Alabama Recommendations for Fertilizing Forage Crops with Secondary Elements and Micronutrients

Introduction

A great deal of soil fertility work has been done in Alabama by Auburn University faculty. This included a number of studies with secondary elements and micronutrients beginning around 1930. Findings from this work included demonstration of the need, at least in some soils or situations, to apply boron to cotton and peanuts, zinc to corn and pecans, molybdenum to soybeans, and iron to certain ornamentals and lawn grasses (Wear, 1976).

However, surprisingly little reference data exists regarding forage fertilization work with secondary elements and micronutrients. Part of the reason is that the primary focus of soil fertility and soil test calibration work within the state has been on row crops. This was a reflection of much more producer interest through the years in fertilization studies with row crops because many producers have tended to see forage as a resource which livestock could scavenge from non-arable land. In many cases they were not much inclined to apply fertilizer containing even the major nutrient elements to such areas.

In addition, there seems to have been less faculty interest in publishing data obtained from secondary elements and micronutrient work with forage crops than was the case with similar work involving row crops. The reason(s) for this is unclear, but there are indications that there has been a good deal of data of this type, which was generated but was never published. It is likely that because preliminary investigations generally obtained no responses, more extensive studies were never conducted. Also, negative results are generally less likely to be accepted for publication.

The forage crop fertilization recommendations regarding secondary elements and micronutrients that are in use at Auburn University have mostly been in place for many years, and in some cases may have been based on unpublished studies done years ago. The general policy at Auburn University is to not make changes in recommendations unless data has been generated that clearly indicates that changes are needed, so such recommendations still stand.

Though over 40 species of forage crops are routinely grown in Alabama and there are a diversity of soil types within the state, the Auburn University policy regarding fertilization with secondary elements and micronutrients is not particularly complex. The following provides background information, a summary of some Alabama research work, and current ecommendations for fertilizing forage crops with these elements.

CALCIUM

Calcium is an essential nutrient that must be present in substantial quantities for high forage yields. Most soils in Alabama require periodic liming to keep the soil pH within a suitable range for good forage crop production and this practice normally ensures adequate levels of calcium in the soil.

Recommendation : When crops are limed according to Auburn University liming recommendations, soils are considered to be adequately supplied with Calcium.

MAGNESIUM

Low magnesium can result in grass tetany danger for grazing animals (Odom, et. al., 1981) or can limit forage yields, and in some situations this element can be deficient in Alabama . Current recommendations regarding application of magnesium to forage crops were extrapolated mainly from a series of trials done with cotton, corn, soybeans, and peanuts ( Adams , 1975) and from knowledge of the magnesium-supplying ability of Alabama soils done from earlier work (Adams and Henderson, 1962; Somner, et.al., 1940). There may be a need to conduct additional studies of the requirements of forage crops for magnesium in Alabama .

Recommendation : If soil tests low in magnesium, dolomitic limestone is recommended as a liming material to correct soil acidity and to supply magnesium. If magnesium is low and lime is not needed, the magnesium can be added in mixed fertilizers.

SULFUR

Early in the 20th century there was extensive use of high sulfur coal both in industry and in heating of homes, which resulted in substantial amounts of sulfur being deposited in rainfall in some areas of the state. In addition, various commercial fertilizers contained sulfur as an incidental component. Both of these sources have since been greatly diminished, so sulfur is much more likely to be a limiting factor in crop production today than it was years ago.

Though sulfur was recognized as an essential element for plant growth as early as about 1860, the first investigations in Alabama of sulfur as a plant nutrient were conducted in the late 1930's. In tests with sericea lespedeza at 7 locations in which yields averaged around 3 tons/acre/year, and with alfalfa at 6 locations with yields averaging about 4 tons/acre/year, there was no response to sulfur ( Ensminger, 1958). These early tests with sericea and alfalfa provided evidence that deep-rooted perennial forages are normally able to obtain sufficient sulfur from subsurface layers.

Subsequent tests as well as farmer experience have revealed that sulfur deficiencies in Alabama occur almost exclusively on deep, sandy soils, especially in the Coastal Plain in South Alabama , and primarily with annuals (e.g. wheat) which are relatively shallow rooted (Mitchell and Mullins, 1990; Mullins and Mitchell, 1990). In low organic matter soils such as are present in Alabama , sulfur exists primarily as sulfate, which tends to leach. The content of sulfur in Alabama soils today is quite variable and we do not conduct analyses of subsoil samples where most of the sulfur available to plants is present.

Recommendation : On all soils it is recommended that at least 10 pounds of sulfur per acre be added annually to forage crops to ensure an adequate supply for good forage production.

IRON

Iron deficiency is not a problem with forage production on most Alabama soils. The exception is on alkaline soils in the Alabama Black Belt area. The first forage crop in which chlorosis caused by iron deficiency was noted was sericea lespedeza (Chandler and Scarseth, 1941). In this study it was found that high levels of available phosphorus aggravated this condition and application of sulfur tended to reduce it.

A study with crimson clover revealed this annual clover is also susceptible to iron chlorosis on these soils ( Rogers , 1947) and more recent experience has revealed the same to be true with arrowleaf clover. In the study with crimson clover an application of ferrous sulfate spray every 3 or 4 days completely eliminated chlorosis, but this treatment is not feasible.

Recommendation : Though some forage crops grown on alkaline soils may be iron deficient, these crops are not recommended to be grown in these areas. Iron is thus not recommended for forage crop production in Alabama .

MOLYBDENUM

Eleven experiments were conducted in five Southern states to determine the response of alfalfa, arrowleaf clover, crimson clover, ladino clover, red clover, and subterranean clover to lime and molybdenum applications (Mortvedt and Anderson, 1982). There were no clover responses to molybdenum, and alfalfa responded only when the soil pH was less than 5.5.

It is likely that the alfalfa response to application of molybdenum was more due to the indirect effect of low molybdenum on the nitrogen fixation process than on the need for this minor element by the plants. Soil pH had a large effect on the relative molybdenum concentrations in alfalfa and clover forage.

More recent research with soybeans in North Alabama (Adams et. al., 1990) as resulted in a molybdenum recommendation for soybeans on acid, clay soils. It is possible that certain forage legumes would respond to molybdenum applications, but this has not been demonstrated in Alabama research. Liming acid soils usually eliminates the need for molybdenum fertilization.

Recommendation : Application of molybdenum is not recommended for forage crops in Alabama .

MANGANESE

Five experiments were conducted in two Southern states to determine the response of alfalfa and ladino clover to manganese. Alfalfa yields were not increased by manganese applications even in high lime treatments where manganese availability was lowest (Mortvedt and Anderson, 1982). However, manganese toxicity can be a problem with forage crops at low pH levels.

Recommendation : Application of manganese is not recommended for forage crops in Alabama .

BORON

In a series of early experiments in Alabama , application of boron increased forage yield of alfalfa, bur clover, red clover, and white clover by 58%, 104%, 16%, and 158% respectively. In addition, seed yields of crimson clover and vetch were increased by 244% and 80%, respectively. In the same tests there were no forage yield responses by Austrian winter peas, blue lupine, alyce clover, or sericea lespedeza ( Rogers , 1948).

The impact of boron on crimson clover seed production was studied in depth. It was found that the greatest response was on sandy soils. Application of more than 10 pounds/acre of borax (about 1 pound of actual boron) resulted in little, if any, increase in seed yields (Wear, 1956). In an experiment with white clover, application of 1/2 pound of boron/acre significantly increased seed production. Application of zinc, manganese, copper, and molybdenum had no effect (Johnson and Wear, 1967).

As has been shown in many other states, application of boron to alfalfa often results in substantial yield increases. In a study at 8 locations, application of at least 15 pounds of borax (around 1.5 pounds of boron) per acre resulted in increased production of alfalfa forage (Table 2; Wear, 1957).

Recommendation : It is recommended that boron be applied to alfalfa at the rate of 3 pounds per/ acre per year. For seed production or reseeding of clovers, 1 to 1.5 pounds per acre are recommended.

ZINC

Response to application of zinc to forage crops has not been observed in Alabama in research trials, nor has zinc deficiency been diagnosed in producer fields. Plant tissue analyses indicate that zinc levels in forages are within the accepted sufficiency ranges.

Recommendation : It is not recommended that zinc be applied to forage crops in Alabama .

COPPER

Response to application of copper to forage crops has not been observed in Alabama in research trials, nor has copper deficiency been diagnosed in producer fields on any field or forage crop. Plant tissue analyses indicate that copper levels in forages are within the accepted sufficiency ranges.

Recommendation : It is not recommended that copper be applied to forage crops in Alabama .

GENERAL

The Mehlich I soil test extraction technique is used by the Auburn University Soil Testing Laboratory. This procedure is used to measure levels of available phosphorus, potassium, calcium, and magnesium in the soil, but not sulfur or the micronutrients. Given the general lack of response of forage crops to these elements, this extraction technique appears to be appropriate to use in Alabama .

An item gleaned from an early Alabama Experiment Station bulletin (Wear, 1957) provides some insight regarding why early researchers who worked on developing fertilizer recommendations for micro-nutrients did not see fit to recommend their application. It reads as follows.

"A minor element treatment has been included in pasture fertility experiments for several years. As a general rule, this treatment was an annual or biennial application of a mixture containing boron, manganese, copper, and zinc. The minor element treatment was applied in conjunction with adequate amounts of lime, phosphorus, and potassium. A survey of yield results from about 25 of these experiments over a wide range of soil types and textures shows that in no case was the growth significantly increased by addition of the minor elements, including boron."

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REFERENCES

• Adams, Fred. 1975. Field experiments with magnesium in Alabama . Ala. Agric. Exp. Sta. Bull. 472.
• Adams, Fred, and J.B. Henderson. 1962. Magnesium availability as affected by deficient and adequate levels of potassium and lime. Soil Soc. Am. Proc. 26:65-68.
• Adams , J.F., C.H. Burmester, and C.C. Mitchell, Jr. 1990. Long-term fertility treatments and molybdenum availability. Fert. Res. 21:167-170.
• Chandler , WV., and George D. Scarseth. 1941. Iron starvation as affected by over-phosphate and sulfur treatment on Houston and Sumter clay soils. J. Amer. Soc. of Agr. 33:93-104.
• Ensminger, L.E. 1958. Sulfur in relation to soil fertility. Ala. Agric. Exp. Sta. Bull. 312.
• Johnson, Wiley C., and John I. Wear. 1967. Effect of boron on white clover (Trifolium repens, L.) seed production. Agron. J. 59:205-206.
• Mitchell, C.C., Jr., and G.L. Mullins. 1990. Sources, rates, and time of sulphur application to wheat . Sulphur in Agric. 14:20-24.
• Mullins, G.L., and C.C. Mitchell, Jr. 1990. Wheat forage response to tillage and sulphur applications . Proc. South Cons. Tillage Conf., Spec. Bull. 89-1 . IFAS - Univ. Fla. , Gainesville , FL.
• Mortvedt, J.J., and O.E. Anderson. 1982. Abstract In Forage Legumes: Diagnosis and Correction of molybdenum and manganese problems. Southern Cooperative Series Bulletin 278, University of Georgia .
• Odom, J.W., R.L. Haaland, C.S. Hoveland, and E.M. Clark. 1981. Grass tetany potential of tall fescue infected with Epichloe typhina. Agron. J. 73:378.
• Rogers, H.R. 1947. Iron Deficiency of crimson clover on a calcareous soil and method of diagnosis . J. Amer. Soc. Agron. 39:638-639.
• Rogers , H.T. 1948. Response and tolerance of various legumes to borax and critical levels of boron in soils and plants. Better Crops With Plant Food, Vol. XXXII, No. 6.
• Somner, Anna L., John I. Wear, and Aaron Baxter. 1940. The response to magnesium of six different crops on sixteen Alabama soils. Soil Sci. Am. 5:205-212.
• Wear, John I. 1956. Boron requirement for crimson clover seed production, its accumulation in soils , and residual effects on sensitive crops. Agron. J. 48:123-134.
• Wear, John I. 1957. Boron requirements of crops in Alabama . Ala. Agric. Exp. Sta. Bull. 305.
• Wear, John I. 1976. Micronutrients for crops in Alabama . Highlights of Agricultural Research, Vos 23, No. 1.