in Florida Pa g e 2Au g ust 1998Using the LBF System with IFAS Standardized Fertilizer RecommendationsThe IFAS Extension Soil Testing Laboratory (ESTL) employs the IFAS Standardized Fertilizer Recommendation System, in which all recommendations are expressed in lb/A. These fertilizer rates are based on typical distances between bed centers for each crop (Table 1). Table 1 also indicates the typical number of planting rows within each bed. Conversions of fertilizer rates from lb/A to lb/100 LBF, based upon these typical bed spacings, are shown in Table 2. Use of lb/100 LBF as a fertilizer rate assures that an appropriate rate of fertilizer is applied, regardless of the total number of LBF in the cropped area. In other words, use of lb/A to express the fertilizer rate requires an adjustment based upon actual cropped area. In reality, the goal is to provide a specific concentration of nutrients to plant roots; that is, a specific amount of fertilizer within a certain volume of soil. This conceptual approach makes sense because most plant roots are largely confined within the volume of soil comprising the bed, especially under the polyethylene in the full-bed mulch system.The use of Table 2: To make correct use of Table 2, the Typical Bed Spacing from Table 1 must be used, even if this value differs from the growers actual bed spacing. For example, the typical bed spacing for eggplant is 6 ft, and the IFAS-recommended nitrogen fertilizer rate is 160 lb/A. Locate the column labeled lb/A . Locate the row labeled under Typical Bed Spacing (fourth row from the top). Reading across the row and down the column, the IFAS-recommended fertilizer rate, expressed in lb/100 LBF, is 2.2 lb N/100 LBF. If the crop is tomato, the Typical Bed Spacing is 6 ft, and the N fertilizer recommendation is 175 lb/A. In this example, there is no column specifically for 175 lb/A. Therefore, the reader needs to read across the row for 6 ft Typical Bed Spacing and add together two values: 1.05 for 75 lb/A in column 6 and 1.38 for 100 lb/A in column 8 to get 2.43 lb N/100 LBF. In the tomato example above, if the grower's actual spacing were 8 ft, the grower should still apply 2.43 lb N/100 LBF to provide adequate, but not excessive, nutrient concentration within the bed. If Table 2 were mistakenly used with an 8 ft bed spacing, the result would be 3.22 lb N/100 LBFa rate that is 30% more fertilizer than the recommended 2.43 lb N/100 LBF and would not increase yield.Calculating Fertilizer Rates in Selected Planting SystemsThe following three examples of common planting systems used in Florida illustrate the use of Table 1 and Table 2. In each of the examples, the specified crop is tomato, and the IFAS-recommended fertilizer rate is 175 lb N/A. If the examples do not address a particular planting pattern of interest to the reader, the same procedures demonstrated here can be used to tailor results to specific cultural practices and crops.Example 1Ruskin RegionA typical diagram of this planting system is shown in Figure 1. Using Table 1, we find that the typical bed spacing for tomatoes in Florida is 6 ft. The alternating pattern of bed and ditch used in the Ruskin region results in good drainage control to handle excessive precipitation. However, the 12 ft spacing between bed centers results in much less land actually in production (reduced cropped area) than for the typical bed spacing of 6 ft.Table 1. Typical bed spacin g s for ve g etables g rown in Florida Ve g etable Spacin g (ft)per bedVe g etable Spacin g (ft)per bed TypicalRows of PlantsTypicalRows of Plants Broccoli62Muskmelon51 Cabba g e 6 2Pepper 6 2 Cauliflower 6 2Summer squash 6 2 Cucumber 6 2Strawberry 4 2 E gg plant 6 1Tomato 6 1 Lettuce 4 2Watermelon 8 1 *Spacin g from the center of one bed to the center of an adjacent bed.
Calculatin g Fertilizer Rates for Ve g etable Crops Grown in Raised-Bed Cultural Systems in Florida Pa g e 3Au g ust 1998From Table 2, using the typical bed spacing of 6 ft and the recommended fertilizer rate of 175 lb N/A, we find that 2.43 lb N/100 LBF is the recommended rate. It is important to use this fertilizer rate, even though the bed centers in this example are spaced 12 ft apart (Figure 1).Example 2Gadsden County RegionFigure 2 indicates that in a typical Gadsden County tomato field there are groups of six beds, each on 6 ft centers and separated by an access road approximately 12 feet wide. This repeating-pattern cropping system (including the access road) uses less than the entire real-estate acre. The recommended fertilizer rate for this example is 2.43 lb N/100 LBFthe same rate as for example 1! The typical bed spacing of 6 ft (Table 1) and the recommended fertilizer rate of 175 lb N/A have not changed. This bed pattern uses more of the real-estate acre for crop production than does the previous example, but the cropped area is still only 70% of the real-estate acre.Example 3Immokalee, Naples and Palm Beach RegionsA typical planting pattern in the Immokalee, Naples and Palm Beach areas is shown in Figure 3. Because neither the typical bed spacing of 6 ft for tomatoes nor the recommended fertilizer rate of 175 lb N/A have changed, 2.43 lb N/100 LBF is still the recommended rate. The cropped area of this planting pattern is 75% of the real-estate acre.SummaryExpression of fertilizer rates in units of lb/100 LBF results in a fertilizer rate that is independent of the total number of LBF in a real-estate acre. This method supplies nutrient concentrations in the bed at recommended levels without risking either underfertilization or overfertilization.Table 2. Conversion of fertilizer rates in lb/A to lb/100 LBF Recommended fertilizer (N, PO, or KO)252Typical -------------------------lb/A ---------------------------------Bed20254050607580100120140160180 Spacin g Resultin g fertilizer rate (N, PO, or KO)252(ft) ------------------------lb/100 LBF ---------------------------126.96.36.1990.360.410.540.550.690.830.961.101.24 188.8.131.520.460.550.690.730.921.101.291.471.65 50.230.290.460.580.690.870.921.151.381.611.842.07 60.280.350.550.700.831.051.101.381.651.932.202.48 80.370.460.730.921.101.381.471.842.202.572.943.31 This table is used correctly by (1) determinin g the typical bed spacin g from Table 1 for the crop; (2) locatin g the column containin g the recommended fertilizer rate in lb/A; and (3) readin g down the column until reachin g the row containin g the typical row spacin g This rate, in lb/100 LBF, should be used even in situations where the g rower's bed spacin g differs from the typical bed spacin g
Calculatin g Fertilizer Rates for Ve g etable Crops Grown in Raised-Bed Cultural Systems in Florida Pa g e 4Au g ust 1998 Figure 1 Sin g le-bed-and-ditch system commonly used in the Ruskin re g ion. The bed top is approximately 3 ft, and bed spacin g is 12 ft. Figure 2 Plantin g system, which includes an access road, used in the Gadsden re g ion. Actual width of bed top is 3 ft with a bed spacin g of 6 ft. Figure 3 Plantin g system used in the Immokalee, Naples, and Palm Beach re g ions. Twelve plantin g beds are combined with both ditchin g and an access road. As before, the bed tops are approximately 3 ft, while the bed spacin g is set at 6 ft.