Livestock Research for Rural Development 3 (1) 1991

Citation of this paper

Forage and soil mineral concentrations over a three-year period in a warm climate region of central Florida. II. Trace minerals

J E Espinoza, L R McDowell, N S Wilkinson, J H Conrad and F G Martin

University of Florida, Gainesville, FL 32611-0691

Florida Agricultural Experiment Station Journal Series No. R-01100

Research supported in part by the US Department of Agriculture under CSRC Special Grant No. 86-CRSR-2-2843 managed by the Caribbean Basin Advisory Group (CBAG)


A three-year study was conducted to determine the trace mineral status of forage (bahiagrass) and soils on a ranch in central Florida. Forage and soil samples were collected twice a year (May and November) for three years. Three composite samples from each of seven pastures were collected each sampling date.

Higher (P<0.01) forage values of Cu, Mn, Mo and Se were found in November. Iron and Zn were higher (P<0.01) in May. In general, higher (P<0.05) trace elements values were found in year 2. Among forage trace minerals, only Mn and Mo were adequate. Concentrations below the critical level were found for forage Co, Cu, Fe, Se and Zn in both seasons in all years.

All soil trace elements were higher (P<0.01) in year 3. Only Cu was higher (P<0.05) in November. Concentrations below critical levels were found for soil Cu in both seasons of year 2 and in May of year 1 and for Mn in both seasons in all years.

KEY WORDS: Trace minerals, forages, protein, deficiency, cattle


Mineral status of soils and forage influence mineral status of grazing livestock, but many other animal factors and mineral interactions also play an important role (Towers and Clark 1983). Grazing livestock have to depend largely upon forages to fulfil their mineral requirements. Forage can rarely satisfy completely the needs for each mineral (McDowell 1977). Mineral composition of forage plants is affected by soil-plant factors, including pH, drainage, fertilization, forage species, forage maturity and interaction among minerals (Gomide 1978; Reid and Hovarth 1980). Soils of subtropical Florida are dominated by Spodosols and Entisols. Most soils in Florida are acid, infertile and sandy in texture (Fiskell and Zelazny 1972). Native Florida pastures have been reported to be low in dry matter yield and to be deficient in some plant nutrients. From Florida, Becker et al (1965) reported that nutritional anaemia or "salt sick" disease in cattle was caused by a Cu, Co and Fe deficiency.

The historical significance of mineral deficiencies and toxicities in the Florida cattle industry has been summarized by Cunha et al (1964) and Becker et al (1965).

The purpose of this study was to evaluate forage and soil trace mineral concentrations over a three-year period in central Florida.

Experimental procedure

An experiment was conducted for three years at Deseret Ranches in Florida. Three herds of crossbred beef cattle (1/4 to 3/8 Brahman crossed to British breeds) were assigned to three treatments of different levels of P supplementation. Pasture fertilization and management and collection procedures for soils and forages are described in the companion paper (Espinoza et al 1990).

Forage and soil samples were collected at the same month and at the same site. The main improved tropical forage species that were collected in all pastures in which the experimental animals grazed was bahiagrass (Paspalum notatum Flugge). To a lesser (less than 5% of total) extent, all pastures were associated with native grasses and legumes. A total of 126 of both forage and soil samples were collected during the three-year period (21 samples per month).

Soil samples were analyzed for Cu, Fe, Mn and Zn according to standardized procedures (Rhue and Kidder 1983). Minerals were extracted from soil using Mechlich I extracting solution method (.05 N HCl + .025 N sulphuric acid). Soil mineral concentrations were then determined by Inductively Couple Argon Plasma (ICAP) in a Thermo Jarrel Ash, Model 9000 (Jarrel-Ash Division 1982).

Forage samples were processed according to methods of Fick et al (1979) and were analyzed for Cu, Fe, Mn and Zn by atomic absorption spectrophotometry (Perkin-Elmer Corp. 1980). Cobalt and Mo were determined by flameless atomic absorption spectrophotometry (Perkin-Elmer Corp. 1984) and Se by a modified fluorometric technique (Whetter and Ullrey 1878). Sulfur concentration was determined using LECO model S-132 S analyzer, Warrendale, Penn. Reference material (e.g., tomato leaves) from the National Bureau of Standards (NBS) was included as an internal standard with all forage samples analyzed for trace mineral content.

Data obtained in the present study were statistically analyzed using a 3 (years) by 2 (seasons) factorial design (Snedecor and Cochran 1980) using the General Linear Models (GLM) procedure of the SAS System (SAS Institute Inc. 1987).

Results and discussion


Year differences (P<0.01) were observed for all soil trace mineral concentrations in both May and November (Table 1). Month differences (P<0.05) were observed only for Cu in year 1, with November highest. Month X year interaction (P<0.05) was observed only for Cu.

Among years, year 3 showed highest (P<0.01) Cu concentrations in May. Mean soil Cu values below critical level of 0.3 ppm (Rhue and Kidder 1983) were observed in May of year 1 and in May and November of year 2. Higher values (0.3 ppm to 0.7 ppm) of soil Cu were reported (Mooso 1982) from the same area. Soils with less than 0.6 ppm of extractable Cu are considered deficient for pastures and crops (Horowitz and Dantas 1973).

Among years, soil Fe concentration was higher (P<0.01) in year 3 during May. No month differences (P>0.05) were observed in soil Fe for any of the years. Mean Fe values were generally high compared to the critical level of 2.5 ppm (Viets and Lindsay 1973) for Florida soils. Higher soil Fe values (6 ppm) were reported by Mooso (1982). Merkel et al (1990) from north central Florida reported 14.3 ppm as mean Fe content in soils.

Table 1: Soil trace mineral concentration as related to season and year
Variable Month Year 1 Year 2 Year 3 SE
Cu, ppm May 0.089** **** 0.095** 0.337* 0.053
  Nov 0.350* *** 0.128** 0.354* 0.053
Fe, ppm May 6.09** 5.58** 10.15* 1.34
  Nov 5.77* ** 3.52** 8.70* 1.34
Mn, ppm May 0.88** 1.82** 3.22* 0.47
  Nov 1.02** 2.67* 3.40* 0.47
Zn, ppm May 0.70** 1.24** 4.37* 0.6
  Nov 0.77** 2.01** 4.42* 0.6


Least square means are based on 21 samples per month with two months per year for three years;
SE = standard error of the least square mean;
*, ** Means among years for the same month with different superscripts differ P<0.01;
***, **** Means between seasons for the same year with different superscript differ P<0.05;


Among years, higher (P<0.01) soil manganese was found in year 3 in May. In November, year 3 was higher (P<0.01) than year 1 but similar (P>0.05) to year 2. Mean soil Mn values observed were below the critical level of 5 ppm (Rhue and Kidder 1983). Mooso (1982) also reported low values ranging from 0.9 ppm to 2.2 ppm Mn in soils of the same area. Even though soil Mn was low, it apparently was adequate since forage concentrations of the mineral were adequate (i.e., 39 ppm to 66 ppm). Manganese availability is affected by soil acidity, with Mn more available for pH values around 4.0 (Leeper 1947). Also, higher concentrations of organic matter result in increased Mn solubility.

Year 3 had higher (P<0.01) soil Zn content in both months. Mean soil Zn values below the critical level of 1.5 ppm (Sanchez 1976) for normal plant growth were found in May and November during year 1 and in May in year 2. Previous studies on the same ranch (Mooso 1982) showed soil values ranging from 0.7 to 2.2 ppm of Zn.


Mean forage trace mineral concentrations for May and November of the three years are presented in Table 2. No year effect (P>0.05) was observed on forage trace mineral concentrations, except for Cu (P<0.05), iron (P<0.05) and molybdenum (P<01). Month differences (P>.05) were observed for iron, molybdenum and zinc. Year X month interactions (P<0.05) was observed in all forage trace mineral concentrations observed.

Table 2: Forage trace minerals related to season and year (dry basis)
Variable Month Year 1 Year 2 Year 3 SE
Co, ppm May 0.05 0.07 0.03 0.01
  Nov 0.05 0.04 0.07 0.01
Cu, ppm May 2.8** 3.6* 4.2* 0.4
  Nov 4.4* 2.9** 4.2* 0.4
Fe, ppm May 42.6** **** 49.1* **** 42.0** ***** 1.7
  Nov 37.3** ***** 36.6** ***** 47.6* **** 1.7
Mn, ppm May 48.4 60.2 38.6 6.2
  Nov 54.6 55.8 66.0 6.2
Mo, ppm May 0.42 0.57 0.48***** 0.2
  Nov 0.29*** 0.84** 3.63* **** 0.2
Se, ppm May 0.07 0.05***** 0.06 0.007
  Nov 0.07 0.09**** 0.07 0.007
Zn, ppm May 17.7 20.6**** 22.2**** 1.8
  Nov 16.6 13.8***** 11.0***** 1.8


Least square means are based on 21 samples per month;
*, **, *** Means among years for the same month (P<0.05);
****, ***** Means between months (P<0.01)


Mean forage Co concentrations were all below the NRC (1984) requirement of 0.1 ppm. Cobalt concentrations ranging from 0.09 ppm to 0.11 ppm in four regions of Florida were reported by McDowell et al (1982). Low concentrations of Co also were reported by Merkel et al (1990) for the northern central region of Florida. There are factors that interfere with Co absorption by ruminants; Grace (1983), cited by Mayland et al (1987), indicated that Mn and Fe reduce Co absorption. McDowell et al (1984) reported that, with the exception of P and Cu, Co deficiency is most often the limiting element for grazing livestock in tropical areas.

Mean forage Cu concentrations were lower (P<0.05) during May in year 1 and during November in year 2. Forage Cu values were all below the critical level of 8 ppm (Jones 1972). Similar values (3.4 ppm to 5.2 ppm) were reported by Merkel et al (1990) from the north central part of Florida. McDowell et al (1982) reported higher values varying from 22.3 to 51.5 for the dry and wet season, respectively. High concentrations of Mo and S interfere with Cu absorption. A Cu-Mo ratio in herbage of 2.0 or greater is desirable to avoid molybdenosis (Ward 1978).

Forage Mo concentrations were different (P<0.05) among years in November but not in May. Month difference was observed only in year 3, with the November collection highest (P<0.01). Mean Mo values were all below the toxic level of 6 ppm suggested by McDowell (1985). Similar values were reported from Florida by McDowell et al (1982) and Merkel et al (1990). The critical Cu-Mo ratio of 2 or less (Ward 1978) was reached during November in year 3.

Forage Fe concentrations varied (P<0.05) among years in both months. All mean forage Fe concentrations observed were below the critical level of 50 ppm (Jones (1972). McDowell et al (1982) reported mean values ranging from 127 ppm to 130 ppm for the winter and fall seasons, respectively. Similar normal values also were reported by Merkel et al (1990). Iron deficiency is rare in grazing cattle due to a generally adequate content in forages (McDowell et al 1984). However, under Florida conditions, Fe deficiency in cattle grazing on sandy soils has been reported (Becker et al 1965).

Forage Mn levels were similar (P>0.05) among years and between months (P>0.05). All Mn values, except that of May in year 3, were adequate according to the critical value of 40 ppm (McDowell 1985). Under Florida conditions, higher concentrations of Mn in forage were reported by McDowell et al (1982) and Merkel et al (1990).

Forage Se values among years were similar (P>0.05) in both months. Month differences were observed only in year 2, with higher (P<0.01) concentrations in November. All mean forage Se values were below the critical level of 0.2 ppm (NRC 1984). Similar low values also were reported for the same general area by McDowell et al (1982) and Merkel et al (1990). In some areas, cattle can grow normally on pastures containing 0.03 ppm of Se (Mayland et al 1987).

Forage Zn concentrations were similar (P>0.05) among years in both months. Month differences were found only in years 2 and 3 with higher (P<0.01) Zn concentration in May. Mean forage Zn concentrations found were below 25 ppm suggested as a critical level (Mayland et al 1980). Previous studies in the same area (Mooso 1982) indicate that bahiagrass Zn concentrations vary from 17.3 ppm to 27.6 ppm. Zinc concentrations may be as high as 30 ppm and occasionally higher, but this concentration declines rapidly as plants mature and levels can decrease to less than 15 ppm (Mayland et al 1987).


Becker R B, Henderson J R and Leighty R B 1965 Mineral malnutrition in cattle. Florida Agricultural Experiment Station Bulletin 699.

Cunha T J, Shirley R L, Chapman H L, Ammerman C B, Davis G K, Kirk W G and Hentges J F 1964 Minerals for beef cattle in Florida. Florida Agricultural Experiment Station Bulletin 683. University of Florida, Gainesville

Espinoza J E, McDowell L R, Wilkinson N S, Conrad J H and Martin F G 1990 Forage and soil mineral concentrations over a three-year period in a warm climate region of central Florida: I Macrominerals. Livestock Research for Rural Development (submitted)

Fick K R, McDowell L R, Miles P H, Wilkinson N S, Funk J D and Conrad J H 1979 Methods of Mineral Analysis for Plant and Animal Tissues (2nd edition) Animal Science Department, University of Florida, Gainesville

Fiskell J G A and Zelazny L W 1972 Acid properties of some Florida soils: I. pH-dependent cation exchange. Soil and Crop Science Society of Florida Proceedings 31:145

Gomide J A 1978 Mineral composition of grasses and tropical leguminous forage. In: Latin American Symposium on Mineral Nutrition with Grazing Ruminants (Editors: J H Conrad and L R McDowell) University of Florida, Gainesville pp32-40

Grace N D, Ulyatt M J and MacRae J C 1974 Quantitative digestion of fresh herbage by sheep: 3. Movement of Mg, Ca, P, K and Na in digestive tract. Journal of Agricultural Science 82:321

Horowitz A and Dantas H S 1973 The geochemistry of minor elements in Pernambuco soils: III. Copper in the zone Litoral. Pesquisa Agropecuaria Brasileira 8:169

Jarrel-Ash Division 1982 Jarrel-Ash ICAP-9000 Plasma Spectrophotometer Operator's Manual. Jarrel-Ash Division, Fisher Scientific Co., Franklin, Massachusetts

Leeper G W 1947 The forms and reactions of manganese in soils. Soil Science 63:79

Mayland H F, Kramer T R and Johnson W T 1987 Trace elements in the nutrition and immunological response of grazing livestock. In: Grazing Livestock Nutrition Conference proceedings. University of Wyoming, Jackson, Wyoming

Mayland H F, Rosenau R C and Florence A R 1980 Grazing cow and calf responses to zinc supplementation. Journal of Animal Science 51:96

McDowell L R 1976 Mineral deficiencies and toxicities and their effect on beef production in developing countries. In: Beef Cattle Production in Developing Countries (Editor: A J Smith) University of Edinburgh, Centre for Tropical Veterinary Medicine pp216-241

McDowell L R 1977 Geographical distribution of nutritional diseases in animals. Animal Science Department, University of Florida, Gainesville

McDowell L R 1985 Calcium, phosphorus and fluorine. In: Nutrition of Grazing Ruminants in Warm Climates (Editor: L R McDowell) Academic Press, Orlando, Florida pp189-212

McDowell L R, Conrad J H and Ellis G L 1984 Mineral deficiencies and imbalances and their diagnosis. In: Symposium on Herbivore Nutrition in Subtropics and Tropics (Editors: F M C Gilchrist and R I Mackie) University of Pretoria, South Africa pp67-88

McDowell L R, Kiatoko M, Bertrand J E, Chapman H L, Pate F M, Martin F G and Conrad J H 1982 Evaluating the nutritional status of beef cattle from four soil order regions of Florida: II. Trace minerals. Journal of Animal Science 55:38-47

Merkel R C, McDowell L R, Popenoe H L and Wilkinson N S 1990 Mineral status comparisons between water buffalo and Charolais cattle in Florida. Buffalo Journal 1:33

Mooso G D 1982 Warm-season grass production and nutritive uptake with liquid and solid N-P-K fertilizers. M.S. Thesis, Brigham Young University

NRC 1984 Nutrient requirements of domestic animals (No. 4). Nutrient Requirement of Beef Cattle (6th revised edition). National Academy of Sciences, National Research Council, Washington, DC

Perkin-Elmer Corp 1980 Analytical Methods for Atomic Absorption Spectrophotometry. Author, Norwalk, Connecticut

Perkin-Elmer Corp 1984 Analytical Methods for Furnace Atomic Absorption Spectrometry. Perkin-Elmer, Norwalk, Connecticut

Reid R L and Horvath D J 1980 Soil chemistry and mineral problems in farm livestock: a review. Animal Feed Science and Technology 5:95

Rhue E D and G Kidder 1983 Analytical procedures used by the IFAS extension soil testing laboratory and the interpretation of results. Soil Science Department, University of Florida, Gainesville

Sanchez P A 1976 Properties and management of soils in the tropics. John Wiley and Sons, New York

SAS Institute Inc 1987 SAS/STAT Guide for Personal Computers (Version 6 edition) SAS Institute Inc., Cary, North Carolina

Snedecor J W and Cochran W G 1980 Statistical Methods (7th edition) The Iowa State University Press, Ames

Towers N R and Clark R G 1983 Factors in diagnosing mineral deficiencies. In: The mineral requirements of grazing ruminants. Occasional publication No 9, New Zealand Society of Animal Production

Viets F G and Lindsay W L 1973 Testing soil for zinc, copper, manganese and iron. In: Soil Testing and Plant Analysis (Editors: L M Walsh and J Beaton) Soil Science Society of America Inc., Madison, Wisconsin pp153-172

Ward G M 1978 Molybdenum toxicity and hypocuprosis in ruminants: A review. Journal of Animal Science 46:1078

Whetter P A and Ullrey D E 1978 Improved fluorometric method for determining selenium. Journal of the Association of Analytical Chemistry 61:927


(Received 30 October 1990)