Soil Fertility Management

North Carolina Cooperative Extension

Prepared by:
Ronald E. Jarrett, Crop Science Extension Specialist (Small Grains)

Jack V. Baird, Soil Science Extension Specialist (Fertilizers and Soil Fertility)
Dated 3/90

Placed on the Web 2/95 by the Center for Integrated Pest Management, NCSU


Soil Testing Provides Precision Management

The principles involved in soil fertility management for small grains are similar to those for many other important feed grains. Small grains are very important throughout the state. Since they are often an important component of many cropping systems, nutrient needs must be kept at optimum levels both for small grain and for crops that follow.

Soil tests from specific fields are the best way to determine how much lime and fertilizer-supplied nutrients should be added. Some fields may need significant amounts of lime, phosphate, potash, or micronutrients. Other fields may have some nutrient reserves that will permit liming and fertilizing more economically. Furthermore, soil tests will aid in providing an adequate supply of nutrients for subsequent crops. Soil samples should be collected and tested approximately 2 to 3 months before planting. This will allow adequate time to apply lime and fertilizer if needed.

Small grains grow best at a pH of 5.8 to 6.2

Small grains grown on soils with a pH of 5.5 or less will show reduced or slow growth and, therefore, reduced yields. The lower the pH, the greater the damage will be from increased aluminum toxicity, and possible manganese toxicity. Generally, wheat, oats, and rye are more tolerant of a low pH than barley. Rye can be grown on marginal soils if a grain market is available.

In contrast, a pH greater than 6.5 may also reduce yields because of decreased availability of certain micronutrients such as manganese, iron, boron, copper, and zinc.

Remember, a soil test is the best way to determine lime and nutrient needs accurately. Soil testing and plant analysis are services provided by the Agronomic Division of the N.C. Department of Agriculture. Their reports usually include interpretations and recommendations that will help produce the best crop possible. For information on collecting and submitting soil samples, see Extension publication AG-372, Careful Soil Sampling.

General Fertilizer Recommendations

General fertilizer suggestions (in absence of soil test information) have been developed from a review of thousands of small grain soil tests compiled from the N.C. Department of Agriculture's soil test summaries. An evaluation of over 10,000 soil samples collected 11 coastal plain counties suggested that from 200 to 250 pounds per acre of 3-9-18 fertilizer, or its equivalent, should be applied at planting time. Additional nitrogen may be needed at planting. Many coastal plain fields have quite high phosphorus levels as a result of many years of adequate crop fertilization and because phosphorus does not leach from soils. In the piedmont, over 1,800 soil samples from 1985 to 1987 were evaluated from 12 counties. These suggest that from 400 to 450 pounds per acre of 5-10-5 fertilizer, or its equivalent, is quite adequate. It is usually desirable to broadcast some phosphate, such as 0-20-0 or 0-46-0, to supplement the mixed fertilizer, especially if the appropriate ratio is difficult to purchase.

In the organic soils of the tidewater region, approximately 400 pounds per acre of 5-10-10 fertilizer, or its equivalent, could be used. It should be emphasized again that a soil sample for analysis should be taken from each field to determine more accurately the small grain's nutrient needs. Although the general suggestions apply, some fields may need a different kind and amount of fertilizer.

Animal waste can be used for small grain production. Wise use of nutrients in animal waste may reduce production costs, reduce erosion, and improve water quality. Animal waste may be applied before planting or as a topdressing. Before using poultry litter and other livestock waste, have it tested for nutrient content. Test results should be used to determine the need for additional fertilizer nutrients. If animal waste is applied as a topdressing, at least 50 percent of the nitrogen may be lost to the atmosphere. All other nutrients contained in the waste will be available for use by the small grains and the crop that follows.

Specific Nutrient Recommendations

Nitrogen. Topdressing with nitrogen is a very important practice for portable small grain production. It can often mean the difference between a high yield and a low one. This nutrient is crucial because it promotes tillering, ensures a large number of kernels per head, and increases the weight per kernel. All lead to increased yields. Topdressing should be done by growth stage 5 (see Fig. 1). This stage of growth generally occurs by mid-March. The suggested rates for topdressing (including nitrogen applied at planting) are given in Table 1.

Split applications of nitrogen at topdressing time have, in some cases, reduced severity of diseases and lodging and have increased yields. Apply one half of the nitrogen growth stage 3 (see Fig. 1) and the remaining half at growth stage 5. These growth stages coincide approximately with mid-February and mid-March. The success of this practice has not been consistent and depends heavily on varietal response, soil type, and weather. Split applications of nitrogen are more likely to be effective in the coastal plain on sandy soils than in the piedmont on heavy clayey soils.

On most North Carolina piedmont and mountain soils, all of the nitrogen may be applied in the fall without great loss from leaching. This approach eliminates an extra trip over the field. It also decreases the possibility of having to delay topdressing because of bad weather that can cause poor traction for the application equipment. However, applying all of the nitrogen in the fall can increase the possibility of cold damage resulting from excessive growth and succulent plants. It can also result in the early onset of insect and disease problems.

Some varieties respond to higher rates of nitrogen than those suggested. However, be prepared to control diseases and lodging by using foliar fungicides and a growth regulator. See Small Grain Production Guide No. 10, Keys to Intensive Wheat Management for more information. Where small grains will be grazed, apply a higher nitrogen rate (140 pounds per acre) in a split application.

Reduce the amount of nitrogen topdressing if the small grain follows peanuts and soybeans. Residues from these crops may supply as much as 40 and 30 pounds per acre, respectively, to the small grain. Using this management technique can decrease production costs.

Several satisfactory sources of nitrogen are available for topdressing small grain. Nitrogen solutions (approximately one-half ammonium nitrate and one-half urea dissolved in water) are popular and widely used. These solutions contain from 30 to 32 percent actual nitrogen. Although the solution may cause slight foliar burn, there is no likelihood of reduced yields from this effect. Ammonium nitrate (33.5 percent nitrogen) is a good topdressing material. This source may not always be as readily available as solution nitrogen. A third source is ammonium sulfate (21 percent nitrogen).

Ammonium sulfate is readily available, especially in eastern North Carolina. This source also contains sulfur (24 percent). This nutrient may be important in fields with rather deep sandy surfaces and to which no other sulfur was applied within the past one or two years.

In recent years urea (45 percent nitrogen) has been readily available. Its popularity stems from its high nitrogen content, its usually competitive price, and its low degree of metal corrosion. Under certain conditions, volatility losses can occur when urea is applied to sandy soil. However, if it is broadcast as early as possible in the spring when the soil surface is moist, wind speed is at a minimum, temperature is relatively low, and humidity is high, no loss should occur. When applied to silty or clayey soil surfaces, volatilization does not seem to be a problem.

Phosphorus. In contrast to nitrogen, phosphorus does not leach. However, adequate levels are needed to obtain high yields. Phosphorus aids in developing good root systems and vigorous vegetative growth. A phosphorus deficiency reduces plant respiration and delays maturation. The suggested application rate for phosphorus is 30 to 50 pounds of P205 if needed.

Piedmont soils frequently test lower in phosphorus than coastal plain soils. Phosphorus deficiencies do not occur often in small grain production, however. Phosphorus applications may be reduced or may not be needed when small grain is planted after tobacco and other heavily fertilized crops such as peanuts, sweetpotatoes, and vegetable crops. Planting after these crops can reduce production costs.

Potassium. Potassium aids in carbohydrate production and winter survival. The suggested application rate for potassium is 40 to 50 pounds of K20 if needed. Plants lacking in potassium usually remain small and lack vigor. Winter hardiness is reduced, and the heads formed are small and compact. Potassium deficiencies seldom occur in small grain. Higher rates of phosphorus and potassium may be needed under an intensively managed system.

Sulfur. Sulfur is a constituent of several amino acids. It is involved in electron transport, metabolism, and activities of many enzymes. Sulfur is a component of protein and very essential in small grain production. Plants cannot use nitrogen efficiently if adequate sulfur is not available. Sulfur deficiency may lead to stunted growth and small spindly plants with a light green to yellow color (chlorosis) in the younger leaves ( Fig. 2). The symptoms are very similar to nitrogen deficiency ( Fig. 3) except that the younger leaves show yellowing first.

Sulfur in the form of sulfate may leach readily, and deficiencies generally occur in sandy soils. Thus, topsoils frequently test low in sulfate sulfur. However, sulfate sulfur accumulates in the subsoil (B horizon or clay layer). If the roots can reach this layer, a deficiency may not occur. A deficiency can be corrected by applying 20 to 30 pounds of sulfur per acre.

Several forms are available in fertilizers such as gypsum (CaS04)2S04. Some foliar fungicides and micronutrient materials also contain small amounts of sulfur. The best time to apply sulfur is before planting. A response to sulfur will most likely occur when sandy soil surfaces are more than 16 to 18 inches deep.

Copper. The role of copper in small grain production is associated in some way with chlorophyll development and enzyme activities. Since copper is needed in a very minute amount, there is no universally accepted application rate. However, copper deficiencies often occur in the tidewater area in some poorly drained soils of the coastal plain. Organic matter and copper form a "complex," reducing its availability. The deficiency frequently causes a stunted, yellow (chlorotic) plant with twisted, dying leaf tips ( Fig. 4). The general symptoms resemble cold injury (Fig. 5).

Copper deficiency can be corrected by applying 8 to 24 pounds of copper sulfate (25 percent copper) per acre. The other forms of copper available are liquids formulated with ammonia, chlorides, and nitrates. Chelates and organic complexes used at equivalent elemental rates are just as effective but quite expensive. Oxides and most oxysulfates of copper, except when thoroughly incorporated into the soil several months before planting, are usually not as effective. Copper should be applied at the rate of 2, 4, or 6 pounds of actual copper per acre for mineral, mineral-organic, or organic soils, respectively.

The copper can be incorporated into the fertilizer or applied as a foliar spray. The best time to apply copper is when planting in the fall. However, an application can be made in February or March, during Growth stages 3 to 5, if the grain is dormant. Apply no more than 1/4 pound of actual copper per acre. A foliar application will correct the deficiency only temporarily. When an application of 2 to 6 pounds of actual copper per acre has been made, there is no need to apply more copper for at least 8 to 10 years. Soil test indexes for copper will help in determining when the next application should be made.

Applying too much copper as a foliar spray may cause burning and reduce yield. The addition of 1/2 pound of hydrated lime for each 1/4 pound of copper in the spray solution will reduce leaf burn. Applying too much copper in the soil may result in a toxic level.

Response to copper will vary. Generally, wheat will give a good response, barley and oats a medium response, and rye a poor response. If applied at the suggested rates, there is no danger of adversely affecting other crops in the rotation. In fact, corn and soybeans may benefit from the copper applied to small grains.

Manganese. The role of manganese in small grain production is similar to that of copper. It is associated with chlorophyll synthesis and certain enzyme activities. Manganese, a micronutrient, is needed in small amounts. The availability of manganese decreases as soil pH increases. A deficiency ( Fig. 6) causes yellowing (chlorosis) between the veins of the younger leaves, which sometimes also show a light green or whitish color ( Fig. 7). No manganese deficiency has been noted in the piedmont or mountain region. Manganese deficiency can be corrected by applying manganese sulfate (25 to 28 percent). Other forms give similar results. Manganese can be incorporated into the fertilizer used at planting time or can be applied as a foliar spray.

Other sources of manganese are liquids formulated with ammonia, chloride, and nitrates. As with copper sources, chelated or organic complexes used at equivalent elemental rates are just as effective but quite expensive. Oxides and most oxysulfates of manganese, except when thoroughly incorporated into the soil several months before planting, are usually not as effective.

This micronutrient should be applied at a rate of 10 pounds of actual manganese per acre on coarse or sandy soils and 20 pounds per acre on fine-textured (clay) and organic soils. A foliar application of 1/2 pound per acre can be made during the growing season. As with copper, a foliar application is only a temporary correction. A repeat application of 1/2 pound per acre may be needed in about two weeks. Use the same precautions for foliar applications as with copper.

Plant Tissue Analysis

Information gained from an analysis of small grain plant parts can help in determining whether adequate levels of certain necessary nutrients are available to the plants. This information will supplement that gained from analysis of soil samples from the same field. The plant is, for all practical purposes, the final product of management, including the matching of soil-supplied nutrients with those necessary from fertilizer and lime. This analysis can determine whether an adequate amount of fertilizer has been applied. If not, the application rate can be adjusted for the next crop. Furthermore, analysis results, when obtained from the laboratory quickly, can be used to supply supplemental nutrients to the current crop, improving its yield.

Plant analysis is particularly useful in gaining information about the mobile nutrients, -- that is, nitrogen, sulfur, boron, and molybdenum. Soil tests for these nutrients are of little predictive value. Furthermore, plant analysis can supplement soil test information about micronutrient deficiencies. Analysis of tissue samples will help to verify whether low soil test values for manganese, copper, or zinc correlate with low plant tissue content and, conversely, whether high concentrations in plant tissues have reached toxic levels.

Proper collection procedures for plant parts can be obtained from agricultural Extension agents, N.C. Department of Agriculture regional agronomists, or a qualified crop consultant. Table 2 gives sufficient guidelines for small grains.

Table 1. Nitrogen Rate Suggestions for Small Grains


                                  Total Nitrogen in pound per acre
                  ---------------------------------------------------------------
                    Wheat           Oats        Barley       Rye        Triticale

Coastal Plain 120 100 100 80 100 Piedmont, Mts. 100-120 80-100 80-100 80 80-100 Tidewater 120 100 100 80 100
Table 2. Nutrient Sufficiency Ranges for Small Grains

Nitrogen (N)*           . . .          . . .            <2.59%          2.59-3.50

Phosphorus (P)          <25         25-50 medium      0.11-0.20%        0.21-0.55
                                     50 + high

Potassium (K)           <25         25-50 medium      1.00-1.50%        1.51-3.00
                                      50 + high

Copper (Cu)             <25            25+              3-4 ppm          5-20 ppm

Manganese (Mn)          <25            25+             10-16 ppm       17-200 ppm

Sulfur (S)**            <25            25+            0.15-0.21%        0.22-0.60

* No figures are given for nitrogen because this nutrient is very mobile. Tests can be conducted but have little predictive value. Recommended rates are based on research and observation of many field trials.

** Sulfur is quite mobile in soils with sandy surface layers. Although a surface soil sample may indicate low sulfur levels, adequate sulfur may still be within reach of most root systems. Therefore, a sulfur soil test has unreliable predictive value. Source: Taken from information furnished by N.C. Department of Agriculture, Agronomic Division.